Laminin distribution during corticospinal tract development and after spinal cord injury

The First Postlesion Minutes: An In Vivo Study of Extravasation and Perivascular Astrocytes Following Cerebral Lesions in Various Experimental Mouse Models

The immediate alterations following lesions cannot be investigated by using fixed tissues. Here, we employed two-photon microscopy to study the alterations to the permeability of blood-brain barrier and to glio-vascular connections in vivo during the first minutes following cortical lesions in mice. Four models were used: (1) cryogenic lesion, (2) photodisruption using laser pulses, (3) photothrombosis, and (4) bilateral carotid ligation. Sulforhodamine101 was used for supravital labeling of astrocytes and dextran-bound fluorescein isothiocyanate for the assessment of extravasation. Transgenic mice, in which the endothelium and astrocytes expressed a yellow fluorescent protein, were also used. Astrocytic labeling in vivo was verified with postmortem immunostaining against glial fibrillary acidic protein (GFAP). Summary of results: (1) the glio-vascular connections were stable in the intact brain with no sign of spontaneous dynamic attachment/detachment of glial end-feet; (2) only direct vascular damage (photodisruption or cryogenic) resulted in prompt extravasation; (3) even direct damage failed to provoke a prompt astroglial response. In conclusion, the results indicate that a detachment of the astrocytic end-feet does not precede the breakdown of blood-brain barrier following lesions. Whereas vasogenic edema develops immediately after the lesions, this is not the case with cytotoxic edemas. Time-lapse recordings and three-dimensional reconstructions are presented as supplemental materials.

Postmortem immunohistochemical alterations following cerebral lesions: A possible pathohistological importance of the β-dystroglycan immunoreactivity

The frequency of cerebrovascular injuries raises the importance of their immunohistological investigation in postmortem materials. Most injuries involve the impairment of the blood-brain barrier. The barrier is maintained by the glio-vascular connections which break up following injuries. Some immunohistochemical alterations may refer to the impairment of the gliovascular connections. Laminin and the components of the dystroglycan complex show characteristic immunohistochemical alterations following various experimental injuries (stab wound, cryogenic lesion, arterial occlusions): immunoreactivity of β-dystroglycan, α-dystrobrevin and aquaporin 4 disappeared while that of utrophin and laminin appeared along the vessels, whereas α-syntrophin visualized the reactive astrocytes but not the resting ones. The aims of the present study were to investigate whether these post-lesion alterations: (i) are reproducible with immersive fixation, which is used in postmortem histology; (ii) are resistant to a postmortem delay before fixation; and (iii) are to be attributed to a direct effect of the lesion, or are mediated by processes occurring only in the living brain. Three models were investigated: (i) following lesions, some brains were fixed by transcardial perfusion, others by immersion; (ii) following lesions, the animals were decapitated and stored at room temperature for 8 or 16 h before fixation; and (iii) the lesions were performed after decapitation. Cryogenic lesions were performed by applying a dry ice cooled copper rod to the brain surface of ketamine-xylazine anesthetized rats. The immunohistochemical reactions were performed on free-floating sections cut with vibratome. Both immunoperoxidase and immunofluorescence methods were used. The fixation method - perfusive or immersive - did not change the post-lesion phenomena investigated. The postmortem delay did not influence the β-dystroglycan immunoreactivity, that is its lack delineated the area of the lesion. However, in the case of the other substances, various lengths of postmortem delay rendered the immunohistochemistry uninterpretable. The results suggest β-dystroglycan immunostaining could be applied in the neuropathology to detect cerebrovascular impairments.

Correlation Between Extravasation and Alterations of Cerebrovascular Laminin and β-Dystroglycan Immunoreactivity Following Cryogenic Lesions in Rats

The blood-brain barrier becomes "leaky" following lesions. Former studies revealed that following lesions the immunoreactivity of cerebrovascular laminin becomes detectable whereas that of β-dystroglycan disappears. These alterations may be indicators of glio-vascular decoupling that may result in the impairment of the blood-brain-barrier. This study investigates correlation between the post-lesion extravasation and the above-mentioned immunohistochemical alterations. Following cryogenic lesions, the survival periods lasted 5, 10, 30 minutes, 1 or 12 hours, or 1 day. Some brains were fixed immediately post-lesion. Immunofluorescent reactions were performed in floating sections. The extravasation was detected with immunostaining for plasma fibronectin and rat immunoglobulins. When the survival period was 30 minutes or longer, the area of extravasation corresponded to the area of altered laminin and β-dystroglycan immunoreactivities. Following immediate fixation some laminin immunoreactivity was already detected. The extravasation seemed to precede this early appearance of laminin immunoreactivity. The β-dystroglycan immunoreactivity disappeared later. When the extravasation spread into the corpus callosum, vascular laminin immunoreactivity appeared but the β-dystroglycan immunoreactivity persisted. It seems that extravasation separates the glial and vascular basal laminae, which results in the appearance of laminin immunoreactivity. The disappearance of β-dystroglycan immunoreactivity is neither a condition nor an inevitable consequence of the 2 other phenomena.

