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Object: Local spinal cord cooling (LSCC) is associated with beneficial effects when applied following ischemic or traumatic spinal cord injury (SCI). However, the clinical application of LSCC is associated with many technical difficulties such as the requirement of special cooling devices, emergency surgery, and complicated postoperative management. If hypothermia is to be considered for future application in the treatment of SCI, alternative approaches must be developed. The objectives of the present study were to evaluate 1) the relationship between systemic and epidural temperature after SCI; 2) the effects of modest systemic hypothermia on histopathological damage at 7 and 44 days post-SCI; and 3) the effects of modest systemic hypothermia on locomotor outcome at 44 days post-SCI., Methods: A spinal cord contusion (12.5 mm at T-10) was produced in adult rats that had been randomly divided into two groups. Group 1 rats (seven in Experiment 1; 12 in Experiment 2) received hypothermic treatment (epidural temperature 32-33 degrees C) 30 minutes postinjury for 4 hours; Group 2 rats (nine in Experiment 1; eight in Experiment 2) received normothermic treatment (epidural temperature 37 degrees C) 30 minutes postinjury for 4 hours. Blood pressure, blood gas levels, and temperatures (epidural and rectal) were monitored throughout the 4-hour treatment period. Twice weekly assessment of locomotor function was performed over a 6-week survival period by using the Basso-Beattie-Bresnahan locomotor rating scale. Seven (Experiment 1) and 44 (Experiment 2) days after injury, animals were killed, perfused, and their spinal cords were serially sectioned. The area of tissue damage was quantitatively analyzed from 16 longitudinal sections selected from the central core of the spinal cord., Conclusions: The results showed that 1) modest changes in the epidural temperature of the spinal cord can be produced using systemic hypothermia; 2) modest systemic hypothermia (32-33 degrees C) significantly protects against locomotor deficits following traumatic SCI; and 3) modest systemic hypothermia (32-33 degrees C) reduces the area of tissue damage at both 7 and 44 days postinjury. Although additional research is needed to study the therapeutic window and long-term benefits of systemic hypothermia, these data support the possible use of modest systemic hypothermia in the treatment of acute SCI.

The present study addresses the effects of moderate posttraumatic hypothermia (32 degrees C) on the temporal and regional profile of polymorphonuclear leukocyte (PMNL) accumulation after traumatic spinal cord injury (SCI). We hypothesized that posttraumatic hypothermia would reduce the degree of inflammation by reducing PMNL infiltration. Rats underwent moderate spinal cord injury at T10 using the NYU impactor device. In the first study, the temporal profile of myeloperoxidase (MPO) activity (a marker of neutrophil accumulation) under normothermic (37 degrees C) conditions was determined. The animals were allowed to survive for 3 or 24 h, or 3 or 7 days after SCI. Spinal cords were dissected into five segments rostral and caudal to the injury site. Additional animals were studied for the immunocytochemical visualization of MPO. In the second study, rats were sacrificed at 24 h after a monitoring period of normothermia (36.5 degrees C/3 h) or hypothermia (32.4 degrees C/3 h) with their controls. In the time course studies, MPO enzymatic activity was significantly increased at 3 and 24 h within the traumatized T10 segment compared to controls. MPO activity was also increased at 3 h within the rostral T8 and T9 segments and caudal T11 and T12 segments compared to controls. At 24 h after trauma, MPO activity remained elevated within both the rostral and caudal segments compared to control. By 3 days, the levels of MPO activity were reduced compared to the 24-h values but remained significantly different from control. Neutrophils that exhibited MPO immunoreactivity were seen at 6 and 24 h, with a higher number at 3 days. PMNLs were located within the white and gray matter of the lesion and both rostral and caudal to the injury site. Posttraumatic hypothermia reduced MPO activity at 24 h in the injured spinal cord segment, compared to normothermic values. The results of this study indicate that a potential mechanism by which hypothermia improves outcome following SCI is by attenuating posttraumatic inflammation.

Dynorphin A is an endogenous opioid peptide, which has previously been shown to produce a long-lasting allodynia and hyperalgesia in mice, behavioral states consistent with signs of clinically observed neuropathic pain. This dynorphin-induced allodynia was used as a pharmacological, central model of neuropathic pain. In this study, we examined the involvement of the cytokine IL-1beta, the transcription factor nuclear factor kappa B (NF-kappaB), and de novo protein synthesis in the development of allodynia induced by intrathecal (i.t.) administration of dynorphin in male ICR mice. Pretreatment with the protein synthesis inhibitor cycloheximide (0. 3-85nmol), the NF-kappaB inhibitor pyrrolidinedithiocarbamate (PDTC) (0.001-1000pmol), the IL-1 receptor antagonist (IL-1ra) protein (0. 01-100ng), the caspase-1 inhibitor (YVAD) (0.1-300pmol), and the anti-inflammatory cytokine IL-10 (0.1-300ng) all dose-dependently reduced the induction of dynorphin-induced allodynia. Finally, IL-10 administered within the first 24h after the dynorphin insult prevented the development of chronic allodynia. These results demonstrate that the anti-inflammatory cytokines IL-10 and IL-1ra impede the development of dynorphin-induced allodynia. These results also suggest that production of new proteins through NF-kappaB activation is required for the induction of allodynia. We speculate that IL-1ra, IL-10, PDTC and cycloheximide interfere with the central pro-inflammatory cascade. Modulation of cytokine activity in the spinal cord may therefore prove to be an effective therapeutic strategy for the treatment of chronic pain.

