Postnatal development of the serotonin innervation of the hippocampus and dentate gyrus following raphe implants.

Serotoninergic (5-HT) neurons derived from the embryonic raphe nuclear area (brainstem, embryonic days (E 16-18) were implanted into the entorhinal cortex of 6-day-old (P6) neonatal rat recipients which had received a fimbria lesion and entorhinal cortex ablation on P3. The hippocampus, dentate gyrus, and the raphe implant area were examined with 5-HT immunohistochemistry 7, 14, 21, 30, and 60 days after implantation. The pattern of 5-HT reinnervation was compared to that of normal and lesioned animals, and to previous studies in which rats received septal or striatal implants. In the hippocampus adjacent to the implant 5-HT-immunoreactive fibers were first observed by 7 days postimplantation and increased in density and in their septotemporal and dorsoventral extent with increasing time postimplantation. Moderately dense fiber networks were diffusely distributed in the hippocampus and dentate gyrus at 30 and 60 days postimplant. Little, if any, indication of lamination was present. Retrogradely labeled neurons (the majority of which contained 5-HT immunoreactivity) were observed in the raphe implant following injections of Fast Blue into the hippocampal formation. A few retrogradely labeled cells did not contain 5-HT, methionine-enkephalin (ME), or substance P (SP) immunoreactivity, although ME- and SP- immunoreactive neurons were observed in the implants. The lamination patterns and the increased density of 5-HT-immunoreactive fibers following a raphe implant into the entorhinal cortex clearly differ from the normal 5-HT pattern and from the patterns of lamination following a striatal or septal implant.

Locus coeruleus neurons in the rat containing neuropeptide Y, tyrosine hydroxylase or galanin and their efferent projections to the spinal cord, cerebral cortex and hypothalamus.

The efferent projections of locus coeruleus neurons which contain neuropeptide Y-, tyrosine hydroxylase- or galanin-like immunoreactivity were investigated using the indirect immunofluorescence technique combined with the retrograde transport of the fluorescent substance Fast Blue. Four groups of rats received injections of Fast Blue: (1) bilaterally into the mid-thoracic spinal cord (T6-T7); (2) unilaterally into the low cervical spinal cord (C4-C5); (3) unilaterally into the paraventricular, periventricular and dorsomedial hypothalamic nuclei; and (4) unilaterally into five sites in the cerebral cortex (frontal, cingulate and striate cortex). Efferent projections to the spinal cord, hypothalamus and cerebral cortex from neuropeptide Y-, tyrosine hydroxylase- and galanin-containing locus coeruleus cells were observed. A higher percentage of the peptidergic locus coeruleus neurons projected to the hypothalamus than to the spinal cord or cerebral cortex. The distribution and morphology of the neuropeptide Y- and galanin-containing neurons in the locus coeruleus were also investigated. Neuropeptide Y-like immunoreactivity and galanin-like immunoreactivity were found in small, medium and large multipolar neurons, as well as in fusiform locus coeruleus cells. The neuropeptide Y- and galanin-immunoreactive neurons were found throughout the locus coeruleus. In the caudal locus coeruleus, they were primarily located in the dorsal portion. Neuropeptide Y-like immunoreactivity and galanin-like immunoreactivity were only seen in a few tyrosine hydroxylase-positive neurons of the subcoeruleus group. The data show that the peptide-containing locus coeruleus neurons have efferent projections to the spinal cord, hypothalamus and cerebral cortex. The locus coeruleus may be divided into functional subdivisions dependent on the region of the locus coeruleus, the neurotransmitter/neuropeptide(s) contained within the neurons and their efferent projections.

Multiple putative neuromessenger inputs to the phrenic nucleus in rat.

Immunohistochemical reactions for 12 putative neuromessengers combined with retrograde labeling of phrenic motoneurons identified seven neuromessengers (5-hydroxytryptamine, substance P, thyrotropin-releasing hormone, methionine enkephalin, cholecystokinin, galanin, neuropeptide Y) located within terminal varicosities in the phrenic nucleus. The degree of terminal labeling in the phrenic nucleus varied depending on the peptide. Substance P, thyrotropin-releasing hormone and methionine enkephalin were each tested for colocalization with 5-hydroxytryptamine within terminal varicosities in the phrenic nucleus, and the coincidence of double-labeling varied for each peptide. These results indicate that phrenic motoneurons are subject to modulation by many peptide neuromessengers that may alter their responsiveness to primary excitatory and inhibitory inputs.