Immunohistochemical detectability of cerebrovascular utrophin depends on the condition of basal lamina

Utrophin is an autosomal homologue of dystrophin. Dystrophin is a member of the dystrophin-glycoprotein complex, which is a cell surface receptor for basal lamina components. In recent opinions utrophin occurs in the cerebrovascular endothelium but not in the perivascular glia. Cerebrovascular laminin immunoreactivity can only be detected in the subpial segments of the vessels, in circumventricular organs lacking blood-brain barrier, in immature vessels and following brain lesions. In our former experience utrophin immunoreactivity showed similar phenomena to that of laminin. The present study investigates the parallel occurrence of vascular utrophin and laminin immunoreactivity in the brain tissue, especially in the circumventricular organs, and during the parallel postnatal regression of both utrophin and laminin immunoreactivity. Their cerebrovascular immunoreactivity observed in frozen sections renders plausible the role of hidden but explorable epitopes, instead of a real absence of laminin and utrophin. The laminin epitopes are supposed to be hidden due to the fusion of the glial (i.e. brain parenchymal) and vascular basal laminae (Krum et al., Exp. Neurol. 111 (1991) 151). In all cases including its post-lesion re-appearance published formerly by us, laminin immunoreactivity may be attributed to the separation of glial and vascular basal laminae. Utrophin is localized, however, intracellularly, therefore a more complex molecular mechanism is to be assumed and it remains to be investigated how structural changes of the basal lamina may indirectly affect the immunoreactivity of utrophin. The results indicate that immunoreactivity may be influenced not only by the presence or absence of macromolecules but also by their functional state.

Extracellular matrix alterations, accelerated leukocyte infiltration and enhanced axonal sprouting after spinal cord hemisection in tenascin-C-deficient mice

The extracellular matrix glycoprotein tenascin-C has been implicated in wound repair and axonal growth. Its role in mammalian spinal cord injury is largely unknown. In vitro it can be both neurite-outgrowth promoting and repellent. To assess its effects on glial reactions, extracellular matrix formation, and axonal regrowth/sprouting in vivo, 20 tenascin-C-deficient and 20 wild type control mice underwent lumbar spinal cord hemisection. One, three, seven and fourteen days post-surgery, cryostat sections of the spinal cord were examined by conventional histology and by immunohistochemistry using antibodies against F4/80 (microglia/macrophage), GFAP (astroglia), neurofilament, fibronectin, laminin and collagen type IV. Fibronectin immunoreactivity was significantly down-regulated in tenascin-C-deficient mice. Moreover, fourteen days after injury, immunodensity of neurofilament-positive fibers was two orders of magnitude higher along the incision edges of tenascin-C-deficient mice as compared to control mice. In addition, lymphocyte infiltration was seen two days earlier in tenascin-C-deficient mice than in control mice and neutrophil infiltration was increased seven days after injury. The increase in thin neurofilament positive fibers in tenascin-C-deficient mice indicates that lack of tenascin-C alters the inflammatory reaction and extracellular matrix composition in a way that penetration of axonal fibers into spinal cord scar tissue may be facilitated.

Using extracellular matrix for regenerative medicine in the spinal cord

Regeneration within the mammalian central nervous system (CNS) is limited, and traumatic injury often leads to permanent functional motor and sensory loss. The lack of regeneration following spinal cord injury (SCI) is mainly caused by the presence of glial scarring, cystic cavitation and a hostile environment to axonal growth at the lesion site. The more prominent experimental treatment strategies focus mainly on drug and cell therapies, however recent interest in biomaterial-based strategies are increasing in number and breadth. Outside the spinal cord, approaches that utilize the extracellular matrix (ECM) to promote tissue repair show tremendous potential for various application including vascular, skin, bone, cartilage, liver, lung, heart and peripheral nerve tissue engineering (TE). Experimentally, it is unknown if these approaches can be successfully translated to the CNS, either alone or in combination with synthetic biomaterial scaffolds. In this review we outline the first attempts to apply the potential of ECM-based biomaterials and combining cell-derived ECM with synthetic scaffolds.

