Nerve growth factors in chick tissues

Choroid coat extract and ciliary neurotrophic factor strongly promote neurite outgrowth in the embryonic chick retina

Previous studies have shown that extracts from the target optic tectum stimulate neurite outgrowth from retinal explants. The present study indicates that the choroid coat is an even richer source of retinotrophic activity. We thus studied the effects of recombinant rat ciliary neurotrophic factor (CNTF) on primary cultures of dissociated chick ciliary ganglion neurons and retinal explants for a comparison with choroid coat extract from the E18 chick. For our assays, E9 ciliary neurons were incubated in collagen gels and retinal explants were cultured on collagen gels with the addition of the trophic factors and maintained for two or four days. Survival of ciliary neurons per area as well as maximal neurite length in retinal cultures were determined. Growth responses occurred in a dose-dependent manner both to CNTF and choroid extract. Immunofluorescence examination of cells and developing processes showed 200 kdal neurofilament positivity demonstrating that the cells studied were neurons with neurites. It is concluded that a trophic activity of the choroid as well as the recombinant CNTF stimulate retinal neuron survival and neurite extension. The results suggest that CNTF may have developmental functions in the establishment of the visual pathways.

Effects of ocular injury and administration of brain-derived neurotrophic factor on survival and regrowth of axotomized retinal ganglion cells

Optic nerve transection in adult rats results in the death of approximately 50% of the axotomized retinal ganglion cells (RGCs) by 1 week and nearly 90% by 2 weeks after injury. The capacity of brain-derived neurotrophic factor (BDNF) to prevent this early, severe loss of RGCs was investigated in vivo by intravitreal injections of BDNF [5 micrograms in 5 microliters of bovine serum albumin/phosphate-buffered saline (BSA/PBS)] or vehicle (5 microliters of BSA/PBS). Using quantitative anatomical techniques, we show that (i) all RGCs survived 1 week after a single injection of BDNF at the time of axotomy. (ii) RGC densities decreased in the BDNF-treated retinas by 2 weeks but remained significantly greater than in the untreated controls. (iii) An enhanced RGC survival was obtained with single injections of BDNF from 6 days before to 5 days after axotomy. (iv) Repeated injections resulted in greater numbers of surviving RGCs, an effect that declined to undetectable levels by 6 weeks. (v) There were indications for an endogenous local source of trophic support whose expression was triggered by ocular injury, particularly to the anterior part of the eye. (vi) With multiple BDNF injections, there was profuse axonal sprouting around the optic disc. This remarkable intraretinal growth was not, however, reflected in increased RGC innervation of the peripheral nerve grafts, which are known to facilitate regeneration when used as optic nerve substitutes.

The developing chick brain shows a dramatic increase in the omega-conotoxin binding sites around the hatching period

omega-Conotoxin CVIA, a 27 amino acid neuropeptide toxin believed to target voltage sensitive calcium channels (Cruz et al., 1987, Biochemistry 26 (3), 820-824) was bound to developing chick brain at embryonic day 9-post hatch day 10. A two-fold increase was observed in omega-Conotoxin binding sites around chick hatching, embryonic days 18-20. Depolarization induced 45Ca fluxes also increased around hatching. omega-Conotoxins block > or = 80% of these 45Ca fluxes throughout development. Competition binding did not detect large differences in the binding affinity of sites during development. We conclude from these data that the increases in omega-Conotoxin binding sites and 45Ca fluxes around chick hatching are related to one of the presynaptic mechanisms of neuronal maturation necessary for normal neuronal function and chick behavior after hatching.

