The role of axonal transport in the regulation of enzyme activity in sympathetic ganglia of adult rats

The relationship of perikaryal and presynaptic enzyme activity to axonal transport was studied in adult sympathetic neurons in the rat superior cervical ganglion (SCG). Surgical axotomy or local colchicine application to the postganglionic nerves resulted in a significant decrease in ganglionic tyrosine hydroxylase (T-OH) activity without a significant alteration in choline acetyltransferase activity. Colchicine did not appear to block axonal impulse conduction since pupillary and eyelid function remained normal. Consequently, the reduced T-OH activity resulted from alteration of other axonal functions. Axotomy or colchicine application decreased T-OH activity in decentralized ganglia, suggesting that the depression of perikaryal T-OH was not secondary to altered orthograde transsynaptic interactions. Colchicine did not prevent transsynaptic induction of T-OH by reserpine, suggesting that axonal transport is not necessary for enzyme induction. Nerve growth factor (NGF) treatment partially prevented the effects of colchicine application. It is concluded that in adult sympathetic neurons both orthograde transsynaptic mechanisms and the retrograde transport of NGF normally govern perikaryal T-OH activity.     

p75 and TrkA receptors are both required for uptake of NGF in adult sympathetic neurons: use of a novel fluorescent NGF conjugate

We have developed and tested the biological activity and specificity of a novel fluorescent dextran-Texas Red–nerve growth factor (DTR–NGF) conjugate. DTR–NGF was found to promote survival and neurite outgrowth in cultured dissociated sympathetic neurons similarly to native NGF. The conjugate was taken up and transported retrogradely by terminal sympathetic nerves innervating the iris to neurons in the ipsilateral superior cervical ganglion (SCG) of young adult rats. Uptake and transport was assessed by counting numbers of labelled neurons and by measuring intensity of neuronal labelling using confocal microscopy and image analysis. DTR–NGF labelling in SCG neurons was shown to be dose-dependent with an EC₅₀ of 75 ng. Similar concentrations of unconjugated DTR resulted in no neuronal labelling. DTR–NGF uptake was competed off using a 50-fold excess of native NGF, resulting in a 73% reduction in numbers of labelled neurons. Pretreatment of nerve terminals with function-blocking antibodies against the low (p75) and high (TrkA) affinity NGF receptors resulted in a large (85–93%) reduction in numbers of DTR–NGF labelled neurons. Anti-p75 and anti-TrkA antibodies had comparable effects which were concentration-dependent. These findings indicate that both receptors are required for uptake of NGF in adult rat sympathetic neurons. In particular, the results provide strong evidence that the p75 receptor plays a more active role in transducing the NGF signal than has been proposed.     

Effects of gonadal steroids on nerve growth factor receptors in sympathetic and sensory ganglia of neonatal rats

The numbers of neurons in the rat superior cervical sympathetic ganglion (SCG) differ in males and females, with the males having 30% more SCG neurons than females at 60 days of age. This sex difference arises during the early postnatal period, when testosterone administration increases the numbers of neurons and alters the nerve growth factor (NGF) content of the rat SCG. In contrast, there is no gender difference in number of neurons in the L1 dorsal root ganglion. In both males and females, the amount of NGF bound per ganglion increased between postnatal days 5 and 15 (P5 and P15) in both dorsal root ganglia (DRGs) and the SCG. There is also a gender difference in NGF binding: SCGs and DRGs of female rats at both P5 and P15 bind more NGF per ganglion than do those of males. This effect was more marked in DRGs than in the SCG. Treatment of neonatal females with testosterone reduced NGF binding in both SCGs and DRGs to levels comparable to males at P5, and in DRGs at P15. In contrast, treatment of males with testosterone from birth resulted in a 2-3 fold increase of NGF binding in both SCGs and DRGs as compared to controls at P15. At P15, testosterone treatment of females increased NGF binding in the SCG. Males and females had opposing responses to neonatal exposure to estradiol. Treatment with estradiol from birth increased NGF binding in SCGs and DRGs of females, but had no effect on NGF binding of SCGs, and reduced NGF binding in DRGs of males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of autoimmune NGF deprivation in the adult rabbit and offspring

An experimental autoimmune approach to the production of nerve growth factor deprivation, which we have previously described in the rat and guinea pig, has been applied to the rabbit. This species was chosen for study because of several potential advantages. The rabbit produces large litters and has a relatively short gestation period. More importantly, rabbits generate high titers of antibody against mouse NGF and large amounts of maternal antibody are passively transferred to the developing rabbit fetus compared to most other species, particularly the rat. The sympathetic nervous system of adult rabbit immunized against mouse NGF underwent degeneration with up to an 85% decrease in neuronal numbers in the superior cervical ganglion after 10 months of immunization, thus providing further evidence that NGF is required for the survival of mature sympathetic neurons. Despite the fact that newborn rabbits born to anti-NGF producing mothers had much higher titers of anti-NGF than did rats, the effects on the developing sympathetic and sensory nervous systems were not found to be any greater than in rats. Reductions in norepinephrine levels in the heart and spleen of adult rabbits born to anti-NGF producing mothers were greater than in small intestine. Prenatal exposure to maternal anti-NGF caused reductions (up to 70%) in the number of neurons in the dorsal root ganglia. Substance-P immunoreactivity was reduced in the substantia gelatinosa of the spinal cord of rabbit exposed to maternal anti-NGF. These changes, however, were not greater than seen in the rat. We conclide that although the rabbits offers some advantage in the study of the effects of NGF deprivation in the adult animal, it appears less well suited than the rat or guinea pig to the study of the effects of NGF deprivation on development.     

Target organ regulation of sympathetic neuron development.

