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A common presentation of the P102L prion protein mutation is Gerstmann-Straussler-Scheinker syndrome. Rudge et al. show that serial measurement of lower limb thermal thresholds predicts, within a relatively narrow time window, conversion to the symptomatic phase of the disease, and that synaptic deposition of PrPSc in the spinal cord underpins the pathology., A common presentation of inherited prion disease is Gerstmann-Sträussler-Scheinker syndrome, typically presenting with gait ataxia and painful dysaesthesiae in the legs evolving over 2–5 years. The most frequent molecular genetic diagnosis is a P102L mutation of the prion protein gene (PRNP). There is no explanation for why this clinical syndrome is so distinct from Creutzfeldt-Jakob disease, and biomarkers of the early stages of disease have not been developed. Here we aimed, first, at determining if quantitative neurophysiological assessments could predict clinical diagnosis or disability and monitor progression and, second, to determine the neuropathological basis of the initial clinical and neurophysiological findings. We investigated subjects known to carry the P102L mutation in the longitudinal observational UK National Prion Monitoring Cohort study, with serial assessments of clinical features, peripheral nerve conduction, H and F components, threshold tracking and histamine flare and itch response and neuropathological examination in some of those who died. Twenty-three subjects were studied over a period of up to 12 years, including 65 neurophysiological assessments at the same department. Six were symptomatic throughout and six became symptomatic during the study. Neurophysiological abnormalities were restricted to the lower limbs. In symptomatic patients around the time of, or shortly after, symptom onset the H-reflex was lost. Lower limb thermal thresholds were at floor/ceiling in some at presentation, in others thresholds progressively deteriorated. Itch sensation to histamine injection was lost in most symptomatic patients. In six patients with initial assessments in the asymptomatic stage of the disease, a progressive deterioration in the ability to detect warm temperatures in the feet was observed prior to clinical diagnosis and the onset of disability. All of these six patients developed objective abnormalities of either warm or cold sensation prior to the onset of significant symptoms or clinical diagnosis. Autopsy examination in five patients (including two not followed clinically) showed prion protein in the substantia gelatinosa, spinothalamic tracts, posterior columns and nuclei and in the neuropil surrounding anterior horn cells. In conclusion, sensory symptoms and loss of reflexes in Gerstmann-Sträussler-Scheinker syndrome can be explained by neuropathological changes in the spinal cord. We conclude that the sensory symptoms and loss of lower limb reflexes in Gerstmann-Sträussler-Scheinker syndrome is due to pathology in the caudal spinal cord. Neuro-physiological measures become abnormal around the time of symptom onset, prior to diagnosis, and may be of value for improved early diagnosis and for recruitment and monitoring of progression in clinical trials.

Objectives: The transcranial magnetic stimulation (TMS) technique of threshold-tracking short-interval intracortical inhibition (T-SICI) has been proposed as a diagnostic tool for amyotrophic lateral sclerosis (ALS). Most of these studies have used a circular coil, whereas a figure-of-8 coil is usually recommended for paired-pulse TMS measurements. The aim of this study was to compare figure-of-8 and circular coils for T-SICI in the upper limb, with special attention to reproducibility, and the pain or discomfort experienced by the subjects. Methods: Twenty healthy subjects (aged: 45.5 ± 6.7, mean ± SD, 9 females, 11 males) underwent two examinations with each coil, in morning and afternoon sessions on the same day, with T-SICI measured at interstimulus intervals (ISIs) from 1−7 ms. After each examination the subjects rated degree of pain/discomfort from 0 to 10 using a numerical rating scale (NRS). Results: Mean T-SICI was higher for the figure-of-8 than for the circular coil at ISI of 2 ms (p < 0.05) but did not differ at other ISIs. Intra-subject variability did not differ between coils, but mean inhibition from 1−3.5 ms was less variable between subjects with the figure-of-8 coil (SD 7.2% vs. 11.2% RMT, p < 0.05), and no such recordings were without inhibition (vs. 6 with the circular coil). The subjects experienced less pain/discomfort with the figure-of-8 coil (mean NRS: 1.9 ± 1.28 vs 2.8 ± 1.60, p < 0.005). Discussion: The figure-of-8 coil may have better applicability in patients, due to the lower incidence of lack of inhibition in healthy subjects, and the lower experience of pain or discomfort.

Primary afferent sensory neurons are incredibly long cells, often traversing distances of over 1 m in humans. Cutaneous sensory stimuli are transduced in the periphery by specialised end organs or free nerve endings, which code the stimulus into electrical action potentials that propagate towards the central nervous system. Despite significant advances in our knowledge of sensory neuron physiology and ion channel expression, many commonly used techniques fail to accurately model the primary afferent neuron in its entirety. In vitro experiments often focus on the cell somata and neglect the fundamental processes of peripheral stimulus transduction and action potential propagation. Despite this, these experiments are commonly used as a model for cellular investigations of the receptive terminals. We demonstrate that ratiometric calcium imaging performed in compartmentalised sensory neuron cultures can be used to directly and accurately compare the sensitivity and functional protein expression of isolated neuronal regions in vitro. Using microfluidic chambers, we demonstrate that the nerve terminals of cultured dorsal root ganglion neurons can be depolarised to induce action potential propagation, which has both tetrodotoxin-resistant and tetrodotoxin-sensitive components. Furthermore, we show that there is a differential regulation of proton sensitivity between the sensory terminals and somata in cultured sensory neurons. We also demonstrate that capsaicin sensitivity is highly dependent on embryonic dissection age. This approach enables a comprehensive method to study the excitability and regional sensitivity of cultured sensory neurons on a single-cell level. Examination of the sensory terminals is crucial to further understand the properties and diversity of dorsal root ganglion sensory neurons.

Background Complete brachial plexus avulsion injury is a severe disabling injury due to traction to the brachial plexus. Brachial plexus reimplantation is an emerging surgical technique for the management of complete brachial plexus avulsion injury. Objective We assessed the functional recovery in 15 patients who underwent brachial plexus reimplantation surgery after complete brachial plexus avulsion injury with clinical examination and electrophysiological testing. Methods We included all patients who underwent brachial plexus reimplantation in our institution between 1997 and 2010. Patients were assessed with detailed motor and sensory clinical examination and motor and sensory electrophysiological tests. Results We found that patients who had reimplantation surgery demonstrated an improvement in Medical Research Council power in the deltoid, pectoralis, and infraspinatous muscles and global Medical Research Council score. Eight patients achieved at least grade 3 MRC power in at least one muscle group of the arm. Improved reinnervation by electromyelography criteria was found in infraspinatous, biceps, and triceps muscles. There was evidence of ongoing innervation in 3 patients. Sensory testing in affected dermatomes also showed better recovery at C5, C6, and T1 dermatomes. The best recovery was seen in the C5 dermatome. Conclusions Our results demonstrate a definite but limited improvement in motor and sensory recovery after reimplantation surgery in patients with complete brachial plexus injury. We hypothesize that further improvement may be achieved by using regenerative cell technologies at the time of repair.