Chicken NGF and non-NGF trophic factor synthesis and release by sciatic nerves in vitro

The time course of production and release of nerve growth factor (NGF) and non-NGF neuronotrophic factors for sympathetic neurons by chicken and rat sciatic nerves in culture was examined. These tissues actively synthesize and release neuronotrophic activity as metabolically poisoning nerves with azide dramatically reduced the amount of trophic activity released into the culture medium. The sustained release of this activity also was shown to be dependent on the presence of low-molecular-weight dialysable molecules present in foetal calf serum and amniotic fluid from day 11 chicken embryos. Affinity-purified antimouse NGF antibodies were used to show that sciatic nerves in culture release both NGF and non-NGF trophic factors. These antibodies inhibited all bioactivity of both mouse NGF and of a partially purified preparation of chicken NGF. Immunoblot studies confirm that the antibodies recognize both rodent and avian NGF. Excess antibody inhibited only about 50% of the trophic activity in media conditioned over rat or chicken nerves for the first 24 hr. Relatively similar amounts of this non-NGF trophic activity were released throughout 6 days in culture, and this trophic activity kept sympathetic neurons alive in culture in the absence of NGF for more than 4 days. NGF levels were quantified with a two-site enzyme-linked immunoassay and found to parallel changes in NGF bioactivity. Rat nerves released increasing amounts of NGF with time in culture. Whole chicken sciatic nerves, however, released decreasing amounts of NGF with time in culture, but when these nerves were desheathed by removal of the epineurium and attached tissue, the pattern of NGF release was similar to that observed in the smaller rat sciatic nerves. These studies therefore characterize antibodies recognizing chicken NGF, demonstrate that peripheral nerve tissue synthesize trophic factors other than NGF, and identify factors that influence NGF synthesis.

Effects of injecting antibodies to mouse nerve growth factor into the chick embryo

The function of NGF in chick embryos was studied by injecting antibodies to mouse nerve growth factor (NGF). The uptake of mammalian antibodies into the 8- to 15-day-old chick embryo was followed by an enzyme-linked immunoassay. Normal rabbit antibodies (250 micrograms) were administered to the yolk, of which less than 5% was found in the embryo (300 ng of IgG per g wet wt of embryo). The concentration was proportionally lower when 100 micrograms anti-NGF antibodies were injected (40 ng/g). The concentration of anti-NGF antibodies was 1.5 times higher following injection directly into the body of the embryos. The effects of injecting antibodies at days 3-7 were studied in 10-day-old embryos by measuring the diameter frequencies of neurons in sympathetic and sensory ganglia. In comparison with controls, significantly smaller neurons were found in the sympathetic ganglia in embryos directly injected with anti-NGF. In the spinal ganglia, distribution of neuron diameters did not differ between anti-NGF-treated embryos and controls. Finally, the ability of different antibodies to mouse NGF to inhibit the in vitro activity of recombinant chick NGF was investigated. Total block was found at 1000-2000 ng of IgG per ml for most of the antibodies tested, levels not reached when injecting the embryo with antibodies to NGF. We conclude that the main reason for the limited effects in chick embryos by injection of NGF antibodies is due to the low levels of penetration of the anti-NGF IgG into the embryo.

Endogenous chicken nerve growth factor from sheath cells is transported in regenerating nerve

We report the presence of endogenous nerve growth factor (NGF) in chicken peripheral nerve. The molecule has been detected with antibodies to mouse salivary gland NGF, using immunohistochemical and immunoelectrophoretic techniques. Previous studies have shown that these antibodies inhibit the survival activity of extracts of chicken peripheral nerve. The NGF accumulated distal, but not proximal, to a ligature placed on a peripheral sympathetic nerve demonstrating that it was retrogradely transported. This transport was detected in intact nerve fibers as well as in nerves from which the peripheral target had been ablated 6 hr or 7 days previously. The results indicate that avian NGF is present in adult chicken peripheral nerves and that this molecule shares antigenic determinants with the mouse molecule. The results further demonstrate that regenerating neurons retrogradely transport NGF supplied by cells within the peripheral nerve (presumably Schwann). The possibility that these cells also provide NGF to intact neurons is discussed.

