Neurite-promoting factors from embryonic neurons

Biocompatibility of layer-by-layer self-assembled nanofilm on silicone rubber for neurons

Electrostatic layer-by-layer (LbL) self-assembly, a novel method for ultrathin film coating has been applied to silicone rubber to encourage nerve cell adhesion. The surfaces studied consisted of precursor layers, with alternating cationic poly(ethyleneimine) (PEI) and anionic sodium poly(styrenesulfonate) (PSS) followed by alternating laminin and poly-D-lysine (PDL) layers or fibronectin and PDL layers. Film growth increased linearly with the number of layers. Every fibronectin/PDL and laminin/PDL bilayer was 4.4 and 3.5 nm thick, respectively. All layers were more hydrophilic than the unmodified silicone rubber surface, as determined from contact angle measurements. Of the coatings studied, a PDL layer was the most hydrophilic. A multilayer film with composition [PSS/PEI]3+[fibronectin/PDL]4 or [PSS/PEI]3+[laminin/PDL]4 was highly favorable for neuron adhesion, in contrast to bare silicone rubber substrate. The film coated on silicone rubber is biocompatible for cerebellar neurons with active viability, as shown by lactate dehydrogenase (LDH) assay and fluorescence cellular metabolism observations. These results demonstrate that LbL self-assembly provides an effective approach to apply films with nanometer thickness to silicone rubber. Such only few nanometer thick films are biocompatible with neurons, and may be used to coat devises for long-term implant in the central nervous system.

The disposition of early-generated neurons in the rat embryo predicts the pattern of major axonal tracts

During embryogenesis, the fiber tracts grow in a highly stereotyped pattern. A very small number of predetermined paths, preceding the growth of fasciculi, are present in the young neural tube (10-12, 15). What is the origin of these substrate pathways defined by Katz et al. (16) as "... a set of similar guidance cues which are aligned in a continuous discrete pathway..."? Could the first neurons play a role in the guidance of early nerve fibers? Observations in the brain stem revealed the presence of two longitudinal columns of early-generated neurons. These longitudinal columns were associated with well-differentiated marginal zones, characterized by cell-free spaces and representing the prospective site of the medial longitudinal (mlf) and lateral longitudinal (llt) tracts. Nerve fibers were also traced in the brain stem of young embryos. Axons were seen to travel in the early mlf and llt, in close proximity to the regions of early-generated neuronal columns. The data suggest that the precocious neurons that are organized in a definite pattern could somehow be involved in the guidance of some longitudinal axonal tracts, either by directly promoting the formation of an adequate terrain in the marginal layer, or by inducing other cells to do so.

Developmental changes in beta-citryl-L-glutamate concentration and its synthetic and hydrolytic activities in neuronal cells cultured from chick embryo optic lobes

Developmental changes in the concentration of beta-citryl-L-glutamate(beta-CG) have been examined in the cerebrum and optic lobe of the developing chick brain and in primary cultured neuronal cells from the chick embryo optic lobes with gas chromatographic and HPLC methods originated in our studies. A sharp peak was shown by beta-CG, with a maximal concentration at 13 days of incubation in the optic lobe of the developing chick brain but decreasing markedly to adult levels. The developmental change in primary cultured neurons was similar to that in the optic lobe of the developing chick brain. Changes in synthetic and hydrolytic activities of beta-CG were studied during growth of primary cultured neurons. Incorporation of radioactivities from radiolabeled pyruvate and alanine into beta-CG increased significantly on day 3 of culture, reaching a plateau on day 6, whereas that from radioactive glutamine and glutamate increased gradually from day 3 to day 12 of culture. The hydrolyzing enzyme activity of beta-CG during neuron growth was low until day 3 of culture, when it increased significantly until day 12. Similar developmental changes were observed in the developing chick embryo optic lobes.

