Glial activity during axonal regrowth following cryogenic injury of rat spinal cord

The molecular cloning of glial fibrillary acidic protein in Gekko japonicus and its expression changes after spinal cord transection

The glial fibrillary acidic protein (GFAP) is an astrocyte-specific member of the class III intermediate filament proteins. It is generally used as a specific marker of astrocytes in the central nervous system (CNS). We isolated a GFAP cDNA from the brain and spinal cord cDNA library of Gekko japonicus, and prepared polyclonal antibodies against gecko GFAP to provide useful tools for further immunochemistry studies. Both the real-time quantitative PCR and western blot results revealed that the expression of GFAP in the spinal cord after transection increased, reaching its maximum level after 3 days, and then gradually decreased over the rest of the 2 weeks of the experiment. Immunohistochemical analyses demonstrated that the increase in GFAP-positive labeling was restricted to the white matter rather than the gray matter. In particular, a slight increase in the number of GFAP positive star-shaped astrocytes was detected in the ventral and lateral regions of the white matter. Our results indicate that reactive astrogliosis in the gecko spinal cord took place primarily in the white matter during a short time interval, suggesting that the specific astrogliosis evaluated by GFAP expression might be advantageous in spinal cord regeneration.

Support of axonal regrowth by endogenous mechanisms following spinal cord injury in adult rats

Because of its non-invasive nature and ease of regulation, a closely monitored cryogenic method of tissue injury was used to create a degree of spinal cord injury within which there would be an extended regrowth of axons. The parameters of cooling used in the present study resulted in an injury length of 1 cm through which 3 mm of measured axonal regrowth and 8 mm of observed regrowth occurred over a 56-day period in the ascending fibers of the dorsal column of the mature rat. This was associated with the development of a cellular matrix consisting of macrophages, macroglia and Schwann cells which gradually expands within the injured area initially dominated by macrophages. It is the authors' impression that the presence of a substantial microglial component within the macrophage population may be a significant factor in the success of the axonal regrowth. Under this influence and that of the invading axons, the astrocyte, which provides the immediate cell support to the growing axon, can be maintained in a functional state that is supportive and not obstructive to the axon, presumably through the recruitment of astrocyte precursors from an indigenous stem cell population. These tissue changes indicate that adult mammalian spinal cord tissue does have the capacity to develop on its own a matrix capable of supporting the regrowth of axons.

Neural tissue formation within porous hydrogels implanted in brain and spinal cord lesions: ultrastructural, immunohistochemical, and diffusion studies

A biocompatible heterogeneous hydrogel of poly [N-(2-hydroxypropyl) methacrylamide] (PHPMA), was evaluated for its ability to promote tissue repair and enhance axonal regrowth across lesion cavities in the brain and spinal cord in adult and juvenile (P17 P21) rats. Incorporation of PHPMA hydrogels into surrounding host tissue was examined at the ultrastructural level and using immunohistochemical techniques. In addition, and in parallel to these studies, diffusion parameters (volume fraction and tortuosity of the gel network) of the PHPMA hydrogels were evaluated pre- to postimplantation using an in vivo real-time iontophoretic method. The polymer hydrogels were able to bridge tissue defects created in the brain or spinal cord, and supported cellular ingrowth, angiogenesis, and axonogenesis within the structure of the polymer network. As a result, a reparative tissue grew within the porous structure of the gel, composed of glial cells, blood vessels, axons and dendrites, and extracellular biological matrices, such as laminin and/or collagen. Consistent with matrix deposition and tissue formation within the porous structure of the PHPMA hydrogels, there were measurable changes in the diffusion characteristics of the polymers. Extracellular space volume decreased and tortuosity increased within implanted hydrogels, attaining values similar to that seen in developing neural tissue. PHPMA polymer hydrogel matrices thus show neuroinductive and neuroconductive properties. They have the potential to repair tissue defects in the central nervous system by replacing lost tissue and by promoting the formation of a histotypic tissue matrix that facilitates and supports regenerative axonal growth. () ()

Astrocytes and oligodendrocytes reactions after a total section of the rat spinal cord

Regeneration after an injury in the Central Nervous System is dependent on intrinsic and extrinsic factors. Among the latter are the reactions of glial cells. Using the model of total section of adult rat spinal cord, we have studied the spatial and temporal responses of astrocytes and oligodendrocytes to the lesion of spinal cord axons. We studied at molecular and cellular levels the specific markers GFAP (glial fibrillary acidic protein) for the astrocytes, CNP (2'-3' cyclic 3' nucleotide phosphodiesterase) which is principally expressed by immature oligodendrocytes, and MBP (myelin basic protein) implicated later in the myelin compaction, and which is more specific of mature oligodendrocytes. After injury, all astrocytes, but more markedly those of the grey matter, reacted by an increase of GFAP messenger and protein. This increase was very rapid for messenger, and peaked at 3 days. This increase was more protracted for the protein and persisted after 3 weeks. Messenger increase is more marked and more protracted below than above the lesion. Oligodendrocytes also reacted quickly by an increase of CNP and MBP messengers. For CNP, both messenger and protein increased rapidly and returned to control level after 1 week. MBP showed the same time course of changes, with lower and slower decrease above the lesion. Counts of oligodendrocytes showed that the percentage of the less mature form (light oligodendrocytes) increased dramatically above and below the lesion. After 1 week, above the lesion, this percentage was well below that of the control, whereas below the lesion, it reverted to control value. These results indicate that, following a lesion, astrocytes react quickly and intensely, but more so below the lesion; oligodendrocytes resume a sequence of maturation which is eventually completed above the lesion where remyelinisation can occur and which is prematurely interrupted below the lesion. However, intact oligodendrocytes persist below the lesion, where they constitute a potential for remyelinisation of regenerated and/or transplanted axons.

