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Electrical field stimulation (EFS)-induced non-adrenergic non-cholinergic (NANC) relaxation responses in the rabbit vaginal wall were investigated. These NANC responses were partially inhibited with the nitric oxide synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME; 500 microM), N(G)-nitro-L-arginine (300 microM) or N-iminoethyl-L-ornithine (500 microM) or the selective soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM). Application of L-NAME and ODQ concomitantly did not increase the degree of inhibition. L-NAME or ODQ were observed to be more effective at low frequencies. The resistant part of the responses was more pronounced at higher frequencies and was completely inhibited by tetrodotoxin (1 microM). Exogenous application of the peptides vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activating peptide (PACAP-27 and PACAP-38), peptide histidine methionine (PHM), peptide histidine valine (PHV), helospectin-I or -II induced a relaxation response. Calcitonin gene-related peptide or substance P did not cause any relaxation. The peptidase alpha-chymotrypsin (type II; 2 units ml(-1)) did not affect non-nitrergic NANC responses, although it did inhibit relaxation responses elicited by exogenous VIP, PACAP-27, PACAP-38, PHM, PHV, helospectin-I or -II. K(+) channel inhibitors apamin (1 microM) or charybdotoxin (100 nM) when used alone or in conjunction did not affect non-nitrergic NANC responses. The non-nitrergic NANC responses were not associated with any increase in intracellular cyclic adenosine-3', 5'-monophosphate (cyclic AMP) or cyclic guanosine-3', 5'-monophosphate (cyclic GMP) concentrations. The peptide-induced relaxations were all associated with increases in cyclic AMP concentrations. These results suggest that a neuronal factor elicits non-nitrergic NANC responses in the rabbit vaginal wall. The identity of this factor remains to be established.

1. Over the past 5 years, there has been emerging evidence that the vestibular system regulates sympathetic nerve activity in humans. We have studied this issue in humans by using head-down rotation (HDR) in the prone position. 2. These studies have clearly demonstrated increases in muscle sympathetic nerve activity (MSNA) and calf vascular resistance during HDR. These responses are mediated by engagement of the otolith organs and not the semicircular canals. 3. However, differential activation of sympathetic nerve activity has been observed during HDR. Unlike MSNA, skin sympathetic nerve activity does not increase with HDR. 4. Examination of the vestibulosympathetic reflex with other cardiovascular reflexes (i.e. barorereflexes and skeletal muscle reflexes) has shown an additive interaction for MSNA. 5. The additive interaction between the baroreflexes and vestibulosympathetic reflex suggests that the vestibular system may assist in defending against orthostatic challenges in humans by elevating MSNA beyond that of the baroreflexes. 6. In addition, the further increase in MSNA via otolith stimulation during isometric handgrip, when arterial pressure is elevated markedly, indicates that the vestibulosympathetic reflex is a powerful activator of MSNA and may contribute to blood pressure and flow regulation during dynamic exercise. 7. Future studies will help evaluate the importance of the vestibulosympathetic reflex in clinical conditions associated with orthostatic hypotension.

We clarified whether the intraocular pressure (IOP) response elicited by stimulation of the cervical sympathetic nerve (CSN) is influenced by changes in the baseline of IOP level and by beta-adrenergic blockade. The CSN was stimulated electrically for 30 seconds (10 V, 0.1-100 Hz, 2 milliseconds pulse duration) in urethane (100 mg/kg i.v.)-chloralose (50 mg/kg i.v.)-anesthetized, paralyzed cats. The IOP was monitored manometrically, and a controlled saline infusion was delivered into the anterior chamber to gradually increase IOP. CSN stimulation was delivered at the various baseline IOP levels so obtained. When required, a beta-adrenergic blocker timolol (2%) was delivered into the conjunctival cul-de-sac. The normal IOP in our cats was 25+/-3 mmHg. This value decreased transiently on CSN stimulation. The amplitude of this IOP response depended on stimulus frequency and the pre-stimulus baseline IOP level. Topical administration of timolol increased the IOP response to CSN stimulation at a given baseline level. These results suggest that beta-adrenergic blockade increases the alpha-adrenergic mediated-IOP reduction elicited by CSN stimulation at given baseline IOP level.

Electrical field stimulation (EFS) of dog gallbladder strips induced a frequency-dependent contractile response followed by an off-relaxation that was turned into a pure inhibitory response after atropine pretreatment. Guanethidine reduced the atropine-induced relaxing responses, so an adrenergic mechanism can partially account for the nerve-mediated gallbladder relaxation. However, guanethidine pretreatment also revealed a nonadrenergic noncholinergic (NANC) relaxation induced by EFS, which was frequency independent. NANC relaxations were reduced by L-arginine methyl ester (L-NAME, 100 micromol L-1), a nitric oxide synthase inhibitor (D-p-Cl-Phe6, Leul7; 10 micromol L-1), a vasoactive intestinal peptide (VIP) receptor antagonist, and an inhibitor of haem oxygenase, (copper protoporphyrin IX; CuPP-IX; 10 micromol L-1), suggesting that nitric oxide (NO), VIP and carbon monoxide (CO), respectively, are released in response to EFS. Immunoreactivities for haem oxygenase-2 (HO-2) and VIP, and histochemical staining for NADPH diaphorase were observed in nerve cell bodies and fibres, demonstrating the presence of CO, VIP and NO as putative NANC neurotransmitters in dog gallbladder. These data support the hypothesis that NO, VIP and CO contribute to NANC relaxation of the canine gallbladder.

Objectives: The study was done to define the role of the autonomic nervous system in postoperative tetralogy of Fallot., Background: Subsequent to surgical correction of tetralogy of Fallot, patients are at long-term risk of sudden death owing to ventricular electrical instability. The status of the sympathetic nervous system in these patients, known to play an important role in other patients at risk, remains unknown., Methods: We used (123)I metaiodobenzylguanidine (MIBG) with tomographic imaging, combined with assessment of heart rate variability (HRV), to evaluate the activity of the sympathetic nervous system. We analyzed 22 patients who had undergone total correction of tetralogy of Fallot: 13 with either no or minor ventricular arrhythmias, and 9 with sustained ventricular tachycardia or ventricular fibrillation., Results: Analysis of HRV revealed a reduction in vagal control and sympathetic dominance in all patients compared with a healthy control group of 20 subjects. A significant difference was found in the standard deviation of all the adjacent intervals between normal beats (SDNN) in patients with or without severe ventricular arrhythmias. A significant reduction in uptake of (123)I MIBG was demonstrated 30 min after IV injection, and a trend toward reduction after 5 h, associated with reduced washout indices. These data reflect a decrease in the number of nerve endings in the right and left ventricular walls, and an inhomogeneous distribution of the adrenergic nervous system. The uptake of MIBG was significantly reduced in the patients at risk of ventricular tachycardia or fibrillation., Conclusions: Subsequent to surgical correction of tetralogy of Fallot, the positive correlation between myocardial uptake of MIBG, SDNN and the QRS dispersion confirmed the usefulness of analysis of the adrenergic nervous system to stratify patients at risk of life-threatening arrhythmias.

We examined whether the extent of sympathetic sprouting in the dorsal root ganglion was a function of the number of injured nerve fibers. We compared two groups of rats. One group was subjected to unilateral superior and inferior caudal trunk transections at the level between the S1 and S2 spinal nerves (S-I group) and the other group was subjected to unilateral superior caudal trunk transection at the same level (S group). Immunohistochemical staining with tyrosine hydroxylase (TH) antibody of the S1 DRG revealed that the degree of TH-immunoreactive fibers was more extensive in the S-I group than in the S group. However, there was no difference in the severity of neuropathic pain behaviors between the two groups. These results suggest that the extent of sympathetic sprouting in the DRG following peripheral nerve injury is proportionally related to the amount of injured nerve fibers, but not related to the degree of neuropathic pain behaviors.

