Somatosensory corticospinal tract axons sprout within the cervical cord following a dorsal root/dorsal column spinal injury in the rat

The corticospinal tract (CST) is the major descending pathway controlling voluntary hand function in primates, and though less dominant, it mediates voluntary paw movements in rats. As with primates, the CST in rats originates from multiple (albeit fewer) cortical sites, and functionally different motor and somatosensory subcomponents terminate in different regions of the spinal gray matter. We recently reported in monkeys that following a combined cervical dorsal root/dorsal column lesion (DRL/DCL), both motor and S1 CSTs sprout well beyond their normal terminal range. The S1 CST sprouting response is particularly dramatic, indicating an important, if poorly understood, somatosensory role in the recovery process. As rats are used extensively to model spinal cord injury, we asked if the S1 CST response is conserved in rodents. Rats were divided into sham controls, and two groups surviving post-lesion for ~6 and 10 weeks. A DRL/DCL was made to partially deafferent one paw. Behavioral testing showed a post-lesion deficit and recovery over several weeks. Three weeks prior to ending the experiment, S1 cortex was mapped electrophysiologically, for tracer injection placement to determine S1 CST termination patterns within the cord. Synaptogenesis was also assessed for labeled S1 CST terminals within the dorsal horn. Our findings show that the affected S1 CST sprouts well beyond its normal range in response to a DRL/DCL, much as it does in macaque monkeys. This, along with evidence for increased synaptogenesis post-lesion, indicates that CST terminal sprouting following a central sensory lesion, is a robust and conserved response.     

Reorganization of descending motor tracts in the rat spinal cord

Following lesion of the central nervous system (CNS), reinnervation of denervated areas may occur via two distinct processes: regeneration of the lesioned fibres or/and sprouting from adjacent intact fibres into the deafferented zone. Both regeneration and axonal sprouting are very limited in the fully mature CNS of higher vertebrates, but can be enhanced by neutralizing the neurite outgrowth inhibitory protein Nogo-A. This study takes advantage of the distinct spinal projection pattern of two descending tracts, the corticospinal tract (CST) and the rubrospinal tract (RST), to investigate if re-innervation of denervated targets can occur by sprouting of anatomically separate, undamaged tracts in the adult rat spinal cord. The CST was transected bilaterally at its entry into the pyramidal decussation. Anatomical studies of the RST in IN-1 antibody-treated rats showed a reorganization of the RST projection pattern after neutralization of the myelin associated neurite growth inhibitor Nogo-A. The terminal arborizations of the rubrospinal fibres, which are normally restricted to the intermediate layers of the spinal cord, invaded the ventral horn but not the dorsal horn of the cervical spinal cord. Moreover, new close appositions were observed, in the ventral horn, onto motoneurons normally receiving CST projections. Red nucleus microstimulation experiments confirmed the reorganization of the RST system. These observations indicate that mature descending motor tracts are capable of significant intraspinal reorganization following lesion and suggests the expression of cues guiding and/or stabilizing newly formed sprouts in the adult, denervated spinal cord.     

BDA皮质脊髓束神经顺行示踪在大鼠脊髓损伤模型中的应用

目的本研究采用生物素标记葡聚糖(Biotin Dextran Amine,BDA)顺行示踪技术来观察大鼠皮质脊髓束(CST)在中枢神经系统中的走行及脊髓损伤后的表现特征。方法20只雌性成年Sprague-Dawley大鼠,分为脊髓损伤组(n=10)和损伤对照组(n=10)。在相当于T7椎板水平用做好标记的显微剪刀剪断脊髓的后2/3。对照组动物术中仅咬除棘突、椎板,不切断脊髓。术后第15 d,所有动物通过立体定向开颅,将10％BDA溶液注入右侧的感觉运动区皮质内。BDA注射2周后,取出大脑和脊髓组织,采用自由漂浮法行BDA染色显影。实验动物于脊髓损伤术前、术后3d、1周、2周、4周采用Basso、Beatlie、Bresnahan(BBB)评分法测量运动功能,所得数据采用两组均数比较t检验进行统计学处理。结果1.脊髓损伤组动物双后肢瘫痪,BBB运动功能评分明显低于损伤对照组,统计学比较差异十分显著(P<0.01);2.BDA顺行示踪显示大脑皮层BDA注射区内见大脑皮层的锥体细胞及其发出的轴突呈阳性染色,BDA阳性染色的皮质脊髓束神经纤维在中脑、桥脑及延髓的腹侧面行走,但在锥体交叉后皮质脊髓束主要(约99％)在对侧脊髓白质的后索中行走。在致伤组动物中,位于脊髓白质后索中的皮质脊髓束纤维在脊髓损伤处终止;在对照组皮质脊髓束纤维染色可一直延伸至L1水平。结论BDA顺行神经     