Syringomyelia: clinical observations and experimental studies.

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.

Calcitonin gene-related peptide (CGRP)-like immunoreactivity in motoneurons of the human spinal cord following injury.

Changes that occur in the localization of calcitonin gene-related peptide-like-immunoreactivity (CGRP-LI) in motoneurons, following injury to the human spinal cord, were examined. CGRP-LI above and below the level of injury was compared to normal human spinal cord. Vibratome sections were cut and processed for immunostaining using the avidin-biotin immunoperoxidase method. Whereas motoneurons above the lesion contained CGRP-LI, below the lesion the CGRP-LI was reduced. In 3 spinal cords from patients who had survived between 1 and 8 years after injury, CGRP-LI in motoneurons of lumbar spinal cord was absent or considerably diminished. In the spinal cord from one patient who had died several years after injury, there was a unilateral augmentation of CGRP immunostaining. The results suggest that CGRP levels in motoneurons are affected by spinal cord injury in humans and that CGRP levels in motoneurons may be regulated either by supraspinal afferent inputs or by muscle activity.

In vitro labeling strategies for identifying primary neural tissue and a neuronal cell line after transplantation in the CNS.

Potential labels for identifying embryonic raphe neurons and a clonal, neuronally differentiating, raphe-derived cell line, RN33B, in CNS transplantation studies were tested by first characterizing the labels in vitro. The labels that were tested included 4',6-diamidino-2-phenylindole hydrochloride, 1,1'-dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate, the Escherichia coli lacZ gene, Fast Blue, Fluoro-Gold, fluorescein-conjugated latex microspheres, fluorescein isothiocyanate-conjugated or nonconjugated Phaseolus vulgaris leucoagglutinin, methyl o-(6-amino-3'-imino-3H-xanthen-9-yl) benzoate monohydrochloride, or tetanus toxin C fragment. Subsequently, the optimal in vitro labels for embryonic raphe neurons and for RN33B cells were characterized in vivo after CNS transplantation. In vitro, 1,1'-dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate (DiI) optimally labeled embryonic neurons. The Escherichia coli lacZ gene optimally labeled RN33B cells. Most labels were rapidly diluted in cultures of embryonic astrocytes and proliferating RN33B cells. Some labels were toxic and were often retained in cellular debris. In vivo, DiI was visualized in transplanted, DiI-labeled raphe neurons, but not in astrocytes up to 1 mo posttransplant. DiI-labeled host cells were seen after transplantation of lysed, DiI-labeled cells. beta-Galactosidase was visualized in transplanted, Escherichia coli lacZ gene-labeled RN33B cells after 15 days in vivo. No beta-galactosidase was seen in host cells after transplantation of lysed, lacZ-labeled RN33B cells. The results demonstrate that labels for use in CNS transplantation studies should be optimized for the specific population of donor cells under study, with the initial step being characterization in vitro followed by in vivo analysis. Appropriate controls for false-positive labeling of host cells should always be assessed.

A computerized grid walking system for evaluating the accuracy of locomotion in rats.

A microcomputer-based system employing photoelectric devices to record rat movements and footfalls in the grid walking test paradigm was developed and evaluated. Behavioral data obtained from the system were: distance traversed on the grid, time taken to traverse the distance, number of footfalls, times of footfalls, positions of footfalls, durations of footfalls, and whether the footfall was due to a hind or a fore limb. Validation of the system was performed by comparing the data obtained from the videotape analysis with that obtained from the computerized system. Correlation coefficients between the data obtained from the two methods were found to be 0.92 for one observer, 0.84 for a second observer, and 0.88 with the mean of the two observers. An experimental study in which a group of rats was administered dorsal hemisection lesions of the spinal cord was also conducted. Animals in the lesion group took the same amount of time to cross the runway as the control animals, but made more footfalls per crossing and had longer durations per footfall. The studies validate the capacity of the computerized system to efficiently detect fine locomotory deficits, suggesting that it is a viable tool for the evaluation of neurological dysfunctions in experimental rats.