Purpose: To demonstrate the phenomenon of adrenergic denervation supersensitivity in rabbit choroidal blood vessels after superior cervical ganglionectomy., Methods: Twenty four albino rabbits of both sexes weighing 2-3 kg were randomly separated into two groups. Twelve rabbits received bilateral superior cervical sympathectomy 2 weeks prior to the study (group s). The other 12 rabbits served as controls (group n). Four different concentrations of 0.1 ml phenylephrine, 0.05%, 0.025%, 0.013%, and 0.007% were slowly injected into the vitreous body near the retinal surface in group (n) and (s) rabbits (n = 6 in each group). The choroidal blood flow (PF), blood volume (CMBC), and velocity (V) were measured simultaneously by laser Doppler flowmetry (Perimed, PF 4001)., Results: The PF showed similar decreases in group (n) and (s) rabbits after injection of 0.05%, 0.025%, and 0.013% phenylephrine. With 0.007% phenylephrine, the PF remained unchanged in group (n) rabbits, but decreased significantly in group (s) rabbits (p = 0.0007). Velocity decreased similarly in both group (n) and (s) rabbits except for the 0.007% phenylephrine, concentration in which velocity decreased significantly in group s rabbits (p = 0.0001). There was no statistical difference in CMBC between group n and s rabbits at any of the test concentrations., Conclusions: The difference in PF decrease between group (n) and (s) rabbits with 0.007% phenylephrine demonstrated the existence of choroidal blood vessel denervation supersensitivity. The decrease in PF was achieved mainly through a decrease in blood cell velocity.

Modulation of voltage-activated Ca2+ channels by adenosine was investigated in male rat major pelvic ganglion (MPG) neurons by using the whole-cell variant of the patch-clamp technique. Adenosine inhibited high voltage-activated (HVA) Ca2+ currents in a concentration-dependent manner with an EC50 of 313 nM and a maximal inhibition of 36%, respectively. Inhibition of HVA Ca2+ currents in adrenergic and cholinergic MPG neurons was similar. Adenosine did not modulate T-type Ca2+ channels present in adrenergic MPG neurons. Reverse transcription-polymerase chain reaction analysis indicated that MPG neurons express mRNAs encoding A1 and A2a receptors. Ca2+ current inhibition by adenosine was mimicked by N6-cyclopentyladenosine, an A1-selective agonist (EC50 = 63 nM) and prevented by 100 nM 8-cyclopentyl-1,3-dipropylxanthine, an A1-selective antagonist. Conversely, CGS 21680, an A2a-selective agonist, displayed a relatively low potency (EC50 = 2200 nM) for inhibiting Ca2+ currents. The action of adenosine was significantly attenuated by 2 mM guanosine-5'-thiodiphosphate or 500 ng/ml pertussis toxin. The voltage dependence of adenosine-induced current inhibition was evident by 1) a bell-shaped profile between the current inhibition and test potentials, 2) kinetic slowing in the presence of agonist, and 3) relief of the current inhibition by a conditioning prepulse to +80 mV. Finally, 1 microM omega-conotoxin GVIA occluded adenosine-induced current inhibition. Taken together, we concluded that adenosine inhibits N-type Ca2+ currents by activation of A1 receptors via a voltage-dependent and PTX-sensitive pathway in rat MPG neurons. Our data may explain how adenosine acts as an inhibitory modulator of ganglionic and neuromuscular transmission in the pelvic plexus.

Muscle sympathetic nerve activity (MSNA) can be directly recorded from human peripheral nerves in situ using microneurography. MSNA plays an essential role to control systemic blood pressure against gravitational stress. MSNA was enhanced by changing posture against terrestrial gravity from lying to sitting, and from sitting to standing. This activity was enhanced by head-up tilt depending on the gravitational input from the head to the leg (+Gz) in the human body. Orthostatic hypotension occurred when MSNA response to gravitational stress was impaired both in high and low responders of this sympathetic outflow. Syncope was preceded and/or associated by a withdrawal of MSNA. MSNA was suppressed by short-term exposure to microgravity but was enhanced after long-term exposure to microgravity. Orthostatic intolerance after exposure to prolonged microgravity was associated with a reduction of increased MSNA response to gravitational stress. Aging influenced gravity-related responses of MSNA.

To examine whether myocardial contractility is suppressed during recovery from strenuous sympathetic nerve activity, the cardiac sympathetic nerve was stimulated for 1 min at 20 Hz in open-chest anesthetized dogs (n = 6). Myocardial contractility was compared between stimulation at 20 Hz (strenuous) and stimulation at 2 Hz (physiological range). Inotropic activity was assessed as the maximal value of the first derivative of left ventricular pressure. The inotropic activity was significantly below the prestimulation control level at 5 min after the end of the strenuous stimulation (68+/-7% of the control value; p < 0.05). The inotropic activity then increased toward the prestimulation level. In contrast, the inotropic activity with 2-Hz stimulation decreased toward the prestimulation level but never fell below that level during recovery. In another experiment (n = 10), 50% glucose solution was injected 5 min after the end of the strenuous stimulation (20 Hz), i.e. when the inotropic activity reached the nadir. The inotropic activity increased significantly (p < 0.01) above the prestimulation level between 7 and 20 min after stimulation. Maximal response (121+/-7% of the control value) was observed at approximately 10 min. These results suggest that transient myocardial suppression occurs after strenuous sympathetic nerve activity and that high-energy phosphate is substantially consumed during strenuous sympathetic activity, resulting eventually in myocardial suppression.

To evaluate the mechanism of neurally mediated syncope (NMS), we investigated basal autonomic nerve function using a conventional pharmacological method and [123I]-metaiodobenzyl-guanidine (MIBG) single photon emission computed tomography (SPECT). Nine patients with NMS, whose syncope was induced by head-up tilt test with or without isoproterenol, underwent [123I]-MIBG SPECT. Eight of nine NMS patients showed reduced myocardial uptake (two patients, diffuse; four patients, anteroseptal and inferior; one patient, anteroseptal; one patient, inferior). In the study of pharmacological autonomic nervous function test, atropine sulfate (atr.) (0.04 mg/kg), isoproterenol (isp.) (5 x 10(-3) microg/kg/min), propranolol (prop.) (0.2 mg/kg), phenylephrine (phenyl.) (0.4 microg/kg/min), and phentolamine (phent.) (0.2 mg/kg) were successively administered to patients with NMS (n = 5) and control subjects (n = 5). The heart rate (HR) after atr. and prop., and systolic blood pressure (SBP) after phent. were defined as intrinsic HR (IHR) and intrinsic SBP (ISBP). Parasympathetic activity (increase in HR by atr.), beta-sympathetic tone (HR after atr. minus IHR), beta-sensitivity (change in HR by 1 microg isp./kg/min), beta-secretion (beta-tone/beta-sensitivity), alpha-sympathetic tone (SBP before phenyl. minus ISBP), alpha-sensitivity (change in SBP by 1 microg phenyl./kg/min) and alpha-secretion (alpha-tone/alpha-sensitivity) were also calculated. The beta-secretion was decreased (0.0027+/-0.0008 versus 0.0060+/-0.0004 microg/kg/min/isp.; p < 0.05), while the beta-sensitivity was increased (5850+/-947 versus 3150+/-292 beats/microg/kg/min isp.; p < 0.05) in NMS compared with control subjects. In the other indexes, there were no significant differences between two groups. The results of the present study suggest that increased beta-sensitivity may contribute hypercontraction of left ventricles, which might partially explain the mechanism of NMS.