Decorin promotes robust axon growth on inhibitory CSPGs and myelin via a direct effect on neurons

Inhibitory chondroitin sulfate proteoglycans (CSPGs) and myelin-associated molecules are major impediments to axon regeneration within the adult central nervous system (CNS). Decorin infusion can however suppress the levels of multiple inhibitory CSPGs and promote axon growth across spinal cord injuries [Davies, J.E., Tang, X., Denning, J.W., Archibald, S.J., and Davies, S.J., 2004. Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries. Eur. J. Neurosci. 19, 1226-1242]. A question remained as to whether decorin can also increase axon growth on inhibitory CSPGs and myelin via a direct effect on neurons. We have therefore conducted an in vitro analysis of neurite extension by decorin-treated adult dorsal root ganglion (DRG) neurons cultured on substrates of inhibitory CSPGs or myelin membranes mixed with laminin. Decorin treatment promoted 14.5 and 5-fold increases in average neurite length/neuron over untreated controls on CSPGs or myelin membranes respectively. In addition to suppressing inhibitory scar formation, our present data shows that decorin can directly boost the ability of neurons to extend axons within CSPG or myelin rich environments.

Comparative postnatal development of spinal, trigeminal and vagal sensory root entry zones

Somatic and visceral sensory information enters the central nervous system (CNS) via root entry zones where sensory axons span an environment consisting of Schwann cells in the peripheral nervous system (PNS) and astrocytes and oligodendrocytes in the CNS. While the embryonic extension of these sensory axons into the CNS has been well-characterized, little is known about the subsequent, largely postnatal development of the glial elements of the root entry zones. Here we sought to establish a comparative developmental timecourse of the glial elements in the postnatal (P0, P3, P7, P14) and adult rat of three root entry zones: the spinal nerve dorsal root entry zone, the trigeminal root entry zone, and the vagal dorsal root entry zone. We compared entry zone development based on the expression of antigens known to be expressed in astrocytes, oligodendrocytes, oligodendrocyte precursor cells, Schwann cells, radial glial fibres and the PNS extracellular matrix. These studies revealed an unexpected distribution among glial cells of several antigens. In particular, antibodies used to label mature oligodendrocytes (RIP) transiently labelled immature Schwann cell cytoplasm, and a radial glial antigen (recognized by the 3CB2 antibody) initially decreased, and then increased in postnatal astrocytes. While all three root entry zones had reached morphological and antigenic maturity by P14, the glial elements comprising the PNS-CNS interface of cranial root entry zones (the trigeminal root entry zone and the vagal dorsal root entry zone) matured earlier than those of the spinal nerve dorsal root entry zone.

Characterization of non-neuronal elements within fibronectin mats implanted into the damaged adult rat spinal cord

Previous studies have shown that mats made from fibronectin (FN) integrate well into spinal cord lesion sites and support extensive axonal growth. Using immunohistochemistry, we have investigated the non-neuronal factors that contribute to these properties. Extensive vascularization was observed in FN mats by 1 week along with heavy macrophage infiltration by 3 days post-implantation. By 1 week post-implantation, laminin tubules had formed and were associated with axons and p75 immunoreactive Schwann cells. By 4 weeks post-implantation, most axons were associated with Schwann cell derived myelin. Few oligodendrocytes were present within the mat, even with an increase in the number of oligodendrocyte precursors around the implant site by 7 days post-implantation. Astrocyte proliferation also occurred in the intact tissue, with a prominent glial scar forming around the implant within 4 weeks. However, by 2 months post-implantation astrocytes were present in the FN implant site and were intermingled with the axons. Axonal ingrowth and integration of the FN mats is probably due to the ability of FN mats to support and organize infiltration of Schwann cells and deposition of laminin. At later time points, myelinated axons remain in the implant site, even after other elements (e.g. macrophages and laminin) have disappeared. Both of these properties are likely to be important in the design of biomaterial bridges for CNS regeneration.

Disappearance of the post-lesional laminin immunopositivity of brain vessels is parallel with the formation of gliovascular junctions and common basal lamina. A double-labelling immunohistochemical study

Previous studies revealed that during development the laminin immunopositivity gradually disappeared from the brain vessels, but temporarily re-appeared in them around lesions. The question of the present study was the correlation between the post-lesional vascular immunopositivity to laminin and the glial reaction. Following stab wounds, double fluorescent immunohistochemical labelling was performed against laminin (using a polyclonal antiserum against laminin 1) and glial fibrillary acidic protein. A number of vessels exhibited intense immunopositivity to laminin within the lesioned tissue. Where these laminin immunopositive vessels entered the perilesional brain substance, the astroglia formed contacts on them, and the separate vascular and glial basal laminae fused. The disappearance of the post-lesional laminin immunopositivity seemed to coincide with these phenomena. When monoclonal antibodies were applied against the beta1 and gamma1 laminin chains, vessels proved to be immunopositive at the lesion, but none in the intact brain tissue. No immunoreactivity was detected in the cases of alpha2 and beta2 chains. The results suggest that the disappearance of laminin immunopositivity may be attributed to that the epitopes become inaccessible for antibodies owing to the formation of gliovascular junctions and common basal lamina between astroglia and vessel. The possible role of an alteration in the laminin composition and the effect of fixation are discussed.