Suppression of fibrous scarring in spinal cord injury of rat promotes long-distance regeneration of corticospinal tract axons, rescue of primary motoneurons in somatosensory cortex and significant functional recovery

Traumatic injury of the central nervous system results in formation of a collagenous basement membrane-rich fibrous scar in the lesion centre. Due to accumulation of numerous axon-growth inhibitory molecules the lesion scar is considered a major impediment for axon regeneration. Following transection of the dorsal corticospinal tract (CST) at thoracic level 8 in adult rats, transient suppression of collagenous scarring in the lesion zone by local application of a potent iron chelator and cyclic adenosine monophosphate resulted in the delay of fibrous scarring. Treated animals displayed long-distance growth of CST axons through the lesion area extending for up to 1.5-2 cm into the distal cord. In addition, the treatment showed a strong neuroprotective effect, rescuing cortical motoneurons projecting into the CST that normally die (30%) after thoracic axotomy. Further, anterogradely traced CST axons regenerated through both grey and white matter and developed terminal arborizations in grey matter regions. In contrast to controls, injured animals receiving treatment showed significant functional recovery in the open field, in the horizontal ladder and in CatWalk locomotor tasks. We conclude that the fibrous lesion scar plays a pivotal role as a growth barrier for regenerating axons in adult spinal cord and that a delay in fibrotic scarring by local inhibition of collagen biosynthesis and basement membrane deposition is a promising and unique therapeutic strategy for treating human spinal trauma.     

Regeneration of primary sensory axons into the adult rat spinal cord via a peripheral nerve graft bridging the lumbar dorsal roots to the dorsal column

This study investigated the feasibility of using a peripheral nerve autograft (NAG) to promote and guide regeneration of sensory axons from the caudal lumbar dorsal roots to the rostral dorsal column following a lower thoracic cordotomy in adult rats. After a left hemicordotomy at the T13 vertebra level and ipsilateral L3 and L4 rhizotomies, a peripheral NAG (peroneal nerve) was connected to the distal roots stumps, then implanted into the left dorsal column 10 mm rostral to hemicordotomy site (n = 12). After surgery, all animals of the experimental group experienced complete anesthesia in their left hindlimb. Three months later, a slight response to nociceptive stimulation reappeared in L3 and/or L4 dermatomes in 6 of the 12 experimental animals. None of these animals exhibited self-mutilation. Nine months after surgery, we performed retrograde tracing studies by injecting horseradish peroxidase (HRP) into the left dorsal column 30 mm rostral to the NAG implantation site. In eight animals, we found HRP-stained neurons in the left L3 and/or L4 dorsal root ganglia (DRG). The mean number of HRP-stained neurons per DRG was 71 +/- 92 (range 2-259). In control groups, no HRP-stained neurons were found in L3 or L4 DRG. Histological analysis of the NAG showed evidence of axonal regeneration in all 8 animals with positive retrograde labeling of DRG neurons. However, we did not find a statistical correlation between the number of HRP-stained neurons and the degree of sensory recovery. This study demonstrates that an NAG joining dorsal roots to the dorsal column, thus shunting the original CNS-PNS junction, can support regeneration of central axons from DRG primary sensory neurons into the dorsal column over distances of at least 30 mm despite the inhibitory influence of the CNS white matter.     