Aim: To analyze the cotransmission characteristics of contractile responses to electric field stimulation with submaximal voltage and short train in the rabbit saphenous artery., Methods: Isometric vasoconstriction of the rabbit saphenous arterial rings was recorded, and the sympathetic nerves of the arterial rings were activated with electric field stimulation., Results: Electric stimulation produced contractile responses in a frequency-dependent manner in the rabbit saphenous artery. Selective alpha1-adrenoceptor antagonist, prazosin (1 micromol/L) did not affect the vasoconstriction induced by electric stimulation at 2 Hz significantly, but inhibited 39.9 % - 53.8 % of the vasoconstriction at 8 - 16 Hz. On the other hand, desensitization of the P2X1 receptor with alpha,beta-methylene ATP (3 micromol/L) abolished all the vascular responses induced by stimulation at 2 Hz, and obviously potentiated those induced by stimulation at 16 Hz, but it did not affect the concentration-dependent response curves for exogenous norepinephrine. The vasoconstriction responses induced by electric stimulation were all abolished by the treatment of a combination of prazosin (1 micromol/L) and alpha,beta-methylene ATP (3 micromol/L)., Conclusion: The sympathetic and purinergic contractile responses can be induced by 2 Hz stimulation, and ATP is the sole transmitter causing the vasoconstriction in the rabbit saphenous artery. Contractile responses to higher frequencies are related to both norepinephrine and ATP. Desensitization of the P2X1 receptor with alpha,beta-methylene ATP potentiates the vascular responses to electric stimulation via a presynaptic mechanism.

Breakdown of short-term fractal-like behaviour of HR indicates an increased risk for adverse cardiovascular events and mortality, but the pathophysiological background for altered fractal HR dynamics is not known. Our aim was to study the effects of pharmacological modulation of autonomic function on fractal correlation properties of heart rate (HR) variability in healthy subjects. Short-term fractal scaling exponent (alpha1) along with spectral components of HR variability were analysed during the following pharmacological interventions in healthy subjects: (i) noradrenaline (NE) infusion (n=22), (ii) NE infusion after phentolamine (PHE) (n=8), (iii) combined NE + adrenaline (EPI) infusion (n=12), (iv) vagal blockade with high dose of atropine (n=10), (v) and vagal activation by low dose of atropine (n=10). Then alpha1 decreased progressively during the incremental doses of NE (from 0.85 +/- 0.250 to 0.55 +/- 0.23, P<0.0001). NE also decreased the average HR (P<0.001) and increased the high frequency spectral power (P<0.001). Vagal blockade with atropine increased the alpha1 value (from 0.82 +/- 0.22 to 1.24 +/- 0.41, P<0.05). Combined NE + EPI infusion and vagal activation with a low dose atropine did not result in any changes in alpha1, and alpha-adrenergic blockade by PHE did not completely reverse the effects of NE on alpha1. Increased levels of circulating NE result in reduction of short-term correlation properties of HR dynamics. The results suggest that coactivation of cardiac vagal outflow at the time of high levels of a circulating sympathetic transmitter explains the breakdown of fractal-like behaviour of human HR dynamics.

Ten normotensive hemodialysis patients with severe anemia participated in the study. Human recombinant erythropoietin (rHuEpo) was administered i.v. 3 times a week in doses of 50 U/kg of body weight. During 12 weeks of observation, the mean hematocrit value increased from 19%, before start of therapy, to 32%. Simultaneous monitoring of serum plasma noradrenaline (NA) concentration showed an elevation from 202 to 281 pg/ml. An increase of NA concentration after a cold pressure stimulating test (CP) was not statistically significant after as compared to before treatment, but became statistically significant after 12 weeks of rHuEpo therapy (281 pg/ml before to 441 pg/ml after CP test, p < 0.01). The mean arterial blood pressure increased from 92 - 109 mmHg after 12 weeks of rHuEpo therapy (p < 0.001). We have demonstrated significantly increased NA blood concentrations after 12 weeks of rHuEPO therapy in normotensive patients, which correlated with increased MAP. This may suggest that the observed increase of noradrenaline concentration as a vasoactive substance after the CP test may contribute to hypertension during rHuEPO therapy.

This study aimed to assess the effects of the antidepressant drug imipramine (IMI) on the neuronal M-type K+ current (IK(M)). We show that IMI reversibly reduces IK(M) with an IC50 of 7 microM. The V0.5 and slope factor of the steady state activation curve remained unchanged after IMI, indicating a mode of action that is voltage insensitive for blocking the M-channel. Patch pipette application of IMI elicits same inhibitory response suggesting a binding site on the M-channel accessible from both sides of the cell membrane. Accordingly, the inhibitory effect of IMI is larger by rising external pH near to the pKa of the drug. Therefore, we propose that a neutral form of IMI binds more efficiently to M-channels to exert its inhibitory action by a voltage-independent mechanism.

Unlabelled: Previously, sympathetic reinnervation of the transplanted heart has been described using invasive catheterization techniques and noninvasive radionuclide imaging techniques. However, little is known about the agreement between these 2 methods. Thus, correlation between (11)C-hydroxyephedrine (HED) PET and invasively measured norepinephrine (NE) release was investigated in transplant recipients in this study., Methods: Using PET and the catecholamine analog HED, 17 patients were studied between 2 mo and 13.6 y after transplantation. Based on results in completely denervated hearts, areas with HED retention >7%/min were defined as reinnervated. Additionally, transcardiac NE release induced by intravenous tyramine (55 microg/kg) was measured by coronary sinus and aortic catheterization within 1 wk of the PET study. NE levels between coronary sinus and aortic root, DeltaNE(CS-AO), were calculated at baseline and after tyramine administration. Differences of more than 3 SD of baseline (>163 pg/mL) were interpreted as reinnervation., Results: HED retention indicated reinnervation in 10 patients. Maximal HED retention ranged from 4.3%/min to 16.4%/min. DeltaNE(CS-AO) 1 min after tyramine administration ranged between -10 pg/mL and 1157 pg/mL, and 8 patients were above the reinnervation threshold. Fisher's exact test demonstrated good agreement between results of PET and DeltaNE(CS-AO) measurements (P = 0.002). Maximal HED retention was also significantly correlated with NE release (r = 0.69; P = 0.001)., Conclusion: Results of invasively measured NE release and noninvasive (11)C-HED PET are well correlated. This study further supports the usefulness of PET as a noninvasive approach for detection of reappearance of catecholamine uptake sites after heart transplantation.

Mechanisms underlying acetylcholine-induced endothelium-independent vasodilation were studied in the rat mesenteric vascular bed isolated from Wistar rats. In preparations without endothelium, and contracted by perfusion with Krebs solution containing methoxamine (2-7 microM), perfusion of acetylcholine (1-100 microM) for 1 min produced a concentration-dependent vasodilation. Denervation of denuded preparations by cold storage (4 degrees C for 72 h) abolished the acetylcholine-induced vasodilation; 10 and 100 nM atropine abolished 1 and 10 microM acetylcholine-induced vasodilation, but it inhibited only 20% of vasodilation by 100 microM acetylcholine. The acetylcholine-induced atropine-resistant vasodilation was inhibited by 10 and 100 microM hexamethonium, 5 microM guanethidine, 50 microM bretylium, in vitro 6-hydroxydopamine (2 mM for 20 min, twice), 1 microM capsaicin and 0.5 microM calcitonin gene-related peptide (CGRP)-(8-37) (CGRP receptor antagonist). These findings suggest that the acetylcholine-induced endothelium-independent nicotinic vasodilation requires the presence of intact adrenergic nerves, and is mediated by endogenous CGRP released from CGRP-containing nerves.

In vitro experiments using isolated atria with and without superfusion can be used to quantify the dopamine-2 (DA-2) receptor stimulating activity of compounds. This receptor mechanism decreases the amount of norepinephrine released from sympathetic nerve terminals by neuronal impulses. DA-2 receptor agonists (stimulants) are very active and induce several physiological changes, such as bradycardia, hypotension, lower intraocular pressure, etc. In this unit, tissue preparation and dopamine receptor assays are described for isolated cat atria with field stimulation or with superfusion, and isolated guinea pig atria with field stimulation.

