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

Modulation of ethanol neurotoxicity by nerve growth factor

Dorsal root ganglion (DRG) neurons were cultured with varying concentrations of ethanol and NGF. At low concentrations of NGF (0.1 ng/ml) moderate initial ethanol levels (250 mg/dl) significantly suppressed neurite outgrowth. Higher NGF concentrations (5 ng/ml) protected against this neurotoxicity. At this higher NGF concentration, neuronal survival was not significantly affected by exposure to 0.25-4 g/dl ethanol, although survival was significantly diminished at 5 and 6 g/dl. Neurite outgrowth was a more sensitive indicator of ethanol neurotoxicity in this population, with significant decreases in process extension seen with 1 g/dl ethanol. When cultures were supplemented with 10 ng/ml NGF, however, process elaboration was significantly greater at 1 g/dl ethanol than that measured with 5 ng/ml NGF, and in fact did not differ from NGF controls. These studies indicate that NGF can provide neuroprotective effects against ethanol toxicity under these conditions. The results are discussed in relation to other recent reports of trophic factor neuroprotection.

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.

Developmental regulation of a neurite-promoting factor influencing statoacoustic neurons

The present study investigated a target-derived, neurite-promoting factor (NPF) released by the developing chick otocyst and its effects on statoacoustic ganglia (SAG). SAG explants cultured in the absence of otocysts produced little neurite outgrowth at all stages of development examined (E4-E13). However, extensive neurite outgrowth was seen when E4-E6 SAG were cultured in the presence of otocysts of the same age. The amount of neurite outgrowth observed in cocultures steadily decreased at later developmental stages. E7-E9 cocultures produced less outgrowth and E10-E13 cocultures produced the least outgrowth compared to E4-E6 cocultures. Additionally, otocysts from older stages were unable to promote outgrowth of E4 SAG. Thus, the level of the factor released by the otocysts declined during development. In contrast, neurite outgrowth was promoted when E10-E15 SAG were cocultured in the presence of younger stage otocysts. Our data indicate that the release of NPF from chick otocysts decreased from E6 to E13, although the ability of SAG neurons to respond to the NPF was maintained throughout development.

Extension of sympathetic neurites in vitro towards explants of embryonic and neonatal mouse heart and stomach: ontogeny of neuronotrophic factors

In order to establish when target organs first produce neuronotrophic factors, extension of neurites in vitro from sympathetic ganglia (superior cervical and coeliac) of 1-day neonatal mice towards explants of 10-, 11-, 14- and 17-day embryonic and 1-day neonatal atrium and stomach was examined in co-cultures. Longer neurites extended from ganglia towards, than away from, atrial targets at all stages examined, and was most marked towards 17-day embryonic and neonatal explants. Treatment of atrial co-cultures with antiserum to nerve growth factor (NGF) almost totally blocked preferential neurite outgrowth. Directional growth of neurites towards stomach explants in co-cultures was not as pronounced as that towards atrium; extension of neurites was most marked when stomach was provided by 11-, 14- and 17-day embryos. Such outgrowth was only partially blocked by antiserum to NGF, significant preferential extension of neurites towards stomach persisting in the presence of the antiserum. These results indicate that atrium and stomach produce neuronotrophic factors from the earliest ages studied; the evidence indicates that in the case of atrium, NGF predominates but that stomach produces NGF as well as another factor immunologically distinct from NGF. It is of interest that both types of target explanted before they receive sympathetic innervation show evidence of producing NGF in culture.

A method for the quantitative analysis of nerve growth in vitro

A method is described for the quantitative analysis of the nerve-growth-promoting activity of biological molecules in tissue culture. The criteria used for the evaluation of this activity is based on the neurite length as well as the total number of neurites produced by the explant of whole dorsal root ganglia from 12-d-old chick embryos. A nerve growth index (NGI) is given to each ganglion during each of a 5-d culture period. The NGI is defined as the product of average neurite length in millimeters and the total number of neurites. We report that with increasing concentrations of fetal bovine serum, there was a proportional increase in NGI due to increased neurite density while the neurite length was not greatly affected. The NGI of several proteins with known nerve growth promoting activity, namely nerve growth factor, insulin, transferrin, and fibronectin were investigated for their activity and compared with that of fetal bovine serum.