Immunocytochemical localization of serotonin in the rat dentate gyrus following raphe transplants.

The ultrastructural features of the serotoninergic innervation of the rat dentate gyrus in normal adults and in animals receiving raphe nuclear area transplants was investigated using an antibody to serotonin (5-HT). Neonatal rats received a lesion of the fimbria-fornix and entorhinal cortex. Three days later, a portion of embryonic (E-16-18) raphe nuclear area was transplanted to the entorhinal cavity and the animals were allowed to survive for 60 days. Animals were processed for the immunocytochemical localization of 5-HT using the peroxidase-antiperoxidase method. Light microscopic observation showed that 5-HT-containing fibers from transplanted raphe neurons densely innervated the hilar and molecular zones of the dentate gyrus. Electron microscopic analysis showed that 5-HT immunoreactivity was contained only in axons and axon varicosities. There were no differences in the ultrastructural characteristics of axons and axon terminals between normal animals and those which had received raphe transplants. A mixture of both conventional synaptic junctions and non-synaptic axonal swellings were found in both groups.

A comparative study of the immunohistochemical localization of a presumptive proctolin-like peptide, thyrotropin-releasing hormone and 5-hydroxytryptamine in the rat central nervous system.

A proctolin (PROC)-like peptide was studied immunohistochemically in the hypothalamus, lower brainstem and spinal cord of the rat using an antiserum against PROC conjugated to thyroglobulin. Neuronal cell bodies containing PROC-like immunoreactivity (PROC-LI) were observed in the dorsomedial, paraventricular and supraoptic nuclei of the hypothalamus and in the nucleus raphe magnus, nucleus raphe pallidus, nucleus raphe obscurus and nucleus interfascicularis nervi hypoglossi in the medulla oblongata. Fibers containing PROC-LI were seen in the median eminence and in other hypothalamic nuclei, and in the lower brainstem in cranial motor nuclei including the dorsal motor nucleus of the vagus nerve, the motor trigeminal nucleus, the facial nucleus and nucleus ambiguous, and in lower numbers in the nucleus of the solitary tract and locus coeruleus. Fibers containing PROC-LI were also located in the spinal cord, in the intermediolateral cell column at thoracic levels and in the ventral horns at all levels of the spinal cord. After transection of the spinal cord, all PROC-immunoreactive fibers below the lesion disappeared. Following injection of Fast blue into the thoracic spinal cord, retrogradely labeled cells in the nuclei raphe pallidus, obscurus and magnus and nucleus interfasciculari nervi hypoglossi were seen to contain PROC-LI. PROC-LI had a similar distribution as thyrotropin-releasing hormone (TRH)-LI in the above-mentioned areas and coexistence of TRH-LI and PROC-LI was shown in cell bodies in the hypothalamus and medulla oblongata. PROC-LI could also be shown to coexist with 5-hydroxytryptamine (5-HT)-LI in neuronal cell bodies in the lower brainstem. The results demonstrate the occurrence of a PROC-like peptide in the mammalian nervous system, and these neurons seem to be at least largely identical to previously described TRH systems. A possible involvement of the PROC-like peptide in spinal motor control is discussed in relation to the well-established role of PROC in control of motor behavior in insects and invertebrates.

Changes in bone in a model of spinal cord injury.

Bone calcium, histomorphometry, and mechanical strength were evaluated in a model of spinal cord injury. Cortical bone area and rates of formation and apposition at the tibiofibular junction (TFJ) and midshaft of the humerus were measured at 35-42, 42-77, and 77-94 days after transection of the spinal cord. All comparisons were between the animals with a spinal lesion and control animals. A 0.34% difference in the length of the tibia of the two groups of animals was observed, the dry weight of the tibia was 28.4% less in rats with a lesion, and there was no significant difference in the amount of calcium per milligram of bone. At 35 days after surgery, the cortical area in the midshaft of the humerus was slightly less (11%) in rats with a lesion, but by 94 days there was no difference in cortical or medullary area. The final (day 94) cortical area at the TFJ in rats with a lesion was less than that in the controls. Bone formation at the TFJ was similar in both groups in the period of 35-42 days and was similar at 77-94 days in the animals with a lesion, and rates of formation and apposition were greater in the humerus of rats with a lesion; the rates did not differ significantly between groups at either site. At 94 days, trabecular bone area in the tibial metaphysis was 41% less in rats with a lesion. Mechanical parameters were significantly less in the femora, but not the humeri, of rats with a lesion.

