Effects of a nerve-growth factor, embryo age and metabolic inhibitors on growth of fibres and on synthesis of ribonucleic acid and protein in embryonic sympathetic ganglia

Survival of chick embryo sympathetic neurons in cell culture

Changes in neuronal numbers during the development of the chick embryo paravertebral sympathetic nervous system have been examined using cell culture techniques. Early sympathetic ganglia contain predominantly cells having neuronal phenotypes and these increase in number until embryonic day 9. Subsequently there is a large decrease in the number of neurons and an increase in the population of non-neuronal cells. This in vivo pattern is maintained when the neurons are grown in vitro, where Nerve Growth Factor more readily prevents the death of neurons cultured from 12-day or older embryos than those from earlier stages of development.

Blocked MAP kinase activity selectively enhances neurotrophic growth responses

Bone morphogenetic proteins (BMPs) 4 and 6 as well as MEK inhibitors PD98059 and U0126 potentiate neurotrophin 3 (NT3)- and neurturin (NTN)-induced neurite outgrowth and survival of peripheral neurons from the E9 chicken embryo. Preexposure to BMP4 or PD98059 was sufficient to prime the potentiation of subsequently added NT3. Phosphorylation of Erk2, induced by NT3, was reduced by MEK inhibition but unaffected by BMP signaling. Real-time PCR showed that neither BMP stimulation nor MEK inhibition increased Trk receptor expression and that the BMP-induced genes Smad6 and Id1 were not upregulated by PD98059. In contrast, both MEK inhibition and BMP signaling suppressed transcription of the serum-response element (SRE)-driven Egr1 gene. A reporter assay using NGF-stimulated PC12 cells demonstrated that MEK/Erk/Elk-driven transcriptional activity was inhibited by Smad1/5 and by PD98059. Thus, suppression of SRE-controlled transcription represents a likely convergence point for pathways regulating neurotrophic responses.

Beta-adrenergic and fibroblast growth factor receptors induce neuronal process outgrowth through different mechanisms

The mechanisms that initiate and direct neuronal process formation remain poorly understood. We have recently described a neuronal progenitor cell line, AS583-8.E4.22 (AS583-8) which undergoes neurite formation in response to beta2-adrenergic and basic fibroblast growth factor (bFGF) receptor activation [Kwon, J.H. et al., (1996) Eur. J. Neurosci., 8, 2042-2055]. In the present study, a comparison of these responses revealed that isoproterenol (ISO), a beta-adrenergic receptor agonist, induces multiple, highly branched processes within 30 min while bFGF induces fewer, unbranched processes within 24 h. In contrast to the ISO response, bFGF induces mitogen-activated protein kinase activation and c-fos expression in the cell line and results in neurite outgrowth that is dependent on new mRNA and protein synthesis. Two-dimensional isoelectric focusing-sodium dodecyl sulphate-polyacrylamide gel electrophoresis of cytoskeletal preparations revealed different patterns following ISO vs. bFGF exposure suggesting selective changes in protein expression and/or post-translational modifications. Immunoblot analysis of these preparations for beta-tubulin, tyrosinated alpha-tubulin and acetylated alpha-tubulin also revealed different patterns following each type of treatment. Follow-up confocal microscopy revealed that following ISO, the distribution of tyrosinated tubulin extends to the distal ends of processes whereas acetylated alpha-tubulin is diminished within distal ends. This pattern has been reported to be associated with enhanced microtubule dynamics, a state in which process outgrowth is facilitated. In contrast, following bFGF treatment the distributions of tyrosinated and acetylated alpha-tubulin were identical, a state associated with a diminution of microtubule dynamics. These results, a different time course of neurite formation, dependency on new gene expression and differential expression and cellular distribution of major cytoskeleton proteins suggest that neurite outgrowth induced by ISO vs. bFGF is mediated by two distinct intracellular effector mechanisms in AS583-8 cells. In addition, studies, using the differential distribution of post-translational modified alpha-tubulins in neurites of primary neuronal cultures as marker for the two distinct processes of neurite formation suggest, that similar mechanisms are present in vivo. Therefore, the AS583-8 cell line provides a useful model to study these signalling mechanisms that couple neurotransmitter and growth factor receptor activation to the cytoskeletal changes that mediate neurite formation.

Activation of mitogen-activated protein kinases is not required for the extension of neurites from PC12D cells triggered by nerve growth factor