Intraspinal injection of the AMPA/metabotropic receptor agonist quisqualic acid (QUIS) results in excitotoxic injury which develops pathological characteristics similar to those associated with ischemic and traumatic spinal cord injury (SCI) (R. P. Yezierski et al., 1998, Pain 75: 141-155; R. P. Yezierski et al., 1993, J. Neurotrauma 10: 445-456). Since spinal injury can lead to partial or complete deafferentation of ascending supraspinal structures, it is likely that secondary to the disruption of spinal pathways these regions could undergo significant reorganization. Recently, T. J. Morrow et al. (Pain 75: 355-365) showed that autoradiographic estimates of regional cerebral blood flow (rCBF) can be used to simultaneously identify alterations in the activation of multiple forebrain structures responsive to noxious formalin stimulation. Accordingly, we examined whether excitotoxic SCI produced alterations in the activation of supraspinal structures using rCBF as a marker of neuronal activity. Twenty-four to 41 days after unilateral injection of QUIS into the T12 to L3 spinal segments, we found significant increases in the activation of 7 of 22 supraspinal structures examined. As compared to controls, unstimulated SCI rats exhibited a significant bilateral increase in rCBF within the arcuate nucleus (ARC), the hindlimb region of S1 cortex (HL), parietal cortex (PAR), and the thalamic posterior (PO), ventral lateral (VL), ventral posterior lateral (VPL), and ventral posterior medial (VPM) nuclei. All structures showing significantly altered rCBF are associated with the processing of somatosensory information. These changes constitute remote responses to injury and suggest that widespread functional changes occur within cortical and subcortical regions following injury to the spinal cord., (Copyright 2000 Academic Press.)

Intraspinal injection of quisqualic acid (QUIS) produces excitotoxic injury with pathological characteristics similar to those associated with ischemic and traumatic spinal cord injury (SCI). Inflammatory responses appear to be a major component of the secondary neuronal injury initiated by SCI and play a role in the pathogenesis of QUIS-induced injury. IL-10 is a potent antiinflammatory cytokine that has been shown to reduce inflammation and improve functional outcome in human and animal models of inflammatory diseases. We propose the administration of IL-10 following excitotoxic SCI will attenuate the inflammatory response, thus resulting in increased neuronal survival. Female, Sprague-Dawley rats were given intraspinal injections of QUIS followed by either intraspinal (5 ng, n = 8) or systemic injections (5 microgram n = 14) of IL-10. Survival times were varied (2-3 days) in order to produce a range of injury states and inflammatory involvement. When administered intraspinally, IL-10 significantly exacerbated the QUIS damage (P < 0.05), resulting in an 11.2% increase in lesion volume. When given systemically, IL-10 significantly decreased lesion volume by 18.1% in the more advanced injury (P < 0.05), but did not effect the more acute injury. These divergent effects were attributed to the modest inflammatory response in the short-term injury compared to the more robust inflammatory response in the more chronic injury. In conclusion, reducing the inflammatory response to SCI by systemic administration of IL-10 resulted in a significant reduction in neuronal damage, suggesting that targeting injury-induced inflammation may be an effective treatment strategy for acute SCI., (Copyright 1999 Academic Press.)

Background and Purpose: Recent experimental data have shown that an increase of excitatory amino acids and the initiation of inflammatory responses within the injured spinal cord may play a role in post-traumatic syringomyelia. The purpose of this study was to determine whether diffusion-weighted MR imaging with apparent diffusion coefficient (ADC) maps could provide earlier evidence of spinal cord cavitation in a rat model of syringomyelia than available with conventional MR imaging., Methods: The spinal cord gray matter of four rats was injected with the alpha-amino-3 hydroxy-5 methyl-4 isoxazole propionic acid/metabotropic receptor agonist quisqualic acid. Animals were sacrificed at 1, 4, or 8 weeks after injection, and the spinal cords were fixed in formalin for 1 week and imaged with T1-, T2-, and diffusion-weighted sequences. One control specimen was also imaged. ADC maps were constructed from the diffusion-weighted data. Histopathologic analyses of sections stained with cresyl violet were compared with the MR images., Results: By 1 week after injection, ADC maps at the level of injection showed areas within the gray matter of increased intensity and increased ADC values as compared with the control specimen. These bright areas corresponded to cysts or cavities within the cord parenchyma on the histopathologic sections. The ADC values within affected gray matter areas progressively increased at 4 and 8 weeks, also corresponding to cyst formation. Conventional T1- and T2-weighted images showed corresponding lesions with cystic characteristics at 4 and 8 weeks, but not at 1 week., Conclusion: In an animal model of syringomyelia, diffusion-weighted imaging with ADC maps detected cystic lesions within spinal cord gray matter before they were seen on conventional T1- and T2-weighted images.

Objectives: To determine the perceived difficulty in dealing with consequences of spinal cord injury (SCI) and to explore patterns of how these complications are perceived., Design: Postal survey., Setting: General community., Participants: Individuals with traumatic SCI (n = 430)., Methods: Subjects (n = 877) were selected from The Miami Project database and were sent a questionnaire in which they were asked to rate their difficulty in dealing with 10 consequences of SCI, on a scale ranging from 0 (not hard at all) to 10 (extremely hard)., Results: The questionnaire was returned by 430 individuals (49%). Five consequences (decreased ability to walk or move, decreased control of bowel, decreased control of bladder, decreased sexual function, and pain) were rated highest (means, 8.2 to 6.2). High ratings of feeling sad were associated with high ratings of most other consequences, and a cluster analysis revealed interrelationships between the ways the various consequences were perceived., Conclusions: Several consequences of SCI are frequently perceived as being very difficult to deal with. Sadness may influence how well a person deals with other consequences of SCI. The observed patterns in perceived difficulty dealing with complications of SCI need to be explored further because they are important in our understanding and treatment of the medical conditions that may follow SCI.

