Neuroprotective Effects of Ebselen on Experimental Spinal Cord Injury in Rats

Spinal cord injury (SCI) results in rapid and significant oxidative stress. This study was aimed to investigate the possible beneficial effects of Ebselen in comparison with Methylprednisolone in experimental SCI. Thirty six Wistar albino rats (200–250 g) were divided in to six groups; A (control), B (only laminectomy), C (Trauma; laminectomy + spinal trauma), D (Placebo group; laminectomy + spinal trauma + serum physiologic), E (Methylprednisolone group; laminectomy + spinal trauma + Methylprednisolone treated), F (Ebselen group; laminectomy + spinal trauma + Ebselen treated), containing 6 rats each. Spinal cord injury (SCI) was performed by placement of an aneurysm clip, extradurally at the level of T11–12. After this application, group A, B and C were not treated with any drug. Group D received 1 ml serum physiologic. Group E received 30 mg/kg Methylprednisolone and, Group F received 10 mg/kg Ebselen intraperitoneally (i.p.). Rats were neurologically examined 24 h after trauma and spinal cord tissue samples had been harvested for both biochemical and histopathological evaluation. All rats were paraplegic after SCI except the ones in group A and B. Neurological scores were not different in traumatized rats than that of non-traumatized ones. SCI significantly increased spinal cord tissue malondialdehyde (MDA) and protein carbonyl (PC) levels and also decreased superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) enzyme activities compared to control. Methylprednisolone and Ebselen treatment decreased tissue MDA and PC levels and prevented inhibition of the enzymes SOD, GSH-Px and CAT in the tissues. However, the best results were obtained with Ebselen. In groups C and D, the neurons of the spinal cord tissue became extensively dark and degenerated with picnotic nuclei. The morphology of neurons in groups E and F were very well protected, but not as good as the control group. The number of neurons in the spinal cord tissues of the groups C and D were significantly less than the groups A, B, E and F. We concluded that the use of Ebselen treatment might have potential benefits in spinal cord tissue damage on clinical grounds.     

Brainstem-evoked muscle potentials: their prognostic value in experimental spinal cord injury in the rat

Recording myoelectric motor-evoked potentials is frequently used as an in vivo evaluation technique in experimental studies of spinal cord injury (SCI). The aim of the present study was to determine whether specific neuronal pathways conduct these potentials. Stainless steel screws were permanently implanted into the cranium of 18 rats for stimulation of brainstemevoked muscle potentials (B-MPs). Twelve rats were subjected to spinal cord lesions that restricted the continuity of the spinal cord to different discrete sections of the lateral and/or ventral white matter (WM) of the left hemicord. Sham rats ( n = 6) were subjected to laminectomy only. Left hind limb B-MPs and motor function (open field walking test) were recorded before surgery and weekly thereafter for six consecutive weeks. Motor function was severely affected by SCI in all rats but recovered significantly during the first 14 postoperative days. The degree of functional recovery depended not only on the amount of spared WM but also on the particular section of WM that had been spared. In contrast, B-MP amplitudes also were severely reduced by SCI, but did not recover during the survival period. Moreover, B-MP amplitudes correlated only weakly with the amount of spared WM and were not influenced by which section of WM had been spared. While functional recovery correlated significantly with the amount of spared WM, no correlation was found between B-MP amplitudes and functional recovery. B-MP conduction velocities were not affected by SCI. It is therefore believed that B-MPs have little prognostic value for experimental studies of SCI in the rat.     

Brainstem-evoked muscle potentials: their prognostic value in experimental spinal cord injury in the rat

Recording myoelectric motor-evoked potentials is frequently used as an in vivo evaluation technique in experimental studies of spinal cord injury (SCI). The aim of the present study was to determine whether specific neuronal pathways conduct these potentials. Stainless steel screws were permanently implanted into the cranium of 18 rats for stimulation of brainstem-evoked muscle potentials (B-MPs). Twelve rats were subjected to spinal cord lesions that restricted the continuity of the spinal cord to different discrete sections of the lateral and/or ventral white matter (WM) of the left hemicord. Sham rats (n = 6) were subjected to laminectomy only. Left hind limb B-MPs and motor function (open field walking test) were recorded before surgery and weekly thereafter for six consecutive weeks. Motor function was severely affected by SCI in all rats but recovered significantly during the first 14 postoperative days. The degree of functional recovery depended not only on the amount of spared WM but also on the particular section of WM that had been spared. In contrast, B-MP amplitudes also were severely reduced by SCI, but did not recover during the survival period. Moreover, B-MP amplitudes correlated only weakly with the amount of sparedWM and were not influenced by which section ofWM had been spared. While functional recovery correlated significantly with the amount of spared WM, no correlation was found between B-MP amplitudes and functional recovery. B-MP conduction velocities were not affected by SCI. It is therefore believed that B-MPs have little prognostic value for experimental studies of SCI in the rat.     