Numerous studies with PC12 cells have suggested that the mitogen-activated protein (MAP) kinase pathway might play a major role in the neuronal differentiation that is induced by nerve growth factor (NGF). Cells of the PC12D subline extend neurites within several hours in response to NGF in the presence of inhibitors of the synthesis of RNA and protein. We examined the effects of a specific inhibitor 2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD98059) of the MAP kinase kinase (MEK)/MAP kinase pathway on the NGF-induced outgrowth of neurites in PC12D cells. The increase in MAP kinase activity in response to NGF was reduced by 80% upon treatment of PC12D cells with 50 microM PD98059, whereas the NGF-dependent formation of ruffles and the subsequent outgrowth of neurites were not blocked by PD98059 at this concentration. The outgrowth of neurites from conventional PC12 cells by NGF was suppressed by the addition of 50 microM PD98059 as reported by Pang et al. [L. Pang, T. Sawada, J. Stuart,S.J. Decker, A.R. Saltiel, Inhibition of MAP kinase kinase blocks the differentiation of PC12 cells induced by nerve growth factor, J. Biol. Chem. 270 (1995) 13585-13588]. In contrast, the rapid regeneration of neurites from PC12 cells primed with NGF, was not altered in the presence of the same dose of the inhibitor of MEK. It appeared, therefore, that the activation of the MAP kinase pathway was not necessarily required for the NGF-dependent extension of neurites. When PC12D cells were transfected with the dominant inhibitory Ha-ras Asn-17 gene, the induction of the mutant Ras protein led the suppression of the rapid outgrowth of neurites in response to NGF but not to dibutyryl cyclic AMP (dbcAMP). The result implies a direct involvement of Ras protein in the NGF-induced signal transduction that lead to the formation of neurites in PC12D cells. We can conclude that the activation of MAP kinase and selective gene expression are required for the differentiation of conventional PC12 cells to sympathetic neuron-like cells and that activation of Ras protein and, subsequently, of a MAP kinase-independent pathway might be involved in the extension of neurites from PC12D cells or in the regeneration of neurites from primed PC12 cells in response to NGF.

Beta-adrenergic receptor activation promotes process outgrowth in an embryonic rat basal forebrain cell line and in primary neurons

A clonal cell line, AS583-8.E4.22, from the embryonic day 15 rat basal forebrain was established using retrovirus-mediated transduction of a temperature-sensitive mutant of the simian virus 40 (SV40) large tumour antigen. The cell line expresses cytoskeletal and neurotransmitter features indicative of neuronal commitment. In response to agents that increase intracellular cAMP, including forskolin and catecholamines, the cell line exhibits rapid process outgrowth and growth cone formation that does not require new gene expression or protein synthesis. The neurite outgrowth induced by catecholamines is mediated by beta 2-adrenergic receptors and is characterized by a rapid, reversible redistribution of filamentous actin. Neurons from primary cultures of embryonic day 15 basal forebrain were also found to respond to beta-adrenergic receptor agonists by enhancing growth cone formation. These results suggest that catecholamines provide cues that induce cytoskeletal rearrangements leading to neuronal process outgrowth and growth cone formation in the developing basal forebrain and possibly other neuronal progenitor cell populations. The neuronal basal forebrain cell line provides an ideal model to study the signalling mechanisms underlying the catecholamine-induced process outgrowth.

Sustained tyrosine phosphorylation of p140trkA in PC12h-R cells responding rapidly to NGF

The PC12h cell, a subclone of PC12 cells, has considerable activities of tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) and shows an NGF-induced increase in both enzyme activities. The TH activity and its inducibility by NGF in PC12h cells were stably maintained in the passage of > 200 generations whereas the ChAT activity was not. We isolated a new cell line, PC12h-R (originally clone 8), from a long-term culture of PC12h cells. PC12h-R cells still showed the considerable TH activity, but not the ChAT activity, and maintained the inducibility of TH activity by NGF. Thus, the responses of PC12h-R cells to NGF were similar to those of chromaffin cells and sympathetic neurons. PC12h-R cells were found to extend neurites and differentiate into sympathetic neuron-like cells in response to NGF much more rapidly than PC12h cells. In addition, PC12h-R cells showed sustained NGF-induced tyrosine phosphorylation of p140trkA and several cellular proteins, including 42-, 44- and 54-kDa proteins, in comparison with PC12h cells. We suggest that the NGF-induced sustained tyrosine phosphorylation signal in PC12h-R cells may be correlated closely with their rapid NGF-induced differentiation into neuron-like cells.

Development of trophic interactions in the vertebrate peripheral nervous system

During embryogenesis, the neurons of vertebrate sympathetic and sensory ganglia become dependent on neurotrophic factors, derived from their targets, for survival and maintenance of differentiated functions. Many of these interactions are mediated by the neurotrophins NGF, BDNF, and NT3 and the receptor tyrosine kinases encoded by genes of the trk family. Both sympathetic and sensory neurons undergo developmental changes in their responsiveness to NGF, the first neurotrophin to be identified and characterized. Subpopulations of sensory neurons do not require NGF for survival, but respond instead to BDNF or NT3 with enhanced survival. In addition to their classic effects on neuron survival, neurotrophins influence the differentiation and proliferation of neural crest-derived neuronal precursors. In both sympathetic and sensory systems, production of neurotrophins by target cells and expression of neurotrophin receptors by neurons are correlated temporally and spatially with innervation patterns. In vitro, embryonic sympathetic neurons require exposure to environmental cues, such as basic FGF and retinoic acid to acquire neurotrophin-responsiveness; in contrast, embryonic sensory neurons acquire neurotrophin-responsiveness on schedule in the absence of these molecules.

