Replacement of nerve-growth factor by ganglionic non-neuronal cells for the survival in vitro of dissociated ganglionic neurons

Review : Axons, Schwann Cells, and Neurotrophic Factors

As most elegantly confirmed by the recent success in deriving mice with null mutations in the genes for specific neurotrophic factors or their respective receptors, it is clear that neurotrophic factors alone or in combination are essential for the development of many classes of neurons. Specific neurotrophic factors have now been characterized that have actions on primary sensory afferents, sympathetic and parasym pathetic neurons, and motor neurons—the major contributors to the axon bundles that comprise the periph eral nervous system. The peripheral tissues or "end organs" that these neurons innervate have traditionally been thought of as the key source of neurotrophic factor support, but it is now evident that this "target- derived neurotrophic factor hypothesis" has restricted validity. Rather, the totality of neurotrophic support required to promote the survival, maturation, and maintenance of a neuron appears to be derived not only from targets, but also from support cells and possibly even neurons themselves. In this article, we review the role played by multiple sources of neurotrophic factors, especially factors derived from non-neuronal cells, not only in development, but also in the maintenance and regenerative responses of the adult PNS. In par ticular, we focus on neurotrophic factors of the neurotrophin family and ciliary neurotrophic factor. The Neuro scientist 1:192-199, 1995

In vitro responses of sympathetic neurons to nerve growth factor and other macromolecular agents

Cells in the dissociated state from the sympathetic ganglia (SG) of 11-day-old chick embryos, and monolayer cultures of these cells are used to illustrate some of th extrinsic influences that regulate neuronal performance. In culture, the survival of SG neurons can be measured, as an assay for survival-promoting agents. Among the requirements of the SG discussed are: (1) nerve growth factor and other trophic factors that can replace it, (2) serum, and a defined mixture (N1) that can substitute for it, and (3) a minimal presence of non-neuronal cells. Also reviewed are factors that confer neurite-promoting competence on certain culture substrata. Suspensions of SG cells permit analysis of "short-latency" events triggered within minutes of the presentation of nerve growth factors and provide an insight into its possible mode of action. The most striking such event is its control over Na+/K+ pumps, since ionic control is a fundamental feature of living cells and may well mediate their regulation by trophic factors, hormones or mitogens.

Myenteric plexus of the hind-gut: developmental abnormalities in humans and experimental studies

Intraluminal pressure studies on patients with congenital aganglionosis showed that the aganglionic rectum contracted in an uncoordinated manner and failed to relax. Histochemical assessment of the innervation helped to explain the variable severity of the symptoms in this condition. It is concluded that (1) absence of ganglia prevents normal coordinated peristalsis and creates an obstructive element; (2) absence of reflex relaxation adds to the obstruction; (3) the degree of uncoordinated motor activity in distal aganglionic bowel probably relates to the number of cholinesterase-positive nerves in the circular muscle and adds another variable obstructive element; and (4) deficient innervation of distal ganglionic bowel probably creates a poor propulsive force and so accentuates more distal obstructive factors. Neurohistochemical and functional studies in the anorectum of cats reveal a somewhat different innervation pattern from that in humans but show that sphincteric tone is mainly due to alpha-adrenergic neural activity. Reflex relaxation of the internal anal sphincter is a complex function in which inhibitory responses override motor responses, and it involves an important non-adrenergic non-cholinergic component. The role of cholinergic nerves in the sphincter remains uncertain. Neurohistochemical assessment of full thickness biopsy specimens of rectal muscle from patients with disabling constipation shows that developmental neuronal dysplasias of the hind-gut may be divided into three main categories: (1) aganglionosis (Hirschsprung's disease), (2) hypoganglionosis and (3) hyperganglionosis, and that the different neuronal elements may be affected to differing degrees in individuals within each group. Resection of the aganglionic bowel is required in congenital aganglionosis but the combined diagnostic-therapeutic procedure of anorectal myotomy has been found beneficial in patients with hypoganglionosis.

Superior cervical ganglion regenerating axons through peripheral nerve grafts and reversal of behavioral deficits in hemiparkinsonian rats

The superior cervical ganglion (SCG) has been grafted to the brain of adult rats in an attempt to reverse the parkinsonian syndrome that follows destruction of central dopamine systems. However, the main limitation to this approach is the massive cell death that occurs in the grafted SCG after direct transplantation into the brain. In adult rats, 6-hydroxydopamine (6-OHDA) was stereotactically injected into the right substantia nigra (SN). One month later, dopamine denervation was assessed using the apomorphine-induced rotational test. In rats with a positive test, an autologous peripheral nerve (PN) graft was tunneled from the right cervical region to the ipsilateral parietal cortex. One end of PN graft was sutured to the transected postganglionic branch of the SCG and the other end was inserted into a surgically created cortical cavity. The apomorphine test was repeated at 3 days and again at 1, 3, and 5 months after surgery. The brain, SCG, and PN graft were studied under light and electron microscopy and with the tyrosine hydroxylase immunohistochemical and horseradish peroxidase tracing methods. Three days after grafting, there were no significant differences on the apomorphine test as compared to the preoperative test. Conversely, 1,3, and 5 months after grafting, the number of rotations was reduced by 69% (+/-20.2), 66.6% (+/-17.1), and 72.5% (+/-11.3), respectively. Control rats that received a free PN graft to the brain and underwent section of the postganglionic branch of the SCG did not show significant changes on the apomorphine test after surgery. Histological examination revealed that the PN graft was mostly reinnervated by amyelinic axons of small caliber. Approximately 40% of the SCG neuronal population that normally projects to the postganglionic branch survived axotomy and regenerated the transected axons into the PN graft. Axons arising from the SCG elongated the whole length of the graft, crossed the graft-brain interface and extended into brain regions adjacent to the denervated striatum up to 2037 micrometer from the graft insertion site. This work shows that the ingrowth of catecholamine-regenerating axons from the SCG to dopamine-depleted brain parenchyma significantly reduces behavioral abnormalities in hemiparkinsonian rats. This effect cannot be ascribed either to the brain cavitation or to the PN tissue placement in the brain.