Contuse lesion of the rat spinal cord of moderate intensity leads to a higher time-dependent secondary neurodegeneration than severe one. An open-window for experimental neuroprotective interventions

Secondary neurodegeneration takes place in the surrounding tissue of spinal cord trauma and modifies substantially the prognosis, considering the small diameter of its transversal axis. We analyzed neuronal and glial responses in rat spinal cord after different degree of contusion promoted by the NYU Impactor. Rats were submitted to vertebrae laminectomy and received moderate or severe contusions. Control animals were sham operated. After 7 and 30 days post surgery, stereological analysis of Nissl staining cellular profiles showed a time progression of the lesion volume after moderate injury, but not after severe injury. The number of neurons was not altered cranial to injury. However, same degree of diminution was seen in the caudal cord 30 days after both severe and moderate injuries. Microdensitometric image analysis demonstrated a microglial reaction in the white matter 30 days after a moderate contusion and showed a widespread astroglial reaction in the white and gray matters 7 days after both severities. Astroglial activation lasted close to lesion and in areas related to Wallerian degeneration. Data showed a more protracted secondary degeneration in rat spinal cord after mild contusion, which offered an opportunity for neuroprotective approaches. Temporal and regional glial responses corroborated to diverse glial cell function in lesioned spinal cord.     

Dorsal horn administration of muscimol abolishes the muscle pressor reflex.

The purpose of this study was to determine the effect of blocking synaptic transmission in the dorsal horn on the cardiovascular responses produced by activation of muscle afferent neurons. Synaptic transmission was blocked by applying the GABA(A) agonist muscimol to the dorsal surface of the spinal cord. Cats were anesthetized with alpha-chloralose and urethane, and a laminectomy was performed. With the exception of the L(7) dorsal root, the dorsal and ventral roots from L(5) to S(2) were sectioned on one side, and static contraction of the ipsilateral triceps surae muscle was evoked by electrically stimulating the peripheral ends of the L(7) and S(1) ventral roots. The dorsal surface of the L(4)--S(3) segments of the spinal cord were enclosed within a "well" created by applying layers of vinyl polysiloxane. Administration of a 1 mM solution of muscimol (based on dose-response data) into this well abolished the reflex pressor response to contraction (change in mean arterial blood pressure before was 47 +/- 7 mmHg and after muscimol was 3 +/- 2 mmHg). Muscle stretch increased mean arterial blood pressure by 30 +/- 8 mmHg before muscimol, but after drug application stretch increased MAP by only 3 +/- 2 mmHg. Limiting muscimol to the L(7) segment attenuated the pressor responses to contraction (37 +/- 7 to 24 +/- 11 mmHg) and stretch (28 +/- 2 to 16 +/- 8 mmHg). These data suggest that the dorsal horn of the spinal cord contains an obligatory synapse for the pressor reflex. Furthermore, these data support the hypothesis that branches of primary afferent neurons, not intraspinal pathways, are responsible for the multisegmental integration of the pressor reflex.     

Differential gene expression in the EphA4 knockout spinal cord and analysis of the inflammatory response following spinal cord injury