Degradation of chondroitin sulfate proteoglycan enhances the neurite-promoting potential of spinal cord tissue

The contribution of chondroitin sulfate proteoglycan (CSPG) in the suppression of axonal growth in rat spinal cord has been examined by means of an in vitro bioassay in which regenerating neurons are grown on tissue section substrata. Dissociated embryonic chick dorsal root ganglionic neurons were grown on normal and injured adult spinal cord tissue sections treated with chondroitinases. Neuritic growth on normal spinal cord tissue was meager. However, both the percentage of neurons with neurites and the average neurite length were substantially greater on sections treated with chondroitinase ABC. Enzymes that specifically degraded dermatan sulfate or hyaluronan were ineffective. Neuritic growth was significantly greater on injured (compared to normal) spinal cord and a further dramatic increase resulted from chondroitinase ABC treatment. Neurites grew equally within white and gray matter regions after chondroitinase treatment. Observed increases in neurite outgrowth on chondroitinase-treated tissues were largely inhibited in the presence of function-blocking laminin antibodies. These findings indicate that inhibitory CSPG is widely distributed and predominant in both normal and injured spinal cord tissues. Additionally, inhibitory CSPG is implicated in negating the potential stimulatory effects of laminin that might otherwise support spinal cord regeneration.

Spatiotemporal patterns of expression of extracellular matrix molecules in the developing and adult rat olfactory system

Using immunocytochemical methods, we have examined extensively the spatial and temporal patterns of expression of three extracellular matrix molecules-laminin, fibronectin, and type IV collagen-in the embryonic, postnatal (days 2 and 11) and adult rat olfactory system. The study started at embryonic day 14 when olfactory fibres and their associated migrating cells course through the nasal mesenchyme. From embryonic day 14 to the adult, a sheet-like pattern of labelling for laminin, fibronectin and type IV collagen was observed along the basal surface of the olfactory epithelium and around the telencephalon. This type of labelling was continuous around the telencephalic vesicle, whereas it appeared disrupted in the basal lamina of the olfactory epithelium to permit exit of the olfactory axons and their associated migrating cells into the mesenchyme. From embryonic day 14 to day 20, punctate labelling for the three molecules studied was observed along the mesenchymal olfactory pathway, the ventral part of the olfactory bulb, the olfactory nerve layer and the presumptive glomerular layer, respectively. By embryonic day 17, the punctate labelling initially detected in the mesenchymal olfactory pathway was replaced by a sheet-like pattern related to the mature basal lamina surrounding the olfactory axon fascicles. Punctate labelling for laminin and type IV collagen persisted in the olfactory nerve layer and around the glomeruli through adult life whereas that of fibronectin declined and disappeared by postnatal day 2. The spatiotemporal distribution of the punctate pattern for laminin, fibronectin and type IV collagen observed in the embryonic olfactory system suggests a role in delineating the pathway for olfactory axon elongation. The continuous expression of laminin and type IV collagen in the adult olfactory bulb may be related to the regenerative activity and high plasticity of the olfactory system.

Distribution of the ten known laminin chains in the pathways and targets of developing sensory axons

Laminins are heterotrimers of alpha, beta, and gamma chains. At present, five alpha, three beta, and two gamma chains have been described. The best characterized laminin (laminin 1 = alpha 1, beta 1, gamma 1) promotes neurite outgrowth from virtually all classes of developing neurons, implying that laminins may serve as axon guidance molecules in vivo. Moreover, different laminin trimers exert distinct effects on subsets of laminin-1-responsive cells, suggesting that isoform diversity may underlie some axonal choices in vivo. As a first step toward evaluating these hypotheses, we have documented the expression patterns of all 10-known laminin chains in the peripheral nervous system and spinal cord of the murine embryo. The alpha 2, alpha 4, beta 1, and gamma 1 chains are expressed in peripheral axonal pathways by embryonic day (E) 11.5, when sensory and motor axonal outgrowth is underway. Thus, laminins (but not laminin 1) may promote peripheral axonal outgrowth. By E 13.5, laminin chains are differentially expressed in the limb-bud, with prominent expression of alpha 2 and alpha 4 in muscle and of alpha 3 and alpha 5 in skin. This pattern raises the possibility that laminin isoform diversity contributes to the ability of cutaneous and muscle sensory axons to distinguish their targets. Later in development, some chains (e.g., alpha 2, alpha 4, and beta 1) are downregulated in peripheral nerve while others (e.g., gamma 1), continue to be expressed by Schwann cells into adulthood. In contrast to peripheral nerves and ganglia, laminin chains are expressed at low levels, if at all, in the developing spinal cord gray matter.