On the basis of current literature, clinical and neuropathologic features of idiopathic autonomic neuropathy is presented. Idiopathic autonomic neuropathy is a disease characterized by acute or subacute onset, monophasic course over a period of several years, it is often preceded by an infection. The spectrum of autonomic changes ranges from cholinergic or adrenergic dysfunction to pandysautonomia, leading to heterogeneity of its clinical features. Possible sympathetic system abnormalities found in autonomic neuropathy are: poor pupillary response to light in darkness, orthostatic hypotension leading to syncope, hypotension without compensatory tachycardia, ejaculation disturbances and vasomotor instability. Possible parasympathetic dysfunctions are: salivation and lacrimation disturbances, absent pupillary constriction to light and near gaze, gastrointestinal tract immobility and impairment of gastrointestinal function, atonic bladder with large residual volume, erectile impotence. Pandysautonomia is thought to result from an immune mediated mechanism and responds well to plasmaferesis and intravenous immunoglobin therapy leading to gradual, sometimes not full, recovery. Moreover in this article we pay attention to the clinical value of many tests like cardiovascular or pharmacological studies in the diagnosis of pandysautonomia and in differentiation of pre- and postganglionic changes. In order to diagnose idiopathic autonomic neuropathy one has to rule out a large number of diseases with autonomic dysfunction e.g.: diabetes, malignant neoplasms, acute intermittent porphyria, Shy-Drager syndrome, Riley-Day's dysautonomia, Parkinson's disease, amyloidosis and others.

Altered neuronal responses to trophic factors may play a role in neuronal maintenance in adulthood and may also be involved in neuronal atrophy in old age. We have investigated this issue in the rat iris, studying responsiveness of sympathetic and sensory iridial nerves to a range of NGF concentrations in mature and aged rats. We show here that growth responses of sensory nerves to NGF, as measured by quantitative immunohistochemistry and image analysis, were unchanged in old rats. In contrast, there was a small but significant reduction in responsiveness of aged sympathetic neurons. The shapes of the dose-response curves for sensory and sympathetic neurons were different, with a larger response over a narrower range of concentrations in sensory neurons. Lower levels of p75 immunoreactivity were observed in iridial nerves from old compared to young rats. NGF treatment had no effect on receptor staining in young rats but restored 'young' levels of p75 staining in old rats. Our results do not support the hypothesis of a primary role for NGF in maintenance or atrophy of nerves in ageing.

The sympathetic innervation of white adipose tissue (WAT) appears to be a dominant mechanism triggering lipolysis. The purpose of this study was to determine the neurochemical phenotype of neurons comprising the sympathetic outflow from brain to WAT. This was accomplished by injecting Siberian hamster WAT with a viral retrograde transneuronal tract tracer, the pseudorabies virus (PRV), in combination with immunocytochemical characterization of several neurotransmitters or their synthetic enzymes in the brain. Catecholaminergic (tyrosine hydroxylase [TH] and dopamine-beta-hydroxylase [DBH] immunoreactivity) and peptidergic (arginine vasopressin [AVP] and oxytocin [OXY] immunoreactivity) neurons were part of this outflow, but the percentage of double-labeled cells was small, consistent with previous studies. Brainstem PRV + TH- or PRV + DBH-labeled cells were in previously identified noradrenergic areas (A5, A6, and subcoeruleus, rostroventrolateral medulla [RVL], some reticular nuclei). Forebrain double labeling was greatest in the paraventricular (TH, AVP, OXY) and suprachiasmatic (AVP) nuclei, both implicated in the central control of lipolysis. Differences between the PRV double labeling reported here for WAT versus that of other sympathetic peripheral targets were PRV + DBH in A5 and RVL, and PRV + TH in RVL and in the lateral paragigantocellular and lateral reticular nuclei. Collectively, these results begin to identify the neurochemical identity of the sympathetic outflow from brain to WAT.

Experiments were undertaken, using laser-Doppler flowmetry, to determine the nature of adrenoceptors mediating sympathetic nerve evoked nasal vasoconstrictor responses in anesthetized rats. Presence of sympathetic tone was confirmed by a large (330%) increase of nasal blood flow following section of the ipsilateral preganglionic cervical sympathetic nerve. Electrical nerve stimulation produced reproducible, frequency-related nasal vasoconstrictor responses with near maximal response, observed at less than 10 Hz. Evoked nasal vasoconstrictor responses were largely blocked with intravenous treatment with the non-selective alpha-adrenoceptor antagonists, phentolamine (5 mg kg(-1)) and phenoxybenzamine (2 mg kg(-1)), as well as with the selective alpha(1)-adrenoceptor antagonist, prazosin (300 microg kg(-1)). alpha(2)-Adrenoceptor antagonism with rauwolscine (500 microg kg(-1)) potentiated neurally evoked nasal vasoconstriction. Neither atropine (1 mg kg(-1)) nor propranolol (1 mg kg(-1)) altered the evoked responses. Rats with intact cervical sympathetic nerves responded to rauwolscine with a modest constriction. Subsequent prazosin administration produced an increase of nasal blood flow of approximately 275%. These results suggest that the nasal vasculature of the rat is under intense sympathetic tone and that the resulting neurogenic vasoconstriction is mediated exclusively by activation of alpha(1)-adrenoceptors.

The effect of interleukin 1beta on the thymus of control and chemically sympathectomized adult and aged rats was studied with the aim of assessing the importance of adrenergic nerve fibres (ANF) in the regulation of some immunological functions. The whole thymus was removed from normal, sympathectomized (with the neurotoxin 6-OH-dopamine) and treated (interleukin 1beta) rats. Thymic slices were stained with eosin orange (for the recognition of microanatomical details of the thymic microenvironment) and with Bodian's method for staining of nerve fibres. Histofluorescence microscopy was employed for staining ANF and immunofluorescence was used for detecting NPY-like immunoreactivity. All images were submitted to quantitative morphometrical analysis and statistical analysis of data. Moreover, the amount of proteins and noradrenaline was measured on thymic homogenates. The results indicate that in normal conditions the formation of the thymic nerve plexi in the rat is complex: the majority of ANF are destroyed after chemical sympathectomy with 6-OH-dopamine and do not change after treatment with interleukin 1beta; on the contrary, treatment with interleukin 1beta induces substantial changes in the fresh weight of the thymus, the thymic microenvironment, thymic nerve fibers, ANF, NPY-like positive nerve fibres, and on the total amount of proteins and noradrenaline in rat thymic tissue homogenates. Immunostimulation with interleukin 1beta induces substantial changes in the whole thymus, in its microenvironment and in ANF and NPY-like nerve fibres. After chemical sympathectomy, no significant immune response was evoked by interleukin 1beta, since the majority of ANF was destroyed by chemical sympathectomy.

Sympathetic skin response (SSR) was performed before and 1 year after surgical release of the median nerve in 20 subjects (mean age 52.8 years) with unilateral idiopathic carpal tunnel syndrome (CTS). SSR was evoked by stimulation of the ulnar nerve at the wrist contralateral to the side with CTS, recording from the palm, third (M3) and fifth fingers, and from the third finger contralateral to the side of CTS (M3c). Before surgery, anomalies of M3 SSR were found in 8 hands (40%): M3 SSR was absent in 1 hand; and the M3c/M3 SSR largest area ratio was abnormal in 7 hands, 3 of which also had abnormal mean differences between M3 and M3c SSR latencies. M3 SSRs were not significantly modified after surgery. The absence of postsurgical improvement may be due to the poor reinnervation capacity of sympathetic fibers., (Copyright 2001 John Wiley & Sons, Inc.)