Modulation of sprouting in organ culture after axotomy of an identified molluscan neuron

We examined a variety of factors that might modulate the initiation of neurite outgrowth in an attempt to identify means by which its initiation might be accelerated. We examined this initiation from an identified molluscan neuron, Helisoma trivolvis buccal neuron B5 after axotomy, and determined whether the site of injury, temperature, ion channel blockers, pH, the second messenger cAMP, and protein synthesis affect the initiation of neurite outgrowth. Neurite outgrowth was assayed from axotomized neurons by filling the neurons intracellularly with Lucifer Yellow and examining the percentage of axons that extended (sprouted) new process after 9 or 24 h in organ culture. About one-third (31%) of axotomized neurons sprouted from the site of injury after 9 h (n = 22), and 88% (n = 20) sprouted after 24 h in saline at 22 degrees-24 degrees C when the injury was located 800 microns from the soma. Elevating the temperature to 32 degrees C or moving the lesion site to 400 or 1500 microns from the soma did not significantly alter the incidence of sprouting. Blocking sodium channels with tetrodotoxin [TTX (2 x 10(-5) M)] did not significantly reduce the incidence of sprouting, whereas the sodium channel agonist, veratridine (10(-5) M) did. The calcium channel blocker lanthanum (10(-6)-10(-4) M), stimulated neurite outgrowth; however, the organic calcium channel blocker verapamil (10(-3)-10(-5) M), and the calcium ionophore A23187 (10(-5) M), had no effect on sprouting. Exposure of neurons to the potassium channel blocker tetraethylammonium [TEA (20 mM)], elevation of intracellular pH with NH4Cl (5 mM), or treatment with the adenylate cyclase activator forskolin (10(-5) M) reduced the incidence of sprouting, whereas dideoxy-forskolin (10(-5) M) had no effect. Inhibition of protein synthesis with anisomycin (2 x 10(-4) to 2 x 10(-6) M) did not significantly suppress sprouting 24 h after axotomy. Both D and L isomers of glutamate (300 microM) stimulated sprouting. The present results suggest that the initiation of sprouting is regulated locally at or near the site of injury, and that blocking specific ion channels may either inhibit or enhance the initiation of neurite outgrowth.

Changes in levels of microtubule-associated proteins in relation to the outgrowth of neurites from PC12D cells, a forskolin- and nerve growth factor-responsive subline of PC12 pheochromocytoma cells

Immunoblotting analysis and immunofluorescence studies of proteins that react with MAP1- and MAP2-specific antibodies in PC12 rat pheochromocytoma cells were carried out. When cells of the PC12D subline of PC12 cells, which rapidly extend neurites in response to NGF or drugs that elevate intracellular levels of cyclic AMP, were examined, they were found to contain a relatively higher level of MAP1 or of a MAP1-like protein than conventional PC12 cells. Immunoblotting study showed that levels of MAP1 and MAP2 or of MAP1 or MAP2-like proteins increased in PC12D cells, but not in conventional PC12 cells, in response to forskolin. Immunofluorescence studies also revealed increases in levels of MAP1 and MAP2 or of MAP1 or MAP2-like proteins in conjunction with the outgrowth of neurites from the cells. These results support the hypothesis that the induction of MAPs may be one of the first steps required for outgrowth of neurites from PC12 cells. Furthermore, PC12D cells may contain a sufficiently high level of MAP1 or MAP1-like protein to permit the extension of neurites in the absence of the lag period normally required by PC12 cells. The MAP1 or a MAP1-like protein was localized in the cell soma and neurites. An increase of MAP2-specific immunoreactivity in perikarya was observed in the differentiated cells. After immunostaining with a monoclonal antibody that reacted with phosphorylated MAP1, intense fluorescence was seen in the growth cones of neurites. This observation supports the hypothesis that the phosphorylation of MAP1 or of a MAP1-like protein may play a regulatory role in the formation of neurites in growth cones.

Enucleation of the rat pheochromocytoma clonal cell line, PC12: effect on neurite outgrowth

The effect of removal of PC12 cell nuclei on neurite outgrowth was studied. Enucleation (80-90%) was accomplished in the presence of cytochalasin B using a centrifugation technique that exploited the very tight adhesivity of PC12 cells for a substratum composed of an extracellular matrix secreted by bovine corneal endothelial cells in response to epidermal growth factor treatment. Neither nucleated nor enucleated PC12 cells showed significant neurite outgrowth on this particular matrix in the absence of nerve growth factor. In the presence of nerve growth factor both PC12 cell types initiated neurite outgrowth, but whereas neurites from nucleated cells grew continuously for two days, those from enucleated cells reached a maximum length after one day. The results suggest that neurite initiation but not continued neurite growth or stabilization can occur in the absence of transcription.

Neuron-like cells in long-term neural crest cultures are not targets of nerve growth factor

It has been shown previously that a subpopulation of long-term (7-14 days) cultured neural crest cells undergoing differentiation possesses receptors for nerve growth factor (NGF). These cells are likely to be targets of NGF during the early stages of embryonic development. This study was conducted to determine whether cells exhibiting neuron-like characteristics (i.e. process formation, presence of putative neurotransmitters) in neural crest cultures have NGF receptors. This was accomplished by combining 125I-NGF radioautography and immunocytochemistry using antibodies against tyrosine hydroxylase, serotonin, and vasoactive intestinal polypeptide. Examination of light microscopic radioautographs revealed that none of the neuron-like cells with tyrosine hydroxylase-like, serotonin-like, or vasoactive intestinal polypeptide-like immunoreactivity bound 125I-NGF, and, therefore, do not possess NGF receptors. It is not known whether the lack of NGF receptors on neuron-like cells is due to the early developmental stage of these cells, or is caused by a difference in the microenvironment in vitro as compared to in vivo. The identity of the cultured neural crest cells which do possess NGF receptors remains to be determined.