Upon reactivation from latency and during lytic infections in neurons, alphaherpesviruses assemble cytosolic capsids, capsids associated with enveloping membranes, and transport vesicles harboring fully enveloped capsids. It is debated whether capsid envelopment of herpes simplex virus (HSV) is completed in the soma prior to axonal targeting or later, and whether the mechanisms are the same in neurons derived from embryos or from adult hosts. We used HSV mutants impaired in capsid envelopment to test whether the inner tegument proteins pUL36 or pUL37 necessary for microtubule-mediated capsid transport were sufficient for axonal capsid targeting in neurons derived from the dorsal root ganglia of adult mice. Such neurons were infected with HSV1-ΔUL20 whose capsids recruited pUL36 and pUL37, with HSV1-ΔUL37 whose capsids associate only with pUL36, or with HSV1-ΔUL36 that assembles capsids lacking both proteins. While capsids of HSV1-ΔUL20 were actively transported along microtubules in epithelial cells and in the somata of neurons, those of HSV1-ΔUL36 and -ΔUL37 could only diffuse in the cytoplasm. Employing a novel image analysis algorithm to quantify capsid targeting to axons, we show that only a few capsids of HSV1-ΔUL20 entered axons, while vesicles transporting gD utilized axonal transport efficiently and independently of pUL36, pUL37, or pUL20. Our data indicate that capsid motility in the somata of neurons mediated by pUL36 and pUL37 does not suffice for targeting capsids to axons, and suggest that capsid envelopment needs to be completed in the soma prior to targeting of herpes simplex virus to the axons, and to spreading from neurons to neighboring cells., Author summary Human and animal alphaherpesviruses establish lifelong latent infections in neurons of the peripheral nervous system and cause many diseases upon primary infection as well as following reactivation from latency. The highly prevalent human herpes simplex viruses HSV-1 and HSV-2 are responsible for facial and genital herpes, potentially blinding eye infections, and life-threatening encephalitis and meningitis. Here, we asked how these viruses master the bottleneck of being targeted from the neuronal somata to the axons. Our data suggest that only transport vesicles harboring fully matured virus particles can enter axons for spreading infection to the brain or the peripheral organs. Our data imply that the limiting membrane of the transport vesicles must expose viral or host receptors to recruit the microtubule motors required for axonal transport. Inhibiting such viral factors on the surface of the transport vesicles might provide novel therapeutic approaches to prevent the spread of alphaherpesviruses in the nervous system.

Background Tibial SEPs assess the function of the dorsal columns and supraspinal medial lemniscal somatosensory pathways. Lumbar N22 responses (T12/L1) and cervical P30 (Cv7) allow topographic localisation but are challenging to obtain in routine clinical practice. Here, we studied technical parameters that affect spinal and cortical (P40) responses. Materials and methods In a sample of consecutively referred patients, spinal response amplitudes and latencies were studied simultaneously with cup or subdermal needle and different reference electrode montages and correlated with BMI. P30 recordings were trialled and P40 amplitude optimisation was studied with three different montages (Cz’-Fz, Cz’-Cc, Ci-Cc). Results Responses with subdermal needles were of equal or smaller amplitude in 22/37 compared to cup electrodes. Contralateral iliac crest reference (0.74 ± 0.62 μV) gave larger amplitudes than ipsilateral (0.59 ± 0.61 μV; P = 0.017). Spinal N22 responses (cup electrode, contralateral reference) were present in 33/37patients with BMI 25(0.58 ± 0.54 μV) and were not strongly correlated with BMI (Spearman = −0.32). 30/136 recordings had absent spinal responses with recordable P40. A P30 response was not recordable in 115/140 when P40 was present. Amplitudes of Cz’-Cc (3.09 ± 2.01 μV) were significantly greater than Cz’-Fz (2.42 ± 1.83 μV) in 117/150 of recordings (P = 0.001) and Ci-Cc (2.48 ± 1.55 μV) in 97/150 (P = 0.008). There were no significant differences in latencies. Conclusions Subdermal needle and cup electrodes produce comparable N20 recordings and contralateral iliac crest reference provides largest amplitudes. Interestingly, BMI does not significantly influence N22 amplitude. The Cv7 response was often absent when N22 and P40 were normal. P40 amplitude is maximal at Cz’-Cc derivation.

The "Trond" protocol of nerve excitability tests has been used widely to assess axonal function in peripheral nerve. In this study, the routine Trond protocol was expanded to refine assessment of cAMP-dependent, hyperpolarization-activated current (I(h)) activity. I(h) activity is generated by hyperpolarization-activated, cyclic nucleotide-modulated (HCN) channels in response to hyperpolarization. It limits activity-dependent hyperpolarization, contributes to neuronal automaticity, and is implicated in chronic pain states. Published data regarding I(h) activity in motor nerve are scant. We used additional strong, prolonged hyperpolarizing conditioning stimuli in the threshold electrotonus component of the Trond protocol to demonstrate the time-course of activation of I(h) in motor axons. Fifteen healthy volunteers were tested on four occasions during 1 week. I(h) action was revealed in the threshold electrotonus by the limiting and often reversal, after about 100 ms, of the threshold increase caused by strong hyperpolarizing currents. Statistical analysis by repeated-measures analysis of variance enabled confidence limits to be established for variation between subjects and within subjects. The results demonstrate that, of all the excitability parameters, those dependent on I(h) were the most characteristic of an individual, because variance between subjects was more than four times the variance within subjects. This study demonstrates a reliable method for in vivo assessment of I(h,) and also serves to document the normal variability in nerve excitability properties within subjects.

Neurons of the peripheral nervous system detect changes in temperature through activation of specialised ion channels. Members of the transient receptor potential family TRPM8 and TRPA1 are candidates for the principal transducers of cold stimuli. Using ratiometric calcium imaging we now show that 19% of acutely dissociated mouse dorsal root (DRG) and 45% of superior cervical ganglia (SCG) neurons responded to a brief cold stimulus. Amongst cold-responsive DRG neurons 34 ± 2% responded to the TRPM8 agonist menthol, 18 ± 3% to the TRPA1 agonist mustard oil and 5% to both stimuli. A third of the cold-sensitive neurons did not respond to any TRP channel agonist. Cold-sensitive neurons of the SCG did not respond to menthol and only 3% responded to mustard oil. The threshold of SCG neurons was at significantly cooler temperatures than that of DRG neurons. Using real-time PCR, TRPA1 was expressed over 100-fold more in DRG than SCG, while TRPM8 was present in DRG only. The relatively small amount of TRPA1 transcript present in SCG did not correlate with the high level of cold sensitivity. We conclude that cold sensitivity in sympathetic neurons and in a significant proportion of sensory neurons is generated in the absence of TRPM8 and TRPA1.

The existence of heterogeneous populations of dorsal root ganglion (DRG) neurons conveying different somatosensory information is the basis for the perception of touch, temperature, and pain. A differential expression of transient receptor potential (TRP) cation channels contributes to this functional heterogeneity. However, little is known about the development of functionally diverse neuronal subpopulations. Here, we use calcium imaging of acutely dissociated mouse sensory neurons and quantitative reverse transcription PCR to show that TRP cation channels emerge in waves, with the diversification of functional groups starting at embryonic day 12.5 (E12.5) and extending well into the postnatal life. Functional responses of voltage-gated calcium channels were present in DRG neurons at E11.5 and reached adult levels by E14.5. Responses to capsaicin, menthol, and cinnamaldehyde were first seen at E12.5, E16.5, and postnatal day 0 (P0), when the mRNA for TRP cation channel, subfamily V, member 1 (TRPV1), TRP cation channel, subfamily M, member 8 (TRPM8), and TRP cation channel, subfamily A, member 1 (TRPA1), respectively, was first detected. Cold-sensitive neurons were present before the expression or functional responses of TRPM8 or TRPA1. Our data support a lineage relationship in which TRPM8- and TRPA1-expressing sensory neurons derive from the population of TRPV1-expressing neurons. The TRPA1 subpopulation of neurons emerges independently in two distinct classes of nociceptors: around birth in the peptidergic population and after P14 in the nonpeptidergic class. This indicates that neurons with similar receptive properties can be generated in different sublineages at different developmental stages. This study describes for the first time the emergence of functional subtypes of sensory neurons, providing new insight into the development of nociception and thermoreception.