1. The present paper deals with the central mechanisms responsible for the defence-like differential pattern of spinal sympathetic outflow elicited by electrical activation of the midbrain periaqueductal grey (PAG) in urethane-anaesthetized, baroreceptor-denervated cats. The pattern is characterized by increases in the 10 Hz discharges of the inferior cardiac (CN) and renal (RN) sympathetic nerves and a decrease in 10 Hz activity of the vertebral sympathetic nerve (VN) that supplies vasoconstrictor outflow to the forelimb. 2. The model used to explain this pattern is based on the self-organizing properties of a system of coupled brainstem oscillators rather than the activation of point-to-point hard-wired connections leading to increases in sympathetic outflow to some targets and decreases to others. 3. The fact that VN 10 Hz activity was inhibited by PAG stimulus frequencies equal to or just above, but not just below, that of the free-running (control) rhythm argues against a 'hard-wired' model. 4. The evidence supporting the hypothesis that the defence-like pattern is an emergent property of a system of coupled oscillators includes changes in the phase lag of VN 10 Hz activity relative to that in the CN, temporal correlation of the changes in phase angle and 10 Hz powers and the direct relationship between the magnitude of the change in phase angle and the degree to which PAG stimulation reciprocally affected the 10 Hz discharges of the CN and VN. 5. It is proposed that changes in phase angle reflect the reorganization of the coupling of 10 Hz oscillators and that such changes in state lead to differential patterns of spinal sympathetic outflow.

11 syndrome X patients and 8 healthy controls were investigated by myocardial scintigraphy (SPECT) with 123-I-MIBG. Regional defects in cardiac 123-I-MIBG uptake were found in 90% syndrome X patients. Total cardiac 123-I-MIBG uptake appeared significantly higher in syndrome X patients. Perfusion defects on stress 99m-Tc-MIBI scintigraphy were found in 10 syndrome X patients who had also abnormal 123-I-MIBG scintigrams. It is suggested that impairment of efferent cardiac adrenergic nerve fiber function in syndrome X patients may contribute to pathophysiologic and clinical features of syndrome X.

Cardiotoxicity of anthracyclines is a clinical challenge in cancer chemotherapy. Limited data is available on the physiological mechanisms responsible for anthracycline-induced heart failure or its recovery. We studied four patients with a history of severe anthracycline-induced heart failure manifested 2-116 months earlier by using radionuclide ventriculography for the measurement of left ventricular function, indium-111-antimyosin scintigraphy for the detection of myocardial cell injury and iodine-123-metaiodobenzylguanidine (MIBG) scintigraphy for the assessment of cardiac adrenergic innervation. Myocardial perfusion and fatty acid utilization were assessed with iodine-123-paraphenyl pentadecanoid acid (pPPA) and single photon emission computed tomography (SPECT). Symptoms of congestive heart failure (CHF) were still present in two patients whereas the others were asymptomatic at the time of the study. The patients who showed complete clinical recovery had normal or near normal left ventricular ejection fraction (LVEF) (47 and 52%), whereas the patients with symptoms of heart failure had low ejection fractions (21 and 31%). All patients presented with abnormal antimyosin uptake and decreased myocardial MIBG uptake. Patients with low ejection fraction tended to have higher antimyosin uptake suggesting more severe, persistent myocyte injury. All but one patient showed normal fatty acid utilization. These data suggest that patients with a history of severe anthracycline-induced cardiomyopathy have persistent myocardial cell injury and adrenergic dysfunction up to 10 years after the development of heart failure. These findings seem to be present regardless of recovery of left ventricular function.

1. Despite the emerging framework that central neural pathways controlling the activity of the sympathetic nervous system are capable of producing highly selective responses, the specific neural pathways governing different sympathetic outflows are poorly understood. 2. Anatomical studies suggest that five brain areas, namely the rostral ventrolateral medulla, the rostral ventromedial medulla, the caudal raphe nuclei, the region containing the A5 noradrenergic neurons and the paraventricular hypothalamic nucleus, provide dominant supraspinal innervation of sympathetic preganglionic neurons. 3. The anatomical parcellation of different functions within and among these cell groups is uncertain. However, recent studies using transynaptic retrograde labelling of neural pathways connected to various sympathetic targets suggest that the circuits controlling these different targets may be partially distinct. Similarly, anatomical studies relying on stimulus-evoked expression of immediate early genes, such as c-fos, suggest that different sympathetic responses may be controlled by distinct, neural circuits. 4. Thus, although many similarities exist in the anatomical circuits innervating different sympathetic targets, possibly supporting the orchestration of global sympathetic responses, differences are also discernible.

1. Studies are described that indicate that stimulation of different purinergic receptor subtypes (A1, A2A and P2X) located in the sub-postremal nucleus tractus solitarius (NTS) evokes qualitatively and quantitatively different regional haemodynamic and efferent sympathetic responses. 2. Stimulation of A2A receptors evoked the most diverse pattern of regional sympathetic responses: preganglionic adrenal nerve activity (pre-ASNA) was increased, lumbar sympathetic nerve activity (LSNA) did not change, while renal (RSNA) and post-ganglionic adrenal (post-ASNA) sympathetic nerve activity was decreased. Stimulation of A1 receptors evoked qualitatively uniform, although quantitatively different, sympathoactivation: pre-ASNA > RSNA > LSNA. Stimulation of P2X receptors evoked qualitatively uniform, although quantitatively different, sympathoinhibition: RSNA=post-ASNA > LSNA = pre-ASNA. 3. These qualitatively and quantitatively different patterns of regional sympathetic responses strongly suggest that purinergic receptor subtypes may be specifically located and differentially expressed on NTS neurons/neural terminals that control different sympathetic outputs. Different NTS purinoceptors may contribute to patterned autonomic responses observed in specific physiological or pathological situations.

1. The medullary premotor neurons determining the sympathetic outflow regulating cardiac function and vasoconstriction are located in the rostral ventrolateral medulla (RVLM). The present study sought evidence for an alternative location for the sympathetic premotor neurons determining the sympathetic nerve activity (SNA) controlling brown adipose tissue (BAT) metabolism and thermogenesis. 2. The tonic discharge on sympathetic nerves is determined by the inputs to functionally specific sympathetic preganglionic neurons from supraspinal populations of premotor neurons. Under normothermic conditions, BAT SNA was nearly silent, while splanchnic (SPL) SNA, controlling mesenteric vasoconstriction, exhibited sustained large-amplitude bursts. 3. The rostral raphe pallidus (RPa) contains potential sympathetic premotor neurons that project to the region of sympathetic preganglionic neurons in the thoracic spinal cord. Disinhibition of neurons in RPa elicited a dramatic increase in BAT SNA, with only a small rise in SPL SNA. 4. Splanchnic SNA was strongly influenced by the baroreceptor reflex, as indicated by a high coherence with the arterial pressure wave, a significant amplitude modulation over the time-course of the cardiac cycle and a marked inhibition of SPL SNA during a sustained increase in arterial pressure. When activated, the bursts in BAT SNA exhibited no correlation with arterial pressure and were not affected by increases in arterial pressure. 5. Because these characteristics and reflex responses in sympathetic outflow have been shown to arise from the on-going or altered discharge of sympathetic premotor neurons, the marked differences between SPL and BAT SNA provide strong evidence supporting the hypothesis that vasoconstriction and thermogenesis (metabolism) are controlled by distinct populations of sympathetic premotor neurons, the former in the RVLM and the latter, potentially, in the RPa.

Objective: To evaluate the role of the autonomic nervous system in hemodynamic changes during induced hypothermia., Design: Prospective, randomized animal study., Setting: An animal research laboratory in a medical university., Subjects: A total of 29 anesthetized rabbits., Interventions: Animals were anesthetized by intraperitoneal urethane. After tracheostomy and administration of gallamine, respiration was maintained by mechanical ventilatory support. The animals were divided into five groups (one control and the four experimental groups); animals were treated with an intact neuraxis and normothermia (control group), animals with an intact neuraxis (intact group), cervical vagotomized animals (vagotomy group), the carotid sinus and aortic nerves denervated animals (SAD group), and animals with SAD plus vagotomy (SADV group). The left renal sympathetic nerves were exposed by a retroperitoneal approach., Measurements and Main Results: We examined the effects of surface cooling on HR, mean arterial pressure, central venous pressure, and renal sympathetic nerve activity (RSNA) in the animals. Changes of baroreflex sensitivity and plasma catecholamines were also measured simultaneously. Surface cooling caused progressive and profound decreases in HR in all experimental groups. In all groups, RSNAs increased at the early phase, which were followed by return to the precooling level., Conclusions: Hemodynamics and RSNA during induced hypothermia are regulated by mechanisms other than the baroreceptor reflex system, possibly the dermal cold receptors. Suppression of the baroreflex occurred on HR but not on RSNA during hypothermia, which may indicate direct effects of hypothermia on the heart. RSNA responses may be activated earlier than systemic catecholamine responses during induced hypothermia.