Cytokines and neurotrophic factors have been implicated in the pathophysiology of injury to the central nervous system. While some cytokines are considered pro-inflammatory, other factors promote neuronal growth and survival. The present study investigated the neuroprotective effects of interleukins 1 (IL-1), 4 (IL-4), and 6 (IL-6), nerve growth factor (NGF), ciliary neurotrophic factor (CNTF), and basic fibroblast growth factor (bFGF) in a contusion model of spinal cord injury. Female Sprague-Dawley rats (n = 55) sustained a 10-g weight-drop injury to the lower thoracic spinal cord (T10) from a height of 12.5 mm using the NYU impactor. A micro-infusion system (Alzet minipump) was used to continuously deliver drugs or vehicle directly into the epicenter of the contused spinal cord starting 1 or three h postinjury. At the end of 7 days, animals were perfused and the cords removed for histopathological analysis. Longitudinal serial sections were cut on a freezing microtome and stained with cresyl violet. Areas of central necrosis, partial preservation, and total zone of tissue injury were identified and traced by an independent reviewer using a computer based imaging system. The mean total zone of injury in five animals receiving vehicle infusion was 18.04+/-4.20 mm3. The mean zone of partial preservation in these animals was 16.46+/-3.32 mm. Basic fibroblast growth factor reduced the total zone of injury by 33% [p<0.01, least significant difference (LSD) of Fisher] in five animals and the zone of partial preservation by 32% (p<0.01, LSD of Fisher) when compared to controls. There were trends toward reduction in total zone of injury and zone of partial preservation in rats treated with IL-4, CNTF, and NGF versus vehicle; however, none of these reached statistical significance. No significant differences were observed between animals receiving vehicle versus bFGF treatment commencing 3 h after injury. These data demonstrate that the continuous intramedullary infusion of bFGF initiated one hour after moderate contusion injury of the spinal cord significantly reduces the total zone of injury and the zone of partial preservation. These results support the further investigation and possible future clinical application of bFGF in the treatment of acute spinal cord contusion injury.

Previous studies have shown that intraspinal injection of quisqualic acid (QUIS) produces excitotoxic injury with pathological characteristics similar to those associated with ischemic and traumatic spinal cord injury (SCI). Significant changes in the functional properties of sensory neurons adjacent to the site of injury have also been observed in this model. Additionally, following QUIS injections, mechanical and cold allodynia, combined with excessive grooming behavior have been shown to be the behavioral correlates of these pathological and physiological changes. These behaviors are believed to be related to the clinical conditions of spontaneous and evoked pain following SCI. Given the therapeutic properties of adrenal chromaffin cell transplantation in conditions of neuropathic and cancer pain, it is proposed that the neuroactive substances released from chromaffin cells can alter or prevent the onset and progression of QUIS-induced behavioral changes. The effects of adrenal transplants were evaluated in 14 male Long-Evans rats that received intraspinal injections of QUIS. Pain behaviors, including the progression of excessive grooming behavior (n=8) and hypersensitivity to mechanical and thermal stimuli (n=6) were evaluated following transplantation. A 53% increase in mechanical thresholds was observed following adrenal transplants along with a 70% reduction in the area of skin targeted for excessive grooming. These behaviors were not affected in 11 animals receiving transplants of skeletal muscle. The effects of adrenal transplants on cold allodynia consisted of a stabilization of response latencies in contrast to the continued decrease in latencies, i.e., increased sensitivity, following transplants of skeletal muscle. The results are consistent with previous studies showing the therapeutic efficacy of adrenal chromaffin cell transplants in neuropathic pain, and support the use of this treatment strategy for the alleviation of chronic pain following spinal cord injury., (Copyright 1998 Elsevier Science B.V. All rights reserved.)

Intraspinal injection of the nonspecific inhibitor of nitric oxide synthase N-nitro-L-arginine methyl ester (L-NAME) results in a dose-dependent loss of neurons in the rat spinal cord. This effect is thought to result from a reduction in basal levels of nitric oxide (NO), thereby producing an ischemic reaction secondary to vasoconstriction and reduced spinal cord blood flow (SCBF). An important component of this ischemic reaction is the release of excitatory amino acids and the initiation of an excitotoxic cascade. In the present study, microinjections of adenosine A1 and A2 receptor agonists were made in the spinal cord to evaluate the neuroprotective effects of these drugs against neuronal loss produced by L-NAME. Animals were divided into six groups based on the composition of injected solutions: (a) L-NAME; (b) L-NAME + N6-cyclopentyladenosine (CPA, A1 agonist); (c) L-NAME + 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA, A2 agonist); (d) L-NAME + CPA + CPCA; (e) N-methyl D-aspartate (NMDA); and (f) NMDA + CPA. Injections of L-NAME or NMDA produced a unilateral loss of spinal neurons, a local inflammatory response, and darkly stained pyknotic nuclei surrounding the area of neuronal loss. CPA and CPCA significantly reduced the area of L-NAME-induced neuronal loss, and a synergistic effect was observed when ineffective doses of these agonists were co-injected with L-NAME. The excitotoxic effects of NMDA were not affected by CPA. The results have shown that A1 and A2 receptor agonists provide significant neuroprotection against L-NAME induced neuronal loss, presumably by inhibiting ischemia induced release of excitatory amino acids (A1 agonist), or by restoring SCBF secondary to vasodilation (A2 agonist). It is suggested by these results that the intraspinal injection of L-NAME is an effective model to study the pathological consequences of vasoconstriction, reduced SCBF, and ischemia secondary to decreased NO production in the rat spinal cord. Finally, the results provide support for the continued investigation of specific adenosine agonists as therapeutic agents directed against the ischemic and excitotoxic components of spinal injury.

Inflammatory responses are a major component of secondary injury and play a central role in mediating the pathogenesis of acute and chronic spinal cord injury (SCI). The nuclear factor-kappaB (NF-kappaB) family of transcription factors is required for the transcriptional activation of a variety of genes regulating inflammatory, proliferative, and cell death responses of cells. In this study we examined the temporal and cellular expression of activated NF-kappaB after traumatic SCI. We used a contusion model (N.Y.U. Impactor) to initiate the early biochemical and molecular changes that occur after traumatic injury to reproduce the pathological events associated with acute inflammation after SCI. The activation and cellular distribution of activated NF-kappaB was evaluated by using a monoclonal antibody that selectively recognizes activated p65 in a NF-kappaB dimer. Immunohistochemical and Western blot analyses demonstrated that NF-kappaB activation occurred as early as 0.5 hr postinjury and persisted for at least 72 hr. Using electrophoretic mobility shift assays (EMSA), we demonstrate that NF-kappaB is activated after SCI. In our immunohistochemical, Western, and EMSA experiments there are detectable levels of activated NF-kappaB in our control animals. Using double-staining protocols, we detected activated NF-kappaB in macrophages/microglia, endothelial cells, and neurons within the injured spinal cord. Colocalization of activated NF-kappaB with the NF-kappaB-dependent gene product, inducible nitric oxide synthase (iNOS), suggests functional implications for this transcription factor in the pathogenesis of acute spinal cord injury. Although there is considerable evidence for the involvement of an inflammatory reaction after traumatic SCI, this is the first evidence for the activation of NF-kappaB after trauma. Strategies directed at blocking the initiation of this cascade may prove beneficial as a therapeutic approach for the treatment of acute SCI.