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.

Neuronal growth factors from tumours of Von Recklinghausen neurofibromatosis

Explants of 21 neurofibromas from 16 patients with Von Recklinghausen neurofibromatosis (NF-I) plus tumour tissue from 5 comparison patients and normal tissue from one of the NF-I patients were assayed for neuronal growth factor(s) using dissociated embryonic sensory neurons from chick embryo. Twenty-one of 21 neurofibroma explants released detectable quantities of neuronal growth factors, but only 2 of 8 non-neurofibroma tissue explants released activity. While antiserum to mouse nerve growth factor (NGF) fractionally inhibited neurite outgrowth induced by some of the neurofibromas, overall differences between assays containing antibody and controls reached statistical significance in 3 cases; in one case, explants of a separate tumour from the same patient had no detectable NGF-like activity. These data support the hypothesis that local release of neuronal growth factors in neurofibromas are responsible for neurites observed within these tumours. Further evidence that endoneurial tissue of peripheral nerve is a rich source of heterogeneous neuronal growth facts has been provided by these studies.

Developmental regulation of chick embryo retina neurite extension by extrinsic factors

Developmental changes in the control of neurite extension by extracellular factors can be examined by utilizing cultures of neurons from various aged embryos. Several conditioned media and tissue extracts were added to cultures of chick embryo retinal neurons on collagen substrates for 1, 3 and 5 days in vitro. Neurite outgrowth, measured as the percentage of neurons with neurites and the length of neurites, was promoted by optic tectal extract and cornea conditioned medium in retina neurons from younger ages (6- to 12-day embryos), but not from older ages (14- and 16-day embryos). The promotion of neurite outgrowth by optic tectal extracts may be mediated by a promotion of glial cell growth. The developmental changes in neurite extension may be due to either an altered sensitivity to the neurite promoting factors or by an altered intrinsic ability of retinal neurons to extend processes.

Age-dependent stimulation by atrium explants or nerve growth factor of nerve fibre outgrowth from cocultured embryonic rat sympathetic ganglia

Whole sympathetic superior cervical ganglia of 14- and 15-day-old rat embryos were cultured in a collagen gel medium for 24 h with or without explants of heart atrium from the same animals or from newborn rats. The extent of nerve fibre outgrowth was estimated by counting the number of nerve fibres crossing each arc of a sector drawn in the microscope ocular. Only few nerve fibres extended from the ganglia of the 14-day-old embryos cultured in the pure control medium. Addition of exogenous nerve growth factor did not stimulate the poor growth. While the growth of nerve fibres in the presence of atrium explants of newborn rats did not significantly differ from that in cultures without any target tissue, the presence of atrium explants of the same, 14-day-old, embryo resulted in clearly enhanced fibre outgrowth from the ganglia, which was inhibited by antiserum to the nerve growth factor. The ganglia of 15-day-old embryos cultured without target tissue in the control medium produced only sparse fibre outgrowth which was excessively increased by exogenous nerve growth factor. Coculture with atrium explants of 15-day-old embryos or newborn rats produced an increased overall nerve fibre growth, as well as predominance of those fibres growing toward the target tissue. The growth-promoting effect of the atrium of 15-day-old embryos was only partially prevented by antiserum to the nerve growth factor, while that elicited by newborn rat atrium was totally inhibited.(ABSTRACT TRUNCATED AT 250 WORDS)

The survival and growth of embryonic proprioceptive neurons is promoted by a factor present in skeletal muscle

