Apoptosis and delayed degeneration after spinal cord injury in rats and monkeys.

Apoptosis is a morphologically defined form of programmed cell death seen in a variety of circumstances, including immune cell selection, carcinogenesis and development. Apoptosis has very recently been seen after ischemic or traumatic injury to the central nervous system (CNS), suggesting that active cell death as well as passive necrosis may mediate damage after CNS injury. After spinal cord injury (SCI) in the rat, typical post-traumatic necrosis occurred, but in addition, apoptotic cells were found from 6 hours to 3 weeks after injury, especially in the spinal white matter. Apoptotic cells were positive for oligodendrocyte markers. After SCI in monkeys, apoptotic cells were found within remote degenerating fiber tracts. Both secondary degeneration at the site of SCI and the chronic demyelination of tracts away from the injury appear to be due in part to apoptosis. As cytokines have been shown to mediate oligodendrocyte death in vitro, it seems likely that chronic demyelination after CNS injury shares features with chronic degenerative disorders like multiple sclerosis.

Machine intelligence identifies soluble TNFa as a therapeutic target for spinal cord injury.

Traumatic spinal cord injury (SCI) produces a complex syndrome that is expressed across multiple endpoints ranging from molecular and cellular changes to functional behavioral deficits. Effective therapeutic strategies for CNS injury are therefore likely to manifest multi-factorial effects across a broad range of biological and functional outcome measures. Thus, multivariate analytic approaches are needed to capture the linkage between biological and neurobehavioral outcomes. Injury-induced neuroinflammation (NI) presents a particularly challenging therapeutic target, since NI is involved in both degeneration and repair. Here, we used big-data integration and large-scale analytics to examine a large dataset of preclinical efficacy tests combining five different blinded, fully counter-balanced treatment trials for different acute anti-inflammatory treatments for cervical spinal cord injury in rats. Multi-dimensional discovery, using topological data analysis (TDA) and principal components analysis (PCA) revealed that only one showed consistent multidimensional syndromic benefit: intrathecal application of recombinant soluble TNFα receptor 1 (sTNFR1), which showed an inverse-U dose response efficacy. Using the optimal acute dose, we showed that clinically-relevant 90 min delayed treatment profoundly affected multiple biological indices of NI in the first 48 h after injury, including reduction in pro-inflammatory cytokines and gene expression of a coherent complex of acute inflammatory mediators and receptors. Further, a 90 min delayed bolus dose of sTNFR1 reduced the expression of NI markers in the chronic perilesional spinal cord, and consistently improved neurological function over 6 weeks post SCI. These results provide validation of a novel strategy for precision preclinical drug discovery that is likely to improve translation in the difficult landscape of CNS trauma, and confirm the importance of TNFα signaling as a therapeutic target.

Convolutional Neural Network-Based Automated Segmentation of the Spinal Cord and Contusion Injury: Deep Learning Biomarker Correlates of Motor Impairment in Acute Spinal Cord Injury.

BACKGROUND AND PURPOSE: Our aim was to use 2D convolutional neural networks for automatic segmentation of the spinal cord and traumatic contusion injury from axial T2-weighted MR imaging in a cohort of patients with acute spinal cord injury. MATERIALS AND METHODS: Forty-seven patients who underwent 3T MR imaging within 24 hours of spinal cord injury were included. We developed an image-analysis pipeline integrating 2D convolutional neural networks for whole spinal cord and intramedullary spinal cord lesion segmentation. Linear mixed modeling was used to compare test segmentation results between our spinal cord injury convolutional neural network (Brain and Spinal Cord Injury Center segmentation) and current state-of-the-art methods. Volumes of segmented lesions were then used in a linear regression analysis to determine associations with motor scores. RESULTS: Compared with manual labeling, the average test set Dice coefficient for the Brain and Spinal Cord Injury Center segmentation model was 0.93 for spinal cord segmentation versus 0.80 for PropSeg and 0.90 for DeepSeg (both components of the Spinal Cord Toolbox). Linear mixed modeling showed a significant difference between Brain and Spinal Cord Injury Center segmentation compared with PropSeg (P < .001) and DeepSeg (P < .05). Brain and Spinal Cord Injury Center segmentation showed significantly better adaptability to damaged areas compared with PropSeg (P < .001) and DeepSeg (P < .02). The contusion injury volumes based on automated segmentation were significantly associated with motor scores at admission (P = .002) and discharge (P = .009). CONCLUSIONS: Brain and Spinal Cord Injury Center segmentation of the spinal cord compares favorably with available segmentation tools in a population with acute spinal cord injury. Volumes of injury derived from automated lesion segmentation with Brain and Spinal Cord Injury Center segmentation correlate with measures of motor impairment in the acute phase. Targeted convolutional neural network training in acute spinal cord injury enhances algorithm performance for this patient population and provides clinically relevant metrics of cord injury.