Immunocytochemical study of phenotypic plasticity of cultured dorsal root ganglion neurons during development

Rat dorsal root ganglia (DRG) were cultured from different stages of development ranging from embryonic day-14 to adult. The expression of eight neurotransmitter phenotypes was examined with immunocytochemical detection and the percentages of each phenotype were calculated with reference to the whole neuronal population defined by the expression of neuron-specific enolase (NSE). The expression of peptides, calcitonin gene-related peptide (CGRP), substance P (SP), cholecystokinin (CCK) and neuropeptide Y (NPY) was always present whatever the age at onset of the cultures. Although the percentage of CGRP remained stable, that of the other peptides declined progressively. Their in-vitro expression did not differ markedly from that found in vivo. Another group of neurotransmitters, including 5-hydroxytryptamine (5-HT), thyrotropin-releasing hormone (TRH) and gamma-aminobutyric acid (GABA) was never expressed in situ in DRG neurons. In culture, they were expressed in a high percentage of neurons, especially for 5-HT and TRH, and they showed a similar evolution, with a decrease at early postnatal ages followed by a further increase. This profile suggests that the expression of these transmitters is strongly environment-dependent and may be repressed in situ. Finally, somatostatin (SOM) was found only in cultures prepared from adult tissues, whereas it was present in situ from the embryo onwards. The expression of this peptide would thus require a stabilization by a long exposure to environmental factors. We can conclude that the great diversity of phenotypic expression found in DRG neurons in situ is the result of a wide variety of influences occurring at different stages of development in a large potential repertory present in these neurons.

Skeletal muscle extract and nerve growth factor have developmentally regulated survival promoting effects on distinct populations of mammalian sensory neurons

Neurotrophic factors appear to be relevant to the therapy of degenerative diseases as well as neural regeneration. In this respect, we have investigated the neurotrophic effects of skeletal muscle extract on DRG neuron survival by examining the survival and neurite outgrowth promoting activity of factor(s) present in skeletal muscle extracts (SME) on dissociated cultures of embryonic or early postnatal mouse dorsal root ganglion (DRG) sensory neurons. The numbers of surviving neurons resulting from SME addition increased continuously from embryonic day 13 (15%) to birth (55%), then decreased up to 7 days after hatching (0%). Preliminary characterization of the factor(s) present in SME suggests that the active molecule is a protein different from the known neurotrophic factors NGF, BDNF, NT3, CNTF, and bFGF, and that its neurotrophic effect is not mediated by direct interaction with the substratum.

Distinct and different effects of the oncogenes v-myc and v-src on avian sympathetic neurons: retroviral transfer of v-myc stimulates neuronal proliferation whereas v-src transfer enhances neuronal differentiation

Immature avian sympathetic neurons are able to proliferate in culture for a limited number of divisions albeit expressing several neuron-specific properties. The effect of avian retroviral transfer of oncogenes on proliferation and differentiation of sympathetic neurons was investigated. Primary cultures of 6-d-old quail sympathetic ganglia, consisting of 90% neuronal cells, were infected by Myelocytomatosis virus (MC29), which contains the oncogene v-myc, and by the v-src-containing Rous sarcoma virus (RSV). RSV infection, in contrast to findings in other cellular systems, resulted in a reduction of neuronal proliferation as determined by 3H-thymidine incorporation (50% of control 4 d after infection) and in increased morphological differentiation. This is reflected by increased neurite production, cell size, and expression of neurofilament protein. In addition, RSV-infected neurons, unlike uninfected cells, are able to survive in culture for time periods up to 14 d in the absence of added neurotrophic factors. In contrast, retroviral transfer of v-myc stimulated the proliferation of immature sympathetic neurons preserving many properties of uninfected cells. The neuron-specific cell surface antigen Q211 and the adrenergic marker enzyme tyrosine hydroxylase were maintained in MC29-infected cells and in the presence of chick embryo extract the cells could be propagated over several weeks and five passages. Within 7 d after infection, the number of Q211-positive neurons increased approximately 100-fold. These data demonstrate distinct and different effects of v-src and v-myc-containing retroviruses on proliferation and differentiation of sympathetic neurons: v-src transfer results in increased differentiation, whereas v-myc transfer maintains an immature status reflected by proliferation, immature morphology, and complex growth requirements. The possibility of expanding immature neuronal populations by transfer of v-myc will be of considerable importance for the molecular analysis of neuronal proliferation and differentiation.