The effect of the platelet derived wound healing formula and the nerve growth factor on the experimentally injured spinal cord

The main purpose of this study is to investigate the effect of platelet derived wound healing formula (PDWHF) and nerve growth factor (NGF) in the treatment of experimental spinal cord injury. PDWHF is a conglomerate of growth factors which include platelet derived growth factor (PDGF), platelet derived angiogenesis factor (PDAF), transforming growth factor-beta (TGF beta) and platelet factor IV (PF4). Complete spinal cord transection was performed at T12 in rats and the treatment of the spinal cord injury was achieved by filling the dead space with type 1 collagen gel impregnated with PDWHF, or with 2.5S-NGF. Controls were treated with only type 1 collagen gel. Animals were sacrificed at 1, 2 or 3 months. Histopathologically, tissue autolysis and cavity formation by phagocytosis expanded 1-3 mm into the cord stumps and the volume of cavitation was less in the two treated groups. In the NGF group, a greater number of surviving nerve cells were observed in this region. Most of the control animals formed only thin, short axonal bundles, however, increased axonal regrowth was noted in animals treated with trophic factors, especially in the NGF group. The NGF group formed thick axonal bundles and abundant neuroma. Increased angiogenesis was observed in the collagen gel matrix and the injured spinal cord parenchyma, in the PDWHF group. Recent studies have shown that mammalian adult CNS possesses the ability for structural and/or functional plasticity following injury under appropriate circumstances. In this in vivo study, exogenous NGF appeared to induce axomal outgrowth and nerve cell survival. PDWHF produced notable angiogenesis which seemed to improve the extracellular microenvironment. This may be important for the delivery of exogenous trophic factors, nutrients and for the changes of extracellular matrices to support nerve cells and axons.

Cryogenic spinal cord injury induces astrocytic gene expression of insulin-like growth factor I and insulin-like growth factor binding protein 2 during myelin regeneration

To study injury-induced astrocytic responses associated with regrowth of axons and regeneration of myelin, the method of Collins and colleagues was used to make focal cryogenic lesions in spinal cords of adult rats (Collins et al.: J Neuropathol Exp Neurol 45: 742-757, 1986). The duration of cryogenic injury (CI), the size of the cryode, and its temperature were chosen to destroy all myelin sheaths and axons without producing cavities or hemorrhages. Messenger RNA and peptide distributions of insulin-like growth factor I (IGF-I), IGF-I receptor (IGFR-I), IGF binding protein 2 (IGFBP-2), glial fibrillary acidic protein (GFAP), and myelin basic protein (MBP) were studied 3-56 days after CI by in situ hybridization and immunocytochemistry. At 3 days, vimentin-positive, GFAP-negative astrocyte-like cells in the lesion expressed IGF-I mRNA and peptide and 7 days after CI, both were expressed by typical GFAP-positive, hypertrophic astrocytes, many of which also were vimentin-positive. Levels of IGF-I, IGFBP-2, and GFAP mRNA and peptide were higher in lesion astrocytes after 14 days. They attained maximum levels at 21-28 days before declining to near control levels at 56 days. Decreasing relative levels of oligodendroglial MBP mRNA were found in and around lesions 7-14 days after CI; subsequently, rising levels accompanied remyelination. At 28 and 56 days after CI, some transferrin-positive, oligodendroglia-like cells also were immunostained by anti-IGFR-I. Our findings suggest that early astrocytic production of IGF-I and IGFBP-2 may be involved in the myelin regeneration which occurs in this model of spinal cord injury.