Multivariate Analysis of MRI Biomarkers for Predicting Neurologic Impairment in Cervical Spinal Cord Injury.

BACKGROUND AND PURPOSE: Acute markers of spinal cord injury are essential for both diagnostic and prognostic purposes. The goal of this study was to assess the relationship between early MR imaging biomarkers after acute cervical spinal cord injury and to evaluate their predictive validity of neurologic impairment. MATERIALS AND METHODS: We performed a retrospective cohort study of 95 patients with acute spinal cord injury and preoperative MR imaging within 24 hours of injury. The American Spinal Injury Association Impairment Scale was used as our primary outcome measure to define neurologic impairment. We assessed several MR imaging features of injury, including axial grade (Brain and Spinal Injury Center score), sagittal grade, length of injury, maximum canal compromise, and maximum spinal cord compression. Data-driven nonlinear principal component analysis was followed by correlation and optimal-scaled multiple variable regression to predict neurologic impairment. RESULTS: Nonlinear principal component analysis identified 2 clusters of MR imaging variables related to 1) measures of intrinsic cord signal abnormality and 2) measures of extrinsic cord compression. Neurologic impairment was best accounted for by MR imaging measures of intrinsic cord signal abnormality, with axial grade representing the most accurate predictor of short-term impairment, even when correcting for surgical decompression and degree of cord compression. CONCLUSIONS: This study demonstrates the utility of applying nonlinear principal component analysis for defining the relationship between MR imaging biomarkers in a complex clinical syndrome of cervical spinal cord injury. Of the assessed imaging biomarkers, the intrinsic measures of cord signal abnormality were most predictive of neurologic impairment in acute spinal cord injury, highlighting the value of axial T2 MR imaging.

A comparison of the ultrastructure of substance P and enkephalin-immunoreactive elements in the nucleus of the dorsal lateral funiculus and laminae I and II of the rat spinal cord.

The ultrastructure of substance P (SP)- and enkephalin (ENK)-immunoreactive elements in the nucleus of the dorsal lateral funiculus (NDLF) and in laminae I and II of the spinal cord was examined in the rat using the peroxidate-antiperoxidase (PAP) technique. Electron-microscopic observations were made of a large number of immunolabelled terminals (n = 428; many followed in serial sections), axons, and immunoreactive cell bodies and dendrites which were occasionally encountered. Morphometric analysis was used to describe and compare the fine structural features of immunolabelled elements. Both SP- and ENK-immunoreactive terminals contained clear synaptic vesicles and dense-cored vesicles of similar size but the ENK-immunoreactive profiles contained significantly more dense-cored vesicles than SP-immunolabelled profiles. Both SP- and ENK-immunoreactive profiles in the dorsal laminae of the dorsal horn contacted mainly smaller dendritic elements. Only rarely were axo-axonic interactions noted. The NDLF contains widely scattered cell bodies dispersed within a neuropil which is rich in synaptic complexes and is interdigitated between fascicles of myelinated and unmyelinated axons. Numerous SP- and ENK-immunoreactive profiles were observed in the NDLF, many of which made asymmetric synaptic contacts with NDLF neurons. Although both the dorsal gray and NDLF contain large numbers of SP- and ENK-immunoreactive elements which are similar in morphology in both regions, the NDLF can be distinguished from laminae I and II by a number of criteria, including the nature of the neuropil, principle sources of SP innervation, and the termination patterns of ascending projections.