Projection patterns of single mossy fiber axons originating from the dorsal column nuclei mapped on the aldolase C compartments in the rat cerebellar cortex

Although cerebellar mossy fibers are the most abundant cerebellar afferents and are deeply involved in cerebellar function, the organization of their projection has remained obscure, particularly in relation to cerebellar compartmentalization. The dorsal column nuclei (DCN) are a major source of cerebellar mossy fibers and possess distinct somatotopic representations of specific somatosensory submodalities. We reconstructed individual dextran-labeled DCN axons completely from serial sections and mapped their terminals on the longitudinal cerebellar compartments that were visualized by aldolase C immunostaining to clarify their projection pattern. Individual axons branched and formed about 100 rosette terminals in the cerebellar cortex, but infrequently projected to the cerebellar nuclei (1 out of 15 axons). Cortical terminals were clustered in multiple areas in the vermis and pars intermedia mostly, but not exclusively, ipsilateral to the origin of the axon. The gracile, cuneate, and external cuneate nuclei (ECuN) mainly projected to the copula pyramidis and lobule V, paramedian and simple lobules, and lobules I-V and VIII-IX, respectively, although there was some overlap. The majority of terminals were located within aldolase C negative or lightly positive compartments. However, terminals of a single axon can be located on aldolase C-negative as well as on aldolase C-positive compartments. In particular, the rostral ECuN, which is responsive to shoulder movements, projected consistently to lobule IX, which were mostly aldolase C-positive. In sum, DCN-cerebellar axons project to multiple compartments with terminals clustered mainly in the conventional spinocerebellar region with a coarse topography, which shows some relationship to the cortical compartments defined by aldolase C.     

Co-development of proprioceptive afferents and the corticospinal tract within the cervical spinal cord

In maturity, skilled movements depend on coordination of control signals by descending pathways, such as the corticospinal tract (CST), and proprioceptive afferents (PAs). An important locus for this coordination is the spinal cord intermediate zone. Convergence of CST and PA terminations onto common regions leads to interactions that may underlie afferent gating and modulation of descending control signals during movements. We determined establishment of CST and PA terminations within common spinal cord regions and development of synaptic interactions in 4-week-old cats, which is before major spinal motor circuit refinement, and two ages after refinement (weeks 8, 11). We examined the influence of one or the other system on monosynaptic responses, on the spinal cord surface and locally in the intermediate zone, evoked by either CST or deep radial nerve (DRN) stimulation. DRN stimulation suppressed CST monosynaptic responses at 4 weeks, but this converted to facilitation by 8 weeks. This may reflect a strategy to limit CST movement control when it has aberrant immature connections, and could produce errant movements. CST stimulation showed delayed development of mixed suppression and facilitation of DRN responses. We found development of age-dependent overlap of PA and CST terminations where interactions were recorded in the intermediate zone. Our findings reveal a novel co-development of different inputs onto common spinal circuits and suggest a logic to CST-PA interactions at an age before the CST has established connectional specificity with spinal circuits.     

Neurotrophins reduce degeneration of injured ascending sensory and corticospinal motor axons in adult rat spinal cord

Spinal cord regeneration in adult mammals is limited by neurite outgrowth inhibitors and insufficient availability of outgrowth-promoting agents. Formation of degenerative swellings at the proximal ends of severed axons (terminal clubs), which starts early after injury, also may hinder recovery and their rupture may contribute to secondary spinal cord damage. We investigated whether neurotrophins would reduce these degenerative processes. Adult rats received a transection of the dorsal column sensory and corticospinal motor tracts at T9 and anterograde tracing of the axons from the sciatic nerve and motor cortex, respectively. The highest number of terminal clubs was found at 1 day and approximately half remained present until at least 28 days. A single injection immediately after injury of a mixture of nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 into the lesion site, reduced the number of terminal clubs in the sensory system by approximately half at 1 and 7 days (but not 14) after the lesion. Individual or combinations of two neurotrophins were as effective, suggesting that the neurotrophins protected similar axonal populations. The injected neurotrophins did not affect degeneration of corticospinal motor axons. A 7-day continuous intrathecal infusion of neurotrophin-3 was more effective and also reduced terminal club formation of corticospinal axons by approximately 60%. Spinal tissue loss was not affected by the neurotrophin treatments, suggesting that terminal clubs are not major contributors to the pathogenesis of secondary spinal degeneration during the first two weeks. Thus, neurotrophins can reduce axonal degeneration in the spinal cord after traumatic axonal injury.     