Antibodies directed against the beta 1-integrin subunit and peptides containing the IKVAV sequence of laminin perturb neurite outgrowth of peripheral neurons on immature spinal cord substrata

Neuron-substratum interactions regulating axon growth in the developing central nervous system of the rat have been studied by means of an in vitro bioassay: the tissue section culture. We have previously shown that purified chicken sensory or sympathetic neurons grown on natural substrata consisting of cryostat sections of neonatal rat spinal cord elaborate numerous long neurites [Sagot et al. (1991) Brain Res. 543, 25-35]. Perturbation experiments, in which neuron-substratum interactions are modified by antibodies and peptides, have allowed us to analyse some of the molecular determinants which control neurite outgrowth in this system. Antibodies directed against the beta 1-integrin subunit, one of the neuronal receptors for extracellular matrix molecules, reduced the percentage of growing neurons by about 30% and the length of neurites by about 50%. In contrast, antibodies directed against laminin-1 or fibronectin, two extracellular matrix proteins transiently expressed in various areas of the developing central nervous system, were unable to block neurite outgrowth. Paradoxically, a peptide containing the IKVAV sequence, which mimics an active sequence of the laminin alpha 1 chain responsible for neurite extension, also blocked neurite outgrowth on neonatal spinal cord substrata. These results indicate that integrin receptors containing the beta 1 subunit may play a role in regulating axon growth in the developing nervous system. Among the putative extracellular matrix ligands for these receptors, laminin and fibronectin do not appear as prominent candidates in the neonatal spinal cord. However, our data also suggest that the developing central nervous system may contain neurite outgrowth-promoting proteins carrying the IKVAV sequence, different from laminin-1.

Relationship between injury-induced astrogliosis, laminin expression and axonal sprouting in the adult rat brain

Lesion-induced regenerative sprouting of CNS axons is accompanied by structural and metabolic changes of astrocytes. In order to evaluate the effects of these astrocytic changes on axonal regeneration, we investigated the spatio-temporal relationship of gliosis, laminin expression and axonal sprouting in the postcommissural fornix of the adult rat. Using immunocytochemical methods we observed (1) a perilesional area with a transient lack of astrocytes and axons, (2) the reappearance of reactive astrocytes followed by the ingrowth of sprouting fibres and finally an increase in laminin-immunoreactivity, (3) the absence of lesion-induced laminin-expression in reactive astrocytes and (4) the formation and long-lasting (at least 28 months) persistence of a dense plexus of laminin-immunopositive blood vessels at the site of transection and in the proximal and distal stumps. These data indicate that astrogliosis is permeable for regrowing axons and that injury-induced axonal sprouting in the transected postcommissural fornix may be mediated by laminin-independent mechanisms.

Growth and degeneration of axons on astrocyte surfaces: effects on extracellular matrix and on later axonal growth

Cultured astrocytes deposit an extracellular matrix which has been shown by immunocytochemistry to react with antibodies to tenascin, laminin, and fibronectin. Neuronal-glial interaction down-regulates these components of the matrix, causing a reduction in extracellular matrix localized to areas of contact with axons. Axons used for these experiments were from embryonic rat retinal explants. In some experiments explants were removed from the co-cultures and their axons allowed to degenerate. Degeneration of axons did not reverse the local reduction of extracellular matrix brought about by axon outgrowth. The period of axon outgrowth studied was 4-5 days; the period of degeneration was 2-3 days. Astrocytes alone, astrocytes with intact retinal explants, and astrocytes with 2-day degenerated retinal axons were tested for their ability to support neurite outgrowth from embryonic rat cortical neurons. Neurite outgrowth occurred on all astrocyte cultures. Cortical neurite lengths, measured 2 days after plating, were not significantly different between astrocytes alone and astrocytes with degenerated retinal axons. However, there was a tendency for neurites to be shorter on astrocytes with intact retinal axons present. Two conclusions may be drawn from these results. First, the state of differentiation of astrocytes, as marked by their assembly of extracellular matrix, is altered by contact with axons. Second, degeneration of axons alone, in the absence of other cell types, is not a sufficient signal to reestablish assembly of extracellular matrix. However, neither is it a sufficient signal to render astrocytes inhospitable to further axonal outgrowth or regeneration.

Microenvironmental changes during axonal regrowth in the optic nerve of the myelin deficient rat. Immunocytochemical and ultrastructural observations