Ontogeny of glucose metabolism in sympathetic ganglia of chickens. Concurrence of maximum rates in the hexosemonophosphate shunt and in synthesis of lipids but not of ribonucleic acid

Chains of sympathetic ganglia were excised from the lumbar region of white Leghorn chicken embryos, 8-19 days of age, and incubated, usually for 5 h, at 36 degrees C in a bicarbonate-buffered physiological salt solution containing [U-14C]glucose, [1-14C]glucose, [6-14C]glucose, or [5-3H]uridine. Lipid synthesis was measured by the incorporation of 14C into lipids, and RNA synthesis by the accumulation of 3H into macromolecules. The ratio of 14C put out in CO2 during the second hour of incubation in the presence of [1-14C]glucose to that with [6-14C]glucose was used as an index of activity in the hexosemonophosphate shunt (HMS). Both the rate of lipid synthesis and activity in the HMS reached well-defined maxima at about 11 days of embryonic age. There was no evidence of a similar rise and fall of RNA synthesis during the ages studied. Estimates of the rate of NADPH production by the HMS at near-peak lipid synthesis varied over a twofold range that included the rate needed for the observed lipid synthesis. The results thus support, quantitatively as well as qualitatively, the supposition that the HMS is accelerated during development to sustain lipid synthesis.

Wheat germ agglutinin inhibits nerve fiber growth and concanavalin A stimulates nerve fiber initiation in cultures of dorsal root ganglia neurons

Treatment of dorsal root ganglion (DRG) neurons with the lectin wheat germ agglutinin (WGA; 25 micrograms/ml), which binds to N-acetylglucosamine containing glycoconjugates, inhibits nerve fiber growth in culture. DRG neurons treated with WGA have significantly reduced total output in nerve fiber length per neuron as well as reductions in the average length of the individual nerve fibers extended. The inhibition of nerve fiber growth by WGA is concentration-dependent, specific, reversible and not mimicked by treatment with several metabolic poisons. In contrast, treatment with the lectin concanavalin A (25 micrograms/ml), which binds to mannose-containing glycoconjugates, increases the number of nerve fibers produced per neuron. These results suggest that lectins which bind to distinct carbohydrate moieties can differentially regulate nerve fiber growth.

Characterization of nerve growth factor binding to cultured neural crest cells: evidence of an early developmental form of the NGF receptor

Cultured neural crest cells undergoing differentiation have been shown to contain a subpopulation of cells with specific receptors for nerve growth factor (NGF). These cells are the potential targets of NGF during differentiation and development. This study was done to pharmacologically characterize the binding of NGF to long-term (1- to 3-week) cultures of quail neural crest cells. The data indicate that 125I-NGF binding was specific and saturable, with less than 20% nonspecific binding. Scatchard analysis revealed the presence of one type (class) of receptors with a binding constant (Kd) similar to that of the low-affinity binding site described for embryonic dorsal root and sympathetic ganglia (approximately 3.2 nM). This was corroborated by displacement experiments (Kd of 1.3 nM), in which 125I-NGF binding was measured in the presence of increasing concentrations of nonradioactive NGF. In addition, affinity labeling revealed that the 125I-NGF-receptor complex had a molecular weight of about 93K, characteristic of the low-affinity NGF receptor of PC12 cells. The NGF receptor of cultured neural crest cells was trypsin-sensitive, as is typical of the low-affinity NGF binding sites. These findings indicate that differentiating neural crest cells lack high-affinity 125I-NGF binding sites. In contrast, embryonic dorsal root and sympathetic ganglia cells, known NGF targets, have both high- and low-affinity receptors. Measurements of the differential release of surface-bound 125I-NGF indicated that a relatively small amount (about 14%) of NGF is internalized over a 1-hr period. Cultured neural crest cells which bear NGF receptors were also shown by light microscopic radioautographic techniques to incorporate [3H]thymidine. I suggest, therefore, that cultured neural crest cells which have not terminally differentiated, as judged by morphological criteria and continued proliferation, may express an early developmental form of the NGF receptor.

Ontogeny of glucose metabolism in sympathetic ganglia of chickens. Changes in the carbon fluxes to CO2, lactate, and tissue constituents from 8 to 19 days of embryonic age

Chains of sympathetic ganglia were excised from the lumbar region of white Leghorn chicken embryos, 8-19 days of age. The chains were incubated for 5 h at 36 degrees C in a bicarbonate-buffered physiological salt solution containing 5.55 mM unlabeled glucose and tracer amounts of glucose labeled either uniformly or at carbon-1 or carbon-6. Glucose uptake and labeled lactate output were both highest in ganglia from the youngest embryos studied and declined progressively with increasing age. The output of labeled CO2 rose to a peak rate at an incubation age of 10-12 days in the presence of either [U-14C]glucose or [1(-14)C]glucose, but changed relatively little with age in the presence of [6(-14)C]glucose. The incorporation of 14C into tissue constituents was fastest at 10-12 days with all three labeled glucoses. It is concluded that the hexosemonophosphate shunt is most active at an incubation age of 10-12 days, after glycolysis has greatly slowed. The literature on morphological and biochemical changes in the sympathetic ganglia during development is briefly reviewed and discussed in relation to the observed metabolic changes. The early high glycolytic rate may be related to the normal developmental delay in vascularization of the sympathetic chains.