Distribution and morphology of sacral spinal cord neurons innervating pelvic structures in Xenopus laevis.

Relatively little is known about the organization of neural input to pelvic viscera in amphibia. In this study, sacral spinal efferent neurons were labeled in Xenopus laevis frogs by application of horseradish peroxidase (HRP) to the tenth spinal nerve, to pelvic musculature, or to the pelvic nerve. DiI was applied to the pelvic nerve with similar results. Labeled spinal neurons were located in the intermediate gray or in the ventral horn. Neurons in the tenth dorsal root ganglion, but not in the spinal cord, were labeled after application of HRP or DiI to the pudendal nerve. The labeled neurons in the spinal cord intermediate gray were in a position comparable to that of the mammalian sacral parasympathetic nucleus (SPN). Two apparent subdivisions included 1) a medial cluster of cells with mediolaterally oriented dendrites and 2) a lateral group with dorsoventrally oriented dendrites. An intermediate group, not clearly classed with the other two, was also identifiable. In some cases, labeled tenth nerve primary afferents were seen in contact with efferent neurons of the intermediate gray. Labeled neurons in the ventral horn medial to the lateral motor column were small, with dendrites oriented mediolaterally, in a position comparable to that of the mammalian Onuf's nucleus. The peripheral targets of DiI-labeled pelvic nerve axons were the compressor cloaca muscle, cloaca, and bladder. DiI-labeled pudendal nerve axons distributed peripherally to cloacal lip and medial thigh integument. These data suggest that the pudendal nerve in amphibians is purely sensory and that both somatic and autonomic motor axons traverse the pelvic nerve.

A light and electron microscopic analysis of the sacral parasympathetic nucleus after labelling primary afferent and efferent elements with HRP.

Primary afferent input to the cat sacral parasympathetic nucleus (SPN) has been examined by injury filling sacral dorsal roots, ventral roots, or both with horseradish peroxidase (HRP). Appropriate spinal segments were processed for the demonstration of HRP with diaminobenzidine and prepared for sequential light (LM) and electron (EM) microscopy. At the LM level, a large fascicle of primary afferent fibers was observed passing ventrally along the lateral edge of the dorsal horn into the region of the SPN. Varicosities were seen throughout the course of the axons but were particularly abundant within the SPN. Injury filling of the ventral roots with HRP resulted in a Golgi-like labelling of preganglionic neurons and their dendritic arbors, as well as ventral root afferent fibers. Swellings on both dorsal and ventral root afferent axons were observed in close apposition to labelled preganglionic neurons and their dendrites. At the ultrastructural level, afferent terminals were found to contain clear spherical vesicles; 66% of these terminals also contained at least one dense-cored vesicle. Of particular interest was the presence of labelled dorsal and ventral root afferent terminals synapsing on labelled preganglionic neurons. Preganglionic neurons were also postsynaptic to unlabelled terminals containing clear spherical (79.7%) or pleomorphic vesicles (20.3%). These data indicate that preganglionic neurons receive direct input from several sources, and provide the first demonstration of direct input to these cells from sensory fibers in the dorsal and ventral roots. The connections described in the present study provide interesting and, as yet, unexplored possibilities for sensory and autonomic reflex integration.

Differences in synaptic inputs to preganglionic neurons in the dorsal and lateral band subdivisions of the cat sacral parasympathetic nucleus.