To date, the neurotrophic factor requirements of developing sensory neurons have been studied using heterogeneous populations of neurons that innervate a wide variety of different sensory structures. To ascertain the particular neurotrophic factor requirements of different kinds of sensory neurons and to determine whether these requirements are related to the type of sensory receptors innervated, it is necessary to study homogeneous preparations of functionally distinct sensory neurons. For this reason I have studied the influence of a soluble extract of skeletal muscle on the survival and growth of proprioceptive neurons isolated from the trigeminal mesencephalic nucleus (TMN) of the embryonic chick. Explants of the TMN and dissociated glia-free cultures of TMN neurons were established from chick embryos of 10 to 18 days incubation (E10 to E18). Skeletal muscle extract prepared from E18 chick pectoral muscle and enriched for neurotrophic activity by ammonium sulfate fractionation promoted marked neurite outgrowth from explants and substantial survival in dissociated cultures established during the period of natural neuronal death in the TMN. In these latter cultures 70 to 80% of the neurons survived and grew in the presence of the extract compared with less than 2% in control cultures. At later ages, following the period of natural neuronal death, these effects were less marked. The neurotrophic activity of extracts prepared from muscle of different ages increased steadily from E10 to E20 (the oldest muscle studied). The active factor is heat labile, trypsin sensitive, and non-dialyzable, it is neither functionally nor immunochemically related to NGF and it has negligible neurotrophic effect on the predominantly cutaneous sensory neuron population of the trigeminal ganglion. These findings demonstrate that skeletal muscle contains a neurotrophic factor which supports the survival and growth of proprioceptive neurons and suggest that this factor has some specificity among functionally distinct kinds of sensory neurons.

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

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

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.

Regulation of sympathetic trophic factors in smooth muscle

The level and nature of trophic activity present in the chicken expansor secundariorum muscle has been shown to be altered by denervation. This muscle receives a dense, sympathetic innervation and contains high concentrations of trophic factors, which were found to be immunologically and functionally distinct from mouse Nerve Growth Factor. In young birds, denervation increased the number of neurons which could be supported by muscle extract. This difference was apparent with regard to E8 to E16 sympathetic neurons. Innervated but not denervated extract was additive with NGF in promoting neurite outgrowth. In contrast, when extracts of denervated and innervated muscle from mature birds were examined, no difference was seen in the number of neurons supported by each extract. However when the denervated and innervated extracts from mature birds were combined more neurons were supported than by a saturating dose of either extract alone. Furthermore, muscle from mature birds responded to denervation only between 2 and 9 days, whereas in young birds the effect was apparent for at least 3 weeks. Analysis of intact, control muscles during the first 8 weeks posthatch demonstrated that the number of neurons that could be supported by the individual extracts varied with the age of the bird. It is concluded that denervation does not in all instances lead to an increase in trophic activity, but does produce a change in the nature of the activity present, such that a different neuronal subpopulation may be supported.(ABSTRACT TRUNCATED AT 250 WORDS)

The characterization and cellular distribution of a family of antigens related to myelin associated glycoprotein in the developing nervous system

The antigenic epitope detected on myelin associated glycoprotein (MAG) by the monoclonal antibody HNK-1 (Leu 7) was sensitive to degradation by trifluoromethane-sulfonic acid (TFMS) and is therefore probably carbohydrate in nature. This antigen was found to be widely distributed within the rat and chicken embryonic nervous system and was present on cultured central and peripheral neurons (100%), oligodendrocytes (100%) and astrocytes (70-80%) as detected by double marker immunofluorescence. The antigen could be removed from cultured neurons by trypsinization and its resynthesis was blocked by cycloheximide, suggesting that the carbohydrate epitope detected by HNK-1 was attached to a de novo synthesized protein. Several molecular species were detected on Western blots of detergent extracts from 13-15d rat embryonic brain and neuron-enriched cultures from chick spinal cord and dorsal root ganglia. Protein components with molecular weights in the ranges of 90-100 kd to 280 kd were observed and comprise a family of glycoproteins containing the HNK-1 reactive carbohydrate epitope present on MAG. These glycoproteins could play a role in intercellular interactions within the developing nervous system.