Boundary cap cells can generate neurons as well as peripheral glia during embryonic development (Maro, G.S., Vermeren, M., Voiculescu, O., Melton, L., Cohen, J., Charnay, P., Topilko, P., 2004. Neural crest boundary cap cells constitute a source of neuronal and glial cells of the PNS. Nat Neurosci. 7 (9), 930-938), and, recently, the boundary cap was shown to contain multipotent stem cells (Hjerling-Leffler, J., Marmigère, F., Heglind, M., Cederberg, A., Koltzenburg, M., Enerbäck, S., Ernfors, P., 2005. The boundary cap, a source of neural crest stem cells generating multiple sensory neuron subtypes. Development. 132 (11), 2623-2632). The ability of stem cells to generate mature functional glial phenotypes has not been addressed. In this study, we have explored the competence of boundary neural crest stem cells (bNCSCs) to differentiate into mature functional Schwann cells (SCs) in vitro and in vivo. bNCSCs failed to differentiate into SCs in vitro when cultured in a defined media and in vivo when grafted into adult rat sciatic nerves. However, in the presence of neuregulins, during long-term cultures, the majority of bNCSCs differentiated into SCs. After analysis of the in vivo expression of Sox2, Sox10, S100, GFAP, fibronectin and Krox20 in the glial lineages, we used these markers to characterize differentiation of the bNCSCs. Gliogenesis of bNCSCs proceeded similar to that in vivo by sequentially adopting a SC precursor and immature Schwann cell before maturing into myelinating and non-myelinating SCs. In co-culture with explanted dorsal root ganglia (DRG) as well as in vivo in transplants to the axotomized sciatic nerve, these bNCSC-derived SCs myelinated axons as shown by ensheathing of neuronal processes and expression of myelin basic proteins (MBP). These results show that, under appropriate conditions, bNCSCs can generate mature SCs that are functional and can myelinate axons in regenerating nerves.

Clinical investigations of peripheral nerve lesions routinely involve nerve conduction studies and electromyography. Imaging studies are often used to exclude focal mass lesions or external compression and to visualize muscle atrophy. More recently, it has been recognized that magnetic resonance imaging can identify changes in peripheral nerves and secondary neurogenic alterations in skeletal muscle, which may significantly enhance its use in the differential diagnosis of peripheral nerve disease.Acute axonal nerve lesions cause a hyperintense signal on T2-weighted images at and distal to the lesion site, which correlates with Wallerian degeneration and nerve oedema. Superparamagnetic iron oxide particles provide an exciting new tool to detect the invasion of macrophages into the degenerating nerve distal to an axonal lesion. Prolongation of the T2 relaxation time and gadolinium enhancement of denervated muscle develop in parallel to the development of spontaneous activity on electromyography, and are probably the consequence of capillary enlargement and increased muscular blood volume.Magnetic resonance imaging supplements the differential diagnosis of peripheral nerve disease. An advantage over clinical neurophysiological investigations is that it is operator independent and painless. It can identify axonal damage and may thus help to identify a lesion site precisely, where fractionated nerve conduction studies are not applicable. Novel contrast media may potentially be used to detect pathophysiologically relevant mechanisms such as infiltration of the nerve by macrophages. Magnetic resonance imaging also has the advantage of providing a lasting detailed topographical picture of regional variations and avoids localization errors of muscles in electromyography.

Opioid requirements in neonatal patients are reported to be lower than older infants and this may be a reflection of the developmental regulation of opioid receptors. In this study we have investigated the postnatal regulation of Mu opioid receptor (MOR) function in both rat lumbar dorsal root ganglion (DRG) cultures and behavioural mechanical and thermal reflex tests in rat pups. Immunostaining with MOR and selective neurofilament (NF200) antibodies was combined with calcium imaging of MOR function in cultured neonatal and adult rat dorsal root ganglion cells. Calcium imaging showed that a significantly greater number of neonatal DRG neurons expressed functional MOR compared to adult (56.5+/-3.4 versus 39.9+/-1.5%, n=8, mean+/-SEM, P0.001). This expression is confined to the large, neurofilament positive sensory neurons, while expression in small, nociceptive, neurofilament negative neurons remains unchanged. Sensory threshold testing in rat pups showed that the analgesic potency of systemic morphine to mechanical stimulation is significantly greater in the neonate and declines with postnatal age. Morphine analgesic potency in thermal nociceptive tests did not change with postnatal age. These experiments show that the MOR expressed on large DRG neurons in neonates are functional and are subject to postnatal developmental regulation. This changing functional receptor profile is consistent with greater morphine potency in mechanical, but not thermal, sensory tests in young animals. These results have important clinical implications for the use of morphine in neonates and provide a possible explanation for the differences in morphine requirements observed in the youngest patients.

Acute axonal nerve lesions cause a hyperintense signal on T2-weighted (T2-w) magnetic resonance imaging (MRI) at the nerve lesion site and distal to it. The aim of this experimental study was to investigate the spatiotemporal evolution and resolution of MR nerve signal changes following denervation and reinnervation, and to relate these findings to electrophysiology and histology. The proximal sciatic nerve of adult rats was ligated by a tight suture that was removed 1 week later to induce complete axotomy and nerve regeneration upon release. Serial electromyography (EMG) and motor nerve conduction studies were performed parallel to MRI at multiple points of time. Moreover, sciatic nerves were taken for quantitative histological evaluation. Nerve hyperintensity on T2-w MRI was present distal to the lesion at thigh level 24 h after denervation preceding the occurrence of spontaneous activity on EMG by 24 h. After 48 h, the entire sciatic nerve and its branches showed an increased signal down to the level of the lower leg. The increased nerve signal regressed with a proximo-distal gradient beginning from week 2 after onset of nerve regeneration in the thigh. On EMG, the first reinnervation potentials were detected at that time at the respective level. Compound muscle action potential (CMAP) in the foot muscle fully recovered 12 weeks after onset of nerve regeneration, that is, 2 weeks after resolution of the hyperintensity along the entire nerve on MRI. Histology revealed axonal degeneration in the acute phase and later nerve oedema parallel to the increased nerve signal on MRI. MR signal alterations occur as early as 24 h after an axonal nerve lesion and correlate with nerve fiber degeneration and later with nerve oedema on histology. MR findings in denervation and reinnervation parallel the electrophysiological changes. Thus, MRI is a promising diagnostic tool for the early detection of acute axonal nerve lesions and monitoring of nerve regeneration.

A signal increase in denervated muscle on magnetic resonance imaging (MRI) has been described in several clinical and experimental studies. Here, we studied the time course of T2-relaxation time changes in denervation and subsequent reinnervation in a rat model and correlated the findings with electrophysiology and quantitative histology. A prolongation of the T2 relaxation time in muscles was present 48 h after denervation, which was paralleled by spontaneous activity on electromyography (EMG). Histologically, there was a marked enlargement of the capillaries at that time point, indicating increased blood volume. The relaxation time changes peaked 3 weeks after beginning of nerve regeneration identified by EMG. Subsequently, the T2 prolongation normalized until 10 weeks after beginning of regeneration which was associated with a histological regression of the capillary enlargement. MRI closely mirrors the electrophysiological changes following denervation and reinnervation and may thus be used as adjunct to electrophysiology. The pathophysiological basis for the MR relaxation time changes is predominantly the enlargement of the capillary bed.

The neuropeptide galanin is known to have an antinociceptive effect under neuropathic conditions. After axotomy, galanin is upregulated in sensory neurons, presumably in the capsaicin-sensitive ones. Here, the sensitivity to capsaicin and the expression of galanin were simultaneously examined by double-staining in individual, dissociated rat dorsal root ganglion neurons (1) after axotomy of the sciatic nerve for up to 14 days and (2) in culture for up to 4 days without prior nerve injury. Ten days after axotomy, the proportion of capsaicin-sensitive neurons had decreased by 36 percentage points (from 63% to 27%), whereas the proportion of galaninergic neurons had increased by 33 percentage points (from 3% to 36%). These changes were also observed in neurons kept in culture, where the regulation was attenuated by the addition of nerve growth factor (NGF) or glial cell line-derived neurotrophic factor (GDNF) to the medium. After axotomy, galaninergic neurons had a soma size-distribution profile similar to the capsaicin-sensitive neurons, but there was no colocalization of capsaicin sensitivity and galanin expression in individual neurons. In culture, some neurons showed colocalization after 30 h and 48 h, but not after 6 h or 96 h. We conclude that the upregulation of galanin in an individual neuron is preceded by downregulation of its capsaicin sensitivity both in NGF-dependent peptidergic and in GDNF-dependent non-peptidergic neurons, indicating a change in phenotype.