Protein synthesis requirement for the formation of synaptic elements

The formation of synapses in cell cultures of rat cerebellum was examined in the presence of the protein synthesis inhibitor cycloheximide. First, cell survival in the presence of 25 micrograms/ml cycloheximide was determined by phase contrast microscopy, trypan blue exclusion, total protein and uptake of [3H]gamma-aminobutyric acid (GABA). Neurons with 24 h incubation in cycloheximide appeared normal with little cell death, but by 48 h incubation the first signs of cell death were found. Some viable neurons were still found in cultures incubated continuously in cycloheximide for 72 h. Normally, the number of synapses seen in cerebellar cultures with the electron microscope shows an increase during the first several weeks in culture. However, the number of synapses in cultures treated with cycloheximide decreased, indicating that inhibition of protein synthesis at least partially inhibited synaptogenesis. Cycloheximide also inhibited the maintenance of synapses already formed as seen by the decrease in the number of synapses from the time the cycloheximide was added. To determine the sensitivity of the forming presynaptic element to cycloheximide, the development of apparent presynaptic elements was investigated. In cultures treated with polylysine-coated sepharose beads, neurites grew and formed apparent presynaptic elements with the bead taking the position of the postsynaptic element. Cultures pretreated with cycloheximide for 1 h followed by 24 h incubation with both cycloheximide and coated beads showed a normal number of apparent presynaptic elements. The first decrease in numbers was seen after 12 h preincubation and 12 h incubation with both cycloheximide and coated beads. Even after 72 h continuous incubation some apparent presynaptic elements could be formed although at reduced levels. Results presented here suggest that continuous protein synthesis is not necessary for the formation of the presynaptic element, but that active protein synthesis is required for neurons to form and maintain postsynaptic elements.

Lithium ion inhibits nerve growth factor-induced neurite outgrowth and phosphorylation of nerve growth factor-modulated microtubule-associated proteins

LiCl (2.5-20 mM) reversibly suppressed nerve growth factor (NGF)-induced neurite outgrowth by cultured rat PC 12 pheochromocytoma cells. Similar concentrations of LiCl also reversibly blocked NGF-dependent regeneration of neurites by PC12 cells that had been primed by long-term pre-exposure to NGF and by cultured newborn mouse sympathetic neurons. In contrast, transcription-dependent responses of PC12 cells to NGF such as priming and induction of the NGF-inducible large external glycoprotein, occurred despite the presence of Li+. SDS PAGE analysis of total cellular phosphoproteins (labeled by 2-h exposure to 32P-orthophosphate) from neurite-bearing primed PC12 cells revealed that Li+ reversibly inhibited the phosphorylation of a band of Mr 64,000 that was barely detectable in NGF-untreated PC12 cells. However, Li+ did not appear to affect the labeling of other phosphoproteins in either NGF-primed or untreated PC12 cultures, nor did it affect the rapid increase in phosphorylation of several proteins that occurs when NGF is first added to unprimed cultures. Several criteria indicated that the NGF-inducible phosphoprotein of Mr 64,000 is a microtubule-associated protein (MAP). Of the NGF-inducible phosphorylated MAPs that have been detected in PC12 cells (Mr 64,000, 72,000, 80,000, and 320,000), several (Mr 64,000, 72,000, and 80,000) were found to be substantially less phosphorylated in the presence of Li+. Neither a phorbol ester tumor promotor nor permeant cAMP analogs reversed the inhibitory effects of Li+ on neurite outgrowth or on phosphorylation of the component of Mr 64,000. Microtubules are a major and required constituent of neurites, and MAPs may regulate the assembly and stability of neuritic microtubules. The observation that Li+ selectively inhibits NGF-induced neurite outgrowth and MAP phosphorylation suggests a possible causal relationship between these two events.

Nerve growth factor-independent development of embryonic mouse sympathetic neurons in dissociated cell culture

Although ganglia from neonatal mouse sympathetic ganglia require nerve growth factor (NGF) for survival in culture, explanted sympathetic ganglia from early embryonic stages do not require added NGF for survival and growth. To determine whether the change in growth factor requirement is due to changes in the neurons themselves, to variations in neuronal populations, or to changes in nonneuronal cells, we examined the response to growth factors by dissociated sympathetic neurons at various stages of development. Results indicate that neurons from the 14-day gestational (E14) superior cervical ganglion (SCG) do not require NGF for initial survival and neurite extension, but do require the conditioned medium neurite extension factor, CMF. By 2 to 3 days thereafter, whether in vivo or in culture, most neurons have developed a requirement for NGF for survival in culture. During the same period, there is a concomitant increase in responsiveness to NGF alone as a trophic agent. Changes in response to NGF are not due to changes in NGF content of ganglia, to interactions in culture with nonneuronal cells, or to age-related differences in NGF requirements for maximum survival. The changes in growth factor requirements may be related to mechanisms regulating specificity of nerve-target connections.