Correlation between morphological and biochemical effects of ethanol on neuroblast-enriched cultures derived from three-day-old chick embryos

We have shown that ethanol exposure during embryogenesis affects a variety of parameters of neuronal growth. In this study we examined the direct effects of ethanol exposure on developing neuroblasts in culture. Neuroblast-enriched cultures derived from 3-day-old whole chick embryos were grown in the presence of ethanol at doses ranging from 12.5 to 50 mM from culture day 3-14. Cholinergic and GABAergic phenotypic expression were both significantly reduced following ethanol exposure as assessed by the activities of choline acetyltransferase and glutamate decarboxylase, respectively. Morphometric analysis of the growth patterns showed significant differences between control and ethanol-treated cultures. Control cultures exhibited the characteristic pattern of growth consisting of neuronal aggregation with neuritic arborization, i.e., neuritic bundles and fasciculation. Cultures grown in ethanol from culture day 3 consisted of aggregates that measured significantly greater in size than those observed in control cultures. In addition, in ethanol-treated cultures, the primary pattern of neuritic bundles was replaced by a complex network of individual neurites radiating from the central aggregate, forming a defined "neuritic field." Morphometric analysis revealed that both neurite number and neurite length were significantly reduced in ethanol-treated cultures. The biochemical data confirm earlier reports from this laboratory suggesting that ethanol exposure during early embryogenesis alters the normal neuronal pattern of phenotypic expression. In addition, we have presented evidence in this study that ethanol alters the morphological growth patterns of developing neurons. Although ethanol does not alter the ability of these cells to aggregate, there is a significant alteration in neuritic outgrowth.(ABSTRACT TRUNCATED AT 250 WORDS)

Domains of neuronal heparan sulphate proteoglycans involved in neurite growth on laminin

A single neuronal cell assay of neurite growth was utilized to determine types and domains of neuronal proteoglycans involved in neurite growth on laminin. Perturbations of biosynthesis and processing, enzymatic digestion with specific lyases, and competition with glycosaminoglycan side chains produced complementary data consistent with a molecular model implicating glycosaminoglycan (GAG) residues of heparan sulphate proteoglycans (HSPGs) in neurite growth. The observations suggest that HSPGs promote neurite growth on laminin by bridging between binding domains for HSPGs on laminin and on the neuronal cell surface, and that the bridge is tethered at both ends by non-covalent interactions between the binding domains and GAG side chains. Sulphation of the GAGs of HSPGs appears to be critical to the tethering and/or neurite growth-promoting activity of neuronal HSPGs.

Functional interactions of neuronal heparan sulphate proteoglycans with laminin

Quantitative biosynthetic studies using cellular extracts and neuron conditioned medium demonstrated that heparan sulphate proteoglycans (HSPGs) comprised 20-25% of the sulphated proteoglycans produced by neurons while the remainder consisted of chondroitin sulphate proteoglycans (CSPGs). When chromatographic fractions containing guanidine extracted and partially purified proteoglycans from culture medium conditioned by neurons (NCM) were used to pretreat a laminin substrate, neurite formation by sensory neurons was enhanced. Enhanced neurite promoting activity was not apparent if, during the pretreatment of the laminin substrate with NCM, heparan sulphate glycosaminoglycans (HS) were present. To determine the molecular basis of cell surface HSPG interactions with immobilized laminin, adhesion and neurite growth by dissociated sensory neurons were quantified at 4 h in vitro--a time at which there was no apparent contribution of released proteoglycans to neurite growth. Whereas adhesion was not influenced, neurite growth was partially inhibited in a dose-dependent manner if the sensory neurons were coincubated with HS, and if the cells were pretreated, prior to seeding, with heparitinase. The inhibitory effect produced by coincubation with saturating concentrations of HS was no longer apparent if the cells had been pretreated with heparitinase. These findings distinguish quantitatively between neurite growth on laminin and on laminin-HSPG complexes, and suggest that some neuronal cell surface and released HSPGs are involved in neurite growth by virtue of non-covalent interactions with glycosaminoglycan binding domains of laminin.