The role of the p75 neurotrophin receptor for neuronal survival after nerve crush was studied in L5 dorsal root ganglia (DRG) of knockout mice and controls with assumption-free stereological methods. Numbers of neuronal A- and B-cells were obtained using the optical fractionator and optical disector techniques. At birth, the total number of DRG neurons was 10,000 +/- 2,600 in control mice compared with 5,100 +/- 1,300 in p75 knockout mice. During postnatal development, 1,400 neuronal B-cell bodies were lost in p75 knockouts (2P < 0.05) and 1,100 in controls (NS), whereas the A-cell population remained stable. After a sciatic nerve crush, the total neuron loss in controls was 15.4% +/- 3.5% (2P < 0.05) and 22.7% +/- 5.1% (2P < 0.05) at days 14 and 42, respectively. In contrast, there was no loss in total number of neurons after crush in p75 knockout mice. Neuronal A-cell number was unchanged after the crush in p75 knockouts as well as in controls at both times. At 14 days, the population of B-cells was reduced by 24.8% +/- 3.6% in controls and by 6.1% +/- 3.5% in p75 knockouts, this difference being significant (2P < 0.001). At 42 days, the B-cell loss was 29.6% +/- 5.5% in controls and 4.2% +/- 6.4% in p75 knockouts (2P < 0.001). In conclusion, the lack of the p75 receptor results in neuronal DRG cells that are resistant to nerve injury, pointing to a role for the receptor in apoptosis.

TNF-alpha antagonists have been associated with various types of peripheral neuropathies, including multifocal motor neuropathy with conduction block and mononeuropathies [1]. We present two patients treated with infliximab who developed unifocal motor neuropathy with conduction block. A 34-year-old female with Crohn’s disease developed painless weakness of right-hand pincer grip of insidious onset. She had previously received five courses of infliximab infusions (5 mg/kg) and a further dose 3 days after symptom onset. Infliximab partially controlled gastrointestinal symptoms and she was otherwise well. Regular medication included the oral contraceptive pill, levothyroxine, folate, omeprazole, B12 injections, and iron infusions. Examination revealed MRC grade 4 power of the right abductor pollicis brevis, flexor pollicis longus, flexor digitorum profundus (median), and opponens pollicis. Flexor carpi radialis was mildly weak (4?) but forearm pronation remained strong. There were no sensory signs and systemic examination was unremarkable. A detailed four-limb neurophysiological examination 6 weeks after symptom onset revealed isolated severe right median motor conduction block 2.5–6.5 cm proximal to the antecubital fossa skin crease (Fig. 1). Median and other sensory conduction responses were normal. EMG of median innervated forearm muscles including abductor pollicis brevis and flexor pollicis longus was consistent with conduction block, with reduced recruitment of motor units but no spontaneous activity or other evidence of motor axon loss. Right median sympathetic skin response, somatosensory evoked potentials, and thenar thermal threshold testing were all normal. There was evidence for systemic active inflammation with mild leukocytosis, thrombocytosis, and normocytic anemia; ESR 102 mm/h and CRP 51 mg/l. Anti-DNA antibodies, ANCA, ANA, RA latex, glycolipid and antiGAD antibodies, anti-GM1, and anti-GQ1b antibodies were either normal or negative. An MRI with gadolinium showed hyperintensity of the right median nerve in the lower third of the right arm on TIRM and T2-weighted images, with subtle enhancement but no enlargement. This corresponded to the site of conduction block. No specific treatment was given, but there was significant improvement of power in weak muscles within 4 weeks of presentation, and complete recovery at 1 year. Patient 2, a 41-year-old female with ankylosing spondylitis, had been treated with regular infliximab infusions since 2003. In April 2009, she awoke with painless weakness of left finger and wrist extension 3 days after an infliximab infusion (270 mg). Examination revealed MRC grade 0 finger extension and 4wrist extension with radial deviation and no sensory loss. Initial neurophysiological examination 1 week after symptom onset showed profound A. W. Michell (&) Department of Clinical Neurophysiology, Box 124 Addenbrooke’s Hospital, Cambridge CB2 0QQ, UK e-mail: andrew.michell@addenbrookes.nhs.uk

The significance of the p75 low-affinity neurotrophin receptor, for the maintenance and survival of DRG cells, was studied in p75-deficient mice. Perikarya of the L5 DRG of 12-week-old p75 receptor-deficient mice and healthy Balb C mice were compared using stereological techniques. Following systematic sampling, the optical fractionator and the planar vertical rotator were used to estimate the number and mean volume of the cell bodies of the two neuronal subpopulations. The loss of B-cells was 57% (P < 0.00001), numbers being 7300 (CV = 0.12) in controls and 3100 in p75 receptor-deficient mice (CV = 0.18). Also, A-cells showed a significant loss of 39% (P < 0.0001), numbers being 2600 (CV = 0.12) in control mice and 1500 (CV = 0.16) in p75 receptor-deficient mice. The volume of A-cells was reduced by 30% (P < 0.01), from 24.700 µm3 (CV = 0.17) perikarya in p75 knock-out mice to 15.100 µm3 (CV = 0.17) in controls. B-cell volume did not change significantly. It is concluded that the p75 receptor plays a major role in the survival of DRG cells. The predominant loss of small B-cells indicates that the effect of neurotrophins is dependent upon the presence of the p75 low-affinity receptor.

Charcot-Marie-Tooth disease type 1A is the most frequent inherited peripheral neuropathy. It is generally due to heterozygous inheritance of a partial chromosomal duplication resulting in over-expression of PMP22. A key feature of Charcot-Marie-Tooth disease type 1A is secondary death of axons. Prevention of axonal loss is therefore an important target of clinical intervention. We have previously identified a signalling mechanism that promotes axon survival and prevents neuron death in mechanically injured peripheral nerves. This work suggested that Schwann cells respond to injury by activating/enhancing trophic support for axons through a mechanism that depends on upregulation of the transcription factor c-Jun in Schwann cells, resulting in the sparing of axons that would otherwise die. As c-Jun orchestrates Schwann cell support for distressed neurons after mechanical injury, we have now asked: do Schwann cells also activate a c-Jun dependent neuron-supportive programme in inherited demyelinating disease? We tested this by using the C3 mouse model of Charcot-Marie-Tooth disease type 1A. In line with our previous findings in humans with Charcot-Marie-Tooth disease type 1A, we found that Schwann cell c-Jun was elevated in (uninjured) nerves of C3 mice. We determined the impact of this c-Jun activation by comparing C3 mice with double mutant mice, namely C3 mice in which c-Jun had been conditionally inactivated in Schwann cells (C3/Schwann cell-c-Jun(-/-) mice), using sensory-motor tests and electrophysiological measurements, and by counting axons in proximal and distal nerves. The results indicate that c-Jun elevation in the Schwann cells of C3 nerves serves to prevent loss of myelinated sensory axons, particularly in distal nerves, improve behavioural symptoms, and preserve F-wave persistence. This suggests that Schwann cells have two contrasting functions in Charcot-Marie-Tooth disease type 1A: on the one hand they are the genetic source of the disease, on the other, they respond to it by mounting a c-Jun-dependent response that significantly reduces its impact. Because axonal death is a central feature of much nerve pathology it will be important to establish whether an axon-supportive Schwann cell response also takes place in other conditions. Amplification of this axon-supportive mechanism constitutes a novel target for clinical intervention that might be useful in Charcot-Marie-Tooth disease type 1A and other neuropathies that involve axon loss.

Mice lacking the major Schwann cell myelin component P0 show a severe dysmyelination with pathological features reminiscent of the Déjérine-Sottas syndrome in humans. Previous morphological and electrophysiological studies on these mice did not only demonstrate a compromised myelination and myelin maintenance, but were suggestive of an impairment of axons as well. Here, we studied the axonal pathology in P0-deficient mice by quantitative electron microscopy. In addition, we investigated epidermal receptor end organs by immunocytochemistry and muscle pathology by histochemistry.In proximal sections of facial and femoral nerves, axon calibers were significantly reduced, whereas the number of myelin-competent axons was not diminished in 5- and 17-month-old P0-deficient mice. However, in distal branches of the femoral and sciatic nerve (digital nerves innervating the skin of the first toe) the numbers of myelin-competent axons were reduced by 70% in 6-month-old P0-deficient mice. Immunolabeling of foot pads revealed a corresponding loss of Merkel cells by 75%, suggesting that survival of these cells is dependent on the presence or maintenance of their innervating myelinated axons. In addition, quadriceps and gastrocnemius muscles showed pathological features indicative of denervation and axonal sprouting. These findings demonstrate that loss of an important myelin component can initiate degenerative mechanisms not only in the Schwann cell but also in the distal portions of myelinated axons, leading to the degeneration of specialized receptor end organs and impairment of muscle innervation.