Stimulative effect of nerve growth factor on alpha-aminoisobutyric acid uptake and Na,K-ATPase activity in superior cervical sympathetic ganglia excised from adult rats

Effects of nerve growth factor (NGF) on the uptake of non-metabolizable alpha-aminoisobutyric acid (AIB) and on Na,K-ATPase activity in superior cervical sympathetic ganglia (SCG) excised from adult rats were examined during aerobic incubation in vitro. Active uptake of labelled AIB into isolated SCG during 1 to 5 hours incubation at 37 degrees C was significantly accelerated by the addition of NGF to the incubation medium in a dose-dependent manner. Although the Km value of the AIB uptake by the SCG did not change with the addition of NGF, Vmax was nearly doubled. The NGF-evoked increase in AIB uptake was antagonized by the further addition of its specific antiserum in a dose-dependent fashion, and was largely suppressed in a medium containing ouabain. In SCG, axotomized one week prior to the examination, from which most of the neurons had disappeared and reactive proliferation of satellite glial components was in progress, the NGF-induced acceleration of AIB uptake was completely absent. The ganglionic Na,K-ATPase activity was greatly stimulated in the presence of NGF, and the effect was completely eliminated in the axotomized SCG. These results strongly suggest that the NGF-induced acceleration of active AIB uptake by the isolated SCG occurs not in glial cells but exclusively in the neuronal components with the apparent coupling of an Na ion extrusion process.

Detection of endogenous epidermal growth factor-like activity in the developing chick embryo

Epidermal growth factor-like activity has been detected by radioreceptor assay and radioimmunoassay in the developing chick embryo. Very little activity could be detected prior to Day 8 of embryonic life (hatching is at Day 21). A peak of EGF activity was detectable by both assays over Days 10 to 12. The EGF activity then fell to virtually undetectable levels during Days 14 to 17. A later rise in RRA detectable EGF like activity was then observed over Days 18-20. The EGF activity from a Day 11 embryo chromatographed on high-performance liquid chromatography as a single peak, with very high recovery of activity, at a later elution position than mouse EGF or human EGF.

Epidermal and nerve growth factors manifest antilipolytic and lipogenic activities in isolated rat adipocytes

The effects of epidermal growth factor (EGF) and nerve growth factor (NGF) from mouse submaxillary glands on lipolysis and lipogenesis in isolated rat adipocytes were studied. EGF and NGF at nanomolar concentrations augmented basal lipogenesis. The lipogenic responses to EGF and NGF were additive with a submaximal response induced by insulin but not with that of a maximal response to insulin, indicating a similarity in the mechanisms of action of EGF, NGF and insulin. EGF and NGF also inhibited epinephrine-induced lipolysis. The antilipolytic and lipogenic activities of EGF and NGF were considerably less potent by concentration than those of insulin.

Regulation of tubulin and actin mRNA production in rat brain: expression of a new beta-tubulin mRNA with development

The expression of alpha-tubulin, beta-tubulin, and actin mRNA during rat brain development has been examined by using specific cDNA clones and in vitro translation techniques. During brain maturation (0 to 80 days postnatal), these mRNA species undergo a significant decrease in abundance. The kinetics of this decrease varies between the cerebrum and the cerebellum. These mRNAs are most abundant in both tissues during week 1 postnatal, each representing 10 to 15% of total mRNA activity. Both alpha- and beta-tubulin mRNA content decreases by 90 to 95% in the cerebrum after day 11 postnatal, and 70 to 80% decreases in the cerebellum after day 16. Actin sequences also decrease but to a lesser extent in both tissues (i.e., 50%). These decreases coincide with the major developmental morphological changes (i.e., neurite extension) occurring during this postnatal period. These studies have also identified the appearance of a new 2.5-kilobase beta-tubulin mRNA species, which is more predominant in the cerebellar cytoplasm. The appearance of this form occurs at a time when the major 1.8-kilobase beta-tubulin mRNA levels are declining. The possibility that the tubulin multigene family is phenotypically expressed and then this expression responds to the morphological state of the nerve cells is discussed.

Regulation of tubulin and actin mRNA production in rat brain: expression of a new beta-tubulin mRNA with development

The expression of alpha-tubulin, beta-tubulin, and actin mRNA during rat brain development has been examined by using specific cDNA clones and in vitro translation techniques. During brain maturation (0 to 80 days postnatal), these mRNA species undergo a significant decrease in abundance. The kinetics of this decrease varies between the cerebrum and the cerebellum. These mRNAs are most abundant in both tissues during week 1 postnatal, each representing 10 to 15% of total mRNA activity. Both alpha- and beta-tubulin mRNA content decreases by 90 to 95% in the cerebrum after day 11 postnatal, and 70 to 80% decreases in the cerebellum after day 16. Actin sequences also decrease but to a lesser extent in both tissues (i.e., 50%). These decreases coincide with the major developmental morphological changes (i.e., neurite extension) occurring during this postnatal period. These studies have also identified the appearance of a new 2.5-kilobase beta-tubulin mRNA species, which is more predominant in the cerebellar cytoplasm. The appearance of this form occurs at a time when the major 1.8-kilobase beta-tubulin mRNA levels are declining. The possibility that the tubulin multigene family is phenotypically expressed and then this expression responds to the morphological state of the nerve cells is discussed.

Protein synthesis and rapid axonal transport during regrowth of dorsal root axons

Damage to the sciatic nerve produces significant changes in the relative synthesis rates of some proteins in dorsal root ganglia and in the amounts of some fast axonally transported proteins in both the sciatic nerve and dorsal roots. We have now analyzed protein synthesis and axonal transport after cutting the other branch of dorsal root ganglia neurons, the dorsal roots. Two to three weeks after cutting the dorsal roots, [35S]methionine was used to label proteins in the dorsal root ganglia in vitro. Proteins synthesized in the dorsal root ganglia and transported along the sciatic nerve were analyzed on two-dimensional gels. All of the proteins previously observed to change after sciatic nerve damage were included in this study. No significant changes in proteins synthesized in dorsal root ganglia or rapidly transported along the sciatic nerve were detected. Axon regrowth from cut dorsal roots was observed by light and electron microscopy. Either the response to dorsal root damage is too small to be detected by our methods or changes in protein synthesis and fast axonal transport are not necessary for axon regrowth. When such changes do occur they may still aid in regrowth or be necessary for later stages in regeneration.