The neuroprotective properties of the N-methyl-D-aspartate (NMDA) antagonist dizocilpine (MK-801) and the non-NMDA antagonists 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]quinoxaline (NBQX) and alpha-methyl-4-carboxyphenylglycine (MCPG) were evaluated against neuronal injury produced by the intraspinal injection of NMDA and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Forty-nine animals were divided into eight groups in order to evaluate the effects of different drug combinations: (a) NMDA; (b) NMDA + MCPG; (c) NMDA + NBQX; (d) NMDA + MK-801; (e) AMPA; (f) AMPA + MCPG; (g) AMPA + MK-801; and (h) AMPA + NBQX. Drugs were microinjected into spinal segments T12-L3 through a micropipette attached to a Hamilton microliter syringe. Spinal cords were evaluated after a survival period of 48 h at which time NMDA and AMPA were found to produce morphological changes over the concentration ranges of 125-500 mM and 75-500 microM, respectively. Neuronal loss following injections of NMDA + MK-801 or AMPA + NBQX was significantly less than that following injections of NMDA or AMPA alone. By contrast, neuronal loss following co-injections of NMDA or AMPA with inappropriate antagonists, i.e., NMDA + NBQX/MCPG or AMPA + MCPG/MK-801, was not significantly different from that produced by NMDA or AMPA. The results suggest that elevations in spinal levels of glutamate followed by prolonged activation of NMDA and AMPA receptor subtypes initiate an excitotoxic cascade resulting in neuronal injury. Blockade of NMDA and AMPA effects by MK-801 and NBQX respectively confirms the well documented neuroprotective effects of these drugs and lends support to the potential importance of NMDA and especially AMPA receptor antagonists as therapeutic agents in the treatment of acute spinal cord injury.

The problem of pain following spinal cord injury challenges the health care community to develop new treatment strategies for patients requiring pain management. A number of pain syndromes are associated with spinal injury based on the nature of the lesion, neurological structures damaged, and secondary pathophysiological changes. Efforts to identify specific characteristics of each syndrome are an important beginning to the successful diagnosis and treatment of spinal injury pain. Without research directed towards understanding the basic mechanisms of this condition, it is likely that the treatment of these patients will remain basically the same as for any other type of pain. In recent years optimism for the development of more effective treatments for central pain of spinal origin has resulted from efforts directed towards understanding the morphological, neurochemical, and physiological responses to spinal injury. Through the use of different experimental models valuable insights related to the mechanism(s) responsible for the onset of central pain following injury have been obtained. At present there are three hypothesis related to this condition: (a) imbalance of sensory channels; (b) loss of spinal inhibitory tone; and (c) the existence of central pattern generators. Future research related to these hypotheses will need to focus on the use of appropriate injury models that simulate the pathological changes associated with human injuries and which lead to clinically relevant pain-related behaviors. Continued research directed towards an examination of these proposed mechanisms will also require new research strategies and a cooperative working relationship between basic and clinical scientists. In this review the clinical characteristics of spinal injury pain and the results of experimental studies are discussed.

Intraspinal microinjection of the nonspecific nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) was used to determine if inhibition of NOS results in morphological changes in the rat spinal cord. Following spinal injections of 100-750 mM L-NAME (pH 7.0), 1.0-500 mM L-NAME (pH 2.5-5.4), or L-NAME + L-arginine, quantitative analysis of morphological changes revealed a positive dose-response relationship between L-NAME and neuronal loss. This effect was blocked by L-arginine and was inversely related to spinal levels of NOS enzyme activity. Results of this study have shown the importance of basal NOS activity in maintaining the structural integrity of spinal neurons. It is proposed that the effects of L-NAME on nitric oxide (NO) production leads to decreased blood flow, secondary to vasoconstriction, and a hypoxic-ischemic reaction in spinal tissue. The results suggest that a potential contributing factor to neuronal damage in pathological conditions such as spinal cord injury may be the decreased production of nitric oxide.

A behavioral and physiological method has been developed to study thermal detection in the rat. Threshold temperatures signaling (1) disruption of a trained behavior (forelimb bar pressing) and (2) increased heart rate were determined using a gradually increasing thermal stimulus delivered to the hindlimb. Response thresholds for disruption of bar press activity (44.8 degrees C) and heart rate elevation (44.4 degrees C) were statistically equivalent. No differences in thresholds for either response end point were found between the left and right hindlimbs, thus validating the consistency of the technique and reproducibility of the stimulus delivery device during test periods of 3-4 weeks. Advantages of the method include the use of two independent end points that are determined objectively, performance criteria that do not rely upon motor responses from the stimulated limb and the use of quantitative descriptors that enables comparisons to be made between different test groups. The method combines behavior with cardiovascular and somatosensory function in a way that can be used for the assessment of spinal and supraspinal pathways involved in thermal detection in the unanesthetized, behaviorally active rat.

Although cavitary lesions of the spinal cord have been recognized for centuries, only recently have effective, noninvasive imaging techniques allowed antemortem diagnosis of this clinical syndrome. Methods of treatment have not been consistently successful in alleviating or reversing the clinical symptoms caused by these cystic lesions. Incomplete understanding of the underlying pathologic basis for the syringes has impeded the development of effective methods of treatment. This review documents historical considerations regarding clinical observations and experimental studies of this entity and the animal models that have been reported for each of the major types of syringomyelia. Recent studies have suggested that development of a relevant animal model of posttraumatic syringomyelia is imminent. Successful development of an experimental model will not only permit definition of the pathogenesis of cyst formation but also provide methods for testing of therapeutic interventions.