Neuroblastoma cells contain a trophic factor sharing biological and molecular properties with ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) is a protein supporting the in vitro survival of a characteristic spectrum of embryonic chicken and rat peripheral neurons. High-speed supernatants of extracts from two neuroblastoma (NB) cell lines--the mouse C 1300 N2a and the human IMR 32--mimic the effects of CNTF on identical target neurons. Promotion of survival is dose-dependent with an ED50 of 80 micrograms (IMR 32) and 140 micrograms (C 1300 N2a) of protein per ml and saturable at plateau values for surviving neurons identical to those achieved with purified CNTF. Small amounts of a CNTF-like material are also detectable in medium conditioned by NB cells. The activity is destroyed by heat and trypsin and not blocked by antibodies to (mouse) nerve growth factor. Unlike the neurite-promoting and neuronal-survival modulating agent laminin, it cannot be depleted on poly(L-alpha-ornithine)-coated plastic surfaces. NB IMR 32 cell extracts were electrophoresed using NaDodSO4/PAGE and transferred to nitrocellulose. Ciliary ganglion neurons seeded on the blotting paper in culture medium lacking CNTF ("cell blot") exclusively survive on two distinct bands with apparent molecular masses of 24 and 48 kDa. Twenty-four kilodaltons is the molecular mass of a CNTF purified from rat sciatic nerve. These results suggest that NB cells may contain a CNTF-like protein and provide further evidence that neurons may store neurotrophic factors. Purified (chicken) CNTF failed to affect proliferation and neurite growth of NB cells. The biological relevance of CNTF for NB cells, therefore, remains to be elucidated.

Induction of the high-affinity nerve growth factor receptor on embryonic chicken sensory nerve cells by elevated potassium

Culture medium with elevated K+ has been shown to enhance the survival of neurons isolated from several different regions of the nervous system. Nerve growth factor binds to binding sites on sensory and sympathetic neurons through two sites, one of high-affinity (Kd1 approximately 3 X 10(-11) M) and the other of low-affinity (Kd2 approximately 2 X 10(-9) M). Equilibrium binding data generated on dissociated cells derived from E9 chicken embryo dorsal root ganglia, has shown that there is a two-fold increase in the number of high affinity (type I) receptors, with no effect on the affinity, when cells are incubated for 2 hours in buffer containing 59 mM K+. There does not appear to be a significant change in the affinity or the number of low-affinity binding sites. This two-fold increase in type I receptors is dependent on temperature, Ca+2, and active protein synthesis. There does not appear to be an intracellular pool of the type I receptor sufficient to account for this increase. The induction is not observed on sensory nerve cells cultured in 59 mM K+ for 24 hours, either in the presence or absence of nerve growth factor. Additionally, the induction in the number of type I receptors requires that both nerve growth factor and K+ be present simultaneously. Taken in total, this data suggests that there may be a critical period in which the sensory neurons require nerve growth factor exposure to respond. Evidence is presented which indicates that nerve growth factor responsive cells are able to elicit neurites after an acute exposure to nerve growth factor of as little as 4 hours. Finally, there is an approximate two-fold decrease in the concentration of nerve growth factor needed to elicit maximal fiber outgrowth, consistent with the two-fold increase in the number of type I receptors.

Comparative screening for ciliary neurotrophic activity in organs of the rat and chicken

A neuron-survival assay with dissociated ciliary ganglion neurons was used to examine the level of neurotrophic activity in organs of the rat and chicken. All tissue homogenates enhanced neuron survival at increasing protein concentrations, although 50% survival activity (1 trophic unit, TU, per ml) occurred at distinctly different levels in the different organs. Liver, spleen, T-cells, and submandibular gland from the rat were very low in survival-promoting activity (0.1-1.1 TU per mg of protein). Serum and lung were slightly richer (2.4-2.8 mg). Heart, brain, and skeletal muscle stimulated survival well (6.2-13 TU/mg). Unexpectedly, the highest activities were found in the rat kidney (44 TU/mg). The activity in adult chicken organs was less varied (1.6-9.1 TU/mg). Higher trophic activities were found in the chicken embryo, particularly at day 18 of development (20-30 TU/mg). The up to 100-fold difference in trophic level between organs should make it feasible to use subtractive hybridization, differential screening, and transient expression in eukaryotic cells for molecular cloning of the ciliary neurotrophic factor(s).