Mice lacking the axon guidance molecule EphA4 have been shown to exhibit extensive axonal regeneration and functional recovery following spinal cord injury. To assess mechanisms by which EphA4 may modify the response to neural injury a microarray was performed on spinal cord tissue from mice with spinal cord injury and sham injured controls. RNA was purified from spinal cords of adult EphA4 knockout and wild-type mice four days following lumbar spinal cord hemisection or laminectomy only and was hybridised to Affymetrix All-Exon Array 1.0 GeneChips?. While subsequent analyses indicated that several pathways were altered in EphA4 knockout mice, of particular interest was the attenuated expression of a number of inflammatory genes, including Arginase 1, expression of which was lower in injured EphA4 knockout compared to wild-type mice. Immunohistological analyses of different cellular components of the immune response were then performed in injured EphA4 knockout and wildtype spinal cords. While numbers of infiltrating CD3+ T cells were low in the hemisection model, a robust CD11b+ macrophage/microglial response was observed post-injury. There was no difference in the overall number or spread of macrophages/activated microglia in injured EphA4 knockout compared to wild-type spinal cords at 2, 4 or 14 days post-injury, however a lower proportion of Arginase-1 immunoreactive macrophages/activated microglia was observed in EphA4 knockout spinal cords at 4 days post-injury. Subtle alterations in the neuroinflammatory response in injured EphA4 knockout spinal cords may contribute to the regeneration and recovery observed in these mice following injury.     

The transneuronal spread phenotype of herpes simplex virus type 1 infection of the mouse hind footpad.

The mouse hind footpad inoculation model has served as a standard laboratory system for the study of the neuropathogenesis of herpes simplex virus type 1 (HSV-1) infection. The temporal and spatial distribution of viral antigen, known as the transneuronal spread phenotype, has not previously been described; nor is it understood why mice develop paralysis in an infection that involves sensory nerves. The HSV-as-transneuronal-tracer experimental paradigm was used to define the transneuronal spread of HSV-1 in this model. A new decalcification technique and standard immunocytochemical staining of HSV-1 antigens enabled a detailed analysis of the time-space distribution of HSV-1 in the intact spinal column. Mice were examined on days 3, 4, 5, and 6 postinoculation (p.i.) of a lethal dose of wild-type HSV-1 strain 17 syn+. Viral antigen was traced retrograde into first-order neurons in dorsal root ganglia on day 3 p.i., to the dorsal spinal roots on days 4 and 5 p.i., and to second- and third-order neurons within sensory regions of the spinal cord on days 5 and 6 p.i. HSV-1 antigen distribution was localized to the somatotopic representation of the footpad dermatome within the dorsal root ganglia and spinal cord. Antigen was found in the spinal cord gray and white matter sensory neuronal circuits of nociception (the spinothalamic tract) and proprioception (the dorsal spinocerebellar tract and gracile fasciculus). Within the brain stems and brains of three paralyzed animals examined late in infection (days 5 and 6 p.i.), HSV antigen was restricted to the nucleus subcoeruleus region bilaterally. Since motor neurons were not directly involved, we postulate that hindlimb paralysis may have resulted from intense involvement of the posterior column (gracile fasciculus) in the thoracolumbar spinal cord, a region known to contain the corticospinal tract in rodents.     

Biomechanical investigation of post-operative C5 palsy due to ossification of the posterior longitudinal ligament in different types of cervical spinal alignment

Post-operative C5 palsies are among the most common complications seen after cervical surgery for ossification of the posterior longitudinal ligament (OPLL). Although C5 palsy is a well-known complication of cervical spine surgery, its pathogenesis is poorly understood and depends on many other factors. In this study, a finite element model of the cervical spine and spinal cord-nerve roots complex structures was developed. The changes in stress in the cord and nerve roots, posterior shift of the spinal cord, and displacement and elongation of the nerve roots after laminectomy for cervical OPLL were analyzed for three different cervical sagittal alignments (lordosis, straight, and kyphosis). The results suggest that high stress concentrated on the nerve roots after laminectomy could be the main cause of C5 palsy because ossification of ligaments increases spinal cord shifting and root displacement. The type of sagittal alignment had no influence on changes in cord stress after laminectomy, although cases of kyphosis with a high degree of occupying ratio resulted in greater increases in nerve root stress after laminectomy. Therefore, kyphosis with a high OPLL occupying ratio could be a risk factor for poor surgical outcomes or post-operative complications and should be carefully considered for surgical treatment.     

Prenatal development of cutaneous afferent connections in the spinal cord of fetal sheep

In this study we have examined the physiological and neurochemical development of the cutaneous afferent pathways from the hindlimb to the spinal cord in fetal sheep. We have shown that somatosensory input from the hindlimb evokes activity in DRG neurons at 87d gestation and in cells in the dorsal horn at 92d (term, 146d). There is evidence of immunoreactivity for substance P, calcitonin gene-related peptide and glutamine several days prior to this at 77-80 days. The implication of these findings are discussed.     

