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

The identification of proteoglycan, collagen and neuron in precursor cells from human fetal spinal cord

After spinal cord injury (SCI), a loss of myelinating oligodendrocytes and neurons occurs. The functional recovery of injured spinal cords is the principal objective of SCI repair. Cell transplantation may prove beneficial to help replace lost myelin and spinal cord circuitry. In this study, we demonstrated that neural precursor cells (hNPCs) from human fetal spinal cord express three types of proteoglycan proteins-chondroitin sulfate, keratan sulfate, and cartilage proteoglycan (an extracellular matrix detected in normal spinal cord), and non-proteoglycan matrix collagen. Both proteoglycan and collagen evidenced profound immunoreactivity in double-stained cell clusters. In addition, whether or not hNPCs were capable of differentiating into a variety of cells, including GABAergic and cholinergic neurons, were assessed. The differentiated cells of eight passages grown on a monolayer expressed the human nuclear protein (HNu), the progenitor marker nestin, GAD, ChAT, TJU, and MAP-2. These results indicate that hNPCs may prove to be candidate cells for therapeutic SCI strategies.

Polysialic acid limits septal neurite outgrowth on laminin

Polysialic acid (PSA) is a large carbohydrate found exclusively on the neural cell adhesion molecule (NCAM). In the adult brain, PSA is re-expressed by septal axons sprouting and regenerating in an environment rich in laminin. Using an in vitro model, we tested the possibility that PSA limits septal outgrowth by preventing maximal interactions with a laminin substrate. Our results indicate that PSA removal from primary septal neurons plated on laminin significantly increased neurite outgrowth at 12 h (14%, p<0.05) and 24 h (22%, p<0.01). In contrast, the removal of PSA had no impact on septal neurite outgrowth on poly-D-lysine. PSA did not influence the plating adhesion of septal neurons on laminin or poly-D-lysine, indicating that the increase in neurite outgrowth caused by PSA removal on laminin is not related to the initial attachment of the neurons to this substrate. Neurite length on laminin was significantly reduced by the function-blocking beta1-integrin antibody in the presence of PSA (20% decrease, p<0.05), and following PSA removal (34% decrease compared to neurites treated with endoN and without the beta1-integrin antibody, p<0.01). Importantly, the beta1-integrin antibody completely abolished the neurite outgrowth promoting effect of PSA removal on laminin. The beta1-integrin antibody had no impact on septal neurite length on poly-D-lysine. Taken together, these results indicate that the removal of PSA from septal neurons increases neurite outgrowth on laminin by promoting interactions between beta1-integrin and laminin.

Spontaneous and augmented growth of axons in the primate spinal cord: effects of local injury and nerve growth factor-secreting cell grafts

Little is known about molecular and cellular responses to spinal cord injury in primates. In this study, the normal milieu of the primate spinal cord was disturbed by multiple needle penetrations and cell injections in the mid-thoracic spinal cord; subsequent effects on local axons and expression of extracellular matrix (ECM) molecules were examined, together with effects of cellular delivery of nerve growth factor (NGF) to the injured region. Four adult rhesus monkeys each received injections of two grafts of autologous fibroblasts genetically modified to secrete human NGF, and, in control injection sites, two separate grafts of autologous fibroblasts transduced to express the reporter gene, beta-galactosidase. Three months later, Schwann cells extensively infiltrated the region of localized injury and penetrated both NGF and control fibroblast grafts. Marked upregulation of several ECM molecules occurred, including chondroitin and heparan sulfate proteoglycans and type IV collagen, in or adjacent to all injection sites. Schwann cells were an apparent source of some ECM expression. Spinal cord sensory axons and putative coerulospinal axons extended into both graft types, but they penetrated NGF grafts to a significantly greater extent. Many of these axons expressed the cell adhesion molecule L1. Thus, extensive cellular and molecular changes occur at sites of localized primate spinal cord injury and grafting, attributable in part to migrating Schwann cells, and are accompanied by spontaneous axonal plasticity. These molecular and cellular events closely resemble those observed in the rodent spinal cord after injury. Furthermore, as in rodent studies, cellular delivery of a trophic factor significantly augments axonal plasticity in the primate spinal cord.