Evidence suggests that nerve growth factor (NGF) is an important mediator in inflammatory pain states: NGF levels increase in inflamed tissue, and neutralization of endogenous NGF prevents the hyperalgesia which normally develops during inflammation of the skin. Here we asked whether NGF contributes to sensitization of primary afferent nociceptors, which are an important component of pain and hyperalgesia in inflamed tissue. An in vitra skin nerve preparation of the rat was used to directly record the receptive properties of thin myelinated (A delta) and unmyelinated (C) nociceptors innervating normal hairy skin, carrageenan-inflamed skin and carrageenan-inflamed skin where endogenous NGF had been neutralized by application of a trkA-IgG (tyrosine kinase A-immunoglobulin Ci) fusion molecule. Following carrageenan inflammation, there was a marked increase in the proportion of nociceptors which displayed ongoing activity (50% of nociceptors developed spontaneous activity compared to 4% of nociceptors innervating normal uninflamed skin), and this was reflected in a significant increase in the average ongoing discharge activity. Spontaneously active fibres were sensitized to heat and displayed a more than twofold increase in their dischargeto a standard noxious heat stimulus. Furthermore, the number of nociceptors responding to the algesic mediator bradykinin increased significantly from 28% to 58%, By contrast, the mechanical threshold of nociceptive afferents did not change during inflammation. When the NGF-neutralizing molecule trkA-IgG was coadministered with carrageenan at the onset of the inflammation, primary afferent nociceptors did not sensitize and displayed essentially normal response:properties, although the inflammation as evidenced by tissue oedema developed normally. We therefore conclude that NGF is a crucial component for the sensitization of primary afferent nociceptors associated with tissue inflammation.

Following peripheral-nerve lesions there are well-documented events that affect the contralateral nonlesioned structures. These contralateral effects are qualitatively similar to those occurring at the ipsilateral side, but are usually smaller in magnitude and have a briefer time course. It is unclear whether the findings are an epiphenomenon or serve a biological purpose, but in either case the existence of these effects implies the presence of unrecognized signalling mechanisms that link the two sides of the body. Strong circumstantial evidence argues against a peripheral mechanism (for example, via circulating factors) and in favour of a central mechanism, in particular signalling via the system of commissural interneurons that is present in spinal cord and brainstem. While an altered pattern of activity in this system might underlie the phenomenon, there are several reasons for proposing that the changes depend upon chemical signals, possibly growth factors. Because of its relative easy access for experimental manipulation, the spinal cord could serve as a model system to study these transmedian signalling systems.

We report a 5-year follow-up of a patient with Ross syndrome. A biopsy of the anhidrotic skin immunostained with protein gene product 9.5 visualized by confocal microscopy revealed selective loss of sudomotor fibers, whereas epidermal innervation remained intact, providing the first morphologic evidence of selective loss of sudomotor fibers in this syndrome. Among the different treatment strategies employed for the patient's disabling segmental hyperhidrosis, intracutaneous injection of botulinum toxin A was the most helpful.

Neurotrophin-4 (NT4) is the most recently discovered neurotrophic factor in mammals and, functionally, the least well understood. Here, we used mice that lack NT4 to determine whether NT4 is required for the survival of functionally identified subclasses of cutaneous sensory neurons. By using three independent methods of histological and electrophysiological analysis, we show that NT4 is specifically required for the survival of down hair (D-hair) receptors that innervate a subpopulation of hair follicles. All other functionally distinct types of afferents neurons innervating hairy skin were not affected in their survival or in their function. Previous studies have shown that BDNF is required for the mechanical sensitivity of slowly adapting (SA) mechanoreceptors but not for the postnatal survival of myelinated cutaneous afferent fibers. In contrast, the receptive properties of SA mechanoreceptors were not impaired in animals lacking NT4. Consequently, these data show that the two trkB ligands, NT4 and BDNF, have distinct and nonoverlapping roles in supporting cutaneous sensory neurons. Whereas NT4 is required for the survival of D-hair receptors, BDNF supports the mechanical function of SA fibers.

Since the early eighties we have witnessed a surge of major discoveries about mechanisms of a unique plasticity in the central nervous system (CNS) that play an important role in the generation of ongoing pain and hyperalgesia [17]. One spectacular example triggered by short periods of noci­ ceptive activity is the increased efficiency of synaptic transmission at pain-relevant neurons in the dorsal horn of the spinal cord [6,12]. These findings of central hyperexcitability have provided a great advance in our conceptual framework for the explanation of erstwhile enigmatic clinical symptoms such as touch-evoked pain (allodynia). Alterations of the CNS circuitry are also implicated in the consolidation of painful conditions that may persist, perhaps indefinitely, in some situations even in the absence of excitation of nociceptors. Al­ though it has been recognized for some time that changes in the receptive properties of nociceptors are the basis of some forms of hyperalgesia notably to heat [13], the impressive advances in the understanding of CNS plasticity have diverted attention from the periph­ eral events of nociception. It is therefore timely that the article by Carlton and Coggeshall refocuses on the peripheral aspects of nociception. In fact, several lines of evidence now show that changes in the excitability of primary nociceptive afferents may be the single most important factor in the generation and maintenance of acute inflammatory or chronic neuropathic pain in hu­ mans. Thus, local anesthetic blocks of affected nerves or tissues, differential nerve blocks, detailed psychophysi­ cal investigations, and intraneural recording and stimula­ tion experiments using microneurography all converge

Brain-derived neurotrophic factor (BDNF) is a survival factor for certain sensory neurons during development. Using electrophysiology in BDNF-deficient mice, we show here that slowly adapting mechanoreceptors (SAM), but not other types of cutaneous afferents, require BDNF in postnatal life for normal mechanotransduction. Neurons lacking BDNF did not die, but instead showed a profound and specific reduction in their mechanical sensitivity, which was quantitatively the same in BDNF -/- and BDNF +/- animals. Postnatal treatment of BDNF +/- mice with recombinant BDNF completely rescued the mechanosensitivity deficit. Therefore BDNF is important for regulating SAM mechanosensitivity, independent of any survival-promoting function.

Nerve growth factor (NGF) has a well characterized role in the development of the nervous system and there is evidence that it interacts with nociceptive primary afferent fibres, Here we applied a synthetic tyrosine kinase A IgG (trkA-IgG) fusion molecule for 10-12 days to the innervation territory of the purely cutaneous saphenous nerve in order to bind, and thereby neutralize endogenous NGF in adult Fats. Using neurophysiological analysis of 152 nociceptors we now show that sequestration of NGF results in specific changes of their receptive field properties. The percentage of nociceptors responding to heat dropped significantly from a normal 57% to 32%. This was accompanied by a rightward shift and a reduced slope of the stimulus response function relating the intracutaneous temperature to the neural response. The number of nociceptors responding to application of bradykinin was also significantly reduced from a normal of 28% to 8%, In contrast, the threshold for mechanical stimuli and the response to suprathreshold stimuli remained unaltered, as did the percentage of nociceptors responding to noxious cold. The reduced sensitivity of primary afferent nociceptors was accompanied by a reduction in the innervation density of the epidermis by 44% as assessed with quantitative immunocytochemical analysis of the panaxonal marker PGP 9.5. This demonstrates that endogenous NGF in the adult specifically modulates the terminal arborization of unmyelinated fibres and the sensitivity of primary afferent nociceptors to thermal and chemical stimuli in vivo.

Neurotrophins mediate specific effects on sensory neurons through tyrosine kinase receptors. Most of these neurons also co-express the neurotrophin receptor p75 (p75 NTR ) but its function has remained obscure. We now show that nerve growth factor but not brain-derived neurotrophic factor or neurotrophin-3 selectively increases the expression of bradykinin binding sites on cultured dorsal root ganglion neurons from adult mouse via p75 NTR . This up-regulation of bradykinin binding sites did not occur in neurons from mice lacking p75 NTR or in neurons from wild-type mice treated with p75 NTR -blocking antibody, indicating that tyrosine kinase receptors alone are not sufficient to trigger this physiological neuronal response. Thus, the interaction of nerve growth factor with p75 NTR is an important factor contributing to chronic pain conditions.