Impacts of epidural electrical stimulation on Wnt signaling,FAAH, and BDNF following thoracic spinal cord injury in rat

Electrical stimulation (ES) has been shown to improve some of impairments after spinal cord injury (SCI), but the underlying mechanisms remain unclear. The Wnt signaling pathways and the endocannabinoid system appear to be modulated in response to SCI. This study aimed to investigate the effect of ES therapy on the activity of canonical/noncanonical Wnt signaling pathways, brain-derived neurotrophic factor (BDNF), and fatty-acid amide hydrolase (FAAH), which regulate endocannabinoids levels. Forty male Wistar rats were randomly divided into four groups: (a) Sham, (b) laminectomy + epidural subthreshold ES, (c) SCI, and (d) SCI + epidural subthreshold ES. A moderate contusion SCI was performed at the thoracic level (T10). Epidural subthreshold ES was delivered to upper the level of T10 segment every day (1 hr/rat) for 2 weeks. Then, animals were killed and immunoblotting was used to assess spinal cord parameters. Results revealed that ES intervention for 14 days could significantly increase wingless-type3 (Wnt3), Wnt7, β-catenin, Nestin, and cyclin D1 levels, as well as phosphorylation of glycogen synthase kinase 3β and Jun N-terminal kinase. Additionally, SCI reduced BDNF and FAAH levels, and ES increased BDNF and FAAH levels in the injury site. We propose that ES therapy may improve some of impairments after SCI through Wnt signaling pathways. Outcomes also suggest that BDNF and FAAH are important players in the beneficial impacts of ES therapy. However, the precise mechanism of BDNF, FAAH, and Wnt signaling pathways on SCI requires further investigation.     

Adhesion to Carbon Nanotube Conductive Scaffolds Forces Action-Potential Appearance in Immature Rat Spinal Neurons

In the last decade, carbon nanotube growth substrates have been used to investigate neurons and neuronal networks formation in vitro when guided by artificial nano-scaled cues. Besides, nanotube-based interfaces are being developed, such as prosthesis for monitoring brain activity. We recently described how carbon nanotube substrates alter the electrophysiological and synaptic responses of hippocampal neurons in culture. This observation highlighted the exceptional ability of this material in interfering with nerve tissue growth. Here we test the hypothesis that carbon nanotube scaffolds promote the development of immature neurons isolated from the neonatal rat spinal cord, and maintained in vitro. To address this issue we performed electrophysiological studies associated to gene expression analysis. Our results indicate that spinal neurons plated on electro-conductive carbon nanotubes show a facilitated development. Spinal neurons anticipate the expression of functional markers of maturation, such as the generation of voltage dependent currents or action potentials. These changes are accompanied by a selective modulation of gene expression, involving neuronal and non-neuronal components. Our microarray experiments suggest that carbon nanotube platforms trigger reparative activities involving microglia, in the absence of reactive gliosis. Hence, future tissue scaffolds blended with conductive nanotubes may be exploited to promote cell differentiation and reparative pathways in neural regeneration strategies.     

Implanting Glass Spinal Cord Windows in Adult Mice with Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) in adult rodents is the standard experimental model for studying autonomic demyelinating diseases such as multiple sclerosis. Here we present a low-cost and reproducible glass window implantation protocol that is suitable for intravital microscopy and studying the dynamics of spinal cord cytoarchitecture with subcellular resolution in live adult mice with EAE. Briefly, we surgically expose the vertebrae T12-L2 and construct a chamber around the exposed vertebrae using a combination of cyanoacrylate and dental cement. A laminectomy is performed from T13 to L1, and a thin layer of transparent silicone elastomer is applied to the dorsal surface of the exposed spinal cord. A modified glass cover slip is implanted over the exposed spinal cord taking care that the glass does not directly contact the spinal cord. To reduce the infiltration of inflammatory cells between the window and spinal cord, anti-inflammatory treatment is administered every 2 days (as recommended by ethics committee) for the first 10 days after implantation. EAE is induced only 2-3 weeks after the cessation of anti-inflammatory treatment.Using this approach we successfully induced EAE in 87% of animals with implanted windows and, using Thy1-CFP-23 mice (blue axons in dorsal spinal cord), quantified axonal loss throughout EAE progression. Taken together, this protocol may be useful for studying the recruitment of various cell populations as well as their interaction dynamics, with subcellular resolution and for extended periods of time. This intravital imaging modality represents a valuable tool for developing therapeutic strategies to treat autoimmune demyelinating diseases such as EAE.     