A comparative topographical analysis of dorsal column nuclear and cerebral cortical projections to the basilar pontine gray in rats

The somatotopic distribution of dorsal column nuclear projections within the basilar pontine gray was examined in relation to the massive corticopontine projection system that emanates most heavily from motor and somatosensory cortex. The distribution patterns of these two systems were compared by combining autoradiographic and degeneration axonal tracing methods within individual animals. Stereotaxic injections of tritiated leucine (50 microCi/microliter) and lesions by aspiration were made in animals under ketamine hydrochloride anesthesia. The forelimb cortical injections (0.1-0.3 microliter) were centered in either sensory or motor cortical regions as determined by intracortical microstimulation and multiunit recording techniques. Because sensory and motor hindlimb cortical areas overlap extensively in the rat, hindlimb cortical injections (0.1-0.3 microliter) were limited to a single hindlimb sensorimotor cortical region. The corresponding contralateral dorsal column nucleus, cuneatus or gracilis, was then aspirated. A somatotopic distribution of fore- and hindlimb corticopontine fibers were found in discrete regions of the ipsilateral pontine gray. Hindlimb sensorimotor corticopontine fibers distributed caudal to forelimb projections. Similarly, pontine afferents from the dorsal column nuclei terminated somatotopically in the caudal half of the contralateral pontine gray in that gracilopontine fibers distributed caudal to cuneopontine fibers. Within individual animals, partially overlapping terminations were seen from nucleus cuneatus and the forelimb sensory cortical area as well as from nucleus gracilis and the hindlimb sensorimotor cortical area. No overlap existed in the pontine terminations from nucleus cuneatus and the forelimb motor cortical area.     

Ascending myelinated axons of primary sensory neurons of the sciatic nerve in the posterior column of the rat spinal cord

The present study was undertaken to obtain morphologic data about the posterior column of the spinal cord to characterize ascending myelinated axons of primary sensory neurons of the sciatic nerve. By applying doxorubicin to the right sciatic nerve in eight male Wistar rats, selective degeneration of centrally directed axons of these neurons in the posterior column was produced. Epon-embedded transverse sections of the posterior column at spinal cord segments C1, C3, C8, T6, L3 and L5 showed a circumscribed area (R) that contained a cluster of degenerated myelinated fibers. To characterize area R, its size and distances between various defined points on transverse sections of the posterior column were measured and compared at several spinal segments. The location of area R was illustrated in representative rats. The posterior intermediate septum corresponded to the lateral border of area R at C8 and T6. To characterize the putatively degenerating and degenerated myelinated fibers, area L in the left posterior column, corresponding to area R, was defined, and subsequently the number and size distribution of normal-appearing myelinated fibers in areas R and L were evaluated at C3, T6 and L3 in four rats. After comparative evaluation of these data, it was concluded that large myelinated fibers degenerated preferentially in area R. The number of putatively degenerating and degenerated myelinated fibers in area R at segments C3 and T6 was estimated to be 38.6% and 50.1%, respectively, of that at segment L3. Received: 25 August 1995 / Revised, accepted: 25 January 1996     

Anatomical studies of dorsal column axons and dorsal root ganglion cells after spinal cord injury in the newborn rat

The response of dorsal column axons was studied after neonatal spinal overhemisection injury (right hemicord and left doral funiculus). Rat pups (N = 11) received this spinal lesion at the C2 level within 30 hours after birth. The cauda equina was exposed 3 months later in one group of chronic operates (N = 5) and in a group of normal adults (N = 2), and all spinal roots from L5 caudally were cut bilaterally; 4 days later the spinal cord and medulla were processed for Fink-Heimer impregnation of degenerating axons and terminals. In a second group of chronic operates (N = 6) and normal adult controls (N = 4) the left sciatic nerve was injected with a cholera toxin-HRP conjugate (C-HRP), followed by a 2-3 day transganglionic transport period, and then the spinal cord and medulla were processed with tetramethylbenzidine histochemistry. Both control groups have a consistent dense projection in topographically adjacent regions of the dorsal funiculus and gracile nucleus. However, there is no sign of axonal growth around the lesion in either group of chronic experimental operates. Instead, there is a decreased density of projection within the dorsal funiculus near the lesion site. Many remaining C-HRP labeled axons in the experimental operates have abnormal, thick varicosities and swollen axonal endings (5-10 microns x 10-30 microns) within the dorsal funiculus through several spinal segments caudal to the lesion. Ultrastructural analysis of the dorsal funiculus in three other chronic experimental operates reveals the presence of numerous vesicle filled axonal profiles and reactive endings which appear similar to the C-HRP labeled structures. Transganglionic labeling after C-HRP sciatic nerve injections (N = 4) and retrograde labeling of L4, L5 dorsal root ganglion neurons after fast blue injections of the gracile nucleus (N = 6) both suggest that all dorsal column axons project to the gracile nucleus in the newborn rat. Dorsal root ganglion (DRG) cell survival following the neonatal overhemisection injury was also examined in the L4 and L5 DRG. DRG neurons that project to the gracile nucleus were prelabeled by injecting fast blue into this nucleus at birth two days prior to the cervical overhemisection spinal injury. Both normal littermates (N = 9) and spinally injured animals (N = 12) were examined after postinjection survival periods of 10 or 22 days.(ABSTRACT TRUNCATED AT 400 WORDS)     