Molecular cloning of the avian beta-nerve growth factor gene: transcription in brain

A chicken gene cross-hybridizing with a murine beta-nerve growth factor (beta NGF) cDNA probe was identified by Southern blot analysis and isolated from a genomic DNA library. The DNA sequence coding for the putative mature beta NGF protein was determined, providing direct evidence for the existence in birds of a neurotrophic factor sharing a high degree of sequence homology with mammalian beta NGF. In addition this gene is shown to be transcriptionally active in adult avian brain as demonstrated by Northern blot analysis.

Production and transport of endogenous trophic activity in a peripheral nerve following target removal

High concentrations of trophic factor for sympathetic neurones were found in the discrete nerve which innervates the expansor secundariorum muscle of the chicken wing. Mouse nerve growth factor (NGF) was additive with nerve extract in allowing survival of sympathetic neurones. Antiserum to NGF, while inhibiting outgrowth in response to NGF, only partially blocked survival promoted by the nerve extract. In these characteristics, the nerve extract resembled the previously characterized activity of its target organ. However, after surgical removal of the muscle there was no decrease in the concentration of trophic factors in the nerve 7 days later. Likewise sectioning, crushing or removing a piece of nerve 1 cm from the muscle had little effect on trophic levels after muscle removal. Retrograde transport of the activity occurred in the nerve even in the absence of the muscle. Distal to ligatures placed on the nerve stump 24 h earlier, 60% of the trophic activity was inhibited by an antiserum to mouse NGF suggesting that a chicken form of the molecule is present and transported. In culture, cells of the nerve sheath produced trophic factors, and the rate of production increased greatly during the first 24 h of incubation. Two conclusions are made: the major source of trophic activity in the nerve is Schwann cells and at least two molecules are present, one of which is a chicken form of NGF.

Chromaffin cell heterogeneity of process formation and neuropeptide content under control and nerve growth factor-altered conditions in cultures of chick embryonic adrenal gland

Adrenal glands from embryonic day 11 (E-11) chicks were cryostat-sectioned, and it was determined that tyrosine hydroxylase-like immunoreactive (TLI) cells, somatostatin-like immunoreactive (SLI) cells, and methionine-enkephalin-like immunoreactive (ELI) cells occupied chromaffin regions of the gland. Similar age adrenals were dissociated, and the cells were cultured under serum-free conditions. Cultured TLI cells, ELI cells, and SLI cells were characterized according to cell size, cell number, and neurite formation. ELI and SLI cells composed two largely separate populations, with SLI cells tending to have larger cell areas, to be more numerous, and to be less likely to form neurites than ELI cells. The population of TLI cells, although unique in itself, was diverse and numerous enough to include all or portions of the neuropeptide-immunoreactive populations. Neurites of some cells from each of the above populations were strongly immunoreactive for alpha neurofilament protein, and for NAPA73 neurofilament-associated protein. However, neurites could also be observed in all populations that showed poor immunoreactivity for these cytoskeletal proteins. Exogenously added NGF significantly increased neurite-like process formation among TLI and ELI cells, but not among SLI cells. Reductions in the number of neurite-like processes following treatment with anti-nerve growth factor (NGF) were not significant for any of the populations. However, if shorter and broader process were included, anti-NGF caused a significant reduction in total cell processes among TLI and ELI cells. Anti-NGF inhibition of process formation among ELI cells could be reversed with exogenous NGF. Neither NGF or anti-NGF treatments showed a significant effect on cell numbers among TLI and ELI populations. The implications are that a compound of antigenic and physiological similarity to mouse salivary NGF is made by embryonic chick adrenal cells in culture, but the effects of NGF do not appear to be the same for all neural-crest-derived cells from the adrenal, and greater heterogeneity of phenotypes may exist among chromaffin cells than has previously been accepted. Some questions are also raised concerning the neurite-like nature of processes formed by some chromaffin cells in vitro.