Evaluation of the Neuroprotective Effects of Citicoline after Experimental Spinal Cord Injury: Improved Behavioral and Neuroanatomical Recovery

Spinal cord injury (SCI) caused by trauma mainly occurs in two mechanisms as primary and secondary injury. Secondary injury following the primary impact includes various pathophysiological and biochemical events. Methylprednisolone is the only pharmacological agent having clinically proven beneficial effects on SCI. Citicoline has been shown to have clinical and experimental beneficial effects on brain ischemia. This study aims to investigate the neuroprotective effect of citicoline in an experimental SCI model in rats. Sixty adult Wistar albino rats were randomized into five groups. SCI was performed by the weight-drop model. Group 1 underwent laminectomy alone. The Group 2 underwent laminectomy followed by SCI and received no medication. Group3, Group 4 and Group 5 underwent laminectomy followed by SCI and received medication. Group 3 and Group 5 received citicoline and Group 4 and Group 5 received methylprednisolone. The rats were divided into two subgroups for biochemical analysis (sacrificed at 24 h after surgery) and neurobehavioral and histopathological evaluation (sacrificed at 6 weeks after surgery). Malonildialdehyde levels, nitric oxide levels and trauma size ratios were lower and reduced glutathione levels were higher in Group 3, Group 4 and Group 5 as compared to Group 2. Posttraumatic neurological recovery after surgery was significantly better in Group 3, Group 4 and Group 5 compared to Group 2. In conclusion, this study demonstrates that citicoline is as effective as methylprednisolone. The efficacy of citicoline combined with methylprednisolone is not superior to either citicoline or methylprednisolone alone.     

Upregulation of vascular endothelial growth factor receptors Flt-1 and Flk-1 following acute spinal cord contusion in rats.

To investigate the possible role of vascular endothelial growth factor (VEGF) in the injured spinal cord, we analyzed the distribution and time course of the two tyrosine kinase receptors for VEGF, Flt-1 and Flk-1, in the rat spinal cord following contusion injury using a weight-drop impactor. The semi-quantitative RT-PCR analysis of Flt-1 and Flk-1 in the spinal cord showed slight upregulation of these receptors following spinal cord injury. Although mRNAs for Flt-1 and Flk-1 were constitutively expressed in neurons, vascular endothelial cells, and some astrocytes in laminectomy control rats, their upregulation was induced in association with microglia/macrophages and reactive astrocytes in the vicinity of the lesion within 1 day in rats with a contusion injury and persisted for at least 14 days. The spatiotemporal expression of Flt-1 in the contused spinal cord mirrored that of Flk-1 expression. In the early phase of spinal cord injury, upregulation of Flt-1 and Flk-1 mRNA occurred in microglia/macrophages that infiltrated the lesion. In addition, the expression of both receptors increased progressively in reactive astrocytes within the vicinity of the lesion, predominately in the white matter, and almost all reactive astrocytes coexpressed Flt-1 or Flk-1 and nestin. These results suggest that VEGF may be involved in the inflammatory response and the astroglial reaction to contusion injuries of the spinal cord via specific VEGF receptors.     

Reorganization of the ventral nerve cord in the moth Manduca sexta (L.) (Lepidoptera : Sphingidae)

Morphology of the ventral nerve cord of the hawkmoth, Manduca sexta (Lepidoptera : Sphingidae), changes at the larval-pupal transition as several separate larval ganglia fuse to form single ganglia characteristic of the adult. We examined in detail the time course of ganglionic fusion. Changes in the relative positions of the ganglia were studied by staining the tissue with methylene or toluidine blue. Alterations in the positions and structure of individual neurons were studied by filling neurons with a cobalt-lysine complex. The first gross morphological change, anterior movement of the first abdominal ganglion, is visible within the first 24 hr after pupal ecdysis. Adult ventral nerve cord morphology is recognizable 6 days later, approximately 12 days before the adult will emerge. The sequence in which the individual ganglia fuse is invariant. During ganglionic fusion, the neuronal cell bodies and associated neuropil move out of their former ganglionic sheath and through the sheath covering the connectives. Axons between the fusing ganglia form loops in the shortening connectives. The presence of looping axons is a morphological feature that identifies the boundaries between ganglia during intermediate stages of fusion. Some individual adult neurons also show looped axons at the boundaries of fused ganglia. These axonal loops may be a valuable morphological marker by which neurons can be characterized as conserved neurons.     