Rat sciatic nerve Schwann cell microcultures: responses to mitogens and production of trophic and neurite-promoting factors

During embryonic development and in response to injury, the growing axons of peripheral neurons may influence the migration and proliferation of Schwann cells which, in return, may present neurons with a critical supply of factors required for neuronal survival, growth and differentiation. The identification and characterization of agents influencing the proliferation of Schwann cells as well as Schwann cell production of factors affecting neurons is greatly facilitated by the use of in vitro techniques. We describe here a simplified method of obtaining large numbers of purified neonatal rat sciatic nerve Schwann cells for use in generating large numbers of replicate microcultures. We then illustrate the use of these microcultures to examine Schwann cell: i) morphology and survival; ii) proliferation; and iii) production of neuronotrophic and neurite-promoting activities. We report that rat Schwann cells in microculture proliferate in response to serum, laminin and fibronectin, cholera toxin, and chick embryo parasympathetic ciliary neurons. Also, extracts of Schwann cell microcultures contain independently regulated activities which support the survival and neurite outgrowth of peripheral ganglionic neurons.

Age-dependent responses of ciliary ganglion neurons to conditioned media on cells at different stages of embryonic development

Neurons from ciliary ganglia (CG) from 8 to 14 day-old chick embryos were cultured in presence of conditioned media (CM) by eye tissue cells (ETC) on nonneuronal cells from ciliary ganglia (NFGC). These conditioning cells were obtained from 8 and 14 day-old embryos. Two parameters, surviving neurons and neurons displaying neurites, were determined after 48 h of culture. For neuronal survival, CMs did not show an effect on CG14 neurons. In the other neuronal ages ETC-CMs maintained a similar neuronal survival, whereas NFGC-CMs were more effective on older neurons. CM14 media were more effective maintaining neuronal survival than CM8 media respectives. The number of neurons displaying neurites decreased with neuronal ages in presence of all CMs. ETC8-CM was the better promoting neurite extension in all neuronal ages tested.

Stimulation of nerve growth factor mRNA content in C6 glioma cells by a beta-adrenergic receptor and by cyclic AMP

Authentic beta-nerve growth factor mRNA, approximately 1.35 kb in size, has been detected by Northern blot analysis in C6 glioma cells. Exposure of the cells to the beta-adrenergic agonist isoproterenol leads to a three- to fourfold increase in NGF mRNA, which reaches a peak by 2 hr. The EC50 for this effect of isoproterenol is approximately 2nM. The effect can be blocked by the beta-blocker propranolol but not by the alpha-blocker phenoxybenzamine. Treatment of the cells with forskolin also increases NGF mRNA three- to fourfold, with a maximal effect by 2 hr. The stimulation of NGF mRNA by maximal concentrations of forskolin and isoproterenol is not additive; similarly, the two drugs have a nonadditive effect on cyclic AMP content. The results suggest that NGF gene transcription can be stimulated via increases in intracellular cyclic AMP and that regulation of NGF production by glial cells may occur via activation of cell-surface neurotransmitter receptors such as the beta-adrenergic receptor.

Peripheral nerve grafts lacking viable Schwann cells fail to support central nervous system axonal regeneration

Peripheral nerve grafts were implanted bilaterally into the diencephalon of adult hamsters. One graft segment contained both viable Schwann cells and their basal lamina tubes. The Schwann cell population in the second graft segment was killed by freezing prior to implantation. Seven weeks after graft implantations, the extracranial end of each graft segment was exposed, transected and labelled with a fluorescent tracer substance. One week after the labelling procedure each animal was perfused and the diencephalon and midbrain were examined. Ultrastructural analyses of both types of graft demonstrated the persistence of the Schwann cell-derived basal lamina tubes. Retrogradely labelled neurons were found in all cases in which an intact graft remained in place for two months, but were seen in only one case with a frozen graft. Large numbers of myelinated and unmyelinated axons were seen within the intact grafts, but no axons were found in the previously frozen grafts. These results indicate that lesioned CNS axons are able to regenerate vigorously when provided with an environment which includes viable Schwann cells. But, CNS axons regenerate less well, if at all, when Schwann cells are absent. Further, it appears that Schwann cell-derived basal lamina tubes, when isolated from their parent cells, are insufficient to initiate or sustain CNS axonal regeneration.

Effect of retinoic acid on nerve growth factor receptors

Retinoic acid (RA), a naturally occurring metabolite of vitamin A, increased the number of receptors for nerve growth factor (NGF) in cultured human neuroblastoma cells (LA-N-1), as indicated by an immunofluorescence assay of cell surface receptors and by specific binding of 125I-NGF to solubilized receptors. Analysis of 125I-NGF binding showed that RA increased the number of both high affinity and low affinity receptors for NGF without affecting the equilibrium dissociation constants. Neurite outgrowth similar to that produced by NGF occurred following RA-treatment in LA-N-1 cells, in the SY5Y subclone of SK-N-SH human neuroblastoma cells and in explanted chick dorsal root ganglia (DRG). Whether morphological changes following RA treatment are directly related to the increase in NGF receptors is unknown. Data presented here are consistent with literature reports that RA modifies cell surface glycoproteins, including those that act as cell surface receptors for epidermal growth factor and insulin.