In this study we assess the mechanisms of exercise-induced left ventricular (LV) dysfunction in asymptomatic patients with Type 1 diabetes mellitus (T1DM) without coronary artery disease. Fourteen patients and 10 volunteers were enrolled. LV volume, LV ejection fraction (LVEF) and end-systolic wall stress were calculated by two-dimensional echocardiography at rest and during isometric exercise. Myocardial iodine-123 metaiodobenzylguanidine (MIBG) scintigraphy was performed to assess adrenergic cardiac innervation. Diabetic subjects were classified into group A (n=7), with an abnormal LVEF response to handgrip (42 +/- 7%), and group B (n=7), with a normal response (72 +/- 8%). Baseline LVEF was normal in both group A and B patients. In group A patients, the LV circumferential wall stress-LVEF relation showed an impairment in LVEF disproportionate to the level of LV after load. No significant changes in LVEF occurred during dobutamine, whereas post-extrasystolic potentiation (PESP) significantly increased LVEF (60 +/- 6% vs 74 +/- 6%,p < 0.001); PESP at peak handgrip normalized the abnormal LVEF (42 +/- 7% vs 72 +/- 5%, p < 0.001); and MIBG uptake normalized for body weight or for LV mass was lower than in normal subjects (1.69 +/- 0.30 vs 2.98 +/- 0.82 cpm/MBq per g,p = 0.01) and group B diabetic patients (vs 2.79 +/- 0.94 cpm/MBq per g,p = 0.01). A linear correlation between LVEF at peak handgrip and myocardial MIBG uptake normalized for LV mass was demonstrated in the study patients. A defective blunted recruitment of myocardial contractility plays an important role in determining exercise LV dysfunction in the early phase of diabetic cardiomyopathy. This abnormal response to exercise is strongly related to an impairment of cardiac sympathetic innervation.

The purpose of the present study was to evaluate the effect of hypoperfusion to the static-exercised-muscle induced by arm elevation on muscle sympathetic nerve activity (MSNA) recorded from the right tibial nerve (n= 10) by microneurography. Subjects performed static handgrip exercises (SHG) at 30% of maximal voluntary contraction (MVC) for 2 min, followed by 2 min of posthandgrip muscle ischemia (PHGMI) at the heart level (control) and with the arm elevated (50 cm above heart level). Basal heart rate, mean blood pressure and MSNA responses expressed as burst rate (bursts/min) and total MSNA (%) were unaffected by the arm-position. Heart rate response during SHG was not influenced by the arm elevation, while mean blood pressure and MSNA responses were increased by it (P<0.05). MSNA responses were increased during the second minute of the SHG period (P<0.05) and the PHGMI period (P<0.05) in the elevated arm position. In conclusion, arm elevation increased MSNA responses to SHG and PHGMI, suggesting an increased magnitude of muscle metaboreflex.

The role of renal nerves and endothelins, acting at ET(A) receptors, in the regulation of renal excretory function was investigated in male Long-Evans rats. Catheters were placed in the femoral vein for fluid and drug infusion, in the femoral artery for blood pressure recording as well as in the bladder for urine collection. Infusion of 16.4 nmol/kg/min of the ET(A) receptor antagonist BQ-123 for 50 min was performed in freely moving, intact and renal denervated rats. As a result of BQ- 123 infusion, urine flow rate diminished (P < 0.02) and Uosm increased (P < 0.05) in the intact rats, but not in the renal denervated rats. Bilateral renal denervation itself as well as ET(A) receptor inhibition in both intact and renal denervated rats did not change the mean arterial pressure, heart rate, or the excretion of sodium, potassium and chloride. The data obtained suggest an interrelationship between renal nerves and endothelin-A receptors in the regulation of renal water excretion.

The present study was undertaken to examine sympathetic-parasympathetic interactions in the regulation of salivary gland function, with special reference to the possible role of the sympathetic cotransmitter neuropeptide Y (NPY). In dogs anaesthetised with pentobarbitone, electrical stimulation of the parasympathetic nerve to the submandibular gland evoked an increase in glandular blood flow and salivary secretion. Sympathetic nerve stimulation evoked a significant prolonged attenuation of vasodilator and secretory responses to subsequent parasympathetic stimulation. This attenuation was not significantly altered by alpha- and beta-adrenoceptor blockade. Systemic administration of the sympathetic cotransmitter, NPY, mimicked the effect of the sympathetic stimulation by significantly attenuating vasodilatation and salivary secretion. The NPY Y1 receptor agonist, [Leu31, Pro34]NPY and the specific NPY Y2 receptor agonist N-acetyl[Leu28, Leu31]NPY 24-36 both significantly attenuated the vasodilatation and salivary secretion evoked by stimulation of the parasympathetic nerve. The NPY Y1 receptor antagonist, GR231118 significantly antagonised the attenuation of vasodilatation caused by both sympathetic stimulation and the NPY Y1 receptor agonist. GR231118 also inhibited the pressor response of NPY. Intra-arterial injection of methacholine and stimulation of the parasympathetic nerve both caused local vasodilatation in the gland which was significantly attenuated by pretreatment with sympathetic stimulation or the NPY Y1 agonist. The NPY Y2-specific agonist did not attenuate methacholine-induced vasodilatation but did attenuate vasodilatation evoked by parasympathetic stimulation. The results indicate that NPY as a sympathetic cotransmitter may have a role in the regulation of vascular secretory function of salivary glands.

Among the many benefits of long-term hormone replacement therapy to postmenopausal women is a significant reduction in risk for and progression of cardiovascular disease. However, long-term estrogen replacement therapy has been associated with several undesirable, and likely dose-dependent, side-effects. There is some evidence to suggest that the dose of estrogen which confers optimal beneficial effects on the cardiovascular system is much lower than that which is currently prescribed for postmenopausal women. The following experiments were conducted to determine the dose-response relationship of acutely administered estrogen on autonomic tone and reflex control of heart rate in ovariectomized Sprague-Dawley female rats. Rats were anaesthetized with sodium thiobutabarbital (100 mg/kg) and instrumented to record blood pressure, heart rate and efferent parasympathetic and sympathetic nerve activities. The sensitivity of the cardiac baroreflex was tested using intravenous injection of either phenylephrine hydrochloride (0.025-0.1 mg/kg) or sodium nitroprusside (0.0025-0.01 mg/kg). Intravenous injection of estrogen produced dose-dependent increases in the magnitude of the baroreflex sensitivity and parasympathetic tone while reducing sympathetic tone with a maximal effect observed at 1 x 10(-3) mg/kg. Prior administration of the selective estrogen receptor antagonist, ICI 182,780 blocked the estrogen-induced changes in baroreflex sensitivity and autonomic tone. These results demonstrate that acutely administered, low-dose estrogen has beneficial effects on autonomic tone and cardiovascular reflexes.