Variable morphological differentiation of a raphé-derived neuronal cell line following transplantation into the adult rat CNS.

A clonal, neuronally-differentiating cell line, RN33B, was previously developed by retroviral infection of neural tissue derived from embryonic Sprague-Dawley raphé nuclei with a retrovirus encoding the temperature-sensitive allele of SV40 large T-antigen. In the present study, RN33B cells were transplanted into two target areas of the raphé nuclei, the spinal cord and hippocampal formation, of adult allogeneic hosts. Prior to transplantation, RN33B cells were infected in vitro with a retroviral vector carrying the Escherichia coli lacZ reporter gene and were visualized in vivo using a beta-galactosidase immunohistochemical technique. RN33B cells were seen throughout the spinal cord and hippocampal formation of the adult hosts at 15 days post-transplantation. T-antigen-immunoreactive nuclei were detected where RN33B cells were observed, but in much greater numbers than beta-galactosidase-immunoreactive cells. Bipolar RN33B cells were found in the spinal cord grey matter. RN33B cells with multipolar morphologies were visualized in the hippocampal and subicular pyramidal cell layers, and also in the dentate gyrus granule cell and polymorph layers, while bipolar RN33B cells were seen in the remainder of the hippocampal formation. The results suggest that immortalized neural cell lines of CNS origin can differentiate in the adult CNS with their ultimate morphology being determined by local tissue signals. We speculate that endogenous neutrophins may significantly influence RN33B cell differentiation in vivo.

Effect of grafting order on innervation of spinal cord transplants by grafted locus coeruleus neurons in oculo.

Fetal brain stem containing locus coeruleus/subcoeruleus (hereafter referred to as LC) and thoracic spinal cord (SC) were sequentially allografted into the anterior eye chamber of adult Sprague-Dawley albino rats creating two groups: (1) LC graft followed after 11 weeks by an SC graft (LC-SC); (2) SC graft followed after 11 weeks by an LC graft (SC-LC). The cografts were allowed to mature in oculo for 15-18 months. After sacrifice, the grafts were processed for the immunohistochemical localization of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (D beta H) and the extent of fiber ingrowth into the SC graft was measured using computerized image analysis. TH- and D beta H-immunoreactive fibers were found to innervate the SC cograft in five of the six SC-LC graft combinations. The innervation was abundant, but uneven in distribution. The average density of TH-immunoreactive fibers (derived from the LC graft) was 8.29% of the total cross-sectional area of the SC graft neuropil. In contrast, the innervation of the SC graft neuropil was very sparse in the LC-SC graft combinations, with an uneven distribution and an average density of TH-immunoreactive fibers in the SC graft of only 2.28% of the cross-sectional area of the SC graft neuropil. The results support earlier studies of intraspinal grafting of LC neurons, in that embryonic LC neurons upon grafting and during ontogenetic fiber growth are capable of innervating mature spinal cord neuropil devoid of its normal catecholaminergic innervation. However, embryonic spinal cord tissue is a poor stimulant to reinitiate terminal fiber growth from mature LC neurons, in contrast to several other LC target areas such as the cerebral cortex and hippocampus.

Selective hippocampal lesions differentially affect the phenotypic fate of transplanted neuronal precursor cells.