Modulation of the acetylcholine system in the superior cervical ganglion of rat: effects of GABA and hypoglossal nerve implantation after in vivo GABA treatment

gamma-Aminobutyric acid (GABA) was applied to the superior cervical ganglion (SCG) of CFY rats in vitro and in vivo, with or without implantation of a hypoglossal nerve, to evaluate the effects of these experimental interventions on the acetylcholine (ACh) system, which mainly serves the synaptic transmission of the preganglionic input. Long-lasting GABA microinfusion into the SCG in vivo apparently resulted in a "functional denervation." This treatment reduced the acetylcholinesterase (AChE; EC 3.1.1.7) activity by 30% (p less than 0.01) and transiently increased the number of nicotinic acetylcholine receptors, but had no significant effect on the choline acetyltransferase (acetyl-coenzyme A:choline-O-acetyltransferase; EC 2.3.1.6) activity, the ACh level, or the number of muscarinic acetylcholine receptors. The relative amounts of the different molecular forms of AChE did not change under these conditions. In vivo GABA application to the SCG with a hypoglossal nerve implanted in the presence of intact preganglionic afferent synapses exerted a significant modulatory effect on the AChE activity and its molecular forms. The "hyperinnervation" of the ganglia led to increases in the AChE activity (to 142.5%, p less than 0.01) and the 16S molecular form (to 200%, p less than 0.01). It is concluded that in vivo GABA microinfusion and GABA treatment in the presence of additional cholinergic synapses has a modulatory effect on the elements of the ACh system in the SCG of CFY rats.

Neurite formation modulated by nerve growth factor, insulin, and tumor promoter receptors

Until recently, nerve growth factor could be considered the only neurotrophic factor with an established physiological role. We discuss the emerging evidence indicating that the insulinlike factors may constitute a family of related neurotrophic proteins, and the observations suggesting that the receptor for the phorbol ester tumor promoters is closely associated with neuronal differentiation. The emphasis of the discussion is placed on neurite formation under multiple modulation by insulinlike factors, nerve growth factor, and tumor promoter receptors in sensory, sympathetic and human neuroblastoma cells.

Immunohistochemical localization of endogenous nerve growth factor

Nerve growth factor (NGF) has been proposed as a trophic molecule essential for the development of sympathetic and primary sensory neurones. In newborn mice and rats, administration of nerve growth factor results in an increase in the number of surviving neurones, whereas administration of antiserum to NGF decreases neuronal survival. Thus it has been proposed that the factor is produced and secreted by the relevant target tissues to provide trophic support for the ingrowing nerves. The site of synthesis of nerve growth factor is still unknown, and it has been emphasized that a precise physiological role for the molecule cannot be ascribed until the cell types that produce it are known. I report here the use of immunohistochemistry to localize endogenous NGF in the rat iris, a tissue in which there is sound biochemical evidence for the production of NGF activity. Surprisingly, the results reveal that NGF can be detected readily in Schwann cells, but not in smooth muscle cells of the iris when it is sympathetically denervated or cultured.

Characterization of nerve growth factor receptor in neural crest tumors using monoclonal antibodies

The nerve growth factor (NGF) receptor was characterized by using a new series of anti-receptor monoclonal antibodies (MAbs). These MAbs (i) showed significantly greater reactivity with a melanoma cell line expressing higher levels of NGF receptor, (ii) inhibited the binding of 125I-labeled NGF to its receptor, and (iii) immunoprecipitated both metabolically labeled and 125I-labeled NGF affinity-labeled receptor. These experiments defined the receptor as a 75-kDa cell-surface protein. The NGF receptor was visualized by immunoperoxidase staining in tissue sections of human nevi, melanomas, neurofibromas, a pheochromocytoma, and peripheral nerves. Uniform staining of the cytoplasm suggests that, in addition to cell-surface NGF receptors, there is a population of intracellular receptors.

Peripheral neurons and Schwann cells secrete plasminogen activator

The secretion of the protease plasminogen activator (PA) by cells of developing peripheral nerve was demonstrated. Fetal and early postnatal dorsal root ganglia were established in culture as explants or as individual neurons and Schwann cells. A fibrin overlay assay was used to visualize the locations of PA secretion. Fibrinolytic zones formed around the somata of explants and were skewed in the direction of maximal fiber outgrowth. Individual growth cones at the tips of long fasiculated fiber bundles also released PA. Approximately 50% of individual neurons showed PA secretion; especially pronounced release occurred at some growth cones. Culture of nerve growth factor-independent adult neurons showed that PA expression was independent of effects of this growth hormone. A subpopulation of Schwann cells was also active in PA secretion, which could be detected at the soma, at the bipolar processes, or along the entire cell length. Possible functions of neural PA in development and regeneration are discussed.