Marked neurotrophic effects of diffusible substances released from non-target cerebellar cells on thalamic neurons in culture

A primary culture of thalamic cells from 6-day-old postnatal rats was co-cultured for 6 days with neocortical or cerebellar cells (neurons and astrocytes) from the same litter using a Transwell mesh system. The survival of thalamic neurons grown on the lower well, which were affected by substances released from cells grown on the upper wells, was remarkably promoted by both neocortical co-cultures (target for thalamic projection neurons) and cerebellar co-cultures (non-target). When the cells were seeded on mesh at lower density, the neurotrophic effects of neocortical co-cultures on thalamic neurons (204% of control) were significantly greater than those of cerebellar co-cultures (138%). When the cells were seeded on mesh at higher density, the effects of cerebellar co-cultures increased dramatically (517% of control), while the neurotrophic effects of neocortical co-cultures did not change. Morphologically, the survival of multipolar-shaped thalamic neurons was remarkably improved, as compared to the survival of monopolar, bipolar, and tripolar-shaped thalamic neurons. Basic fibroblast growth factor slightly promoted thalamic neuronal survival (136%), whereas nerve growth factor had no effect. These results suggest that neocortical and cerebellar cells release diffusible factor(s) that promote the survival of specific subpopulation of thalamic neurons, and that at least one of the non-target cerebellar cell-derived factor(s) might be more potent than those released from target neocortical cells.

Target cell stimulation and inhibition of norepinephrine uptake in dissociated rat locus coeruleus cultures

Primary cultures from dissociated locus coeruleus (LC) neurons of 14-day-old (E14) fetal rats were grown in vitro in serum complemented medium. Noradrenergic cells were identified using immunocytochemical staining for tyrosine hydroxylase (TH) antibody. Maturation of noradrenergic neurons was assessed by measuring the high-affinity uptake of [3H]norepinephrine (NE). The presence of hippocampal cells stimulated the specific uptake of [3H]NE by LC cells only when plated at low density. Increasing the concentration of hippocampal cells resulted in a 50% decrease in NE uptake by LC cells. A similar inhibitory effect was observed with striatal cells. The inhibition exerted by striatal cells appears to be developmentally regulated, with E18 exerting a stronger inhibitory effect than E15 striatum. The decrease in [3H]NE uptake in hippocampal-LC cocultures was due to a decrease in uptake by individual noradrenergic neurons. For a given plating density, the decrease in uptake of [3H]NE per noradrenergic cell in LC culture was only half the decrease in the cocultures, suggesting a target-associated effect rather than density-derived toxic effect. In culture conditions which favored neuronal but not glial survival, the stimulatory target effect was evident, and the inhibitory effect was absent. Medium conditioned by target glial cells had a marked stimulatory effect on [3H]NE uptake. Glial feader-layer had a strong inhibitory effect on [3H]NE uptake in serum-containing medium. We suggest that both neurons and glia mediate the target-stimulatory effect, whereas the inhibitory effect is mediated by direct contact between target glia and LC neurons.

Molecular basis of growth cone adhesion: anchoring of adheron-containing filaments at adhesive loci

Adhesive contacts made by filopodia of neuronal growth cones are essential for proper neurite elongation and may have a role in the formation of synaptic junctions. Previously we described the appearance of filamentous materials extending from growth cone surfaces that seem to be associated with the strongly adhesive behavior of filopodia (Tsui, H.-C., K. L. Lankford, and W. L. Klein. 1985. Proc. Natl. Acad. Sci. USA. 82:8256-8260). Here, we have used immunogold labeling to determine whether known adhesive molecules might be localized at points of adhesion and possibly be constituents of the filamentous material. Antibodies to an adhesive molecule (neural cell adhesion molecule [N-CAM]) and to an adhesive macromolecular complex of proteins and proteoglycans (adheron) were localized at the EM level in whole mounts of cultured avian retina cells. Labeling of fixed cells showed that N-CAM and adheron molecules were both present on growth cones and on filopodia. However, filamentous materials extending from the cell surface were labeled with anti-adheron but not with anti-N-CAM. If cells were labeled before fixation, patches of anti-N-CAM labeling occurred in random areas over the growth cones, but adheron antibodies concentrated at points of apparent adhesion. Particularly dense clustering of anti-adheron occurred at individual filopodial tips and at points of contact between pairs of filopodia. The different patterns of labeling imply that N-CAMS do not associate with the main antigenic components of adheron on the membrane surface. Most importantly, the data indicate the N-CAMs were mobile in the membrane but that constituents of adherons were anchored at adhesive loci. An appealing hypothesis is that molecules found in adheron preparations have an important role in establishing the adhesive junctions formed by growth cone filopodia.