Microinjections of quisqualic acid were made in the spinal cord to evaluate the excitotoxic effects of this excitatory amino acid agonist on spinal neurons in the rat. Animals were divided into four groups based on post injection survival times of 7-49 days. Injections ranging from 0.3 to 2.0 microL of 8.3, 83, and 125 mM quisqualic acid or normal saline were made in the lower thoracic and upper lumbar spinal cord. At all survival times evaluated unilateral injections of quisqualic acid produced unilateral or bilateral cell death and a prominent inflammatory reaction. In 23/25 animals spinal cavities were also observed. Spinal cord segments at or near quisqualate injection sites contained darkly stained, hypertrophied neuronal profiles, and increased staining for glial fibrillary acidic factor. Immunostaining for glial fibrillary acidic factor was especially intense in areas of neuronal degeneration and in border areas of spinal cavities. The results of this study suggest that the intraspinal injection of quisqualic acid may be an effective method to study the mechanisms of excitatory amino acid neurotoxicity, and the pathogenesis of spinal cavitation following neuronal injury.

Retrograde transport of the fluorescent tracer Fluorogold was used in combination with immunohistochemical staining for the enzyme glutaminase to identify putative glutamatergic neurons belonging to the rat spinomesencephalic tract. Glutaminase-like staining in spinal projection neurons suggests that the relay of nociceptive information from the spinal cord to midbrain may involve the excitatory amino acid glutamate.

The mechanoreceptive properties of rat spinal sensory neurons were evaluated in segments adjacent to those injected with the excitatory amino acid agonist quisqualic acid. Following survival periods of 7-36 days cells recorded in quisqualate injected animals had an increased level of background activity, increased sensitivity to mechanical stimuli, and an increase in the duration of afterdischarge responses. It is suggested that a central mechanism that alters the functional state of neurons may be responsible for the sensory abnormalities, e.g. allodynia and hyperalgesia, that occur following excitotoxic induced cell death associated with ischemic and traumatic spinal cord injury.

Intraspinal injections of lysolecithin were used to produce unilateral demyelination in the dorsal columns of the rat spinal cord. The purpose of this study was to evaluate the effects of demyelination on the conductive properties of axons belonging to a spinal pathway of known origin and site of termination. At 5 and 50 day intervals following injections, animals were prepared for acute experiments during which recordings of tibial nerve evoked potentials were made from the surface of the lumbar spinal cord (L5-L6) and nucleus gracilis (0.5-1.0 mm caudal to obex). Latency, duration, and strength of potentials were evaluated in control (uninjected) and lysolecithin-injected animals. The analysis of these potentials showed increases in latency and decreases in duration and strength of responses recorded 5 days after lysolecithin injections. Animals examined 50 days postinjection showed a decreased latency and increased duration and strength of responses compared to those recorded 5 days postinjection. Ultrastructural examination of lysolecithin injection sites showed these improvements to parallel the remyelination of axons by oligodendrocytes and Schwann cells. The improvement in physiologic characteristics of evoked potentials coupled with the remyelination of dorsal column axons supports the conclusion that remyelination of chemically demyelinated axons is an important factor in reestablishing the functional connectivity of demyelinated axons.

Response and receptive field properties were evaluated for 62 spinomesencephalic tract cells in the upper cervical spinal cord (C1-C3) of cats anesthetized with sodium pentobarbital and alpha-chloralose. Recordings were made from cells in laminae I-VIII and X contralateral to antidromic stimulating electrodes positioned in the rostral, caudal and intercollicular region of the midbrain. The mean antidromic threshold for all cells was 185 +/- 132 microA, and conduction velocities ranged from 2.3 to 38.6 m/sec. Twelve cells were backfired from both midbrain and diencephalic stimulation sites. Receptive fields ranged from simple, i.e., ipsilateral forelimb or face, to complex, i.e., excitatory and/or inhibitory responses from large portions of the body. Peripheral receptive fields included muscles, joints, cornea, dura, forelimbs, hind limbs, tail, and/or testicles. Five functional classes of cells were observed: (a) wide dynamic range (14 cells); (b) high threshold (2 cells): (c) low threshold (4 cells); (d) deep/tap (11 cells); and (e) non-responsive (31 cells). Eight cells were evaluated for responses to different doses (5-150 micrograms) of intravenous (i.v.) serotonin. Two of the 8 cells exhibited excitatory effects, whereas 2 cells classified as deep/tap and 4 cells classified as non-responsive were not affected. The results of this study have shown the upper cervical component of the spinomesencephalic tract is made up of a heterogenous population of cells involved in the integration of varied inputs from large portions of the body. It is proposed that the large population of SMT cells in the upper cervical spinal cord may be involved in pain mechanisms, especially those related to the affective consequences of acute and chronic pain.

The distribution of cells belonging to the rat spinomesencephalic tract was studied by means of the retrograde transport of fluorescent dyes. Bilateral midbrain injections of cytoplasmic and nuclear tracers were made in order to evaluate the location of ipsilateral, contralateral, or bilaterally projecting cells. Spinal neurons with ascending projections to midbrain and descending propriospinal projections were identified by midbrain and spinal injections of different cytoplasmic labels. The locations of spinomesencephalic tract cells included seven regions of the spinal gray matter: marginal zone, lateral neck of the dorsal horn, nucleus proprius, the region around the central canal, the lateral cervical and spinal nuclei and the ventral horn. Cells projecting to the ipsilateral or contralateral midbrain had similar distributions and were frequently found in clusters with overlapping dendritic fields. Approximately 75% of spinomesencephalic cells projected to the contralateral midbrain. The largest contribution to the spinomesencephalic tract cell population was found in cervical cord segments 1-4. Cells with bilateral projections accounted for nearly 2% of all labeled cells, whereas 5% had both ascending and descending projections. Spinomesencephalic cells were found to have varying dendritic fields and morphology, e.g. fusiform, pyramidal, round/oval, and multipolar. The results of the present study lend further support to the view that the spinomesencephalic tract is a multi-component pathway with varied origins and projection targets.

Pieces of fetal rat lumbar spinal cord were transplanted into the anterior eye chamber of adult rat hosts. At least seven months later, extracellular single-unit recordings of spontaneously active graft neurons were made prior to and during the superfusion of either glutamate or gamma-aminobutyric acid (GABA). Superfusion of glutamate produced an increase (five cells), decrease (three cells), or had no effect (two cells) on the firing rate of neurons tested. Superfusion of GABA decreased the firing rate of all twelve neurons tested, while superfusion of the GABA receptor antagonist bicuculline increased the firing rates of all eight neurons tested. The latency and magnitude of the responses to glutamate and GABA were not related to depth of the recording electrode below the graft surface. Together, these data suggest that the intraocular spinal cord graft is suitable for the in vivo study of GABA and glutamate neuropharmacology.