In the cat, preganglionic neurons (PGNs) found in the dorsal portion of the sacral parasympathetic nucleus (dorsal band or DB cells) participate in bowel control, while those found along the lateral edge (lateral band or LB cells) influence bladder function. In order to determine whether differences in the synaptic inputs exist between these two populations, HRP was applied to the sacral ventral rootlets of cats, and the S2 cord segment was prepared for sequential light and electron microscopy. When measured with light microscope, the LB somata had greater cross-sectional areas than did the DB cells. Ultrastructurally, the LB cells had a significantly greater percentage of their membrane apposed by synaptic active sites than did the DB cells. Also, the proximal dendrities of the labelled neurons received greater synaptic input than did the somata. No difference was found in the proportion of terminals containing dense cored vesicles (DCVs) when comparing LB and DB somata; however, the LB proximal dendrites had a higher proportion of their surface contacted by DCV-containing terminals than did the DB dendrites. These ultrastructural results offer evidence that these two populations of preganglionic neurons differ with respect to their synaptic input as well as their peripheral targets.

Descending projections from the nucleus raphe obscurus to pudendal motoneurons in the male rat.

Previous physiological and behavioral studies have shown that the nucleus raphe obscurus (nRO) modulates pelvic floor reflex function (Yamanouchi and Kakeyama [1992] Physiol. Behav. 51:575-579; Beattie et al. [1996] Soc. Neurosci. Abstr. 22:722.4; Holmes et al. [1997] Brain Res. 759:197-204). In the present study, small injections of fluorescent tracers were used to investigate direct descending projections from the rostral and caudal portions of the brainstem nRO to retrogradely labeled pudendal motoneurons (MN) in the male rat. The caudal nRO projects into the ventral and lateral funiculi of the spinal cord, with arborizations in the thoracic intermediolateral cell column; in laminae VII, IX, and X of the lumbosacral cord; and in the sacral parasympathetic nucleus (SPN). Many identified external anal sphincter and ischiocavernosus MNs appeared to be in direct apposition with fibers originating from the caudal nRO; and more than half of the bulbospongiosus MNs that were identified appeared to receive such descending input. In addition to the nRO spinal autonomic and pudendal motoneuronal targets, projections were observed to regions of the intermediate gray that contain interneurons organizing the pelvic floor reflexes and to MN pools that are involved in functionally related somatic activities. Finally, several neurons in the lumbar enlargement were labeled retrogradely with FluoroRuby after injections into the nRO and the immediately adjacent reticular formation. Thus, the nRO may be in a position to modulate the coordinated actions of autonomic preganglionic and functionally related skeletal MN activity involved in sexual and eliminative reflex functions.

The relationship of dorsal root afferents to motoneuron somata and dendrites in the adult bullfrog: a light and electron microscopic study using horseradish peroxidase.

The relationship of lumbar dorsal root afferents to lateral motor column motoneurons was studied using anterograde injury filling of dorsal roots and retrograde injury filling of ventral roots with horseradish peroxidase. At the light microscopic level, horseradish peroxidase labelled dorsal root axons were observed to separate into a medial division of large diameter axons which enter the dorsal funiculus and a lateral division of small diameter axons which form a compact bundle in the dorsolateral funiculus which may be homologous to the mammalian tract of Lissauer. Within the spinal gray, primary afferents terminate in two distinct regions. The more ventral of these terminal fields, which receives collaterals of primary afferent axons in the dorsal funiculus, overlaps the dendritic arborizations of the lateral motor column motoneurons. Some axons leave the ventral terminal field to enter the dorsal lateral motor column. Here they terminate on the primary dendrites and somata of lateral motor column motoneurons. At the electron microscopic level, labelled primary afferent terminals were seen to synapse upon lateral motor column motoneuron dendrites as well as upon the somata of dorsally positioned lateral motor column motoneurons. These terminals contain small spherical vesicles and occasional dense-cored vesicles. The synaptic specializations are characterized by a small amount of postsynaptic material. The lateral motor column may be divided into dorsal and ventral portions on the basis of the primary afferent distribution and this is in accord with functional, physiological and developmental data.