Plasticity of the corticospinal tract following midthoracic spinal injury in the postnatal rat

Rats received a midthoracic spinal cord "overhemisection" including right hemicord and left dorsal funiculus at birth (neonatal operates, N = 15) or 21 days of age (weanling operates, N = 14). In a second experiment neonatal (N = 6), 6-day (N = 3), and 12-day (N = 7) rats sustained a right sensorimotor cortex (SmI) ablation to destroy the left corticospinal tract (CST) at the same time as the spinal injury (double lesion operates). Later (3-12 months) injections of 3H-proline and autoradiography were used to label the left or right CST. The results of the first experiment showed that most right CST axons failed to grow around the spinal lesion in neonatal operates (N = 9). There was an increase in the density of label, mainly to CST projection areas, in a 1-mm zone rostral to the lesion. However, left CST axons bypassed the lesion by growing through the intact tissue in neonatal operates (N = 6). These displaced axons were consistently located within the dorsal portion of the lateral funiculus (dLF) and remained within that location caudal to the lesion, an area normally containing only a few CST axons. In spite of this abnormal position, these axons terminated bilaterally throughout the remainder of the cord in normal CST sites. In weanling operates, CST axons severed by the lesion did not regenerate around the lesion site. An increased density of label over the few spared axons within the left dLF and in CST projection zones immediately caudal to the lesion site suggested axonal sprouting by these axons. The results of the second experiment showed that the lack of growth of right CST axons around this injury in neonatal operates was, at least partially, due to an interaction with left CST axons. In neonatal double lesion operates, right CST axons grew around the spinal injury for a varying distance within the left dLF and distributed bilaterally to normal CST sites. The number of right CST axons bypassing the lesion was related to the configuration of the lesion site. A smaller number of right CST axons bypassed the lesion in 6-day double lesion operates and most terminated within 2-3 mm of the lesion site. Right CST axons failed to grow around this injury in 12-day double lesion operates.(ABSTRACT TRUNCATED AT 400 WORDS)     

Free‐water and free‐water corrected fractional anisotropy in primary and premotor corticospinal tracts in chronic stroke

Measures from diffusion MRI have been used to characterize the corticospinal tract in chronic stroke. However, diffusivity can be influenced by partial volume effects from free‐water, region of interest placement, and lesion masking. We collected diffusion MRI from a cohort of chronic stroke patients and controls and used a bitensor model to calculate free‐water corrected fractional anisotropy (FA_T) and free water (FW) in the primary motor corticospinal tract (M1‐CST) and the dorsal premotor corticospinal tract (PMd‐CST). Region of interest analyses and whole‐tract slice‐by‐slice analyses were used to assess between‐group differences in FA_T and FW in each tract. Correlations between FA_T and FW and grip strength were also examined. Following lesion masking and correction for multiple comparisons, relative increases in FW were found for the stroke group in large portions of the M1‐CST and PMd‐CST in the lesioned hemisphere. FW in cortical regions was the strongest predictor of grip strength in the stroke group. Our findings also demonstrated that FA_T is sensitive to the direct effects of the lesion itself, thus after controlling for the lesion, differences in FA_T in nonlesioned tissue were small and generally similar between hemispheres and groups. Our observations suggest that FW may be a robust biological measurement that can be used to assess microstructure in residual white matter after stroke. Hum Brain Mapp 38:4546–4562, 2017. © 2017 Wiley Periodicals, Inc.     