Diffusible proteins prolong survival of dorsal lateral geniculate neurons following occipital cortex lesions in newborn rats

Removal of the occipital cortex in newborn rats results in the rapid and nearly complete degeneration of the dorsal lateral geniculate nucleus (dLGN) in 5 days. In previous studies we have shown that transplants of embryonic posterior cortex neurons, which are allowed to develop in culture for 5 days prior to transplantation into the site of the lesion, prolong the survival of a particular population of host dLGN neurons for an additional week. In this study we tested the possibility that the transplant cells synthesize diffusible proteins which are responsible for this neurotrophic effect. Culture medium conditioned by explants of embryonic occipital cortex and diencephalon was concentrated by vacuum dialysis or ultrafiltration through membranes with at least a 10-kDa cut-off. This concentrated medium was loaded into polyacrylamide or sodium alginate gels which were then implanted into the cavity of the lesion. Five days after implantation, the alginate-conditioned-medium implants result in a 3-fold increase in dLGN survival compared to unconditioned medium controls, while a two-fold increase in survival of the nucleus is found with the polyacrylamide-conditioned-medium implants. Proteolysis of the conditioned medium eliminates all neurotrophic activity. The results suggest that the death of dLGN neurons following the cortical lesion is due to the loss of diffusible proteinaceous neurotrophic factors--factors that may operate during normal in vivo development of the geniculocortical pathway.

Comparison of the Schwann cell surface and Schwann cell extracellular matrix as promoters of neurite growth

The ability of Schwann cells to influence the direction and rate of neurite growth was investigated in a tissue culture model of the bands of Büngner of injured peripheral nerve. The arrangement of this culture system allowed testing of the growth-promoting properties of the Schwann cell surface and extracellular matrix (ECM) assembled by Schwann cells rather than soluble substances secreted into conditioned medium. Various components of peripheral nerve were examined separately as substrata for regenerating neurites: (i) Schwann cells and their ECM; (ii) Schwann cells alone; (iii) Schwann cell ECM alone; (iv) Schwann cells, fibroblasts, and their assembled ECM; (v) Schwann cells, their ECM and neurites; and (vi) purified laminin. Regenerating peripheral neurites were from explants of foetal rat dorsal root ganglia, which had been cultured for several weeks to rid them of accompanying non-neuronal cells, or from explants of foetal rat superior cervical ganglia, which contained non-neuronal cells. CNS neurites from the somatosensory cortex of embryonic rats were also studied; these neurites may be either first growing or regenerating. Neurites from all types of explants studied grew longer and were guided on a substratum of Schwann cells or Schwann cell ECM compared with a collagen substratum. The presence of fibroblasts during ECM assembly did not enhance the neurite growth-promoting activity. The design of the experiments suggested that the factors by which the Schwann cells or their ECM promoted and guided neurite outgrowth were surface-bound rather than medium-borne. Electron microscopic examination showed that neurites grew on either Schwann cell surfaces or basal lamina material. Attempts to define the chemical nature of the neurite growth-promoting effect of ECM by partial enzymatic digestion did not identify any single component as essential. Purified laminin was a more effective promoter of outgrowth of peripheral neurites than were Schwann cells or Schwann cell ECM. Cortical explants also grew on laminin, but neurites were accompanied on this substratum by a massive migration of non-neuronal cells; the neurites appeared to extend primarily on the non-neuronal cells rather than by direct attachment to the laminin substratum. This characteristic outgrowth of cortical non-neuronal cells on laminin was not consistently seen on Schwann cell ECM. In conclusion, either the Schwann cell surface or the ECM produced and assembled by Schwann cells promotes neurite outgrowth and guides that outgrowth from the several types of peripheral and CNS neurons studied in this report.