A modified Golgi staining technique was used to study the neuronal morphology and organization of the fetal rat spinal cord which had developed in the anterior eye chamber of adult rat hosts. Individual neurons in spinal cord grafts displayed profiles which were strikingly similar to previously described spinal cord neurons stained in situ. Further, for the population of 464 graft neurons studied, the distributions of average cell body diameters and numbers of primary dendrites were comparable to those of previously published in situ studies. An internal organization of graft neurons was also observed. Similar-shaped neurons were grouped together, which made it possible to identify different regions within a graft, such that a comparison could be made with normal spinal cord morphology. These observations provide further evidence that the intraocular spinal cord graft is a suitable model for studying spinal cord growth, development, and plasticity and indicate that the Golgi stain may be useful for the quantitative study of concomitant changes in neuronal morphology.

1. The effects of electrical stimulation at different rostrocaudal levels of the midbrain, and at sites in the rostral medulla ipsilateral and contralateral to spinal recording sites, were evaluated against the responses of 46 cells belonging to the cat spinomesencephalic tract (SMT). 2. Inhibitory and/or excitatory effects of brain stem stimulation were observed on SMT cells that responded best (26 cells) or exclusively (12 cells) to noxious mechanical or thermal stimuli, as well as on 7 cells responding only to tap and/or stimulation of deep tissues. Recording sites for 32 cells were located in laminae V-VIII (27 cells) and laminae I-III (5 cells). 3. Midbrain stimulation sites were located in the superior colliculus, central gray (CG), red nucleus, and the midbrain reticular formation. Both inhibitory-only and excitatory-only effects were observed, although the most common effect of midbrain stimulation was excitation followed by inhibition (mixed effects). The effects of stimulation at different midbrain levels were determined for each cell. Stimulation in the caudal, middle, or rostral midbrain was often found to exert different effects on the same SMT cell. 4. Stimulation in the rostral medulla at sites located in nucleus raphe magnus (NRM), nucleus reticularis gigantocellularis, and nucleus reticularis magnocellularis produced the same complement of effects observed with midbrain stimulation. Excitation followed by inhibition was the most common effect observed. 5. Stimulus intensities required to produce excitatory or inhibitory effects from midbrain were 114 +/- 85 (SD) microA and 210 +/- 91 microA, respectively. Stimulus currents required to produce excitatory or inhibitory effects from medullary stimulation sites were 124 +/- 56 microA and 70 +/- 60 microA, respectively. The mean currents required to produce mixed effects were 221 +/- 120 microA (midbrain) and 127 +/- 71 microA (medulla). Increasing the stimulus intensity used to evaluate brain stem effects increased the magnitude and duration of effects for 33 cells. Mixed effects were observed on 11 cells at stimulus intensities greater than those required to produce inhibitory-only effects. 6. Significant differences were found between the latencies of excitation and inhibition produced from different brain stem levels. These differences suggest that midbrain and medullary stimulation activate descending pathways with a wide range of conduction velocities and/or supraspinal and spinal connectivities. 7. The spinal trajectory of pathways contributing to the varied effects of brain stem stimulation as well as the complex receptive fields (RFs) of SMT cells were evaluated by the placement of lesions in the cervical spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of stimulation in the ventral posterior lateral (VPLc) thalamic nuclei on the activity of primate spinothalamic tract neurons were investigated. All 19 cells studied were strongly inhibited by conditioning trains of stimuli delivered to either ipsilateral or contralateral VPLc. Both background discharges and activity evoked by innocuous or noxious cutaneous stimulation were inhibited.

To identify the midbrain nuclei that project to the medial part of the lower brainstem in the monkey, labeled cells were mapped in the midbrain following the injection of horseradish peroxidase into the medial medulla oblongata. After the general distribution of labeled cells was observed in three animals with large injections, more discrete injections of HRP were made in different locations in six additional animals. The small injections were centered in the nucleus raphe magnus, nucleus reticularis gigantocellularis, or nucleus medullae oblongatae centralis. The five labeled midbrain nuclei were the periaqueductal gray, nucleus cuneiformis, deep layers of the superior colliculus, nucleus of Darkschewitsch, and the interstitial nucleus of Cajal. In addition, the parvocellular division of the red nucleus and the posterior pretectal nucleus contained large numbers of cells when the injection spread into the inferior olive. No major differences in the distribution of labeled cells between different injection sites were found with the exception that the superior colliculus did not contain any labeled cells when the injection was restricted to midline structures. The functional implications of these anatomical findings are discussed in relation to the descending control of pain.

Recordings were made from 90 identified spinomesencephalic tract (SMT) cells in the lumbosacral spinal cord of cats anesthetized with alpha-chloralose and pentobarbital sodium. Recording sites were located in laminae I-VIII. Antidromic stimulation sites were located in different regions of the rostral and caudal midbrain including the periaqueductal gray, midbrain reticular formation, and the deep layers of the superior colliculus. Twelve SMT cells were antidromically activated from more than one midbrain level or from sites in the medial thalamus. The mean conduction velocity for the population of cells sampled was 45.2 +/- 21.4 m/s. Cells were categorized based on their responses to graded intensities of mechanical stimuli and the location of excitatory and/or inhibitory receptive fields. Four major categories of cells were encountered: wide dynamic range (WDR); high threshold (HT); deep/tap; and nonresponsive. WDR and HT cells had excitatory and/or inhibitory receptive fields restricted to the ipsilateral hindlimb or extending to other parts of the body including the tail, forelimbs, and face. Some cells had long afterdischarges following noxious stimulation, whereas others had high rates of background activity that was depressed by nonnoxious and noxious stimuli. Deep/tap cells received convergent input from muscle, joint, or visceral primary afferent fibers. The placement of mechanical lesions at different rostrocaudal levels of the cervical spinal cord provided information related to the spinal trajectory of SMT axons. Six axons were located contralateral to the recording electrode in the ventrolateral/medial or lateral funiculi while two were located in the ventrolateral funiculus of the ipsilateral spinal cord. Stimulation at sites used to antidromically activate SMT cells resulted in the inhibition of background and evoked responses for 22 of 25 cells tested. Inhibitory effects were observed on responses evoked by low/high intensity cutaneous stimuli and by the activation of joint or muscle primary afferent fibers. Based on the response and receptive-field properties of SMT cells it is suggested that the SMT may have an important role in somatosensory mechanisms, particularly those related to nociception.