Specificity of a neuronotrophic factor from rabbit corneal epithelial cultures

Previous studies have demonstrated that of the three major cell types of rabbit cornea, only epithelial cells released a neuronotrophic factor that is active in both promoting survival and inducing neurite outgrowth of dissociated trigeminal neurons. In this study, the specificity of neuronotrophic factor production by selected epithelial cell types and the responsiveness of neurons from several different tissues to this trophic factor were determined. Cell cultures of various epithelia and dissociated neurons from several ganglia of neonatal and adult rabbits were utilized. In comparison with adult corneal epithelium, adult bulbar conjunctiva released a similar amount of trophic factor. Neonatal corneal epithelium released five times more, but adult retinal pigment epithelium and neonatal skin epithelium yielded less than a third and one-sixth respectively, and three cell lines (adult skin, kidney and neonatal lens epithelia) released only negligible amounts. Compared with its effect on neonatal trigeminal neurons, the trophic factor from adult corneal epithelium was similarly active on neonatal dorsal root neurons, but only half as effective on adult trigeminal neurons and less than one-tenth as effective on neonatal superior cervical neurons. The effect of nerve growth factor (from mouse submaxillary gland) on these neurons was tested for comparison. The results indicated that of the tissues studied, neuronotrophic factor was released in abundance only from corneal and conjunctival epithelia, and was active predominantly on trigeminal and dorsal root neurons (sensory neurons). This is consistent with the concept that the developmentally regulated release of trophic factor by target cells may be an underlying mechanism for neurogenesis and nerve regeneration.

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

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

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

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

Nerve growth factor treatment does not prevent dorsal root ganglion cell death induced by target removal in chick embryos

In chick embryos, on the 3rd day of incubation, the developing right wing bud was removed. One group of the operated embryos was treated with a daily dose of 20 micrograms purified nerve growth factor (NGF) from the 5th day of incubation and sacrificed on the 12th day. The other group was sacrificed on the 12th day of incubation and served as control. NGF was also administered to intact, unoperated embryos for comparison. The size of the dorsal root ganglia in segments 13-16 innervating the wings, were estimated and the number of surviving dorsal root ganglion cells counted both on the right (operated) and left (intact) sides. Although NGF brought about an increase in the size of the ganglia and an increase in the number of dorsal root ganglion cells bilaterally, it was not able to prevent excessive cell death of dorsal root ganglion cells on the operated side. The number of surviving neurons in the dorsal root ganglia on the operated side in embryos with or without NGF administration was only about 30-50% of the number of the intact side. These results show that cell death induced by target removal cannot be offset by NGF administration. It is concluded that NGF may act as a growth promoting agent for developing sensory neurons but other peripheral trophic factor/s are also needed for the maintenance and survival of dorsal root ganglion cells.

Retrograde and transganglionic degeneration of sensory neurons after a peripheral nerve lesion at birth

The sciatic nerve of newborn rats (less than or equal to 16 h old) was crushed with a watchmaker forceps. During the first 4 weeks after the injury, examination of ipsilateral L4 through L6 dorsal root ganglia, their dorsal nerve roots, and the dorsal funiculus revealed the presence of degenerating myelin and axons. Chromatolysis was not observed. In the spinal cord, the degenerating argyrophilia was restricted to the medial part of the dorsal funiculus (fasciculus gracilis). This is interpreted as transganglionic degeneration of the central processes of the pseudounipolar cells. Twelve weeks after nerve crush, there was a noticeable reduction in the size of the leg, foot, and muscles innervated by the sciatic nerve as well as a substantial loss (P less than 0.001) of neurons and myelinated axons in ipsilateral spinal ganglia and their dorsal nerve roots. The reduction was most prominent among the larger sensory neurons (greater than 40 microns) and the larger myelinated axons. A total loss of about 60% of sensory neurons was found in the L4 through L6 spinal ganglia. About 58 and 64% of the myelinated axons were lost in L4 and L5 dorsal roots, respectively. The remaining perikarya and dorsal root axons were hypoplastic.