Review of current evidence for apoptosis after spinal cord injury.

The initial mechanical tissue disruption of spinal cord injury (SCI) is followed by a period of secondary injury that increases the size of the lesion. The secondary injury has long been thought to be due to the continuation of cellular destruction through necrotic (or passive) cell death. Recent evidence from brain injury and ischemia suggested that cellular apoptosis, an active form of programmed cell death seen during development, could play a role in CNS injury in adulthood. Here, we review the evidence that apoptosis may be important in the pathophysiology of SCI. There is now strong morphological and biochemical evidence from a number of laboratories demonstrating the presence of apoptosis after SCI. Apoptosis occurs in populations of neurons, oligodendrocytes, microglia, and, perhaps, astrocytes. The death of oligodendrocytes in white matter tracts continues for many weeks after injury and may contribute to post-injury demyelination. The mediators of apoptosis after SCI are not well understood, but there is a close relationship between microglia and dying oligodendrocytes, suggesting that microglial activation may be involved. There is also evidence for the activation of important intracellular pathways known to be involved in apoptosis in other cells and systems. For example, some members of the caspase family of cysteine proteases are activated after SCI. It appears that the evolution of the lesion after SCI involves both necrosis and apoptosis. It is likely that better understanding of apoptosis after SCI will lead to novel strategies for therapeutic interventions that can diminish secondary injury.

A sensitive and reliable locomotor rating scale for open field testing in rats.

Behavioral assessment after spinal cord contusion has long focused on open field locomotion using modifications of a rating scale developed by Tarlov and Klinger (1954). However, on-going modifications by several groups have made interlaboratory comparison of locomotor outcome measures difficult. The purpose of the present study was to develop an efficient, expanded, and unambiguous locomotor rating scale to standardize locomotor outcome measures across laboratories. Adult rats (n = 85) were contused at T7-9 cord level with an electromagnetic or weight drop device. Locomotor behavior was evaluated before injury, on the first or second postoperative day, and then for up to 10 weeks. Scoring categories and attributes were identified, operationally defined, and ranked based on the observed sequence of locomotor recovery patterns. These categories formed the Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale. The data indicate that the BBB scale is a valid and predictive measure of locomotor recovery able to distinguish behavioral outcomes due to different injuries and to predict anatomical alterations at the lesion center. Interrater reliability tests indicate that examiners with widely varying behavioral testing experience can apply the scale consistently and obtain similar scores. The BBB Locomotor Rating Scale offers investigators a more discriminating measure of behavioral outcome to evaluate treatments after spinal cord injury.

Spinal cord injury produced by consistent mechanical displacement of the cord in rats: behavioral and histologic analysis.

We examined the ability of an electromechanical device to produce consistent and incomplete thoracic (T9) spinal cord injuries in rats by brief displacement (Dspl) of the exposed dural surface. Open field walking, inclined plane, grid walking, and footprint analysis, and a determination of the percentage of tissue spared at the lesion center were used to assess chronic outcome (6 weeks postinjury). Laminectomy control animals showed no evidence of a functional deficit or histologic lesion. Complete spinal cord transections in normal rats and in a group of animals previously injured (1.1 mm Dspl) and allowed to recover resulted in complete loss of hindlimb function, demonstrating an important functional role for the remaining spared fibers at the lesion site. Consistent spinal cord displacements (0.80 mm, 0.95 mm, and 1.10 mm) resulted in behavioral groups with low outcome variability over a narrow range of incomplete recovery of neurologic function. Significant behavioral (open field walking, inclined plane, and grid walking) and histologic differences were found between the control and Dspl groups and between the 0.80 mm and 1.10 mm Dspl groups. Significant correlations were observed among the injury parameters, behavioral, and histologic scores. Open field walking and inclined plane performance were sensitive indicators of both the early and late phases of neurologic recovery. Grid walking was most useful in animals with small chronic residual deficits. The footprint analysis resulted in less significant correlations and differences between the behavioral groups than the other outcome measures. This may result from a relatively narrow range of sensitivity (open field walking scores between 3.3 and 4.0) and increased variability within the groups.