Prostaglandins modulate alterations of microvascular permeability, blood flow, edema and serotonin levels following spinal cord injury: an experimental study in the rat

The possibility that prostaglandins influence edema formation, microvascular permeability increase and reduction of blood flow following spinal cord trauma was examined in a rat model. In addition, the influence of prostaglandins on serotonin metabolism of the traumatized spinal cord was evaluated. Trauma to spinal cord (2-mm-deep and 5-mm-long incision in the right dorsal horn of T10-11 segments) resulted in a profound increase of the water content 5 h after injury. At this time, the microvascular permeability to Evans Blue and [131I]sodium was increased by 457 and 394%, respectively. The blood flow was reduced by 30%. The serotonin (5-hydroxytryptamine) content of the spinal cord increased by 205%. The plasma serotonin level rose by 152% in the injured group of rats. Pretreatment with indomethacin (10 mg/kg, i.p.) 30 min before trauma significantly reduced the edema and microvascular permeability increase. The local spinal cord blood flow of traumatized animals was partially restored. The increases of serotonin levels of the spinal cord and plasma were significantly attenuated. These beneficial effects of indomethacin were not present in rats given a lower dose (5 mg/kg). Indomethacin in either dose did not influence these parameters of control rats without trauma to the cord. Since indomethacin is a potential inhibitor of prostaglandins synthesis our observations indicate: (i) that prostaglandins participate in many microvascular responses (permeability changes, edema, blood flow) occurring after a trauma to the spinal cord; (ii) that these effects of the drug seem to be dose dependent, and (iii) that the prostaglandins may influence the serotonin metabolism following trauma to the spinal cord.

New aspects of neurotransplantation

We have examined the possibility of promoting axonal regeneration within lesioned neural tissue using grafted artificial gel matrices. Polymeric matrices which feature a three-dimensional crosslinked macromolecular network were implanted into preformed lesions of the central nervous system (CNS). The host response consisted of matrix invasion by glial elements and the deposition of newly synthesized extracellular molecules. This rearrangement of the brain scarring process into an organized cellular coating promoted axonal regeneration into the gels. Entrapment of embryonic neurons and embryonal carcinoma (EC)-derived neurons, within the gels, was performed to explore the possibility of using polymer brain implants as neural graft microcarriers. Our results suggest that this approach will be useful for the delivery of cells and the promotion of axonal elongation required for successful neurotransplantation.

The effect of growth factor formula (platelet derived wound healing formula) in experimental spinal cord injuries

The main purpose of this study was to investigate the usefulness of platelet derived wound healing formula (PDWHF) in the treatment of experimentally induced spinal cord injuries in cats. The injury model in ten adult cats consisted of the placement of three 22-gauge Teflon catheter sheaths into the spinal cord at the L2 level. Treatment consisted of coating these sheaths with PDWHF in Hydron. Three animals were used as controls. In the 7 remaining cats, treatment was double blinded. Cats were sacrificed at 3 weeks after injury and injured spinal cord segments were excised for histologic evaluation. Electrophysiologic and clinical motor function were evaluated throughout a period of observation. Evoked potentials in both the treated and control groups indicated incomplete spinal cord lesions due to insertion of the needles. There did not appear to be any significant improvement or difference in the evoked response and clinical function as a result of treatment with PDWHF. The histological findings in the PDWHF-treated group showed significant new vessel formation as well as dilation and around the injury site. This neovascularization, both qualitative and quantitative, was noted in the treatment group. This information, with a limited injury and very simple delivery system for growth factor, would suggest there is definite neovascularization occurring as a result of this treatment and this may be useful in the subsequent wound healing response such as axonal growth and scar tissue formation.

The electrolytic lesion as a model of spinal cord damage and repair in the adult rat

The utility of the electrolytic lesion as a model of spinal cord injury and repair has been studied in adult Wistar rats. Lesions were created using an 0.1 mA current applied for 30 s in the right hand intermediate zone of the cord, at the level of the 10th thoracic vertebra. After three months, secondary pathological changes at these sites resulted in a variable degree of grey matter atrophy, cavitation, macrophage infiltration and loss of white matter in the dorsolateral funiculus. Functionally, lesioned animals exhibited an incomplete spastic paraparesis of the right hind limb, had normal scores on the inclined plane test, but showed subnormal performance of the right hind limb on the Tarlov scale. Spinal cord neurones dissociated from E14 rat embryos survived for at least 3 months if transplanted into a freshly made electrolytic lesion. However, these implants had no ameliorating effect on the motor deficit induced by electrolytic lesions. It was concluded that the electrolytic lesion represents a useful model for qualitative studies on secondary histopathological changes in the injured cord. Electrolytic lesions also support long-term survival of implanted spinal neurones. However, the possible trophic influence of these implants on motor and sensory tracts could probably be better studied using neonatal, rather than adult rats.

Interactions of copolymeric poly(glyceryl methacrylate)-collagen hydrogels with neural tissue: effects of structure and polar groups

In a previous study we developed copolymeric glyceryl methacrylate-collagen hydrogels for implantation in surgical lesions of the rat brain. Such materials provide porous matrices that can serve as support systems for oriented growth of scar tissue and axonal growth. In the present work, we have investigated the effect of structural modifications (studied by mercury porosimetry) of polymeric matrices and the effect of polar groups on the response of the brain tissue. The findings show that the fractional porosity and the pore size distribution of matrices are critical for tissue ingrowth and that negative charges, i.e. carboxylic acid groups, incorporated in the polymer have a strong influence on reactive astrocytosis.