1. Stimulation of the sensorimotor cortex was found to excite and/or inhibit nociceptive spinothalamic tract cells. Thirteen wide dynamic range cells were inhibited by cortical stimulation, 6 were excited and 14 were both excited and inhibited. Four of six high-threshold cells were excited and one was inhibited. 2. Intermediate (200 ms) or long (2 s) duration conditioning trains were effective in reducing responses of spinothalamic cells evoked by noxious mechanical or thermal stimuli and by A- and C-fiber volleys in the sural nerve. Preferential inhibition of low-threshold responses with little or no effect on high-threshold discharges was observed in some cases. 3. Inhibitory actions were obtained primarily from stimulation of the SI sensory cortex and area 5, while excitation or excitation followed by inhibition was the dominant effect from motor cortex (area 4). Spinothalamic cells were also excited by stimulation of the medullary pyramid. 4. In eight animals extensive mapping of the sensorimotor cortex showed that for a given cell, stimulation of the sensory cortex produced inhibition while stimulation of motor cortex resulted in excitation. 5. The average latency of inhibition from sensory cortex was 29.8 +/- 10 ms, while the average latency of excitation from motor cortex was significantly shorter, 13.5 +/- 9 ms. The shortest latencies for excitation from pyramidal stimulation in the cases evaluated ranged from 2 to 9 ms. 6. Spinal cord lesions were made in five animals to determine the descending pathway(s) mediating corticofugal effects. Cortical and pyramidal effects were eliminated or considerably reduced by lesions involving the dorsal part of the lateral funiculus. This observation combined with latency data suggest that the corticospinal tract may be involved in the mediation of cortical excitation, while both pyramidal and extrapyramidal pathways are likely to be involved in cortical inhibition.

Retrograde transport of HRP and the fluorescent dye DAPI were used to double label spinothalamic tract cells with dual projections to thalamus and cerebellum. Cells containing both retrograde tracers were found in the intermediate gray zone and in the lateral spinal nucleus of the rat lumbosacral spinal cord. Double labeled cells were easily identified by the presence of granular HRP reaction, product and the blue fluorescence of DAPI. The use of HRP and DAPI provides an effective double labeling technique for the localization of neurons with nonoverlapping projections in the central and/or peripheral nervous system.

Recordings were made from 132 raphe- and reticulospinal tract neurons in the medial part of the lower brain stem in 32 anesthetized monkeys. Recording sites were in the nucleus raphe magnus, the rostral nucleus raphe obscurus, and the reticular formation adjacent to the raphe. The neurons were identified by antidromic activation from the upper lumbar spinal cord. Of the population sampled, 83 cells were activated antidromically from the left dorsal lateral funiculus (DLF), 32 from the right DLF, and 17 from both sides. The mean latency for antidromic activation was 8.2 +/- 7.1 ms, corresponding to a mean conduction velocity of 22.8 m/s. No conduction velocities characteristic of unmyelinated axons were observed. Collision tests indicated that raphe-spinal axons that bifurcated to descend in both DLFs branched within the spinal cord. The effects of stimulation in the periaqueductal gray (PAG) or adjacent midbrain reticular formation were tested on 102 spinally projecting neurons in the medial medulla. Of these, 60 cells were excited, 9 cells were inhibited, 8 showed mixed excitation and inhibition, and 25 cells were unaffected. The mean latency for excitation was 11.6 ms and for inhibition, 17.8 ms. Threshold for excitation of raphe- and reticulospinal neurons ranged from 50 to 400 microA. Raphe- and reticulospinal tract cells could often (31/46 cells tested) be excited following stimulation in the ventral posterior lateral nucleus of the thalamus. The mean latency of excitation was 35.6 ms (range, 6-112 ms). Receptive fields could be demonstrated for 80 raphe- and reticulospinal cells, while 48 neurons possessed no demonstrable cutaneous receptive field. Most cells had large excitatory receptive fields, often encompassing the surface of the entire body and face. Some neurons had complex excitatory and inhibitory receptive fields, whereas other cells had large inhibitory receptive fields over much of the surface of the body and face. For most cells (52/55) with excitatory receptive fields, the only effective stimuli were noxious mechanical or noxious heat stimuli. Nonnoxious mechanical stimuli, such as brushing the skin, were capable of activating only a few (3/55) raphe- and reticulospinal neurons, and these were more effectively excited by noxious stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Eighty-three cell pairs were recorded in dorsal horns of 19 cats. Cross-correlograms were flat in 65 cell pairs; of the remaining 18 pairs, cross-correlograms had broad peaks or troughs suggestive of nonmonosynaptic causal relations in their discharges; one cell pair had a biphasic deviation from base line. 2. No cross-correlograms indicative of monosynaptic interactions were observed. 3. All cell pairs with nonflat cross-correlograms had overlapping receptive fields. 4. It is concluded that monosynaptically connected cell pairs are rare at the interelectrode distances used in this experiment because such cell pairs must lie close together on the somatotopic map or because our recording methods bias against monosynaptically linked cell pairs.