Previous studies in the rat have indicated that the heptapeptide angiotensin-(1-7) has an excitatory action on pressor neurons in the rostral ventrolateral medulla that is equipotent to that evoked by angiotensin II, but which is mediated by separate receptors. In this study we have compared the cardiovascular effects and mechanisms of action of angiotensin-(1-7) with angiotensin II in the rostral and caudal ventrolateral medulla of the rabbit, a species which, unlike the rat, contains a high density of angiotensin receptors, similar to that observed in humans. Microinjections of angiotensin-(1-7) into the rostral and caudal ventrolateral medulla evoked dose-dependent increases and decreases, respectively, in arterial pressure and renal sympathetic nerve activity, but in comparison to angiotensin II much higher doses (approximately 50-fold higher) were required to produce cardiovascular response of similar magnitude. The cardiovascular effects of angiotensin-(1-7) were blocked by prior injection of the selective antagonist [D-Ala(7)]-Ang-(1-7) but were also blocked by the selective AT(1) receptor antagonist losartan. The results demonstrate that in the rabbit angiotensin-(1-7) can excite pressor and depressor neurons in the ventrolateral medulla, but indicate that these effects are mediated by AT(1) receptors. The much lower potency of angiotensin-(1-7) as compared to angiotensin II may be explained as a consequence of it having a much lower affinity to AT(1) receptors. Thus, in contrast to the rat, the results do not indicate that angiotensin-(1-7) has a biologically significant action in the ventrolateral medulla of the rabbit.

ATP released by sympathetic varicosities of the mouse vas deferens binds to P2X receptors which activate fast, ligand-gated channels, resulting in depolarisation of smooth muscle cells. We examined the development of fast neuromuscular transmission at surface longitudinal smooth muscle fibres of the mouse vas deferens. Sympathetic varicosities were visualised using DiOC(2)(5)-fluorescence to aid in positioning loose patch electrodes over small sets of sympathetic varicosities to record the nerve terminal impulse (NTI) and excitatory junction currents (EJCs) evoked during nerve stimulation. At the earliest age at which EJCs could be detected, 21 days postnatal (PN), most recording sites rarely showed a detectable EJC over 100 trials, even though NTIs were recorded without failure. The extent of such intermittence in transmitter release progressively declined between 21 and 42 days PN. In addition, the mean amplitude of spontaneous EJCs (SEJCs) and EJCs increased by 2- and 2.4-fold, respectively, between 21 and 42 days PN. The rise time of EJCs varied widely at each age but declined with development (e.g., 7-14 ms at 28 days PN, 3-12 ms at 42 days PN). All EJCs were abolished by suramin (100 microM). Fast rise time EJCs were rapidly abolished by alpha,beta-methylene ATP (20 microM) while some (34%) of the slower rise time EJCs were resistant to rapid desensitisation of this kind. P2X(1) and P2X(2) mRNAs were detected by reverse transcription and polymerase chain reaction (RT-PCR) to determine whether levels of expression of the receptor subunits might explain the increased EJC amplitude. Between 10 and 42 days PN no marked change was observed in the P2X(2) receptor mRNA or beta-actin mRNA (control). In contrast, the intensity of the RT-PCR band for P2X(1) receptor showed a progressive approximately 4.3-fold developmental increase relative to the P2X(2) band. These observations suggest that both prejunctional and postjunctional mechanisms cause the maturation of fast purinergic junctional transmission at the longitudinal muscle of the mouse vas deferens between 21 and 42 days PN., (Copyright 2000 Wiley-Liss, Inc.)

Reflex patterns in preganglionic neurons projecting in the cervical sympathetic trunk (CST) were analyzed in response to stimulation of various afferent systems. We focused on the question whether these preganglionic neurons can be classified into functionally distinct subpopulations. Reflex responses were elicited by stimulation of trigeminal and spinal nociceptive, thermoreceptive as well as baroreceptor and chemoreceptor afferents. Multi- and single fiber preparations were studied in baroreceptor intact and sino-aortically denervated animals. Spontaneous activity of 36 preganglionic single neurons ranged from 0.2 to 3.5 imp/s (median= 1.11 imp/s). The degree of cardiac rhythmicity (CR) in the activity of sympathetic neurons was 69.5+/-13% (mean+/-S.D.; N=52; range=39-95%). Noxious stimulation of acral skin activated the majority (67%) of sympathetic preparations by 37+/-25% (N=35) above pre-stimulus activity; 15% were inhibited. In these neurons the response to noxious stimulation of acral skin was significantly correlated with the degree of CR (P<0.001, N=52) in that neurons showing the strongest excitation to noxious stimulation displayed the strongest CR. Noxious mechanical stimulation of body trunk skin (N=60) inhibited the majority (80%) of fiber preparations tested (by 34+/-18% of pre-stimulus activity, N=48); an activation was not observed. Cold stimulation of acral (N=9) and body trunk skin (N=42) activated most fiber preparations. Trigeminal stimulation evoked a uniform reflex activation of preganglionic neurons (+79+/-73% of pre-stimulus activity, N=32). Chemoreceptor stimulation by systemic hypercapnia elicited inhibitory (-31+/-19%, N=8) as well as excitatory (+59+/-5%, N=4) responses. These results show that preganglionic sympathetic neurons projecting to target organs in the head exhibit distinct reflex patterns to stimulation of various afferent systems; however, a clear classification into different functional subgroups did not emerge. Furthermore, reflex patterns showed a segmental organization to noxious cutaneous stimulation of acral parts and body trunk reflecting a differential central integration of spinal afferent input. Compared with the cat the reflex organization of sympathetic neurons projecting to the head seems to be less differentiated in the anesthetized rat.

Recordings were obtained from dorsal column nucleus (DCN) neurons in a neonatal rat brain stem-spinal cord preparation to study their basic electrophysiological properties and responses to stimulation of a dorsal root. Whole-cell patch-clamp recordings were made from 21 neurons that responded to dorsal root stimulation with a fast excitatory postsynaptic potential (EPSP). These neurons were located lateral to, but at the level of, the area postrema at depths of 100-268 microm below the dorsal surface of the brain. The neurons could be divided into groups according to the shape of their action potentials or voltage responses to hyperpolarizing current steps; however, the response profiles of the groups of neurons to dorsal root stimulation were not significantly different and all neurons were considered together. Dorsal root stimulation elicited excitatory postsynaptic potentials (EPSPs) in all neurons with a very low variability in onset latency and an ability to follow 100-Hz stimulation, indicating that they were mediated by activation of a monosynaptic pathway. The peak amplitude of the EPSP increased with membrane hyperpolarization, and applications of the non-NMDA receptor antagonists 6-nitro-7-sulfamoylbenzo[f]quinoxaline-2, 3-dione (NBQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) decreased the amplitude of the EPSP to 14.2% of the control response (n = 6). The descending phase of the EPSP decreased with membrane hyperpolarization and was reduced by the N-methyl-D-aspartate (NMDA) receptor antagonist AP-5 (n = 2). The EPSPs were also reduced in amplitude by applications of the gamma-aminobutyric acid-B (GABA(B)) receptor agonist baclofen, which had no effect on membrane potential or input resistance. These results show that fast EPSPs in DCN neurons elicited by dorsal root stimulation are mediated by an excitatory amino acid acting at both non-NMDA and, to a lesser extent, NMDA receptors. In addition, GABA acting at presynaptic GABA(B) receptors can inhibit these responses.

Several lines of evidence suggest that the brain exhibits reduced plasticity with aging. However, a variety of soluble neurite outgrowth-promoting factors, such as neurotrophins, are not decreased in the aged brain, and aged neurons do not possess dramatically reduced growth potential. The possibility that aging results in reduced baseline substrate-bound neurite outgrowth-promoting activity in the central nervous system (CNS) was evaluated using tissue section culture. There were clear differences between brain regions in the extent of neurite outgrowth on both young and aged brain sections. However, no differences in the extent of neurite outgrowth were observed as a function of age. These results suggest that aging of the rat CNS is not accompanied by major alterations in the baseline neurite outgrowth-promoting substrate properties of the tissue.