Nerve growth factor and neural oncology

The precise role of the nerve growth factor protein (NGF) during the growth and development of the human nervous system is not determined. Although it appears to influence a number of neural functions, its mechanism of action is poorly understood. A number of researchers have proposed that NGF may be involved in several pathological conditions including cancer. It has been shown that NGF is secreted by certain sarcoma (23), neuroblastoma (113), and glioma (7,102,136) cell lines and can bind to neuroblastoma and metastatic melanoma cell lines (42). Neuroblastoma (136,181) and pheochromocytoma (165) cells in vitro can be induced by NGF to differentiate toward a morphologically "more benign" state and appropriate NGF treatment of rats can reduce the number of chemically induced gliomas and neurinomas (174,178). NGF can also reduce the growth of intracerebrally inoculated anaplastic glioma cells (172). Anti-NGF treatment of rats (178) and mice (179) can alter the tumor distribution observed following ethylnitrosourea or benzo(a)pyrene treatment (10). In humans, it has been reported that serum levels of NGF are usually elevated in persons "at risk" for neurofibromatosis (156). The precise nature of the NGF role is not known in these instances. Further understanding of the action of NGF could be of clinical importance.

Neuronal stimulation of non-neuronal (glial) cell proliferation: lack of specificity between different regions of the nervous system

Purified and recombined primary cultures of neurons and non-neuronal (glial) cells were prepared from the cerebral hemispheres of 10-day chick embryos. Addition of cerebral neurons to homologous non-neuronal cultures stimulated incorporation of [3H]thymidine by 2.8-fold and increased the frequency of labelling of the non-neuronal cells by 3.5-fold as visualized by autoradiography. In contrast, cerebral neurons did not stimulate the proliferation of either embryonic chick fibroblasts or leptomeningeal cells. Furthermore, addition of either fibroblasts or extra non-neuronal cells did not stimulate non-neuronal cel proliferation. These data demonstrate for the first time that neurons isolated from the central nervous system can selectively stimulate the proliferation of homologous non-neuronal cells. Cell proliferation was also studied in cultures containing both homologous and heterologous combinations of neuronal and non-neuronal cells prepared from several different portions of the nervous system (cerebral hemispheres, optic lobes, sympathetic ganglia, and sensory ganglia). Addition of embryonic neurons stimulated non-neuronal cell proliferation in all cell combinations. Thus, neurons isolated from one region of the nervous system can stimulate the proliferation of non-neuronal cells isolated from other neural regions.

Lectin labeling of sprouting neurons. II. Relative movement and appearance of glycoconjugates during plasmalemmal expansion

To study the dynamics of membrane components during neuritic growth, we carried out a series of pulse-chase experiments with ferritin-conjugated and unconjugated lectins on sympathetic neurons sprouting in vitro. Labeling of aldehyde-prefixed cultures with wheat-germ agglutinin or with the galactose-specific lectin of Ricinus communis is consistently dense near the distal end of the neurites. By contrast, if live cultures are labeled with these lectins and chased for 3-20 min, label-free plasmalemmal areas appear in the most peripheral regions of the growth cone, on filopodia and, furthermore, over vesicle clusters (SPVs). These marker-free areas, however, contain lectin receptors, as can be shown by relabeling the chased cultures with the same lectins after the aldehyde fixation. In a further set of experiments, cultures are labeled with a saturating concentration of native lectin, chased, aldehyde-fixed, and then relabeled with the ferritin conjugate of the same lectin. In this case, the surfaces of filopodia and of SPV clusters are selectively labeled with the ferritin conjugate, indicating the insertion of new lectin receptors into the plasma membrane in the growth cone periphery. These results indicate that plasmalemmal expansion in the neuron occurs by a mechanism of polarized growth, possibly involving SPVs as plasmalemmal precursor vesicles.

Sodium dependence of the nerve growth factor--regulated hexose uptake in chick embryo ganglionic cells

Embryonic dorsal root ganglionic cells, when incubated in vitro in the absence of nerve growth factor (NGF) undergo a general metabolic degeneration which is preceded by certain changes in permeation properties. Previous studies demonstrated that NGF can rapidly modulate permeation properties which regulate the availability to the cell of an important energy source, glucose. Hexose uptake was determined by measuring the ability of the cells to accumulate [3H]labeled 2-deoxy-D-glucose. The work reported here shows that the NGF-dependent portion (about one-third) of the total specific hexose uptake was also dependent on the presence of Na+, with the apparent uptake constant (Kt) for deoxyglucose varying inversely with an external Na+ concentration of 70-140 mM; Vmax was unaffected in this range. Preincubation of ganglionic cells with 10 mM ouabain for 15-60 min, followed by a pulse with [3H]-deoxyglucose, also resulted in 50-95% reduction of the NGF-sensitive uptake. A similar pretreatment of cells with veratridine gave a 25-50% reduction in uptake. The NGF-controlled hexose uptake was also energy dependent, being diminished 50-95% after a 30-90 min preincubation with 2 mM 2,4-dinitrophenol. Uptake activities for other substrates (alpha-aminoisobutyric acid, uridine) which exhibited NGF regulation were likewise Na+-sensitive. These results indicate that availability of major energy substrates to NGF-dependent dorsal root ganglionic neurons is controlled by sodium gradients across their membranes. It is conceivable that NGF provides for maintenance and development of its target neurons by acting on such sodium gradients and, consequently, regulating the intake of essential nutrients.