Nerve growth factor in medium conditioned by embryonic chicken heart cells

The present report demonstrates that embryonic chicken heart cells in culture release different nerve growth promoting factors to their culture medium, one which is biologically and immunologically similar to mouse gland beta NGF. Serum-free heart cell conditioned medium thus promoted neurite outgrowth from sympathetic and ciliary ganglia and supported survival of dissociated ciliary neurons. The addition of affinity purified antibodies against mouse beta NGF does substantially but not completely inhibit the fibre outgrowth from sympathetic ganglia, but does not to any extent diminish the effects on the parasympathetic neurons. The chicken NGF recovered from polyacrylamide gels after electrophoresis greatly enhanced sympathetic fibre outgrowth, an activity completely suppressive by anti-beta NGF antibodies. We conclude that a chicken NGF is being produced by the embryonic heart cells in culture, and that this factor may be produced also in the embryo to fulfill a role in heart innervation.

Effects of nerve growth factor and heart cell conditioned medium on neurite regeneration of aged sympathetic neurons in culture

The effects of nerve growth factor (NGF) and heart-cell-conditioned medium (HCM) on the neurite regeneration of aged sympathetic neurons were investigated in culture. Investigation of HCM was carried out by two different methods: one was the use of whole HCM on collagen substratum, which reflected component(s) effective in solution (HCM-S); the other was the use of polyornithine (PORN)-binding component(s) (P-HCM). Superior cervical ganglion neurons prepared from male mice from 6 to 30 months of age were cultured in MEM-10% FCS on collagen or gelatin-PORN substratum for 3 days. The number of neurons with neurites and the length of neurites were quantified as neurite production and elongation, respectively. Neuronal survival was not affected by addition of NGF, HCM-S or P-HCM. Neurite production of early adult neurons was enhanced by NGF, HCM-S or P-HCM. In contrast, neurite production of aged neurons was enhanced by only HCM-S, but not NGF or P-HCM. HCM-S did not promote neurite elongation in neurons at any age. Neurite elongation of early adult neurons was enhanced by NGF or P-HCM. Neurite elongation of aged neurons was enhanced by P-HCM. However, responsiveness of NGF for neurite elongation varied according to substrata. No age-related difference was found in neurite production and elongation in the absence of NGF, HCM-S or P-HCM. These results indicate that responsiveness of aged sympathetic neurons is various in different growth factors.

Neuronotrophic activity for ciliary ganglion neurons. Induction following injury to the brain of neonatal, adult, and aged rats

The induction of neuronotrophic activity following injury to the brain of neonatal, adult, and aged Sprague-Dawley rats was compared using an improved in vitro assay. The maximal levels of activity in tissue surrounding the wound were reached at 3, 10-15, and about 15 days postlesion in neonatal, adult, and aged animals, respectively. Tissue neuronotrophic levels were always much lower in neonatal animals relative to the older animals. Accumulation of neuronotrophic activity in the gelfoam placed into the wound cavities in neonatal and adult animals lagged behind the levels in tissue by 4-5 days, suggesting that either the neuronotrophic factor itself or the cells which produce it are transferred from the tissue into the gelfoam. Relatively little activity accumulated in the gelfoam taken from aged Sprague-Dawley rats, and this observation was confirmed in aged Fischer rats. Aged animals seem to be unable to produce or release one of a number of neuronotrophic factors in response to injury.