Neurite-promoting factors from embryonic neurons

Dissociated chick embryo peripheral and central nervous system cultures enriched for neurons by differential adherence, defined medium and cytosine arabinoside release to the culture environment molecular species which enhance the performance of neurons in limiting conditions. Culture medium conditioned by the neurons can be depleted of substrate-attached material by serial passage on poly-D-lysine substrate, leaving in the medium factors which promote neurite outgrowth on poly-D-lysine. The substrate-attached material which enhances neuron survival and neurite extension is heat- and trypsin-labile but is not affected by prior treatment with antisera to mouse NGF, human plasma fibronectin or laminin. The autostimulation phenotype displayed by neurons may play a role in neuronal survival or axonal growth during neuronal development.

Serum neuronal growth factor levels in von Recklinghausen's neurofibromatosis

A single neuronal cell biological assay was used to quantitate neuronal growth factors in 87 serum samples from 69 patients in 48 families with von Recklinghausen's neurofibromatosis, plus 16 samples from 16 comparison subjects. Mouse nerve growth factor was used as a standard for the bioassay, and results of serum assays were expressed as nerve growth factor equivalents. Antiserum to mouse nerve growth factor inhibited fractionally serum-induced neurite outgrowth, while kinetics of neurite outgrowth and maximal cellular response to serum differed from those induced by mouse nerve growth factor. The mean values (+/- SD) of neuronal growth factors for the patients were 20.5 +/- 15.7 pg/mg serum protein, while mean values for the comparison group as a whole were 22.3 +/- 15.6 pg/mg serum protein. Sex, race/ethnicity, patient age, and date of sample collection did not significantly influence serum levels among patients or comparison subjects. Three to six serial samples taken from women before pregnancy, during the course of pregnancy, during delivery, and in the postpartum period did not show significant differences from one period to another. These data suggest that human serum does contain non-nerve-growth-factor neuronal growth factors, but that levels of the factors do not contribute to the identification of patients with von Recklinghausen's neurofibromatosis.

Spinal cord contains neurotrophic activity for spinal nerve sensory neurons. Late developmental appearance of a survival factor distinct from nerve growth factor

Several tissues of the developing chick embryo have been reported to contain neurotrophic activity which can sustain the survival of sensory neurons maintained in culture. In a previous study, however, we noted that such nerve growth promoting activity was exceptionally low, if not absent, from extracts of spinal cord from chick embryos of up to 16 days incubation. Since then the combined results from a number of tissue culture studies have suggested that the central nervous system may be the source of a neurotrophic growth factor essential during the late development of sensory neurons. We have therefore carried out an extended range study of the neurotrophic properties of avian spinal cord. Extracts of spinal cord tissue prepared from chicks at stages between the last wk of embryogenesis and 12 wks after hatching were tested for their ability to promote survival and neurite outgrowth from both explant and dissociated neuron-enriched cultures of dorsal root, trigeminal, nodose and paravertebral chain sympathetic ganglia from chick embryos between 8 and 16 days old. We conclude from our results that spinal cord is a potent source of neurotrophic activity for sensory neurons, although this activity appears relatively late in development of the spinal cord. The predominant ontogenic increase in spinal cord neurotrophic activity was seen to occur during the first week after hatching. Sensory neurons from both spinal and cranial nerve ganglia were sustained in culture by spinal cord extracts, whereas sympathetic neurons did not respond. Neurons from older sensory ganglia (12-16 day old embryos) were much more responsive than similar neurons from young embryos (8 day).(ABSTRACT TRUNCATED AT 250 WORDS)

Neural crest-derived spinal and cranial sensory neurones are equally sensitive to NGF but differ in their response to tissue extracts