Death of rat sympathetic ganglion cells in vitro caused by neurite transection: effect of extracellular calcium

Calcium entry into neurons secondary to excitotoxic insults is believed to cause neuronal death after trauma and ischemia, but the role of calcium influx in neuronal death after neurite transection independent of excitotoxicity has not been clearly defined. This study assesses the effect of variations in extracellular calcium concentration ([Ca2+]e) from 50 nM to 5 mM on cell death, in 14-day-old cultures of dissociated sympathetic neurons from the superior cervical ganglia of newborn rats. The neurites were transected with a custom-made injury device, and cell death was assessed with propidium iodide and fluorescence microscopy. We found that neurite transection caused a significant increase (p < 0.05) in cell death at all [Ca2+]e studies, but there was no significant difference in mortality at the various [Ca2+]e. Cell death significantly increased between 2 and 24 h postinjury at all three [Ca2+]e. Cell death increased with decreasing distance between the cell body and the transection site, and there was a significant decrease in mortality at distances greater than 0.66 mm, irrespective of the [Ca2+]e. These results suggest that influx of extracellular calcium is not responsible for posttransection cell death, suggesting that calcium release from internal stores or calcium-independent cell death mechanisms are triggered by neurite transection.

Cellular delivery of neurotrophin-3 promotes corticospinal axonal growth and partial functional recovery after spinal cord injury

The injured adult mammalian spinal cord shows little spontaneous recovery after injury. In the present study, the contribution of projections in the dorsal half of the spinal cord to functional loss after adult spinal cord injury was examined, together with the effects of transgenic cellular delivery of neurotrophin-3 (NT-3) on morphological and functional disturbances. Adult rats underwent bilateral dorsal column spinal cord lesions that remove the dorsal corticospinal projections or underwent more extensive resections of the entire dorsal spinal cord bilaterally that remove corticospinal, rubrospinal, and cerulospinal projections. Long-lasting functional deficits were observed on a motor grid task requiring detailed integration of sensorimotor skills, but only in animals with dorsal hemisection lesions as opposed to dorsal column lesions. Syngenic primary rat fibroblasts genetically modified to produce NT-3 were then grafted to acute spinal cord dorsal hemisection lesion cavities. Up to 3 months later, significant partial functional recovery occurred in NT-3-grafted animals together with a significant increase in corticospinal axon growth at and distal to the injury site. These findings indicate that (1) several spinal pathways contribute to loss of motor function after spinal cord injury, (2) NT-3 is a neurotrophic factor for the injured corticospinal projection, and (3) functional deficits are partially ameliorated by local cellular delivery of NT-3. Lesions of the corticospinal projection may be necessary, but insufficient in isolation, to cause sensorimotor dysfunction after spinal cord injury in the rat.

Trophic-factor modulation of cortical acetylcholinesterase reappearance following transection of the medial cholinergic pathway in the adult rat

Laminar patterns of cortical acetylcholinesterase (AChE) activity are reestablished in the adult, pharmacologically unmanipulated rat following axotomy of the medial cholinergic pathway. The extent to which trophic and/or growth promoting or inhibiting agents modulate AChE fiber reappearance is not fully understood. Such studies, however, would further clarify possible roles for these agents in neuronal plasticity in response to injury, as well as in plastic processes associated with normative functions. In the present experiments, we explored trophic modulation by intracortically infusing nerve growth factor (NGF) or somatostatin into cingulate cortex at a site distal to transection of the medial cholinergic pathway. Comparisons were made with sham-operated or noninfused transected controls, as well as with transected animals infused with renin or antibodies against NGF. Administration began 2 days after axotomy and continued at successive 3-day intervals for 4 weeks. It was found that, proximal to the lesion site, NGF increased and somatostatin decreased optical density of AChE; the number of AChE-containing fibers was unaltered compared to controls. Distal to the knife cut, both NGF and somatostatin increased number of AChE fibers but did not alter overall AChE optical density. Nonetheless, NGF produced an increase in the number of intensely staining puncta both proximal and distal to the cut. Neither renin nor anti-NGF antibodies produced statistically significant effects on optical density or number of fibers at any cortical locus studied. We conclude that NGF and somatostatin have opposite effects on the expression of AChE: whereas NGF increases AChE levels, somatostatin inhibits AChE accumulation in proximal fibers, perhaps by actions on synthesis or transport. Fiber proliferation, which only occurred distally, was affected positively by both NGF and somatostatin, indicating that neurite-promoting effects produced by both agents are confined to tissue regions where neurite extension is stimulated by axotomy. Increases in AChE-positive puncta produced by NGF, however, were not confined to regions of fiber proliferation.