Nerve growth factor action on 2-deoxy-D-glucose transport in dorsal root ganglionic dissociates from chick embryo

Dorsal root ganglionic cells, when incubated in vitro in the absence of nerve growth factor (NGF), undergo a general metabolic degeneration which is preceded by loss of certain permeation properties. To determine in which ways an absence of NGF can also affect the capacity of these cells to take up an important energy source, namely glucose, experiments were carried out in which cells were incubated with or without NGF for varying times, and then presented with the factor and tested for the ability to take up 3H-labeled 2-deoxy-D-glucose. As with exogenous uridine, hexose transport in DRG cells was reduced by NGF deprivation and restored by delayed NGF administration (up to 6 h). Both the initial rate and equilibrium level were affected in an NGF dose-dependent fashion. Calculation of apparent Kt and V max in NGF-deprived and NGF-supported cells showed about two-fold differences between NGF-controlled and NGF-independent hexose transports, suggesting corresponding differences between NGF-dependent and other ganglionic cells. Restoration of hexose transport by delayed NGF administration took place within minutes of presentation of the factor. The delay before onset of restoration and the speed with which restoration was achieved have been found also to be dependent on the NGF concentration, suggesting that they reflect equilibration kinetics between NGF and its binding sites rather then the development of the response within cells. Thus, NGF can rapidly modulate permeation properties which regulate the availability of major energy substrates for the cell. This effect of NGF is discussed in the content of current views on the mode of action of the factor.

Nerve growth factor prevents the death and stimulates the neuronal differentiation of clonal PC12 pheochromocytoma cells in serum-free medium

The PC12 clone is a noradrenergic cell line derived from a rat pheochromocytoma. In culture medium containing horse serum, PC12 cells undergo mitosis; when nerve growth factor (NGF) is included in the medium, the cells cease multiplication and extend neuritis. It is shown here: (a) that PC12 cells are not viable in serum-free medium. When serum is withdrawn, 90 percent of the cells die within 4-6 days and 99 percent by 2-3 wk. (b) If NGF is added at the time of serum withdrawal, the cells undergo one doubling and remain viable for at least 1 mo. (c) Addition of NGF to cultures after more than 2 days in serum-free conditions results in maintenance of surviving cells, but not in an increase in cell number. (d) NGD also induces neurite outgrowth from PC12 cells in serum-free medium. (e) NGF-treated cells exhibit much less cell-cell and neurite-neurite aggregation in the absence than in the presence of serum. (f) The apparent minimum level of 2.5S NGF required for PC12 survival and morphological differentiation in serum-free medium is about 10 ng/ml (approximately 0.4 nM). (g) Withdrawal of NGF in serum-free conditions results in degeneration of neurites and loss of cell viability. (h) Experiments with campotothecin demonstrate that the effects of NGF on survival and neurite outgrowth may be uncoupled and suggest that the survival effects are transcriptionally independent. The present results also suggest that PC12 cells have a requirement for NGF (similar to that of normal sympathetic neurons) and that serum may substitute for this requirement. In addition, the present system of maintaining a highly differentiated cell line in a chemically defined medium suggests certain experimental opportunities.

Nerve growth factor action on membrane permeation to exogenous substrates in dorsal root ganglionic dissociates from the chick embryo

An experimental system has been described, in previous studies, where the ability of chick embryo dorsal root ganglionic cells to incorporate radiouridine into RNA declines in the absence of nerve growth factor (NGF), and is promptly restored by delayed supply of the factor. Following these early and fully reversible events, further NGF deprivation causes progressive irreversible damage. The early decline in RNA labeling and its reversion by NGF are accompanied by similar changes in the accumulation of acid-soluble radioactivity from the exogenous radiouridine substrate. In the present study, it is shown that the NGF-dependent accumulation of "soluble" radiomaterials is independent from, and responsible for, the NGF-dependent alterations in RNA labeling. Both changes are measurable with labeled cytidine and guanosine, as well as uridine, and in all cases accumulation of acid-precipitable and acid-soluble radioactivities are strictly proportional to each other. The acid-soluble responses to NGF are not prevented by actinomycin D or cycloheximide treatments, demonstrating that they require neither ongoing syntheses of RNA or protein nor prior effects of NGF on them. Chromatography of acid-soluble radiopools showed that the NGF-dependent increase was not due to a distortion in the intracellular phosphorylation of uridine; but involved corresponding increases in all the radiouridine derivatives including UTP. The time patterns of the acid-soluble response were comparable to those of the RNA labeling response, and maximal NGF effects occurred within minutes of its presentation. Finally, 2-deoxyglucose and a-aminoisobutyric acid, but not leucine, showed NGF-dependent accumulation patterns similar to those of the 3 nucleosides. It is proposed that regulation of selected membrane permeation properties could be the primary process through which NGF exerts its trophic role.