RN33B cells, a CNS-derived neuronal precursor cell line, transplanted into normal adult rat hippocampus can survive and morphologically differentiate with their ultimate morphology dependent on the integration site. This study examined the differentiation and structural integration of RN33B cells transplanted into the lesioned adult hippocampus. Pyramidal neurons of the CA1-3 regions or granular neurons in the dentate gyrus were preferentially destroyed by unilateral intraventricular kainic-acid or intradentate colchicine injections, respectively. One week after the lesion, a suspension of undifferentiated beta-galactosidase (beta-gal)-labeled RN33B cells was stereotaxically transplanted into the lesioned or the contralateral hippocampus. After 5-7 weeks, sections of the recipient brains were analyzed by toluidine blue staining and immunohistochemistry for beta-gal, GFAP, and OX-42. A reactive gliosis was observed on the lesioned side which persisted up to 7 weeks postlesion (the latest time point examined). RN33b cells survived in the lesioned hippocampus and assumed variable morphologies depending on the hippocampal layer into which they integrated. Only RN33B cells located in intact or partially damaged cell layers or in the unlesioned contralateral hippocampus differentiated with morphologies similar to those of endogenous neurons characteristic of those layers. Cells located in layers completely depleted of endogenous neurons assumed bipolar morphologies or sent out multiple processes with no structural polarity, unlike the neuronal morphologies characteristically seen in intact hippocampal cell layers. These data suggest that the presence of some endogenous neurons and partially conserved cytoarchitectural organization are essential for immortalized neuroepithelial precursor cells to differentiate into region-specific neuronal cell types.

Ultrastructural evidence of synaptic contacts between substance P-, enkephalin-, and serotonin-immunoreactive terminals and retrogradely labeled sympathetic preganglionic neurons in the rat: a study using a double-peroxidase procedure.

A double-peroxidase procedure was used to study the ultrastructural relationships between terminals and fibers containing three putative neurotransmitters and retrogradely identified sympathetic preganglionic neurons (SPNs) located in the intermediolateral cell column (IML) of the rat. SPNs with axons in the cervical sympathetic trunk were retrogradely labeled with horseradish peroxidase. In addition, terminals and fibers containing substance P, enkephalin, and serotonin were detected using immunohistochemistry. Sections containing both retrogradely labeled SPNs and immunoreactive processes were processed for electron microscopy. Ultrastructural examination revealed synaptic contacts between terminals containing each of these three neurotransmitters and retrogradely labeled dendrites from SPNs. Also, immunoreactive terminals were apposed to retrogradely labeled cell bodies. Therefore, these transmitters may alter sympathetic function by their direct action on SPNs.

Two new Wistar-Kyoto rat strains in which hypertension and hyperactivity are expressed separately.

Two inbred strains have been developed from a cross between SHR and WKY. WK-HTs are hypertensive but not hyperactive, and WK-HAs are hyperactive but normotensive. Together with SHR (that express both traits) and WKY (expressing neither trait) we used four strains to follow correlations of biological changes with the expression of hyperactivity or hypertension. We show that the well known sympathetic hyperreactivity of SHRs to acute stress is associated with the hyperactivity trait and not the hypertension among the four strains. Similarly, the well known ventricular hypertrophy in SHRs is more prominent among the hyperactive strains than the hypertensives. Examination of regional brain amine levels revealed an imbalance in forebrain serotonin transmission in the hyperactive strains, and no significant correlations with hypertension. On the other hand, neuropeptides in brainstem and spinal cord revealed a decrease, in hypertension, in neuropeptide Y and PNMT content of terminals of C1 fibers that innervate the spinal cord sympathetic outflow. Also, the two hypertensive strains showed increased TRH-and proctolin-like immunoreactivity in fibers that innervate the C1 cells in the rostral ventrolateral medulla. These findings illustrate the unique advantage provided by WK-HA and WK-HT strains as additional controls for SHRs in studying hypertension and hyperactivity.

The adult CNS retains the potential to direct region-specific differentiation of a transplanted neuronal precursor cell line.

The chronic survival and differentiation of the conditionally immortalized neuronal cell line, RN33B, was examined following transplantation into the adult and neonatal rat hippocampus and cerebral cortex. In clonal culture, differentiated RN33B cells express p75NTR and trkB mRNA and protein, and respond to brain-derived neurotrophic factor treatment by inducing c-fos mRNA. Transplanted cells, identified using immunohistochemistry to detect beta-galactosidase expression, were seen in most animals up to 24 weeks posttransplantation (the latest time point examined). Stably integrated cells with various morphologies consistent with their transplantation site were observed. In the cerebral cortex, many RN33B cells differentiated with morphologies similar to pyramidal neurons and stellate cells. In the hippocampal formation, many RN33B cells assumed morphologies similar to pyramidal neurons characteristic of CA1 and CA3 regions, granular cell layer neurons of the dentate gyrus, and polymorphic neurons of the hilar region. Identical morphologies were observed in both adult and neonatal hosts, although a greater percentage of beta-galactosidase immunoreactive cells had differentiated in the neonatal brains. These results suggest that RN33B cells have the developmental plasticity to respond to local microenvironmental signals and that the adult brain retains the capacity to direct the differentiation of neuronal precursor cells in a direction that is consistent with that of endogenous neurons.