Target cell stimulation of dissociated serotonergic neurons in culture

Dissociated mesencephalic raphe cells from fetal rats (14-18 days) were grown in culture in 96 well Linbro plates. The maturation of serotonergic cells was qualitatively studied using immunocytochemistry with a serotonin antibody and quantitatively by measuring the retention of radioactivity following incubation in the presence of a low concentration of [3H]5-hydroxytryptamine (6 X 10(-8) M). The 5-hydroxytryptamine immunoreactive neurons showed specific staining in the perikaryon, nucleus, dendrites, axons and growth cones. These neurons formed varicose fibers and growth cones after 18 h in culture and survived for up to 21 days in culture. Each serotonergic neuron concentrated approximately 1 fmol of serotonin after 20 min of incubation. Maturation of mesencephalic serotonergic neurons was increased in co-cultures of both normal (hippocampus, cerebral cortex, olfactory bulb and striatum) and abnormal (spinal cord) target neurons. The best stimulation was produced by dissociated hippocampal neurons (14-18 days of gestation) on mesencephalic raphe cells (14 days of gestation) after 4 days in culture. This stimulation was seen in culture conditions which favored neuronal but not glial survival. Our results obtained using cultures of dissociated serotonergic cells are consistent with an expansive network pattern developed by this chemical transmitter system in the adult brain.

Embryonic and regenerating Xenopus retinal fibers are intrinsically different

Growth and guidance behavior of Xenopus embryonic (ER) (optic vesicle stage 25/26) and regenerating retinal fibers (stage 47/50 newly regenerating NR, and actively regenerating RR, respectively) have been studied in vitro on a variety of substrates in serum-free media. RR retinas receive a prior conditioning lesion 12-14 days before explantation while NR retinas are explanted immediately after axotomy. The substrates include plastic (UN), polylysine (PL), polyornithine (PO), laminin (LM), fibronectin (FN), and collagen type I (CO). Two kinds of experimental situations were tested, one in which substrates were derivatized to plastic as a planar surface, while the second involved the addition of a substrate as a soluble supplement to dishes derivatized with PL. A neurite growth index (NGI), based on density of neurite outgrowth and axon lengths, is determined for each fiber type on all substrates. Embryonic and regenerating fibers are phenotypically different fiber types; each displays a specific "substrate preference profile" (SPP), reflecting differential growth on each substrate. ER neurites grow equally well on all planar substrates, including plastic, but do not grow on CO (SPP, LM = FN = PL = PO = UN greater than CO). Both NR and RR neurites show distinct substrate preferences, but RR neurites grow more vigorously (SPP, LM greater than CO greater than PL = PO greater than FN). In media supplemented with LM, FN or CO, the SPPs showed little change but the neurite bundle patterns were qualitatively different. Only regenerating neurites display clockwise growth in laminin (LM) and fibronectin (FN)-supplemented media. Under no conditions do embryonic fibers exhibit this pattern which suggests that embryonic and regenerating retinal fibers also differ in cytoskeletal organization. Evidence of intrinsic growth differences in vitro suggest that embryonic and regenerating retinal fibers may not respond to identical guidance cues during in vivo development and regeneration of retinotectal connections.

Adhesion properties of a neuronal epitope recognized by the monoclonal antibody HNK-1

A carbohydrate epitope on adhesion proteins of the developing nervous system, and on myelin-associated glycoprotein, is recognized by the monoclonal antibody HNK-1. The HNK-1 epitope bearing proteins and the monoclonal antibody alter, in a dose-dependent manner, the interaction between neurons and neurite-promoting substrate-attached materials released from cultured neural cells.