Alpha 1 beta 1 integrin on neural crest cells recognizes some laminin substrata in a Ca(2+)-independent manner

Neural crest cells migrate along pathways containing laminin and other extracellular matrix molecules. In the present study, we functionally and biochemically identify an alpha 1 beta 1 integrin heterodimer which bears the HNK-1 epitope on neural crest cells. Using a quantitative cell adhesion assay, we find that this heterodimer mediates attachment to laminin substrata prepared in the presence of Ca2+. Interestingly, neural crest cells bind to laminin-Ca2+ substrata in the presence or absence of divalent cations in the cell attachment medium. In contrast, the attachment of neural crest cells to laminin substrata prepared in the presence of EDTA, heparin, Mg2+, or Mn2+ requires divalent cations. Interactions with these laminin substrata are mediated by a different integrin heterodimer, since antibodies against beta 1 but not alpha 1 integrins inhibit neural crest cell attachment. Thus, the type of laminin substratum appears to dictate the choice of laminin receptor used by neural crest cells. The laminin conformation is determined by the ratio of laminin to Ca2+, though incorporation of heparin during substratum polymerization alters the conformation even in the presence of Ca2+. Once polymerized, the substratum appears stable, not being altered by soaking in either EDTA or divalent cations. Our findings demonstrate: (a) that the alpha 1 beta 1 integrin can bind to some forms of laminin in the absence of soluble divalent cations; (b) that substratum preparation conditions alter the conformation of laminin such that plating laminin in the presence of Ca2+ and/or heparin modulates its configuration; and (c) that neural crest cells utilize different integrins to recognize different laminin conformations.

Pure Schwann cell suspension grafts promote regeneration of the lesioned septo-hippocampal cholinergic pathway

Regeneration of central nervous system (CNS) axons has been studied in the cholinergic septo-hippocampal system using various 'bridges' able to support fiber growth. In this study, a pure Schwann cell (Sc) suspension labeled with bisbenzimide (Hoechst 33342) was grafted in the lesioned septo-hippocampal pathway. At 2 weeks post-grafting, acetyl-cholinesterase (AChE)-positive fibers invaded the graft and grew in association with the Hoechst-labeled Sc, some of which expressed the low-affinity nerve growth factor receptor (NGF-R). At 2 months and 4 months post-grafting, the dorsal hippocampus was reinnervated with an apparently normal innervation pattern. Analysis of fiber growth in the hippocampus at four months post-grafting revealed a significant increase of reinnervation in the grafted animals (2 mm) compared to the non-grafted ones. No difference was observed in the number of cholinergic septal neurons expressing the NGF-R. These results demonstrate that a Sc suspension grafted into the lesioned septo-hippocampal system, integrates well into the host tissue, and supports axonal CNS outgrowth, implying that Sc by themselves provide an adequate environment for regeneration to occur.

Reactive astrocytes are substrates for the growth of adult CNS axons in the presence of elevated levels of nerve growth factor

To assess the necessary parameters for the growth of axons within the adult rat CNS, we have used intracerebral grafts of primary fibroblasts genetically engineered to express nerve growth factor (NGF). Following the implantation of NGF-producing primary fibroblasts within the striatum, cholinergic axons arising from the nucleus basalis grow toward and penetrate these grafts between 1 and 8 weeks. Grafts of noninfected control cells do not elicit axon sprouting at any time. Unmyelinated axons grow into grafts of NGF-producing cells only on reactive astrocytic processes, which contribute to a surrounding glial border. From our data concerning axon growth within the adult rat CNS, we conclude that reactive astrocytes can act as conducive substrates for growing axons; and only in the presence of elevated levels of NGF will permissive substrates (e.g., astrocytes) support axon growth by NGF-sensitive neurons.

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.