Lesion-induced regenerative sprouting of CNS axons is accompanied by reactions of the supporting glia and vascular and connective tissue which may influence the extent of regeneration. In a previous report, it was shown that after crush injury, the amyelinated optic nerve of the myelin deficient (md) mutant rat contains greater numbers of regrowing axons proximal to the site of crush than that of normally myelinated littermates. The present study was designed to compare the response of the microenvironment, i.e. glial cells and vascular and connective tissue, in md and normally myelinated optic nerves 2, 4 and 6 days after crush injury. In unoperated normal optic nerves monoclonal antibodies to the HNK-1 carbohydrate labelled astrocytic processes at the ultrastructural level whereas in unoperated md mutants HNK-1 staining was restricted to axonal surfaces. Immunoreactivity with monoclonal antibodies to stage-specific embryonic antigen-1 (SSEA-1) was confined to astrocytic surfaces in both md and wildtype animals. After axotomy of md optic nerves regrowing axons were more numerous in the proximal site of the crush and extended further into the lesion than in wildtype animals. In both md and wildtype rats regrowing axons were HNK-1-positive. In md rats strong reaction with antibodies to laminin and fibronectin was only seen in 6-day-old lesions of md rats whereas immunoreactivity was less distinct in operated littermate controls. Immunolabelling was obviously associated with blood vessels, since crush lesions in both md and wildtype rats were Schwann cell-free as assessed by electron microscopy and immunocytochemistry. In both operated md and normal littermates crush lesions contained degenerating astrocytes as well as reactive astrocytes in which the intermediate filaments of the perikarya failed to stain immunocytochemically for GFAP, vimentin, desmin, and a common determinant of intermediate filaments. In contrast, reactive astrocytes in the lesion site of normally myelinated rats expressed the SSEA-1 antigen intracytoplasmically whereas in md mutants astrocytes were completely SSEA-1-negative. Infiltration of crush lesions by macrophages was less extensive in md rats than in normal littermates. However the overall content of macrophages in the peritoneal cavity was also reduced. The present study demonstrates that (1) md optic nerves lack HNK-1-reactive astrocytes; (2) in the axotomized wildtype optic nerve impaired axonal regrowth may be associated with distinct immuno-phenotypes of the supporting glial cells, i.e. SSEA-1-positive astrocytes; (3) laminin and fibronectin seem not to be essential for improved axonal regrowth in md rats.

Laminin immunohistochemistry in brain is dependent on method of tissue fixation

Normal adult and lesioned rat and mouse brains were fixed by formaldehyde perfusion by two methods that differ primarily in the length of the post-fixation period. Sections were subsequently immunostained using monoclonal and polyclonal antibodies to laminin. With relatively short post-fixation periods (up to 4 h), vascular basement membrane (BM)-laminin was immunostained, but intraneuronal laminin-like immunoreactivity was faint. With longer post-fixation periods (18-24 h), intraneuronal laminin-like immunoreactivity was distinct, while vascular BM-laminin immunoreactivity was reduced drastically. These findings are particularly relevant to studies examining laminin immunoreactive blood vessels in response to lesions, especially ischemic stroke. In fact, the present results suggest that the apparent neovascularization or up-regulation of vascular BM-laminin following CNS injury likely relates to differences in regional tissue fixation.

Distinct immunoreactivity to 110 kDa laminin-binding protein in adult and lesioned rat forebrain

A phosphorylated, approximately 110 kDa laminin-binding protein (110 kDa LBP) from mouse brain has been previously identified. This protein recognizes a neurite-outgrowth promoting 19-amino acid synthetic peptide (PA 22-2) derived from the laminin A chain. In the present study, an antibody against the 110 kDa LBP was used to localize immunoreactivity in the normal adult rat brain and also following a stab wound and ischemic lesion. Immunoreactive cells were found in layers II/III and V of the cerebral cortex and within apical dendrites of pyramidal neurons. Specific immunoreactivity was also found in the stratum lucidum in the CA3 region of the hippocampus which exhibited densely stained mossy fibers and terminals. Mechanical and ischemic lesions induced intense immunolabeling of reactive glial cells around the lesion site. The distinct and anatomically restricted localization of the immunostain in adult and lesioned rat brain suggests that 110 kDa LBP-like molecules might have an important function in forebrain structures and may be involved in the response to CNS injury.

Changes in permissivity for neuronal attachment and neurite outgrowth of spinal cord grey and white matters during development: a study with the 'cryoculture' bioassay

We have used the recently developed cryoculture bioassay (Carbonetto et al., J. Neurosci., 7 (1987) 610-620) to document changes during development of CNS tissular ability to support nerve fiber growth. Neuronal attachment and neurite outgrowth of purified neurons cultured on tissue sections of rat spinal cord at various stages of development were quantified. Nerve fiber growth permissivity increased during embryonic stages, reaching as postnatal days 2-4 (P2-P4) a maximum value, higher than that found on adult PNS tissue sections. This permissivity diminished rapidly thereafter, indicating that early postnatally, the nerve fiber growth supporting ability of the CNS environment shifts abruptly from an increasingly permissive mode to an increasingly non-permissive status. Furthermore, after P4, neurite outgrowth permissivity diminished in parallel on white and grey matters, whereas neuronal attachment declined much more drastically on white matter than on grey matter. This indicates that the progressive loss of spinal cord ability to support nerve fiber growth is attributable to both grey and white matters. In several instances it also appeared that neuronal adhesion was not necessarily followed by a comparable level of nerve fiber growth, suggesting that these two processes could be regulated by different factors.