Anatomical distributions of four pharmacologically distinct 3H-L-glutamate binding sites.

Glutamate is thought to serve as a major excitatory neurotransmitter throughout the central nervous system (CNS); electrophysiological studies indicate that its action is mediated by multiple receptors. Four receptors have been characterized by their selective sensitivity to N-methyl-D-aspartate (NMDA), kainic acid (KA), quisqualic acid (QA) and 2-amino-4-phosphonobutyric acid (APB). Electrophysiological evidence indicates that these receptors are all present in the rat hippocampus and that the anatomically discrete synaptic fields within the hippocampus exhibit differential sensitivity to the selective excitatory amino acid agents. Thus, we have used the hippocampus as a model system to investigate possible subpopulations of 3H-L-glutamate binding sites. By using quantitative autoradiography, the pharmacological specificity of 3H-L-glutamate binding in discrete terminal fields was determined. We report here that there are at least four distinct classes of 3H-L-glutamate binding sites which differ in their anatomical distribution, pharmacological profile and regulation by ions. Two of these sites seem to correspond to the KA and NMDA receptor classes, and a third site may represent the QA receptor. The fourth binding site does not conform to present receptor classifications. None of these binding sites corresponds to the major glutamate binding site observed in biochemical studies.

Increased beta-nerve growth factor messenger RNA and protein levels in neonatal rat hippocampus following specific cholinergic lesions.

High levels of NGF have recently been detected in cerebral cortex and hippocampus, and it was suggested that NGF supports cholinergic, basal forebrain neurons. The present study directly examined whether NGF levels are altered in the neonatal hippocampus following cholinergic denervation by transection of the fimbria. Ten days after transection, hippocampal cholinergic innervation, as assessed by AChE histochemistry and CAT immunohistochemistry, was decreased, and both hippocampal NGF mRNA and protein were elevated about 50%. This indicates possible lesion-induced transcriptional control of neonatal hippocampal NGF levels. This increase was specific to lesions of cholinergic systems, as entorhinal cortex ablation, which removes other afferent fibers to the hippocampus, did not cause a similar increase. At 30 d after fimbria transection, hippocampal NGF mRNA and protein did not differ from control levels, but the decrease in AChE and CAT staining persisted. Peripheral sympathectomy carried out in the adult rat resulted in 2- to 5-fold increases in NGF protein levels in heart atrium and ventricle, as well as submandibular gland, with no concomitant increase in NGF mRNA. Therefore, the control of NGF levels in the adult PNS is probably posttranscriptional. Our results strongly suggest that NGF is involved in the regulation of central cholinergic neurons and is transiently elevated in the neonatal hippocampus following cholinergic lesion.

Photochemically induced cystic lesion in the rat spinal cord. I. Behavioral and morphological analysis.

The present study describes the production of a spinal cord lesion which is initiated by vascular occlusion resulting from the interaction between the photosensitizing dye erythrosin B and an argon laser beam. The lesion has characteristics similar to those of the central cavity thought to lead to the production of post-traumatic syringomyelia (PTS) in humans. The present study examines the behavioral and morphological characteristics of this injury over a 28-day period. Histological analysis revealed a cavity extending from the dorsal horns to lamina VIII, with some lateral and ventral pathways being spared. The cavity volume reached a maximum 7 days after lesion induction. Behavioral changes were assessed using six different tests of motor and reflex function (motor function, climbing, waterbath, inclined plane, withdrawal to pain, and withdrawal to extension). Lesioned animals exhibited flaccid paralysis for 3-5 days, which resolved afterward. The photochemically induced cavity should provide a reproducible model for examining the effects of cystic spinal cord injury on locomotor and reflex function.