The distribution of the cells of origin of the primate spinoreticular tract was determined following injections of horseradish peroxidase (HPR) into the pontomedullary reticular formation in Macaca fascicularis. Five animals received large bilateral injections which included the raphe nuclei and seven monkeys received smaller, unilateral injections. Sections sampled were from upper cervical levels, the cervical enlargement, upper and lower thoracic levels, and lumbosacral levels. The laminar distribution of spinoreticular cells in all spinal cord levels was comparable. More than half of the labeled cells were located ventromedially, in laminae VII and VIII. HRP-labeled cells were also found in the dorsal horn, primarily in the lateral reticulated part of lamina V. Some cells were also found in laminae I and X. Spinoreticular cells in the lumbosacral spinal cord mainly projected to the contralateral brainstem. In the cervical enlargement, however, a bilateral distribution of cells was observed following unilateral injections of HRP. Most spinoreticular cells were multipolar neurons with extensive dendritic ramifications. The distribution of spinoreticular cells is similar to the distribution of spinal cord neurons that project to the medial thalamus, but different from that of spinal neurons projecting to the ventrobasal complex. The anatomical organization of the spinoreticular tract is consistent with a role for this pathway in nociception.

Cells of origin of serotonergic and non-serotonergic projections to the caudal brain stem in the primate were examined using a double label technique. Following HRP injections into medullary raphe nuclei and the adjacent reticular formation double labeled cells were found in the dorsal raphe nucleus, the central superior nucleus and the ventrolateral tegmentum. Retrogradely labeled cells that did not stain for serotonin-like immunoreactivity were found primarily in the periaqueductal gray (PAG) and the mesencephalic and pontine reticular formation. The results are discussed in relation to the descending pathway(s) mediating the effects of PAG stimulation.

The effects of serotonin antagonists were examined on the inhibition and excitation of nociceptive spinothalamic tract cells produced by brainstem stimulation with short (200 msec) or long (2 sec) stimulus trains. The inhibitory effects resulting from stimulation in either nucleus raphe magnus (NRM) or in the periaqueductal gray with short stimulus trains were significantly reduced after the administration of serotonin receptor blockers. Reductions in periaqueductal gray inhibition were also observed on inhibition produced by long duration trains, whereas the effects of NRM inhibition were dependent on stimulus duration, current strength and dose of antagonist. The rare excitatory effect of NRM stimulation was also found to be relatively reduced after the administration of a serotonin antagonist. The relatively weak effects of serotonin antagonists on NRM inhibition are discussed in relation to three hypotheses: 1) parallel pathways; 2) multiple receptors; or 3) corelease of serotonin and another transmitter from raphe-spinal neurons.

Response and receptive field properties were determined for 24 spinal neurons backfired from midbrain or midbrain-thalamus in the anesthetized monkey. Recording sites were located in laminae I (11 cells), IV (6), V (6) and VI (1) in the lumbosacral spinal cord. The mean axonal conduction velocity of cells projecting to midbrain was significantly less than that of cells projecting to midbrain-thalamus. Cells backfired only from midbrain had complex excitatory receptive fields whereas those projecting to midbrain-thalamus had excitatory receptive fields confined to a single limb. Cells in both populations had complex inhibitory receptive fields.

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase was used to determine the terminal domain of the projection from the lumbosacral spinal cord to the midbrain in the rat, cat, and monkey. Results have shown that several midbrain regions receiving afferent input from this level of the spinal cord are common to the three species examined. Structures innervated by this projection were located throughout the full rostrocaudal extent of the midbrain. The strongest projections were to the intercollicular region and caudal midbrain contralateral to injection sites in the spinal cord. Terminal labeling in the rostral midbrain, except that observed in the nucleus of Darkschewitsch, was substantially less than that observed at more caudal midbrain levels. Structures receiving the strongest input from the spinal cord included the central gray, nucleus cuneiformis, the deep and intermediate layers of the superior colliculus, and the intercollicular nucleus. Other structures receiving afferent input from the lumbosacral spinal cord included the anterior and posterior pretectal nuclei, red nucleus, Edinger-Westphal nucleus, interstitial nucleus of Cajal, and the mesencephalic reticular formation. It is concluded that the spinal projection to the midbrain is a multicomponent projection consisting of several pathways terminating in discrete midbrain regions. Considering the diverse functions associated with midbrain regions receiving spinal input and the response and receptive field properties of cells belonging to this pathway, the results of the present study are discussed in relation to the potential role of the spinomesencephalic tract in somatic, visceral, and motor function.

Recordings were made from spinothalamic tract (STT) cells in the lumbosacral enlargement of anesthetized monkeys. The cells were identified by antidromic activation from the contralateral ventral posterior lateral nucleus of the thalamus. Electrical stimulation at sites within the periaqueductal gray, the adjacent midbrain reticular formation, or the deep layers of the tectum were found to inhibit the activity of STT cells. In general, midbrain stimulation inhibited the background discharges and the responses of wide dynamic range cells evoked by innocuous and noxious cutaneous stimulation (29 of 37 cases). However, for six cells, midbrain stimulation preferentially inhibited the responses to noxious stimulation. The evoked responses of all 10 high-threshold cells were inhibited. In only two cases was midbrain stimulation ineffective, and no excitatory effects were observed. The mean latency to onset of inhibition resulting from midbrain stimulation was 24.9 +/- 7.2 ms (n = 35). The amount of inhibition produced by midbrain stimulation was graded with stimulus intensity. For example, trains of stimuli (333 Hz) at 50 microA produced a mean inhibition to 81.7 +/- 16.6% of control, while 200 microA resulted in a mean inhibition to 36.3 +/- 21.7%. Not only was the inhibition increased by the use of stronger current intensities, but the duration of inhibition was prolonged. Midbrain stimulation inhibited the responses of STT cells to volleys in both the A-fibers and the C-fibers of the sural nerve. However, there was a selective action in that the responses to C-fiber volleys were more strongly inhibited than were the responses to A-fiber volleys. Lesions placed in the white matter of the upper cervical spinal cord reduced the inhibition produced by stimulation in either the midbrain or the nucleus raphe magnus. The extent to which the inhibition was reduced was proportional to the extent of the cord lesions. However, even when there was an interruption of the entire lateral funiculus on the side of an STT cell and of the dorsal quadrant of the contralateral side, there was still substantial inhibition following stimulation in either brain stem site. It is concluded that while part of the inhibition is mediated by pathways descending in the dorsal lateral funiculus (DLF), at least some depends on pathways coursing through the ventral spinal cord. Inhibition of STT cells may contribute to the neuronal mechanism of the analgesia that results from stimulation in the periaqueductal gray matter in awake, behaving animals.