Retinal neurite growth on astrocytes is not modified by extracellular matrix, anti-L1 antibody, or oligodendrocytes

Two factors that may influence the course of axonal regeneration in the central nervous system (CNS) are extracellular matrix (ECM) and cell surface molecules that may enhance or inhibit neurite outgrowth. Whereas cultured astrocytes have been reported to be a good substratum for neurite outgrowth, there is recent evidence that cultured oligodendrocytes are inhibitory. To test the influences of 1) ECM components, 2) the L1 adhesion molecule, and 3) the inhibitory potential of mature oligodendrocytes in the astrocytic environment, we have utilized a culture system in which neurites from embryonic rat retina grow vigorously on astrocyte monolayers. The major ECM components were assembled in neonatal rat cortical astrocyte-retina co-cultures only when the medium contained serum. In electron microscopic studies of serum containing cultures, retinal neurites were seen to be related to astrocyte surfaces but rarely were found in contact with ECM; in serum-free medium the association between neurites and astrocytes was similar. In addition, the growth of neurites was vigorous whether ECM was present or absent. Presence of antibodies against the cell surface adhesion molecule L1 did not inhibit retinal neurite elongation on glial fibrillary acidic protein-positive astrocytes. When oligodendrocytes from adult rat spinal cord were combined with the astrocytes, retinal neurites grew as well on the mixed glial population as on astrocytes alone. Immunostaining for galactocerebroside showed many oligodendrocyte processes to be aligned in the direction of neurite growth, suggesting association between the two cell types. This association was verified by electron microscopy. Furthermore, retinal explants extended neurites among myelin basic protein-positive oligodendrocytes cultured without astrocytes. Thus, the astrocyte surface is a strong promoter of neurite growth from embryonic rat retina. This growth did not depend upon either ECM or the L1 adhesion molecule. Because neurites grew on astrocytes in the presence of mature oligodendrocytes or among oligodendrocytes alone, we conclude that oligodendrocytes do not inhibit neurite growth under certain conditions.

Development of the rat corticospinal tract through an altered glial environment

The major corticospinal tract (CST) in the rat is located at the base of the dorsal funiculus. It is a late-developing tract, and the growth of its axons into the lumbosacral region of the spinal cord does not occur until postnatal days 5 and 6. This delay is taken advantage of in this study in order to evaluate the effects of a markedly reduced glial population on ingrowth of the CST axons into the lumbosacral spinal cord. A reduction of the glial population is achieved by exposure of this region of spinal cord to X-radiation at 3 days of age. Growth of CST axons into and through the lumbosacral spinal cord in rats in which this region has undergone a radiation-induced depletion of glial cells is compared with that in their non-irradiated littermate controls by axonal tracing techniques using horseradish peroxidase (HRP). The HRP was applied directly to the motor cortices of normal and irradiated rats, and at all ages studied, there was anterograde filling of CST axons and their growth cones. At 3 days postnatally, the age when the lumbosacral spinal cord was irradiated in the experimental animals, CST axons were present in the more rostral thoracic levels. CST axons were observed in the lumbar region of non-irradiated rats on day 5, and by day 7 they were present at sacral levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraneuronal laminin-like immunoreactivity in the human central nervous system

Because laminin possesses potent neurotrophic activity, laminin-like immunoreactivity was investigated in formalin-fixed human brains, using affinity-purified anti-human placental laminin rabbit serum. Distinct laminin-like immunoreactivity was observed in neuronal soma of certain nuclear groups, and a 180-kDa band was noted in an immunoblot study of the supernatant of brain homogenate. These observations imply that many but not all central neurons have laminin-like immunoreactive molecules. Their functional role, however, remains to be clarified.

Changes in glial cell markers in recent and old demyelinated lesions in central pontine myelinolysis

An immunohistochemical study was performed to compare glial reactions in recent and old lesions of central pontine myelinolysis (CPM). Regions of demyelination and destruction of oligodendrocytes, showed reduced immunoreactivity of myelin basic protein (MBP), myelin-associated glycoprotein (MAG), transferrin, and carbonic anhydrase C (CA C). In addition, labeling of glial fibrillary acidic protein (GFAP) and S-100 protein revealed distinct dystrophic alterations of the astroglia. Remarkably, immunolabeling of GFAP was drastically reduced in astrocytic cytoplasm within freshly demyelinated lesions. Immunostaining of vimentin revealed a differential intracytoplasmic decoration of hypertrophic and dystrophic astrocytes in recent and old CPM lesions. Immunolabeling of desmin failed to stain glial cells. Monoclonal antibodies against HNK-1 exhibited greatly increased immunoreactivity both of persisting oligodendrocytes and of reactive fibrillary astrocytes in old CPM foci. In freshly demyelinated lesions, enhanced immunoreactivity of the X-hapten (3-fucosyl-N-acetyllactosamine) was prominent in astroglia and oligodendrocytes. Simultaneously, reactive astrocytes revealed intracytoplasmic labeling of laminin. Quantitation of GFAP+ astroglia in fresh CPM and control cases revealed an increase in the number of astrocytes within the demyelinated foci and in the surrounding non-demyelinated pontine tissue of CPM cases. The occurrence of astroglial alterations in the demyelinated foci of CPM could be interpreted as "astroglial dystrophy" which may represent a pathogenic factor in CPM. Furthermore, it is possible that changes of the glial microenvironment may influence the astroglia to revert transiently back to an immature phenotype as indicated by the enhanced expression of the X-hapten and HNK-1, and the de novo synthesis of vimentin and laminin.