Pure population of viable neurons from rabbit dorsal root ganglia, using gradients of Percoll

Nonneuronal cells complicate the study of neurons in vitro. A pure population of viable neurons can be obtained easily using gradients of Percoll. For each experiment, 20 dorsal root ganglia (DRG) are minced, then sequentially dissociated in collagenase and trypsin, which digest all the intercellular connections. The dissociated tissue is separated first on the basis of density, creating an interphase fraction enriched in neurons and satellite cells, which are then further separated on the basis of size. The neurons, obtained in the final pellet, number approximately 50,000 (2500 per DRG), routinely exhibit a viability of over 80% initially and are of a purity of over 90%. The viability of the neurons is confirmed by the occurrence of neurite outgrowth in culture. Thus, a pure and viable neuronal population is obtained by a simple and rapid method.

Presynaptic modulation of activity and molecular forms of acetylcholinesterase in the rat superior cervical ganglion during early postnatal development

Preganglionic nerve trunk of the rat superior cervical ganglion was transected shortly after birth in order to evaluate the influence of preganglionic nerves on the development of acetylcholinesterase and choline acetyltransferase in ganglionic neurons. In spite of an early decentralization, specific activity of acetylcholinesterase in the ganglion is increasing during the first 3 wk of life until it is about equal to the activity which remains in the superior cervical ganglion decentralized in an adult animal. Thus, the preganglionic nerves, which per se contribute the presynaptic fraction of total ganglionic AChE activity in normal innervated ganglia, apparently exert no significant regulatory effect on the specific activity of the fraction of acetylcholinesterase affiliated with the developing ganglionic cells. However, the absence of innervation during development is strongly reflected in the pattern of acetylcholinesterase molecular forms. The activity of the 16 S molecular form of AChE remains high in the developing superior cervical ganglion, decentralized at birth, in contrast to the substantial absolute and relative decrease of specific activity of this form during development of a normally innervated ganglion. A high proportion of 16 S AChE probably reflects a shift of decentralized immature ganglion nerve cells toward a cholinergic character. In accordance with this assumption, choline acetyltransferase activity in early decentralized ganglia is significantly higher than that in the ganglia decentralized in adult animals.

Serum- and substratum-dependent modulation of neuritic growth

Explants of embryonic day 8 (E8) chicken dorsal root ganglia (DRG) have been cultured with medium containing serum or the serum-free supplement N1 on one of three substrata: collagen, polyornithine (PORN), or PORN exposed to a polyornithine-binding neurite-promoting factor (PNPF-PORN). Replicate cultures were maintained with or without nerve growth factor (NGF). NGF elicited its classical neuritic outgrowth on all three substrata in serum-containing or serum-free medium. In the absence of NGF, however, a gradation of increasing neurite growth was seen with: PNPF-PORN greater than PORN greater than collagen. This response occurred in both media. In addition, the neuritic halo in each instance was markedly more developed in the absence of serum, especially on PNPF-PORN. Nonneuronal behaviors reflected both serum and substratum influences: thus, nonneuronal outgrowth consisted mainly of flat cells with serum and collagen, was nonexistent with serum and PORN or PNPF-PORN, and involved mostly Schwann-like scattered cells in the absence of serum on any one substratum. The serum-dependent behaviors of ganglionic neurites were examined further with explants from chicken E11 sympathetic ganglia. A single substratum was used (PORN), without exogenous trophic factor. Neurite outgrowth was depressed by the presence of fetal calf serum, thus supporting the generality of this phenomenon. Lastly, PC12 cells, a clonal line of rat pheochromocytoma, will grow neurites in the presence of NGF after 48 hr in serum-free, but not serum-containing media. Addition of serum to serum-free cultures at this time results in the rapid and complete retraction of neurites.

Nerve growth factor, laminin, and fibronectin promote neurite growth in human fetal sensory ganglia cultures

The effect of mouse nerve growth factor (NGF) on cultured human fetal sensory neurons was assayed by measuring neurite length, density and rate of growth. Addition of NGF increased adhesion of dissociated sensory neurons cultured on collagen coated surfaces. Almost all neurons of 9 to 10 week old fetuses are postmitotic, contain neuron-specific enolase, (an enzyme linked to differentiation), and require NGF for optimal neurite growth. Sensory ganglia re-explanted on collagen showed maximal neurite length and density when treated with 1 ng/ml of NGF. Neurite density was reduced considerably in the absence of mouse NGF and was almost abolished by addition of antimouse NGF antibodies. Surfaces coated with the matrix glycoproteins laminin or fibronectin further stimulated neurite growth of ganglia in the presence of NGF. Increasing amounts of matrix proteins could partly compensate for the absence of mouse NGF or the inhibition of NGF activity by antibodies. Stimulation of neurite growth by matrix proteins was time-dependent, and neurites showed maximum length at 10 days (2 to 3 mm). Neurite growth was more pronounced with laminin than with fibronectin and collagen, and antibodies to laminin suppressed all neurite growth. In the presence of a constant amount of NGF, mean neurite growth reached 26 microns/hr (at 1 day), and was 2.1 and 1.7 times faster on laminin and fibronectin (respectively) than on collagen. Thus, laminin, and to a lesser degree fibronectin, may enhance neurite growth of human sensory neurons in synergy with NGF.