Serotoninergic innervation of the dorsal column nuclei and its relation to cytoarchitectonic subdivisions: An immunohistochemical study in cats and monkeys (Aotus trivirgatus)

The serotoninergic innervation of the dorsal column nuclei (DCN) was investigated in cats and owl monkeys (Aotus trivirgatus) with immunohistochemical methods. A dense network of serotonin-immunoreactive fibers was present in the reticular regions of DCN in cats, and in the pars triangularis of the cuneate nucleus and the peripheral and caudal regions of the gracile nucleus in owl monkeys. The cat's cluster regions and the monkey's rotund regions were more sparsely innervated. Electron microscopic examination showed that the labeled fibers were thin and unmyelinated. Vesicle-containing, terminal-like structures were small. They were in contact with dendrites, other terminals and cell bodies, but synapses were rare. The results demonstrate that the serotoninergic projection to the DCN in both cats and owl monkeys is heterogeneously distributed in a pattern that is faithfully related to the cytoarchitectonic subdivisions of the DCN. The densely innervated reticular regions in the DCN of cats and the corresponding regions in monkeys are predominantly involved in the processing of sensory information to the cerebellum, either directly, or indirectly through projections to the inferior olive, pontine gray, tectum, pretectum, red nucleus, or zona incerta. Thus, the present findings suggest that the serotoninergic innervation of the DCN is primarily related to the DCN's involvement in motor functions. © 1993 Wiley-Liss, Inc.     

Ascending sensory,but not other long-tract axons,regenerate into the connective tissue matrix that forms at the site of a spinal cord injury in mice

Mice exhibit a unique wound healing response following spinal cord injury in which the lesion site fills in with a connective tissue matrix. Previous studies have revealed that axons grow into this matrix, but the source of the axons remained unknown. The present study assesses whether any of these axons were the result of long tract regeneration. C57Bl/6 mice received crush injuries and were allowed to survive for 6 weeks to 7 months. Biotinylated dextran amine (BDA) was injected into the somato-motor cortex to trace descending corticospinal tract (CST) axons, into the midbrain to label descending brainstem pathways including the rubrospinal and reticulospinal tracts, or into the L5 dorsal root ganglion to trace ascending projections of first-order sensory neurons. Spinal cords from other mice were prepared for immunocytochemistry using antibodies against neurofilament protein (NF), 5-HT to reveal descending serotonergic axons, calcitonin gene-related protein (CGRP) to reveal ascending sensory axons, and chondroitin sulfate proteoglycan (CSPG) to assess the distribution of molecules that are inhibitory to axon growth. NF immunostaining revealed axons in the connective tissue matrix at the lesion site, confirming previous studies that used protargol staining. CST axons did not enter the connective tissue matrix, but did sprout extensively in segments adjacent to the injury site. Rubrospinal and reticulospinal tract axons also did not grow into the lesion site. 5-HT-positive axons extended to the edge of the lesion, and a few axons followed astrocyte processes into the margins of the lesion site. In contrast to the other pathways, BDA-labeled ascending sensory axons did extend into and arborized extensively within the connective tissue matrix, although the subgroup of ascending axons that are positive for CGRP did not. These results indicate that the connective tissue matrix is permissive for regeneration of some classes of ascending sensory axons but not for other axonal systems.     

生物素葡聚糖胺皮质脊髓束顺行示踪技术在大鼠脊髓损伤模型中的应用

目的探讨生物素葡聚糖胺(BDA)神经示踪技术及脊髓半横断损伤模型在大鼠脊髓损伤修复的实验研究中应用。方法采用成年Sprague-Dawley大鼠,分为脊髓致伤组(n=10)和致伤对照组(n=10)。致伤组动物在相当于T7椎板水平横行剪断脊髓的后2/3;对照组动物术中仅切除椎板,不切断脊髓。术后第15d,右侧开颅,用10?A示踪剂注入右侧的感觉运动区皮质内。2周后取出大脑和脊髓组织,采用自由漂乳法行BDA染色显影。术后实验动物功能测评采用BBB运动功能评分,所得数据采用Student'st-test进行统计学原理。结果(1)脊髓损伤组动物双后肢瘫痪,BBB运动功能评分明显低于损伤对照组,统计学比较差异十分显著(P<0.01);(2)BDA顺行示踪显示大脑皮层BDA注射区内见大脑皮层的锥体细胞及其发出的轴突呈阳性染色,BDA阳性染色的皮质脊髓束神经纤维在同侧中脑、桥脑及延髓的腹侧面行走,在锥体交叉后皮质脊髓束主要在对侧脊髓白质的后索中行走。在致伤组动物中,位于脊髓白质后索中的皮质脊髓束纤维在脊髓损伤处终止;对照组皮质脊髓束BDA染色可一直延伸至L1水平。结论大鼠半脊髓切断结合应用BDA顺行示踪技术可以对脊髓损伤后的神经修复状况进行可靠的形态学评判,是研究脊髓损伤后中枢神经纤维再生修复较为理想的动物模型     