Axotomy enhances the outgrowth of neurites from embryonic rat septal-basal forebrain neurons on a laminin substratum

Previous studies have suggested that embryonic (nonaxotomized) and regenerating central nervous system neurons differentially respond to the same substrata. In the present study, we have used an in vitro model to test the ability of laminin and type I collagen to promote the outgrowth of neurites from nonaxotomized and axotomized, embryonic septal-basal forebrain (SBF) neurons. Neurons within explants derived from Embryonic Day (E) 15 rats extended neurites that demonstrated similar growth characteristics on a collagen or laminin substratum. E15 neurons could be induced to extend longer neurites on laminin if they were axotomized in vitro and subsequently replated onto a laminin substratum. The carbocyanine dye DiI indicated that neurons which were axotomized could survive and regenerate processes. These regenerating neurites grew 27% longer on laminin than they did on collagen. Similarly, neurons that were axotomized in situ, i.e., E18 SBF neurons, extended neurites that were 29% longer on a laminin substratum. In contrast, E15 explants that were maintained in suspension culture prior to being plated onto a substratum exhibited similar growth on laminin or collagen. The increase in regeneration by E15 neurons on laminin was augmented, by 22%, if nerve growth factor was supplemented to the culture medium. These results demonstrate that laminin is a better substratum, as compared to collagen, for the elongation of neurites from axotomized SBF neurons. Nonaxotomized neurites, on the other hand, do not appear to prefer one substratum over the other. Furthermore, regeneration from embryonic, SBF neurons on laminin is augmented if NGF is used simultaneously.

Astroglial cell alteration caused by neurotoxins: immunohistochemical observations with antibodies to glial fibrillary acidic protein, laminin, and tyrosine hydroxylase

Kainic acid or 6-hydroxydopamine (6-OHDA) was injected into rat striatum, and their effects on astrocytes, laminin, and catecholamine fibers were examined temporally by immunohistochemical methods in an attempt to understand the roles of reactive astrocytes and laminin on the restoration of central nervous tissue. Kainic acid injection caused a severe neuronal degeneration in the striatum but catecholamine fibers were spared with only transient loss of tyrosine hydroxylase immunoreactivity. Reactive astrocytes appeared around the lesioned area soon after the kainic acid injection, then migrated into that area, and finally covered the lesioned striatum. Laminin immunoreactivity was found only in the lesioned area before the migration of reactive astrocytes and disappeared when the area was covered by astrocytes. 6-OHDA injection, on the other hand, resulted in a severe degeneration of catecholamine fibers, but striatal neurons were mostly spared. From 7 to 28 days after injection, regenerating fibers were found to enter the affected region. In this period reactive astrocytes were seen in the affected region but were only slightly more numerous than those found in control (saline injected) striatum. Laminin-immunoreactive blood vessels seemed to show a distribution similar to that in control striatum. These observations indicate that reactive astrocytes may play an important role in areas of neuronal cell loss and that laminin may aid their migration into such areas. Laminin and reactive astrocytes may not, however, be essential for the regeneration of dopamine fibers.

Transient expression of laminin immunoreactivity in the developing rat hippocampus

We have isolated and characterized a polyclonal antibody that recognizes the extracellular matrix glycoprotein laminin. In the developing rat hippocampus, in addition to staining the basal laminae of blood vessels and the glia limitans, this antibody detects a punctate deposit of non-basal lamina laminin that appears transiently, disappearing on E18. The punctate laminin is distributed throughout the hippocampus from the border of the ependyma and the neuropil to the pial surface, but is particularly concentrated in the presumptive molecular layer (marginal zone). Electron microscopy showed that the punctate laminin was in the extracellular space on the surfaces of cell bodies and, more commonly, their processes. In double-labelling experiments in which neurites were labelled with tau or MAP2 antibodies, there were occasional cases where neurites came into direct contact with punctate laminin. These observations suggest a role for laminin in hippocampal development and possibly in neurite outgrowth.