Mice with a targeted mutation of the p75 low affinity neurotrophin receptor display smaller peripheral nerves and dorsal root ganglia. Here we show that transgenic mice have a significant elevation of thresholds to noxious mechanical and heat stimuli compared with p75+/+ control mice. Immunocytochemical analysis using antibodies against PGP 9.5 (a panaxonal marker) and calcitonin gene related peptide (CGRP, which labels peptidergic neurons) showed a reduction to 73% and 54%, respectively, of the epidermal innervation density. However, analysis of the cell size distribution of toluidine blue-stained dorsal root ganglia showed no selective loss of neurons of particular diameters. Moreover, the neurochemical profile of dorsal root ganglia cells as defined by trkA, CGRP, IB4 and RT97 immunostaining revealed no significant differences in comparison with p75+/+ animals. Staining of the dorsal horn of the spinal cord for CGRP and IB4 was also normal in p75-/- animals. Taking into account a previously reported loss of approximately 50% dorsal root ganglion neurons, we conclude that all types of sensory neurons are equally depleted in p75-/- mice and that the absence of p75 impedes the development of more than one neuronal subtype.

Sympathetic reflex responses were elicited in human volunteers by sustained selective excitation of nociceptors by noxious chemicals, namely topical application of mustard oil which elicited burning pain, or histamine which induced itching in a skin area of 5 cm2 on the volar aspect of one forearm. Stimulus-related sympathetic reflex responses were studied by means of computer-assisted infrared thermography of the palmar aspects of both hands. Nociceptive stimulation induced a decrease of skin surface temperature in both hands interpreted as vasoconstriction. The magnitude of the reflex cooling was correlated with the magnitude of the sensation (r = 0.49), but independent of the quality of sensation (itch or pain). The temperature reduction was maintained for more than 30 min and its time-course matched the time-courses of pain or itch sensations. It is concluded that the sustained and selective excitation of nociceptors elicits a sustained sympathetic reflex response, which adapts very slowly. The time-course of the reflexes suggests that these are not arousal responses, but may be indicators of nociceptive processing in conscious humans. Contralateral temperature decreases were consistently smaller than ipsilateral ones. Thus, sustained nociceptive-specific vasoconstrictor reflexes may be somatotopically organised with an emphasis on areas close to the painful stimulus (homotopic), which has so far only been shown in animals. The study thus demonstrates for the first time in humans the presence of a sympathetic reflex asymmetry, which is specific for nociceptive afferent input.

Previous evidence suggests that, in adult animals, nerve growth factor (NGF) can induce hyperalgesia, and may be an endogenous mediator in some persistent pain states. Here we have studied the effects of single intradermal injections of 50-500 ng of human recombinant NGF into the plantar skin of adult rat hindpaws. We found that doses of 250 ng and more produced a prolonged and stable thermal hyperalgesia to radiant heat. NGF did not produce overt pain behaviour as judged by the absence of paw licking or guarding of the injected paw. In animals subjected to surgical or chemical sympathectomy, by repeated systemic guanethidine treatments, the hyperalgesic effects of NGF were markedly reduced. We also found that NGF produced plasma extravasation in rat skin, using the Evan's blue method, with a dose dependency similar to that determined for hyperalgesia. Together, these findings suggest that NGF can lead to a rapid activation and sensitization of cutaneous nociceptors. However, these actions appear at least partly indirect, requiring the presence of normal sympathetic post-ganglionic terminals.

The peripheral nociceptive nervous system is very malleable and following tissue injury, nociceptors often increase their sensitivity. They accomplish this by a leftward-shift of their stimulus response functions to heat stimuli, the acquisition of responses to new modalities, notably algesic mediators or the expansion of mechanosensitive receptive fields. Moreover, a recently discovered class of nociceptors which is unresponsive to transient noxious stimuli in healthy tissue starts to discharge specifically at the onset of tissue inflammation. Persistent increases of nociceptor excitability can occur after nerve lesion and contribute significantly neuropathic pain states in humans.

Sympathelic vasoconstrictor neurons that had previously innervated blood vessels in hairy skin were made to reinnervate the vasculature of the hairless skin of the paw pad by suturing the central stump of the cut sural nerve to the distal stump of the cut tibial nerve. After allowing sufficient time for the reinnervation, electrical stimulation of the vasoconstrictor pathway in the lumbar sympathetic trunk produced a reduction of the blood flow that was significantly greater than in control animals. There was also a clear sign of a “denervation supersensitivity” of the blood vessels as evidenced by a significantly increased vasoconstriction that followed the systemic application of the alpha 1 -adrenoceptor specific agonist phenylephrine. Neurogenic vasodilatation evoked by antidromic excitation of small diameter primary afferent neurones was significantly impaired although myelinated and unmyelinated primary afferents had re-grown into the target tissue. Electrical stimulation of the intact tibial nerve (containing sympathetic vasoconstrictor axons and nociceptive primary afferent fibres) in control animals, always produced vasodilatation indicating that the neurogenic vasodilatation can override the sympathetic vasoconstrictor response. By contrast, electrical stimulation of cross-unioned nerves consistently produced a robust vasoconstriction. We conclude that sympathetic vasoconstrictor neurons have a high capacity to functionally reinnervate autonomic effector organs in the adult cat. Despite this functional recovery, the blood vessels exhibited stronger than normal responses to an alpha 1 -adrenoceptor agonist. The impaired neurogenic vasodilatation mediated by small diameter afferents may be due to their poor ability to re-establish their efferent vasodilatory function. Alternatively it may be masked by the strong vasoconstriction.

Accumulating evidence shows that adhesion molecules are critically involved in inflammatory demyelination in the focusing of systemic immune responses into the target tissue, the nervous system.Adhesion molecules are upregulated through the action of cytokines. Tumor necrosis factor alpha appears to be of prime importance. Circulating adhesion molecules probably reflect acute inflammatory episodes in the central and peripheral nervous system, but may also function to modulate ongoing inflammatory responses. Cytokines released by T H 1 cells render resident and immigrant macrophages, as well as microglia, activated to synthesize and release increased amounts of inflammatory mediators, such as oxygen radicals, nitric oxide metabolites, and components of the complement system. A more detailed understanding of the sequence of immunopathologic events that culminate in myelin damage in the central and peripheral nervous systems has revealed several sites to which more specific and effective immunointervention can be targeted. NEUROLOGY 1995;45(Suppl 6): S22-S32

Different types of hyperalgesia were studied after experimental induction of inflammation in small skin areas of healthy volunteers either by topical application of capsaicin solution (1% in 70% ethanol) or by briefly freezing a skin area of similar size to -28 degrees C. Sensory tests were performed 30 min after capsaicin application and 22 h after freeze lesions. Heat pain thresholds were lowered after both treatments, probably due to nociceptor sensitization. Hyperalgesia to four types of mechanical stimulation was studied. (i) Hyperalgesia to punctate stimuli was encountered at the skin site directly affected by the noxious chemical or freeze stimulus (1 degree zone) and in the surrounding skin (2 degrees zone) in both models though the area of 2 degrees hyperalgesia to punctate stimuli after freezing was smaller than after capsaicin. (ii) Hyperalgesia to gently brushing the skin was prominent after capsaicin in 1 degree and 2 degrees zone, but almost absent after freezing. It was concluded that both hyperalgesia to punctate stimuli and brush-evoked pain are due to central nervous plasticity changes rather than nociceptor sensitization. As revealed by differential nerve blocks, brush-evoked pain is mediated by low threshold mechanosensitive A beta-fibres, whilst hyperalgesia to punctate stimuli can be elicited when only C-fibres conduct. In contrast to hyperalgesia to punctate stimuli it requires continuous background discharges in nociceptor units. (iii) Pressure hyperalgesia to tonic stimulation with a blunt probe was encountered in the 1 degree zone of both types of inflammation and is probably due to recruitment of sensitized nociceptor units. (iv) Impact hyperalgesia was studied by shooting small bullets against the skin at predetermined velocities. It was found in the 1 degree zone after freezing and absent in the capsaicin model. Differential nerve blocks revealed that it is probably mediated by sensitized C-fibres. In conclusion, different types of inflammatory changes may result in characteristic different patterns of hyperalgesia.