Sequestration requirements for the degradation of 125I-labeled beta nerve growth factor bound to embryonic sensory neurons

Nerve growth factor interacts with responsive cells by binding to cell surface membrane receptors. There are two different receptors on both embryonic sensory and sympathetic neurons, a high-affinity (type I) receptor and a lower-affinity (type II) receptor. Sequestration, which we have defined as bound nerve growth factor that becomes inaccessible to the external milieu with time, occurs through the type I receptor on both sensory and sympathetic neurons. We describe here a process subsequent to sequestration involving internalization and degradation of bound nerve growth factor and showing that bound nerve growth factor is not degraded under the following conditions: (1) low temperature, ie 4 degrees C; (2) when a large excess of unlabeled nerve growth factor is added concomitantly with the labeled nerve growth factor and the temperature is raised from 4 degrees C to 37 degrees C; (3) when metabolic inhibitors sodium fluoride and dinitrophenol are added concomitantly with the labeled nerve growth factor and the temperature is raised from 4 degrees to 37 degrees C. On the other hand, conditions that allow bound nerve growth factor to be degraded are the following: (1) incubation of the sensory nerve cells at low temperature (ie, 4 degrees C) only in the presence of labeled nerve growth factor, then raising the temperature to 37 degrees C; (2) when sodium fluoride and dinitrophenol are added when the temperature is raised to 37 degrees C; (3) when excess unlabeled nerve growth factor is added when the temperature is raised to 37 degrees C. These studies are consistent with the idea that nerve growth factor has to bind to the cells in order to be degraded; however, binding is not sufficient for degradation to occur. Second, the bound nerve growth factor must be sequestered in order to be degraded. Third, the process of internalization of the bound nerve growth factor, unlike sequestration, is not an energy-dependent process. Thus, it seems reasonable to suggest the following steps for the interaction of nerve growth factor with responsive cells: binding to a cell surface membrane receptor, followed by sequestration of the bound nerve growth factor, and finally, internalization of the sequestered nerve growth factor.

Nerve growth factor effects and receptors in cultured human neuroblastoma cell lines

We studied the effects of nerve growth factor (NGF) to determine whether neuroblastoma (NB) cells share the pattern of altered response to growth regulatory factors shown by various malignant transformed cells. NGF induces neurite outgrowth, arrests growth, and enhances survival in normal neurons and in the rat pheochromocytoma, a tumor cell closely related to NB. With respect to neurite outgrowth, lines SK-N-SH, SH-SY5Y, LA-N-5, and CHP-126 were sensitive, IMR-32 was resistant, and SH-EP1, SK-N-MC, MC-IXC, CHP-100, and CHP-134 were unresponsive. Conditioned media from unresponsive cells did not inhibit response in sensitive cells. Unexpectedly, NGF neither reduced the growth rate nor enhanced survival in any NB cell line. Conditioned medium from all NB cell lines enhanced 125I-NGF binding in embryonic sensory cells. Regulation of growth rate and neurite outgrowth, then, are separable. A fundamental defect in NB may be the acquisition of a capacity for growth and survival independent of NGF. 125I-NGF was bound to both Fast and Slow receptors in MC-IXC cells, but only to Slow receptors in NGF-responsive SH-SY5Y and LA-N-5 cells, showing Fast receptors are not required for neurite outgrowth. Independence from NGF-regulated growth and survival is unexplainable by an absence of NGF receptors.

Decrease in the number of lower affinity (type II) nerve growth factor receptors on embryonic sensory neurons does not affect fiber outgrowth

Nerve growth factor binds to two different specific receptors on responsive cells. The relationship of these two receptors is not fully understood at this time. We have studied the binding of labeled NGF to a different strain of white leghorn chicken embryo dorsal root ganglionic cells. The equilibrium dissociation constants for the two sites (KdI = 4.1 +/- 1.8 x 10(-11) M, KdII = 1.0 +/- 0.8 x 10(-9) M) are identical to those obtained previously. Also, the number of type I sites per cell (3.8 +/- 1.3 x 10(3)) is the same as that previously determined. However, the number of type II sites per cell (1.9 +/- 1.3 x 10(4)) is significantly different than that previously determined. This 2.5-fold decrease in the number of type II sites does not affect the concentration of NGF needed to obtain maximal fiber outgrowth from explanted sensory ganglia. The rate of association (1.2 +/- 0.2 x 10(7) M-1 sec-1 at 22 degrees C) of labeled NGF with receptors on sensory neurons from this different strain of chickens is identical to that previously obtained. The rate of association of NGF with its receptors on sensory neurons was also determined at 4 degrees C. This rate constant (2.1 +/- 1.1 x 10(6) M-1 sec-1) along with the rate constants obtained at 22 degrees and 37 degrees C were used to determine an activation energy for the binding of NGF to its receptors. The activation energy obtained (16.2 kcal/mole) suggests that binding is not a diffusion-controlled process.