1. To study post-excitatory changes of conduction velocity, action potentials were recorded from 132 unmyelinated nerve fibres (C fibres) in cutaneous fascicles of the peroneal nerve using microneurography in healthy human subjects. The 'marking' technique was used to assess responsiveness to mechanical and heat stimuli or sympathetic reflex provocation. 2. C fibres were classified into three major classes: mechano-responsive afferent (n = 76), mechano-insensitive afferent (n = 48) and sympathetic efferent C fibres (n = 8). 3. During regular stimulation at 0.25 Hz, conditioning pulses were intermittently interposed. Changes of conduction velocity were assessed for different numbers of conditioning impulses and varying interstimulus intervals (ISIs). For all three fibre classes the latency shift following conditioning pulses at an ISI of 1000 ms increased linearly with their number (n = 1, 2 and 4). However, the absolute degree of conduction velocity slowing was much higher in the 32 mechano-insensitive fibres as compared with 56 mechano-responsive or 8 sympathetic fibres. 4. Single additional pulses were interposed at different ISIs from 20 to 2000 ms. For 20 mechano-responsive fibres conduction velocity slowing increased with decreasing ISI (subnormal phase). In contrast, for 16 mechano-insensitive C fibres the conduction velocity slowing decreased with shorter ISIs, and at values lower than 417 +/- 49 ms (mean +/- s.e.m.) the conduction velocity of the conditioned action potential was faster than before (conduction velocity speeding). This supernormal phase had its maximum at 69 +/- 10 ms. 5. In this study we provide, for the first time, direct evidence of relative supernormal conduction in human mechano-insensitive C fibres. The implications for temporal coding in different afferent C fibre classes are discussed.

Study Design: The segmental levels of dorsal root ganglions innervating the sacroiliac joint in rats were investigated using the retrograde transport method. The pathways and functions of the nerve fibers supplying the sacroiliac joint were determined by immunohistochemical detection of transported tracer., Objectives: To study the sensory innervation of the sacroiliac joint and to elucidate the neural pathways of low back pain originating from the sacroiliac joint., Summary of Background Data: The sacroiliac joint is a possible source of low back pain. The L4-S4 spinal nerves have been regarded as the nerves innervating the sacroiliac joint in humans. However, the origins of nerve fibers have not been analyzed experimentally with tracer methods., Methods: Cholera toxin B subunit, a neural tracer, was injected into the left sacroiliac joint of adult rats, and the bilateral dorsal root ganglions were immunohistochemically examined 4 days after injection. In another rat group, the dorsal root ganglions were examined using the same methods after resection of the left sympathetic trunk from L2 to the most caudal level. Thus, the pathways of the nerve fibers supplying the sacroiliac joint were investigated., Results: Labeled neurons were mainly located in the ipsilateral dorsal root ganglions from L1 to S2 of the unsympathectomized rats and in the ipsilateral dorsal root ganglions from L4 to S2 of the sympathectomized rats., Conclusions: The sacroiliac joint was innervated by sensory neurons in dorsal root ganglions ipsilateral to the joint from L1 to S2. Sensory fibers from the L1 and L2 dorsal root ganglions passed through the paravertebral sympathetic trunk.

This work examined basal heart rate and autonomic cardiac tone as well as sympathetic cardiac reactivity to hypotension induced by systemic nitroprusside injection in dormant toads (dry-cold season), Bufo paracnemis, comparing the values with those of toads collected during the active months (hot-rainy season). Autonomic tone was calculated according to the method of Lin and Horwath ('72), which allows its evaluation as a percentage of intrinsic heart rate. Specimens were maintained in an outdoors terrarium except for the week preceding surgery, when they were transferred to indoor nonclimatized tanks. The heart rate of dormant toads (27.8 +/- 2.7 beats/min) was lower than that of active toads at rest (38.6 +/- 2. 3). Cholinergic tone was higher than adrenergic tone both in active (26.2% and 7.8%, respectively) and aestivated (19.5% and 4.8%, respectively) animals. Thus, cholinergic tone and adrenergic tone were both lower in dormant animals. The reflex tachycardia elicited by nitroprusside-induced hypotension was lower in aestivated toads (9.3 +/- 0.9 beats/min) when compared to active toads (19.9 +/- 1.0), indicating a reduced sympathetic reactivity. Nitroprusside-induced hypotensions were not different in the two groups. We conclude that at rest Bufo paracnemis heart is under the influence of a double cholinergic and adrenergic tone, and that both influences, as well as the reflex adrenergic reactivity to the unloading produced by nitroprusside-induced hypotension, are reduced in aestivated toads.

The findings in humans as to whether elevated sympathetic nerve activity contributes to renovascular hypertension have been less consistent compared with the results obtained in experimental models of renovascular hypertension. Collectively, there are several lines of evidence to support the view that sympathetic nerve activity is elevated in patients with renovascular hypertension. It is uncertain, however, whether this adrenergic overactivity is specific for renovascular hypertension per se, or the cause of severe hypertension with target organ damage. Central or peripheral stimulation of sympathetic nerve activity by angiotensin II, or stimulation of central sympathetic outflow via afferent renal nerves of ischemic kidneys, are possible mechanisms to explain the elevated sympathetic nerve activity in renovascular hypertension. Therapy that diminishes the activity of the sympathetic nervous system and the renin-angiotensin system seems rational and could perhaps also improve the poor prognosis for these patients.

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 microM) and atropine (1 microM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 microM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.

Whole-cell recordings have been used to extensively characterize the voltage-dependent inhibition of N-type calcium current induced by various neurotransmitters. Results from these studies have yielded several predictions on the effect of inhibition on N-channel gating, namely delayed channel opening and inhibition-induced reluctant openings. Previous single N-channel studies observed delayed channel opening but failed to find reluctant openings. However, strong depolarizations may be necessary to see reluctant openings, but this was not tested. We have examined N-channel gating at voltages depolarized to those used previously and found a neurotransmitter-induced open state that has properties predicted for the reluctant open state. The openings had lower open probability (P(o)) and brief open times compared to the dominant gating state observed in control (high P(o)). These reluctant events were reduced after strong depolarizing pulses used to reverse inhibition. The threshold voltage for activation of reluctant events was approximately 30 mV depolarized to that of the normal gating state (high P(o)). However, an action potential will provide sufficient depolarization to open reluctant N-channels.

In normal animals, microstimulation of the medullary reticular formation (MRF) has two effects on efferent neurons in the motor branch of the pudendal nerve (PudM). MRF microstimulation depresses motoneuron reflex discharges (RD) elicited by dorsal nerve of the penis (DNP) stimulation and produces long latency sympathetic fiber responses (SFR). The midthoracic spinal location of these descending MRF-PudM projections was studied electrophysiologically using a variety of acute and chronic lesions. Chronic lesions, in 27 mature male rats, included dorsal (DHx) or lateral (LHx) hemisections or moderate/severe contusions (Cx) at spinal level T(8). Behavioral data (sexual reflex latency, bladder voiding) obtained throughout the recovery period revealed a significant impairment of urogenital function for the DHx and severe Cx groups of animals. Microstimulation-induced PudM-RDs and PudM-SFRs, obtained in terminal electrophysiological experiments 30 days postinjury in the same 27 rats (urethan-anesthetized), were tested for a combined total of 1,404 bilateral MRF sites. PudM-RD was obtained for LHx and moderate Cx groups of animals but not for DHx or severe Cx groups. PudM-SFRs were obtained for LHx, DHx (although significantly weakened) and moderate Cx groups but not for those having received either an over-DHx or a severe Cx injury. PudM responses also were tested for 6 MRF sites in six intact control rats both before and after various select acute spinal cord lesions. For MRF sites producing a robust PudM-RD and PudM-SFR, acute bilateral lesions confined to the dorsolateral quadrant (DLQ) eliminated the PudM-RD but failed to eliminate PudM-SFRs. A deeper lesion encompassing additional white matter located dorsally in the ventrolateral quadrant (VLQ) was necessary to eliminate PudM-SFRs. Overall, these electrophysiological results provide evidence for descending projections conveying information between MRF and the lower thoracic/lumbosacral male urogenital circuitry within the DLQ and the dorsal-most aspect of VLQ at the midthoracic level of spinal cord. The alterations of supraspinal projections observed after chronic injury are likely of important clinical significance for functional recovery in cases of clinically incomplete spinal cord injury at midthoracic spinal cord.