Acute palsies of the peroneal nerve may have a variety of causes. In many patients, the cause remains undetermined. The authors report a patient with a thrombosis of a crural vein causing an acute peroneal nerve palsy. If the clinical history of patients with an acute peroneal nerve lesion is suggestive of venous thrombosis an appropriate diagnostic workup should be considered.

MRI may provide treatment outcome measures in neuromuscular conditions. The authors assessed MRI magnetisation transfer ratios (MTRs) in lower-limb musculature as markers of pathology in peripheral neuropathies and compared the findings with associated clinical data. Ten patients with Charcot-Marie-Tooth disease type 1A (CMT1A) and nine patients with chronic inflammatory demyelinating polyneuropathy (CIDP) were compared with 10 healthy subjects. The MTR in the calf muscles was significantly lower than controls in the two patient groups (both p

The growth factor family of neurotrophins has major roles both inside and outside the nervous system. Here, we report a detailed histological analysis of key phenotypes generated by the ablation of the Kinase D interacting substrate of 220 kDa/Ankyrin repeat-rich membrane spanning (Kidins220/ARMS) protein, a membrane-anchored scaffold for the neurotrophin receptors Trk and p75(NTR). Kidins220 is important for heart development, as shown by the severe defects in the outflow tract and ventricle wall formation displayed by the Kidins220 mutant mice. Kidins220 is also important for peripheral nervous system development, as the loss of Kidins220 in vivo caused extensive apoptosis of DRGs and other sensory ganglia. Moreover, the neuronal-specific deletion of this protein leads to early postnatal death, showing that Kidins220 also has a critical function in the postnatal brain.

1. A total of sixty-five sacral afferent neurones with myelinated fibres supplying the urinary bladder was recorded from the sacral roots S2 in anaesthetized cats. All afferent units were identified with electrical stimulation of the pelvic nerve. The discharge properties were quantitatively evaluated using slow filling at rates of 1-2 ml min-1 and isotonic distension to preset pressure levels. Eight afferents were studied prior to and after acute sacral de-efferentation of the urinary bladder. 2. All afferent units were silent when the bladder was empty and responded in a graded manner to an increase of intravesical pressure. During slow filling the level of afferent activity correlated closely with the level of the intravesical pressure. All afferents behaved like slowly adapting mechanoreceptors with both a dynamic and static component of their discharge. With the exception of two units the intraluminal pressure threshold was below 25 mmHg. Thus virtually all myelinated afferents respond in the pressure range that is reached during a non-painful micturition cycle. 3. The stimulus-response functions of the afferents were similar regardless of whether intravesical pressure was increased by slow filling or by distension. However, during slow filling stimulation response functions often exhibited steeper slopes between 5 and 25 mmHg indicating that relatively small changes of intravesical pressure result in large changes of afferent activity. Nevertheless, all units displayed monotonically increasing stimulus response functions throughout the innocuous and noxious pressure level. 4. The stimulus-response functions of the afferent neurones did not change after acute de-efferentation of the urinary bladder, although the rapid phasic fluctuations of afferent activity that are produced by small contractions of the urinary bladder under normal conditions largely disappeared. This means that contractions and distension activate the afferent endings by a common mechanism. 5. It is concluded that the myelinated sacral afferents of the urinary bladder form a homogeneous population which encodes all information necessary for the normal regulation of this organ. Furthermore, this set of afferents mediates all sensations which may reach consciousness within a normal micturition cycle.

SUMMARY Mutations in the enzyme glycyl-tRNA synthetase (GARS) cause motor and sensory axon loss in the peripheral nervous system in humans, described clinically as Charcot-Marie-Tooth type 2D or distal spinal muscular atrophy type V. Here, we characterise a new mouse mutant, GarsC201R, with a point mutation that leads to a non-conservative substitution within GARS. Heterozygous mice with a C3H genetic background have loss of grip strength, decreased motor flexibility and disruption of fine motor control; this relatively mild phenotype is more severe on a C57BL/6 background. Homozygous mutants have a highly deleterious set of features, including movement difficulties and death before weaning. Heterozygous animals have a reduction in axon diameter in peripheral nerves, slowing of nerve conduction and an alteration in the recovery cycle of myelinated axons, as well as innervation defects. An assessment of GARS levels showed increased protein in 15-day-old mice compared with controls; however, this increase was not observed in 3-month-old animals, indicating that GARS function may be more crucial in younger animals. We found that enzyme activity was not reduced detectably in heterozygotes at any age, but was diminished greatly in homozygous mice compared with controls; thus, homozygous animals may suffer from a partial loss of function. The GarsC201R mutation described here is a contribution to our understanding of the mechanism by which mutations in tRNA synthetases, which are fundamentally important, ubiquitously expressed enzymes, cause axonopathy in specific sets of neurons.

1. Conscious perception of noxious and innocuous distension of the colon as well as the reflex control of anal continence and defecation largely depend on an intact sacral primary afferent innervation. Here we have studied the functional properties of these visceral primary afferent neurons in the dorsal root S2 in 17 cats. Single fibers projecting into the pelvic nerve were identified electrically and studied with innocuous and noxious mechanical stimulation of colon and anal canal. 2. A total of 59 units responding to one of these stimuli were investigated and they could be separated into two subpopulations of afferents. Thirty-six fibers were reproducibly excited by distension of the colon, but not by mechanical stimulation of the anal canal. They were thin myelinated or unmyelinated fibers with a median conduction velocity of 3.2 m/s. The remaining 23 units had receptive fields in the mucosa of the anal canal and responded readily to an innocuous proximodistal shearing stimulus, but not to distension stimuli applied to the same area. All, but two of these afferents were thin myelinated with a median conduction velocity of 7.7 m/s, which was significantly different from the conduction velocity of afferent neurons responding to distension of the colon. 3. Units responding to distension of the colon had thresholds in the innocuous range of the intracolonic pressure. Receptors that were activated only by noxious intraluminal pressure were absent. On the basis of their response to supramaximal isotonic distension, colonic afferents could be subclassified as phasic (n = 17) or tonic (n = 19) units. Phasic afferents were only transiently excited during filling or emptying of the colon, whereas tonic afferents discharged throughout the distension. The two populations had also significantly different median conduction velocities of 8.0 (n = 16) and 1.7 (n = 15) m/s, respectively. 4. Stimulation response functions were evaluated for 12 tonic afferents. All units encoded an increase of intracolonic pressure by the intensity of their discharge frequency. Increases of intracolonic pressure produced significantly higher discharge frequencies from unmyelinated than from thin myelinated afferents. 5. In three animals the percentage of unmyelinated fibers responding to mechanical stimulation of colon and anal canal was determined. Out of 213 electrically identified unmyelinated units projecting into the pelvic nerve, only 11 (5.2%) were excited. Thus, acute innocuous and noxious mechanical stimuli of the large intestine do not appear to be the adequate stimulus for the large majority of unmyelinated pelvic afferents. 6. In conclusion, distension of the colon and mechanical stimulation of the anal canal activates distinct populations of primary afferent neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

The neurophysiological basis of visceral sensations in general and pain in particular have been mainly studied with short-lasting stimuli that simulate the acute events of visceral organ function. Pelvic viscera are supplied by spinal afferents which are involved in the coordinated reflex regulation of continence and evacuation of bowel and bladder and are capable of signalling impending or frank tissue damage. Typically, each afferent neuron innervates one viscus only. The organ-specific subtypes are functionally homogenous and encode by their discharge frequency the information for organ regulation, non-painful and painful sensations. Thus, pain elicited from these organs under physiological conditions is probably not elicited by a specific set of nociceptive visceral afferents. While the use of brief stimuli has yielded invaluable neurophysiological information for normal, healthy viscera, it has fallen somewhat short of providing information about the neuronal basis of chronic visceral pain states. Using pathological models such as experimental inflammation of the urinary bladder and ischaemia of the colon we have shown that the receptor properties of most afferents change dramatically. Of particular interest is the discovery of a novel type of visceral receptor which is not excited by extreme noxious mechanical stimuli applied to the healthy tissue but which is vigorously activated at the onset of an inflammation. This means that the number of functionally active primary afferents is not immutable, but critically depends on the state of the tissue. This new principle of plasticity in the peripheral nervous system bears some considerable importance for the understanding of the genesis of chronic visceral pain states. We suggest that this new type of receptor is present in most viscera and contributes significantly to the primary afferent activity in chronic visceral pain. Furthermore, these afferents may precipitate long-term alterations of spinal reflex pathways and, as a consequence of this, abnormal autonomic activities to visceral organs.