Reconstruction of the contused cat spinal cord by the delayed nerve graft technique and cultured peripheral non-neuronal cells

Previously, surgical reconstruction of the transected dog spinal cord by the delayed nerve graft technique has been shown to result in reinnervation of the nerve graft by axons. In the present study, we compared the results of surgical reconstruction of the severely contused cat spinal cord by the delayed nerve graft technique alone to those after reconstruction with a similar nerve graft plus cultured peripheral non-neuronal cells implanted between the grafted nerve and the spinal cord stumps. The spinal cord-nerve graft junction was examined by light and electron microscopy. The cultured cells were prelabelled with tritiated thymidine and their location after implantation determined by autoradiography. By 3 days after spinal cord reconstruction, the prelabelled cells were present at the junction and had migrated into the nerve graft and also into the spinal cord stumps where they were observed near axons. By 7 days, physical connections were observed bridging the junction between the spinal cord and nerve graft and axons ensheathed by Schwann cells had already penetrated at least 1 mm into the nerve graft. Wound healing took at least a week longer in animals repaired with a nerve graft alone. At one year or later after reconstructive surgery, in both groups of animals, the grafted nerve was reinnervated with myelinated and unmyelinated axons. Thus, the severely contused cat spinal cord could be reconstructed with the delayed nerve graft technique alone but the use of the cultured cells appeared to enhance wound healing and decrease the time required for axon elongation into the nerve graft.

Sequestration of 125I-labeled beta nerve growth factor by embryonic sensory neurons

Nerve growth factor (NGF) binds to two specific receptors on sensory nerve cells. These two receptors are characterized by different equilibrium dissociation constants. The higher affinity (type I) receptors have an equilibrium dissociation constant of 3.3 X 10(-11) M. The lower affinity (type II) receptors have an equilibrium dissociation constant of 1.7 X 10(-9) M. These two receptors are not a result of negative cooperativity, but apparently are different receptors. At 22 degrees C the rate of association is 1 X 10(7) M-1 S-1 and the rates of dissociation are 6.5 X 10(-4) S-1 (type I) and 3.2 X 10(-2) S-1 (type II). After binding, a time-dependent process occurs that makes that NGF inaccessible to the external milieu (sequestered). The sequestration process is energy-dependent, but apparently temperature-independent. The data suggest that only the type I receptors are involved in the sequestration process. This process is similar to that observed on sympathetic neurons and may be the first step in the internalization of NGF by responsive cells.

Neurite growth promoting factors of embryonic chick--ontogeny, regional distribution, and characteristics

A single neuronal cell biological assay for NGF has been used to quantitate factors in soluble extract of chick embryo that promote neurite outgrowth. The neurite growth promoting activity is detected as early as day 1.5 of embryonic life. Specific activity increases to maximum over the first four days and then decreases from day 5 to 6 during a growth spurt of the embryo. The tissue distribution of neurite growth promoting activity at eight embryonic days shows higher specific activity in peripheral structures that are richly innervated. Extract from all embryonic stages and from all tissues studied induces neurite outgrowth that is inhibited only partially by antibody to mouse NGF. Furthermore, the kinetics of neurite outgrowth and the neuronal populations responsive to extract differ from that of NGF. These observations indicate heterogeneity of the neurite growth promoting factors in soluble extracts of embryonic chick and demonstrate the presence of these factors before the responsive neurons leave the cell cycle and begin their differentiation processes.

Survival, proliferation and morphological specialization of mouse Schwann cells in a serum-free, fully defined medium

Neonatal mouse dorsal root ganglionic (DRG) cell dissociates were cultured in a synthetic medium with horse serum or the serum-free supplement N1 (insulin, transferrin, progesterone, putrescine, selenium). Serum-supplemented cultures with added nerve growth factor (NGF) yielded neurons, small flat and spindle cells (Schwann) and large flat cells (fibroblastic elements). However, in serum-free, N1-supplemented medium plus exogenous NGF, neurons and Schwann cells predominated, with very few large flat cells. In the N1 medium most Schwann cells assumed a typical spindle shape and were associated with neuritic processes when neurons were present. Upon addition of serum, virtually all of the Schwann cells appeared to abandon physical contact with the neurites and develop a more flattened morphology. In N1 medium without NGF (no neurites), most Schwann cells still assumed a spindle shape and formed characteristic chain-like associations. Autoradiographic techniques, as well as numerical analyses, demonstrated that in N1 medium Schwann cells were able to proliferate when associated with neurites but only slightly so in their absence. These Schwann cells showed a marked increase in proliferation when serum was added regardless of the presence or absence of neurites. The above observations may provide a basis for the preparation of purified Schwann cells, alone or in combination with their neurons.

Regeneration of spinal electrocyte fibers in Sternarchus albifrons: development of axon-Schwann cell relationships and nodes of Ranvier

The electrocyte fibers in the gymnotid Sternarchus albifrons are highly differentiated myelinated axons which exhibit several types of nodes of Ranvier and characteristically short internode lengths. In the present study, regeneration of the electrocyte fibers following removal of the tail was examined by electron microscopy. By 36 days following extirpation, the regenerating electrocyte axons exhibit Type I nodes of Ranvier, with a normal morphology, and Type II nodes of Ranvier with a large nonmyelinated gap and a polypoid elaboration of the axon surface. Moreover, in the regenerating axons the internode length: diameter ratios are quite small. Thus, relatively normal axons-Schwann cell relations and a relatively normal differentiation of the axon surface are achieved during regeneration of the Sternarchus electrocyte fibers.