The response of two distinct populations of neural crest-derived sensory neurones to nerve growth factor (NGF) and other neurotrophic activities present in extracts of chick tissues has been studied in vitro. Dorsal root ganglia (DRG) and the dorso-medial part of the trigeminal ganglion (DM-TG) from embryonic chicks of 6-11 days of incubation (E6-E11) were grown as either explant or dissociated neurone-enriched cultures. Over the age range studied NGF promoted survival and pronounced neurite outgrowth from both DRG and DM-TG neurones. Whilst extracts of chick eye, liver and spinal cord also elicited a marked response from E8 and older DRG neurones, DM-TG neurones were almost entirely unresponsive to the neurotrophic activity of these extracts.

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.

Neuronotrophic effects of skeletal muscle fractions on neurite development

Soluble fractions of chick embryonic skeletal muscle stimulated radial outgrowth of long neurites from peripheral ganglia. Dorsal root ganglia were more responsive to the growth stimulus of muscle fractions than sympathetic ganglia. Muscle fractions from chicks immobilized with d-tubocurarine chloride (dtc) were significantly more effective in stimulating growth than normal muscle fractions. Neuritic outgrowth stimulated by muscle fractions was not blocked by antisera to the Nerve Growth Factor (NGF) indicating that these neuronotrophic effects were not due to NGF.

Nerve growth activities in rat peripheral nerve

Nerve growth activities in rat sciatic nerves were assayed by recording the neuritic outgrowth from chick embryonic ganglia cultured in collagen gels beside nerve fragments for two days. Living nerve explants released activity that resembled nerve growth factor (NGF) in its effect on sympathetic ganglia and that was almost totally blocked by an antiserum to 2.5 S mouse NGF. Frozen and thawed specimens from normal nerves elicited responses from sympathetic ganglia that were only partially suppressed by anti-NGF and also induced neuritic outgrowth from ciliary ganglia. Thus, from observations on normal nerves, at least two agents promoting axonal extension in vitro were deduced to exist; one substance similar to NGF plus another, non-NGF factor. The level of NGF-like activity was low in killed segments of normal nerves but higher in autologous nerve grafts and degenerating nerves two days after grafting or cutting. However, one or two weeks after nerve transection, distal nerve segments contained little nerve growth activity of either kind. Furthermore, when endoneurial fragments from chronically denervated stumps were cultured, they appeared to have lost some of their capacity to produce NGF-like activity in vitro although the production of activity had, if anything, increased in the perineurial region. In summary, rat peripheral nervous tissue releases two or more soluble substances that stimulate neuritic outgrowth. The level of one or both activities in the endoneurium can be altered by manipulation of nerves in vivo.

Nerve growth factors in chick tissues

Bioassays of factors promoting nerve growth in embryonic ganglia are described. Chick embryo extract evokes fiber outgrowth in both sympathetic and ciliary ganglia explanted into a collagen gel. The response is not suppressed by antibodies directed against mouse nerve growth factor (NGF). Chick embryo extract also supported survival of neurons in both intact and dissociated ganglia. In addition to these non-NGF activities, preliminary evidence is presented for the release of a NGF-like factor from cultured iris of the adult chick.

Peripheral nerve contains heterogeneous growth factors that support sensory neurons in vitro

The availability of dissociated cultures of embryonic neurons has given impetus to a number of studies which have detected trophic factors in many mammalian and avian tissues maintained in vivo and in vitro [1, 2, 4-8, 10, 11, 13, 16, 18-21]. Using a single sensory neuron biological assay for mouse nerve growth factor (NGF) [17] as a reference standard, we report here that neurite promoting activity is highly enriched in segments of adult mouse peripheral nerve. Neurite outgrowth at 30 h, kinetics of neurite appearance and inhibition with rabbit antiserum to mouse NGF indicate that the trophic activities are heterogeneous and support both NGF-dependent and NGF-independent neuron populations of chick embryo sensory ganglia.