Immunohistochemical detection of calcium/calmodulin-dependent protein kinase II in the spinal cord of the rat and monkey with special reference to the corticospinal tract

Calcium/ calmodulin-dependent protein kinase II is a prominent enzyme in the mammalian brain that phosphorylates a variety of substrate proteins. In the present study, monoclonal antibodies that specifically recognize either the α or the β isoforms of this enzyme were used to determine the distribution of these isoforms within the rat and monkey spinal cord. In the rat, the corticospinal tract consists of two components: the dorsal corticospinal tract, which occupies the ventralmost aspect of the dorsal funiculus; and the ventral corticospinal tract, which occupies an area adjacent to the ventral median fissure. Both dorsal and ventral corticospinal tract fibers were strongly immunopositive for the α-antibody. Unilateral ablation of the sensorimotor cortex of the rat eliminated the α-immunoreactive staining in the contralateral dorsal corticospinal tract. The neuropil in the superficial laminae of the dorsal horn (Rexed's laminae I and II) was densely stained with the α-antibody, whereas the neuropil in laminae IV-X was immunonegative. Dense α-immunopositive neurons were also distributed in the head of the dorsal horn (laminae I-IV). In contrast to the strong α-immunoreactivity seen in the dorsal corticospinal tract fibers, only very weak β-immunoreactivity was observed in this tract. Moderate β-immunoreactive products were distributed homogenously throughout the neuropil of the gray matter, although the neuropil of the superficial laminae of the dorsal horn (laminae I and II) was stained more strongly than the other regions of the gray matter (laminae III-X). Neuronal components in all laminae were immunopositive for the β-antibody. Thus, motoneurons in the ventral horn, which were immunonegative for the α-antibody, were immunopositive for the β-antibody. This selective distribution pattern of immunoreactivity of α- and β-antibodies in the rat was also present in the monkey spinal cord, although the α-immunopositive corticospinal tract fibers in the monkey descended in the lateral funiculus as the lateral corticospinal tract instead of passing through the dorsal funiculus, as is the case in the rat. The differential distribution of immunoreactivity in the spinal cord suggests that these two isoforms of calcium/ calmodulin-dependent protein kinase II may have different functional roles in the spinal cord. © Wiley-Liss, Inc.     

Glial and axonal responses in areas of Wallerian degeneration of the corticospinal and dorsal ascending tracts after spinal cord dorsal funiculotomy

Wallerian degeneration (WD), composed of the breakdown and phagocytosis of damaged axons and their myelin sheaths distal to the injury, is a major sequela of spinal cord injury (SCI). To understand the microenvironment within WD that may affect repair following SCI, we investigated the fate of major glial types and axons in this region following acute (1 h), subacute (10 days), and chronic (30 days) dorsal funiculotomy at the eighth thoracic (T8) level. This lesion induces a confined WD in two distinct functional pathways, that is, the corticospinal tract (CST) and dorsal ascending tract (DAT) in opposite directions. Here we report that astrocytes, reactive microglia and macrophages were all significantly increased in areas of WD in both the CST and DAT at subacute and chronic stages compared to the sham‐operated or acute stage. While the level of GFAP⁺ astrocytes remained stable after the subacute stage, the number of OX‐42⁺ microglia and ED‐1⁺ macrophages markedly decreased at the chronic stage. Interestingly, a mild but significant increase in ED‐1⁺ macrophages was also found in the intact fiber tracts 3 mm proximal to the injury at the chronic stage, coinciding with axonal dieback observed at that level. Axons distal to the injury experienced a continued and prolonged degeneration in both fiber tracts. Finally, although a significant decrease of Olig2⁺ oligodendrocyte lineage (OL) cells was found in areas of WD, the presence of these cells at the chronic stage indicates that they are available for endogenous repair. Taken together, our data have provided spatiotemporal evidence for the dynamic pathogenic changes of major cellular components in areas of WD remote to an SCI. Information obtained in this study should be useful for designing experiments aimed at modifying this region to accommodate endogenous or exogenous repair following SCI.