Regulation and localization of neuronal nitric oxide synthase in the ischemic rabbit spinal cord

The expression and cellular localization of neuronal nitric oxide (NO) synthase (nNOS) were studied in the rabbit spinal cord following ischemic injury induced by clamping the descending aorta. In the normal spinal cord, nNOS immunoreactivity was localized to certain motor neurons located in the margin of the ventral horn. Following transient ischemia, immunoreactive spinal neurons increased in number, peaking five days after reperfusion. Quantitative evaluation by western blotting showed that nNOS peaked at 180% of control levels five days after reperfusion and decreased to 120% of controls by 14 days. These findings suggest that overproduced NO may act as a neurotoxic agent in the ischemic spinal cord.     

An animal model for neuron-specific spinal cord lesions by the microinjection of N-methylaspartate, kainic acid, and quisqualic acid

It has been shown that N-methylaspartate (NMA), kainic acid (KA), and quisqualic acid (QA) can produce preferential neuronal damage in various parts of the striatum, hippocampus, and thalamus with relative sparing of axons in transit. Thus far, the evidence that axons in transit escape destruction has been based largely on histological observations. To test the functional integrity of axons in passage, we made unilateral lesions with these agents in the cervical spinal cord of rats and compared the subsequent functional deficits with those seen after spinal cord hemisections. Observations were made in 14 rats. In each case, a laminectomy at the C6-C7 level was performed under general anesthesia. Animals receiving microinjections of KA, QA, or NMA showed motor and sensory deficits only in the ipsilateral forepaw and remained able to use the hindpaws normally. By contrast, animals undergoing spinal cord hemisection developed obvious motor deficits in the ipsilateral hindpaw in addition to the deficits in the forepaw. Histological observations of the spinal cords confirmed an extensive gray matter destruction with relative preservation of the long tracts in animals injected with KA, QA, and NMA. In addition, it was noted that spinal cord neurons appear relatively less sensitive to KA and more sensitive to QA than neurons in the thalamus, striatum, or hippocampus. The possible application of these findings for the production of dorsal root entry zone lesions will be discussed.     

Properties of descending dorsal unpaired median (DUM) neurons of the locust suboesophageal ganglion

A group of six dorsal unpaired median (DUM) neurons of the suboesophageal ganglion (SOG) of locusts was studied with neuroanatomical and electrophysiological techniques. The neurons are located posteriorly in the SOG and have axons that descend into the ganglia of the ventral nerve cord, some as far as the terminal abdominal ganglion. Within thoracic ganglia the neurons have profuse dendritic ramifications in many neuropiles, including ventral sensory neuropiles. Based on their projection patterns three different morphological types of neurons can be distinguished. These neurons receive excitatory inputs through sensory pathways that ascend from the thoracic ganglia and are activated by limb movements. They may be involved in the modulation of synaptic transmission in thoracic ganglia.     

Time of origin of cells in the histiogenesis of the spinal cord]

In order to establish the moment of appearance of neuroblasts and ectoglia of the spinal cord the autoradiographic study with the use of H3-thymidine and C14-thmidine injected to pregnant mice with the intervals between injections 121/2 or 24 hours was undertaken. It was establised that spinal neurons were removed from the nervous tube beginning from the 10th up to 13th days of embroyogenesis. The motoneurons of the anterior horn were the first to appear (10th-12th days), the neurons of the intermideate zone were the next to appear (11th - 12th days) and the last were the neurons of posterior horn (13th day). Beginning from the 13th day of embryogenesis there appeared the ectoglia which migrated following meurblasts two days later. The saturation of the grey matter with glial cells and the saturation of the white matter with Schwann cells was brought about by means of additional multiplication at the site of the glioblasts removed from the nervous tube. The main function of the matrix layer neuroepithelium of the nervous tube as a provider of cells to the spinal cord terminated on the 15th day of embryogenesis.