1. The ventral roots of the spinal cord contain a large number of unmyelinated primary afferent neurones. There is some controversy, however, about the function of these fibres and the route of their central projection. Here we have used electrophysiological techniques to quantify the central projection patterns of these neurones in the segment S2 of adult chloralose-anaesthesized cats. 2. A total of 1185 single unmyelinated units were recorded in small filaments isolated from intact and de-efferented ventral roots or intact dorsal roots of the segment S2 in nineteen cats. The projection patterns of these neurones were tested using supramaximal electrical stimulation of the pelvic and pudendal nerve (the main tributaries of the spinal nerve of this segment) and of the segmental companion root (dorsal or ventral as appropriate). 3. The principal finding of this study is that 85% of unmyelinated afferent axons in the ventral root are direct and exclusive projections. They constitute a separate class of afferents which is only capable of transmitting information from the periphery via the ventral roots. However, the proportion of these fibres that enter the central nervous system is unknown and it seems likely that some of them peter out as they approach the spinal cord and end blindly. The functional role of such afferents remains obscure. 4. For the remaining 15% of unmyelinated ventral root afferents, a projection into the segmental dorsal root was found. The majority of those fibres (about two-thirds) are primary afferent neurones innervating the pia mater. Some of these units had a small spot-like receptive field and responded to mechanical stimuli such as pressure and stretch of the root. They did not have axon projections in a peripheral nerve. 5. A few (5%) unmyelinated ventral root fibres are collateral branches of normal primary afferents projecting through the dorsal root. These trifurcating neurones are a small population which make up only some 0.5% of all dorsal root ganglion cells. The functional significance of this population too is unknown. 6. For none of the fibres that projected into both dorsal and ventral root was there positive evidence for the existence of looping axons that merely make a detour into one of the roots. Although the existence of loops cannot completely be excluded, our evidence suggests that they can constitute at most 5% of the unmyelinated ventral root afferents.

Activation of unmyelinated primary afferents produces vasodilatation and plasma extravasation in the skin. Here, using the laser Doppler technique to measure changes in blood flow and the Evans blue technique for quantification of plasma extravasation, we have asked whether the stimulation of C-fibre precipitates the same phenomena in the spinal cord. Our results show that there is an increase of blood flow, but no extravasation in the ipsilateral lumbar enlargement of the spinal cord following supramaximal electrical stimulation of the sciatic nerve. The blood flow increases were small and short-lived compared with those seen in skin, and could be completely explained by concomitant blood pressure changes. Hence, whilst the same substances are apparently released from the peripheral and central terminals of primary afferent fibres, their ability to produce vasodilatation and extravasation is absent or severely restricted in the spinal cord.

Purpose of reviewClinical investigations of neuromuscular diseases routinely involve genetic, neurophysiological, biochemical and histopathological methods. More recently, various magnetic resonance imaging techniques have become available and extended the differential diagnostic possibilities.Recent findingsUsing magnetic resonance imaging it is now possible to quantify muscle volume in selected body regions and measure wasting and exercise-induced muscle hypertrophy. Evidence is forthcoming that many hereditary myopathies are characterized by distinct patterns of muscle degeneration and this helps in selecting other relevant genetic and biochemical investigations. With diffusion-weighted tensor imaging it is possible to identify the microstructure of normal and diseased muscles. Arterial spin labelling is an emerging non-invasive tool to assess blood-flow changes in individual muscles. Magnetic resonance spectroscopy now provides an exciting opportunity to visualize metabolic changes and the pathophysiologically relevant cellular perturbations in muscle channelopathies affecting the muscle-specific sodium-channel isoform Na-v 1.4.SummaryMagnetic resonance imaging supplements investigations for the differential diagnosis of neuromuscular diseases. An advantage over routine neurophysiological or histopathological methods is that they are operator-independent, non-invasive and painless. Magnetic resonance imaging also has the advantage of providing a lasting detailed topographical picture of regional variations and allows robust measurements of muscle volume and various functional parameters.

Objective To establish an in vitro model for measurement of the excitability properties of cutaneous sensory axons. Methods We used a saphenous skin–nerve preparation from adult rat in combination with computerized threshold tracking. We measured strength–duration time constant, the recovery of excitability after a supramaximal stimulus and the accommodation to conditioning subthreshold polarizing stimuli (threshold electrotonus, current–threshold relationship) and compared these with previously published recordings from sensory axons in human median nerve. Results Threshold electrotonus and the amplitude of superexcitability were indistinguishable between human median nerve in vivo and rat saphenous nerve in vitro, but several excitability parameters were significantly different in the rat: strength–duration time constant was significantly shorter (0.19 ± 0.01 vs. 0.53 ± 0.02 ms); the refractory period was shorter (1.9 ± 1.1 ms vs. 3.5 ± 1.0 ms) and late subexcitability was smaller (6.3 ± 0.3% vs. 11.3 ± 0.5%); thirdly, during recording of current–threshold relationship, rat nerves displayed more inward rectification to strong hyperpolarizing currents. Parameters were stable over more than 3 h. Conclusions Excitability changes of sensory Aβ-fibres can be reliably studied in the rat in vitro and are qualitatively similar to humans. Significance This rat model will facilitate pharmacological studies of nerve excitability and work on models of neuropathy.

Acute brachial diplegia with normal findings of the legs, "man-in-the barrel" (MIB) syndrome, is generally thought to be caused by bilateral supratentorial brain lesions of the prerolandic cortical and subcortical area. We report 1 patient with a sudden onset of MIB syndrome with no supratentorial lesion but a hemodynamically induced atypical anterior spinal cord infarction after unilateral vertebral artery dissection. Thus, in MIB syndrome an infratentorial lesion site, including the cervical spinal cord, should also be considered.

A local elevation of H+-ion concentrations often occurs in inflammation and usually evokes pain by excitation of primary nociceptive neurons. Expression patterns and functional properties of the capsaicin receptor and acid-sensing ion channels suggest that they may be the main molecular substrates underlying this proton sensitivity. Here, we asked how the capsaicin receptor TRPV1 and acid-sensing ion channels (ASICS) contribute to the proton response in subpopulations of nociceptive neurons from adult rats and mice (wildtype C57/Bl6, Balb/C and TRPV1-null). In cultured dorsal root ganglion neurons, whole cell patch clamp recordings showed that the majority of capsaicin-sensitive rat dorsal root ganglion neurons displayed large proton-evoked inward currents with transient ASIC-like properties. In contrast, the prevalence of ASIC-like currents was smaller in both mouse wildtype strains and more frequent in capsaicin-insensitive neurons. Transient ASIC-like currents were more frequent in both species among isolectin B4-negative neurons. A significantly reduced proton response was observed for dissociated dorsal root ganglion neurons in TRPV1 deficient mice. Unmyelinated, but not thin myelinated nociceptors recorded extracellularly from TRPV1-null mutants showed a profound reduction of proton sensitivity. Together these findings indicate that there are significant differences between rat and mouse in the contribution of TRPV1 and ASIC subunits to proton sensitivity of sensory neurons. In both species ASIC subunits are more prevalent in the isolectin B4-negative neurons, some of which may represent thin myelinated nociceptors. However, the main acid-sensor in isolectin B4-positive and isolectin B4-negative unmyelinated nociceptors in mice is TRPV1.