Nerve growth factor stimulates the development of substance P in sensory ganglia

The development of the putative neurotransmitter substance P (SP) in rat dorsal root ganglion (DRG) was defined in vivo. The sixth cervical DRG of newborn rats contained 70 pg of SP, and the ganglionic content increased 5.5-fold during the first 5 weeks of life. Forelimb amputation partially prevented the normal developmental increase of SP in the sixth cervical DRG destined to innervate that limb. Conversely, treatment with nerve growth factor (NGF) increased both ganglionic SP and total ganglion protein. Moreover, NGF administration prevented the failure of SP development that followed amputation, suggesting that NGF may mediate the limb-DRG interaction. However, treatment with antiserum to NGF failed to significantly inhibit development of ganglion SP. Consequently, neonatal ganglia may remain responsive to NGF, without requiring the protein for survival. SP appears to be an excellent index of the maturation of neurons in dorsal root ganglia.

Experimental autoimmune model of nerve growth factor deprivation: effects on developing peripheral sympathetic and sensory neurons

An experimental autoimmune model of nerve growth factor (NGF) deprivation has been used to assess the role of NGF in the development of various cell types in the nervous system. Adult rats immunized with 2.5S mouse NGF in complete Freund's adjuvant produced antibodies that crossreacted with their own NGF and that were transferred in utero to the fetus and in milk to the neonate. Cross-fostering experiments were carried out to separate the effects of exposure to anti-NGF in utero from those due to exposure through the milk. Anti-NGF transferred in utero and in milk resulted in the destruction of peripheral sympathetic neurons assessed by morphological methods (light microscopy) and biochemical methods (tyrosine hydroxylase activity, choline acetyltransferase activity, and protein content). No effects were observed on the adrenal medulla. Offspring of NGF-immunized females exposed to anti-NGF in utero had a decreased protein content in the dorsal root ganglia and were unable to transport (125)I-labeled NGF injected in the forepaw to the dorsal root ganglia. These results suggest that a subpopulation of sensory neurons is dependent on NGF for survival during some period of fetal development. This model offers the potential for determining the degree and time of dependence of various cell types on NGF.

Regeneration and myelination in autonomic ganglia transplanted to intact brain surfaces

Fragments of superior cervical ganglia (SCG) from donor rats between newborn and three months of age were transplanted either into the fourth ventricle, onto the dorsal surface of the medulla or in contact with the area postrema of recipient rats aged 6--14 days (allografts) and 3--4 weeks (autografts). Except for the meninges, the entire brain surface and parenchyma was undisturbed. The regenerative capacity of the transplanted ganglia and its interaction with the brain surfaces was followed for post-operative periods between 1 h and six months. Both ependymal and glial cells reacted to the transplant even though there was no mechanical damage to the brain. Ependymal cells developed luminal fronds that projected into the ventricle and the subpial glia displayed a very subtle gliosis in the form of thin multi-laminated processes. Schwann cells from the transplant tended to cover the free surfaces of the brain. The transplants, often incorporated into the stroma of the choroid plexus, received an extensive vascular supply of both fenestrated and non-fenestrated vessels. In contrast to SCG in tissue culture, the perinatal explants quickly degenerated while all those from older donors, at least 3--4 weeks of age, regenerated briskly in the ambient cerebrospinal fluid. Thriving SCG neurons, which diminished in number over time, sprouted numerous neurites as early as one week; growth cones and synaptic contacts between cell processes were still evident at six months. The trasplanted mature SCG fragment underwent a redevelopment after an initial period of degeneration. It seems likely that the survival of the allografted ganglion cells depends on their acquisition of a target site in their new environment. By four to six months many axons became enclosed by myelin produced by SCG Schwann cells that normally do not form myelin in situ. Other Schwann cells appeared reactive in that they had a great increase in cytoplasmic filaments and formed gap junctions, two characteristics of C.N.S. astrocytes. It is possible that the proximity to the C.N.S. changes the character of certain Schwann cells or, alternatively, resulted in the migration of glial cells out of the brain. If the glial cells have migrated into the transplant, they may support alien neural tissue. This system in which the transplantation site is easily accessible with a minimum of trauma could lend itself to the study of some underlying mechanisms of the growth and regulation of both central and autonomic neurons and their supporting cells.

Persistence of an amine uptake system in cultured rat sympathetic neurons which use acetylcholine as their transmitter

Cultures of dissociated rat superior cervical ganglion neurons (SCGN) were treated with the sympatholytic agent, guanethidine. When treated within the first couple of weeks in vitro, the neurons were rapidly destroyed. The cells grew less susceptible to the toxic effects of guanethidine with age in vitro. Moreover, the apparent affinity, Km, of the transport molecule for norepinephrine (NE) and guanethidine remained essentially unchanged between 2 and 7 wk in culture, as did the maximum velocity of transport (Vmax). This is at a time when previous studies have shown these neurons to be using acetylcholine (ACh) as their neurotransmitter. Cultures which were grown without supporting cells and from which cholinergic synaptic interactions were recorded physiologically were processed for autoradiography after incubation with [3H]NE. All cell bodies and processes seen had silver grains accumulated over them. These experiments show that sympathetic neurons in vitro maintain their amine uptake system relatively unchanged, even though they use ACh as their transmitter. The implications of these findings are discussed.