Three-dimensional computer-assisted analysis of graded contusion lesions in the spinal cord of the rat.

Histological analysis of spinal cord injury in experimental animals has focused primarily on the microanatomy of damaged tissue. The current study presents an analysis of the three-dimensional structure of lesion sites in the spinal cord of rats contused with an injury device which produces consistent lesions. Three levels of injury were produced by systematically varying the cord displacement and the duration of the displacement during impact. The resulting groups of subjects exhibited mild, moderate, and severe neurological deficits. Comparisons of equivalent mild impacts made at thoracic versus lumbar spinal cord levels were also made. The results indicate that the overall shape of the lesions is generally biconical, with extensions in the base of the dorsal funiculus, irrespective of the degree of damage or the spinal level of the injury. Lower displacement injuries yielded shorter lesions rostrocaudally with less spread into the white matter. Similar impacts in the lumbar versus thoracic spinal cord produced shorter, more truncated lesion sites at lumbar levels with less involvement of the white matter than in the thoracic lesions. Three-dimensional analyses can can provide additional information about the lesion beyond that available from conventional histopathological measures. Such information could be useful in assessing the results of posttraumatic manipulations which are directed at reducing tissue damage or tissue replacement via transplantation.

External anal sphincter hyperreflexia following spinal transection in the rat.

In the present study, long-term and short-term rat preparations were used to develop a model for investigating external anal sphincter (EAS) reflexes in intact and spinal cord-injured (SCI) rats. In this model, EAS distension with an external probe elicits reflex contractions of the EAS in intact, unanesthetized animals. At 2 h after spinal cord transection, none of the lesioned animals displayed EAS EMG activity. In fact, once distended, the EAS was incapable of maintaining closure of the anal orifice. Over a period of 4 days, spinalized animals developed a hyperreflexia of the EAS response. By 48 h, the rectified, integrated EAS EMG was significantly elevated in comparison with nonlesioned controls (EAS hyperreflexia). In addition, the duration of the EAS EMG bursts in response to sphincter distension had significantly increased. At 6 weeks after injury, the EAS was significantly hyperreflexic as measured by EMG burst duration and burst area. As with intact animals, posttransection EAS reflexes were highly anesthesia sensitive. These studies indicate that (1) brief distension of the anal orifice is sufficient to evoke a physiologically relevant reflexive activation of the EAS in the rat, (2) the 2- to 24-h postinjury areflexia observed in these experiments may be a suitable model for the study of spinal shock, and (3) the observed EAS hyperreflexia after chronic SCI may represent the permanent effects of removing descending inhibitory circuits and segmental plasticity, making this reflex an appropriate measure of defecatory dysfunction after spinal cord injury.

MASCIS evaluation of open field locomotor scores: effects of experience and teamwork on reliability. Multicenter Animal Spinal Cord Injury Study.

The Multicenter Animal Spinal Cord Injury Study (MASCIS) adopted a modified 21-point open field locomotor scale developed by Basso, Beattie, and Bresnahan (BBB) at Ohio State University (OSU) to measure motor recovery in spinal-injured rats. BBB scores categorize combinations of rat hindlimb movements, trunk position and stability, stepping, coordination, paw placement, toe clearance, and tail position, representing sequential recovery stages that rats attain after spinal cord injury. A total of 22 observers from 8 participating centers assessed 18 hindlimbs of 9 rats at 2-6 weeks after graded spinal cord injury. The observers were segregated into 10 teams. The teams were grouped into 3 cohorts (A, B, and C), consisting of one experienced team from OSU and two non-OSU teams. The cohorts evaluated the rats in three concurrent and sequential sessions. After viewing a rat for 4 min, individual observers first assigned scores without discussion. Members of each team then discussed and assigned a team score. Experience (OSU vs. non-OSU) and teamwork (individual vs. team) had no significant effect on mean scores although the mean scores of one cohort differed significantly from the others (p = 0.0002, ANOVA). However, experience and teamwork significantly influenced reliability of scoring. OSU team scores had a mean standard deviation or discordance of 0.59 points, significantly less than 1.31 points for non-OSU team scores (p = 0.003, ANOVA) and 1.30 points for non-OSU individual scores (p = 0.001, ANOVA). Discordances were greater at the upper and lower ends of the scale, exceeding 2.0 in the lower (< 5) and upper (> 15) ends of the scale but were < 1.0 for scores between 4 and 16. Comparisons of non-OSU and OSU team scores indicated a high reliability coefficient of 0.892 and a correlation index (r2) of 0.894. These results indicate that inexperienced observers can learn quickly to assign consistent BBB scores that approach those given by experienced teams, that the scores are most consistent between 4 and 16, and that experience improves consistency of team scores.