Development of mouse spinal cord in tissue culture: IV. Effects of embryonic extracts on neuron formation and migration

Possible influences upon patterns of neurogenesis expressed in vitro were examined quantitatively by the use of microfragment cultures of embryonic day 10 mouse neural tube. Crude extracts were prepared either from whole embryos (day 13 or 15 of gestation) or from embryonic brains (day 18 of gestation) and added to the culture medium for the first 10 days of culturing. Neuronal outgrowth zones surrounding individual microfragments were reduced in area (indicating restricted neuronal migration) and in number of neurons present (indicating restricted production of neurons) following treatment with either of the extracts. The severity of reductions observed were related to the developmental age of embryonic tissue used for preparing the extract, as greatest reduction resulted from addition of embryonic day 18 brain extracts and to concentration employed, higher doses further restricting neuronal outgrowth. By increasing the concentrations of extract the proportional number of large-sized neurons forming the outgrowth zones became greater relative to the small neuron contribution, indicating an enhanced survival for this neuronal population. The formation and migration of astroglial precursor cells was not affected by the addition of any of the extracts. The number of neurons remaining within the original portions of neural tube microfragments was not significantly altered following culturing in the presence of embryonic extract. This suggested that the reduction in neuron number in the outgrowth zone actually reflected a decreased neuron production and was not simply the result of a retention of neurons within the remaining portion of the microfragment. The results suggest the presence of substances within mouse embryos that have regulatory effects on aspects of development of the central nervous system. Indications are that survival and maturation of postmitotic neuroblasts are promoted in vitro while the formation of additional neuronal progenitor cells may be partially inhibited by the addition of embryonic mouse extracts to the medium. We propose that an endogenous negative feedback mechanism may be involved in the coordination of patterns of neurogenesis.

Hormones and growth in poultry

The hormonal control of growth in poultry and other species is complex. The available evidence supports the concept that growth hormone and the thyroid hormones are the principal hormones responsible for the attainment of normal growth in the domestic fowl. Other hormones, including somatomedins, epidermal growth hormone, sex steroids, and vitamin D metabolites, are also involved in the control of growth. Considerable study will be required for the elucidation of the exact roles of the various hormones in avian growth.

Nerve growth factor in three neurologically deficient mouse mutants

The activity of nerve growth factor (NGF) in the salivary glands and in the sciatic nerve was compared between normal mice and mice affected by either of three neurological mutations by the use of a biological assay. No evidence was obtained for defects in amount or activity of NGF associated with the sprawling or splotch mutations. A reduction in the NGF content was found in salivary glands and sciatic nerve in homozygous dystonia musculorum mice. It is pointed out that the low amounts of NGF in dtJ/dtJ mice is likely to be a consequence of the general disturbances in development seen in this mutant rather than the specific cause for the neurological disorder.

Peripheral nerve extract promotes long-term survival and neurite outgrowth in cultured spinal cord neurons

The hypothesis that peripheral, skeletal muscle tissue contains a trophic factor supporting central neurons has recently been investigated in vitro by supplementing the culture medium of spinal cord neurons with muscle extracts and fractions of extract. We extended these studies asking whether or not a trophic factor is present in peripheral nerves, the connecting link between muscle and central neurons via which factors may be translocated from muscle to neurons by the retrograde transport system. Lumbar, 8-day-old chick spinal cords were dissociated into single cells and then cultured in the presence of peripheral nerve extract. Cytosine arabinoside was added to inhibit proliferation of nonneuronal cells. In the presence of nerve extract, spinal cord neurons survived for more than a month, extended numerous neurites, and showed activity of choline acetyltransferase. In the absence of extract, neurons attached and survived for a few days but then died subsequently in less than 10 days. Neurite outgrowth did not occur in the absence of extract. Withdrawal of extract from the medium of established neuronal cultures caused progressive loss of both cells and neurites. Other tissues also contained neuron supporting activity but less than that found in nerve extract. These studies indicate that peripheral nerves contain relatively high levels of spinal cord neuron-directed trophic activity, suggesting translocation of neurotrophic factor from muscle to central target neurons. The neurotrophic factor has long-term (weeks) effects, whereas short-term (days) survival is factor independent.