Laminin supports short-term survival of rat septal neurons in low-density, serum-free cultures

Septal neurons from embryonic rats do not survive for 24 hr when dissociated and cultured at low density in a serum-free medium. Laminin at 5-40 micrograms/ml acts as a survival-promoting agent in the presence of 1 mM pyruvate. Laminin is effective in promoting survival only if it is added before or during cell plating; it does not support survival if added after cell attachment. Variations in laminin concentration do not effect the total number of cells attaching to the culture plate. The percentage of septal cells with neurites is increased in a dose-dependent manner by laminin as early as 45 min after cell plating, suggesting an effect of laminin on the rate of neurite initiation. Neurite extension at 24 hr is also dependent on laminin concentration. This study suggests that some interaction between cells and the substrate, independent of cell attachment, has a profound effect on cell physiology, increasing both cell survival and the rate of neurite extension. This study also defines the survival requirements of septal neurons in a chemically defined environment in a low-density situation where cellular interactions are at a minimum.

Nerve regeneration through biodegradable polyester tubes

One approach to repair of transected nerves is to attempt extrinsic guidance of axons across the gaps. We inserted the proximal and distal stumps of severed mouse sciatic nerves into opposite ends of biodegradable polyester tubes. The nerves and ensheathing tubes were examined after postoperative survival times of as long as 2 years. Myelinated fiber number in each successfully regenerated nerve was measured and correlated with the tube's residual lumen size. In selected regenerated nerves axonal sizes and myelin sheath widths were sampled and compared with control values. Swelling and deformation of tube walls occurred in nearly all tubes. Successful regeneration was obtained through more than half of the implants, and was more probable in tubes with larger initial lumens. Myelinated fiber number in regenerated nerves ranged from 231 to 3561 (normally 3900 to 4200); larger values again were found in tubes with larger initial lumens. Mean axonal areas in regenerated nerves were roughly half of normal, though myelin sheaths became appropriately thick. We concluded that the more biodegradable a tube, the more likely it was to incur distortion and luminal narrowing. Tube composition per se seemed of importance mainly as it related to maintenance of adequate luminal size over the length of the degrading tubes; luminal adequacy, not tube composition, seemed paramount in determining the extent of nerve regeneration.

Neurite-promoting factors from a sympathetically innervated target tissue

Previous studies have demonstrated that various cell types can produce and secrete polyornithine-attachable neurite promoting factors when cultured. This study describes an endogenous source of polyornithine-attachable neurite promoting factors. The active material extracted from an avian smooth muscle, the expansor secundariorum, is able to enhance neurite outgrowth from embryonic chick sympathetic neurons when applied to a polyornithine substrate. Unlike other polyornithine attachable factors, the material is also able to support the neurons for at least 72 hr in the absence of any added survival factors. Partial purification of the active material was achieved by affinity chromatography on polyornithine-Sepharose. The findings support the proposal that neurite promoting factors may have a definite physiological role in addition to their well established in vitro activity.

Accelerated regenerative neurite formation by a neuronal surface epitope reactive with the monoclonal antibody, Leu 7

A family of glycoproteins sharing an epitope with myelin associated glycoprotein as recognized by the monoclonal antibody Leu 7 (HNK-1) has been found to be present on neurons grown in culture from embryonic chicks and rats. Immunofluorescent staining demonstrates that, in vitro, 100% of the neurons from dorsal root ganglia and spinal cord from 7-8 day chick embryos react with Leu 7. Analysis of in vitro regenerative neurite formation by neurons on substrates enriched with Leu 7 showed accelerated regenerative process formation under limiting conditions. These results indicate that the Leu 7 epitope on neurons is appropriate for substrate adhesion and promotes rapid process extension.

Ethanol neurotoxicity: effects on neurite formation and neurotrophic factor production in vitro

The effects of ethanol on chick embryo sensory and spinal cord neurons growing on one of several biological substrates (poly-D-lysine, laminin, or neuron-produced neurite-promoting materials) were examined. Ethanol inhibited process formation by the neurons in a dose-dependent manner and inhibited the production of neurotrophic factors. Neuronal attachment to the substrates, survival of attached neurons, and receptor interactions of sensory neurons with nerve growth factor were not influenced by ethanol. It appears that ethanol alters certain metabolic characteristics of developing neurons.