An analysis of changes in sensory thresholds to mild tactile and cold stimuli after experimental spinal cord injury in the rat.

Changes in sensory function including chronic pain and allodynia are common sequelae of spinal cord injury (SCI) in humans. The present study documents the extent and time course of mechanical allodynia and cold hyperalgesia after contusion SCI in the rat using stimulation with graded von Frey filaments (4.97-50.45 g force) and ice probes. Fore- and hind-paw withdrawal thresholds to plantar skin stimulation were determined in rats with a range of SCI severities (10-g weight dropped from 6.25, 12.5, or 25 mm using the MASCIS injury device); animals with 25-mm injuries most consistently showed decreased hind-paw withdrawal thresholds to touch and cold, which developed over several weeks after surgery. Stimulation of the torso with graded von Frey hairs was performed at specified locations on the back and sides from the neck to the haunch. Suprasegmental responses (orientation, vocalization, or escape) to mechanical stimulation of these sites were elicited infrequently in the laminectomy control rats and only during the first 3 weeks after surgery, whereas in 25-mm SCI rats, such responses were obtained for the entire 10 weeks of the study. These data suggest that rats with contusion SCI may exhibit sensory alterations relevant to human spinal cord injuries.

Dorsal root afferents contact migrating motoneurons in the developing frog spinal cord.

Dorsal and ventral roots of Rana catesbeiana tadpole lumbar spinal cord were labeled with horseradish peroxidase during development of the hindlimb. Labeled motoneurons in the process of migrating were found in the region of the developing terminal arbors of dorsal root axons. Electron microscopy showed that some of these dorsal root terminals contacted the migrating motoneurons.

Primary afferent projections from dorsal and ventral roots to autonomic preganglionic neurons in the cat sacral spinal cord: light and electron microscopic observations.

HRP applied to cut dorsal and ventral roots of the cat sacral spinal cord labeled afferent axons with swellings in close apposition to labeled preganglionic neurons (PGNs) in the sacral parasympathetic nucleus. Electron microscopy allowed characterization of synaptic contacts between afferents and PGNs. The results suggest that both the dorsal and ventral root afferents can directly activate autonomic preganglionic neurons.

Testosterone-induced plasticity of synaptic inputs to adult mammalian motoneurons.

The effects of testosterone administration on penile reflexes, and on the motoneurons of the spinal nucleus of the bulbocavernosus which innervate perineal muscles involved in these reflexes, were investigated in castrated male rats. Penile reflexes were restored following 48 h of testosterone administration initiated 6 weeks after castration. The amount of synaptic input to the identified motoneurons was increased following short term testosterone treatment, compared to that seen in animals receiving no testosterone, albeit to a lesser extent than that seen in animals receiving long term testosterone treatment. This increase in synaptic inputs in the short term testosterone group occurred despite the lack of an increase in somatic area. Thus, plasticity of the synaptic input to these neurons, as well as recovery of penile reflexes, occurred as a result of alterations in the hormonal state of the animal, and such changes occurred relatively rapidly.