The role of target organs in the morphological and biochemical development of sympathetic neurons was examined in the neonatal rat. The superior cervical ganglion (SCG) and its end organs, the salivary glands and iris were employed as a model system. Unilateral sialectomy and iridectomy prevented the normal developmental increase in ipsilateral ganglion tyrosine hydroxylase (T-OH) activity, a marker for adrenergic maturation. Enzyme activity remained depressed by approximately 30% for at least 6 months, the longest time tested. Ganglion morphometry was performed to investigate the basis of the abnormal biochemical ontogeny. Target organ removal significantly decreased the number of adrenergic neurons in the Scg by approximately 30%. Total ganglion volume was reduced in a parallel fashion. Thus, end organ extirpation may prevent the biochemical maturation of the SCG by decreasing adrenergic neuron survival. Sialectomy without iridectomy prevented the normal postnatal increase in ganglion T-OH activity, but did not alter iris activity. These observations suggest that target removal prevents the development of only those neurons destined to innervate that organ. In addition to preventing normal adrenergic neuron ontogeny, target extirpation also prevented the normal development of presynaptic choline acetyltransferase activity. Presynaptic ganglion terminal may have failed to mature normally secondary to adrenergic destruction, or may have responded in some other manner to target organ extirpation.     

Trophic regulation of nodose ganglion cell development: evidence for an expanded role of nerve growth factor during embryogenesis in the rat

Peripheral sensory neurons are derived from two distinct embryonic tissues, the neural crest and epibranchial placodes. Studies in the chick suggest that embryonic lineage and trophic dependence are interrelated, such that many crest-derived cells depend on NGF for survival during development, whereas placodal derivates, including nodose ganglion neurons, do not (30). It remains controversial, however, whether or not a similar dichotomy exists in mammalian species, in which trophic requirements during early development of placodal ganglia have not been defined. To approach this issue, the present study examined the effects of nerve growth factor (NGF) on neuronal survival in embryonic rat nodose ganglion cultures. Treatment of E13.5-14.5 nodose explants with 20 ng/ml NGF resulted in a four-fold increase in neuronal survival that was blocked by anti-NGF antiserum. Increased neuronal survival and neurite outgrowth were also observed in neuron-enriched dissociated cell cultures; these effects were seen within 12 h of plating, indicating that NGF-responsive neurons or neuroblasts were already present in the ganglion at the time of explantation. This was further supported by immunocytochemical staining of nodose cell bodies in situ with the monoclonal antibody 192-IgG against the NGF receptor (12). These findings indicate that NGF may be important in regulating nodose development during early gangliogenesis in mammals and suggest that NGF plays a more widespread role in peripheral nervous system ontogeny than previously recognized.     

Harmonal regulation of adult sympathetic neurons: the effects of castration on tyrosine hydroxylase activity

The effects of the hormone testosterone on neurotransmitter synthesis in peripheral sympathetic ganglia were examined in adult male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH), the rate limiting enzyme in catecholamine biosynthesis was examined in the hypogastric (HG), coeliac (CG), and superior cervical ganglion (SCG) subsequent to castration. Initial studies indicated that 2 weeks after surgery, HG T-OH activity fell to approximately 30% of control. In order to more clearly define the pattern of testosterone effects, HG was examined 1, 2 and 4 weeks after surgery. T-OH activity was 67%, 50% and 11% of control at these 3 respective time points, and the observed alteration in T-OH activity appeared to parallel changes in the size of pelvic target organs. Similar hormonal effects did not occur in other peripheral sympathetic ganglia; T-OH activity was unchanged in SCG and CG when examined 1 month after castration. Enzyme activity was restored following replacement therapy with testosterone, whereas the neural metabolite 17-beta estradiol was without effect. The recovery in T-OH activity was associated with partial recovery of target organ size. These studies suggest that hormonal factors regulate neurotransmitter synthesizing enzymes in adult sympathetic neurons and may do so via consequences of alterations in target organs. These observations parallel similar events in the developing nervous system.     

Hormonal regulation of sympathetic neuron development. The effects of neonatal castration

The effects of neonatal castration on neuronal ontogeny were examined in peripheral sympathetic ganglia in male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH) activity, the rate-limiting enzyme in catecholamine biosynthesis and a marker of noradrenergic maturation, was examined in the hypogastric (HG) and superior cervical ganglion (SCG). Initial studies characterized the normal development of T-OH activity in HG ganglia. Neonatal castration at 10-11 days of age prevented the normal ontogeny of HG T-OH activity: T-OH activity failed to develop normally and was 17% of sham-operated littermate controls when examined at 8 weeks of age, and less than 5% when studied 10 weeks after surgery. In contrast to the effects in HG, there was no change in enzyme activity in the SCG. Replacement therapy with testosterone decanoate completely reversed the developmental alteration in enzyme activity. These observations suggest that hormonal factors modulate noradrenergic ontogeny in peripheral sympathetic ganglia but these effects appear restricted to ganglia whose targets include hormonally dependent sex organs.     

Immunization of adult rats against 2.5 S NGF: Effects on the peripheral sympathetic nervous system

The biochemical and morphological changes effected by immunization of adult rats with 2.5 S mouse nerve growth factor (NGF) were studied in sympathetic ganglia and in representative target organs. This immunization procedure maintains high levels of circulating anti NGF-antibody for periods of months. Morphological analysis revealed a general reduction in the size of the adrenergic neurons in the superior cervical ganglion (SCG) which was also reflected at the biochemical level by a 30% decrease in total protein content and a 50--60% reduction in the total activities of all norepinephrine-synthesizing enzymes. However, there was no change in total choline acetyltransferase activity. The biochemical and morphological changes observed in the SCG seem to be confined to the neuronal cell body, since at any stage of immunization target organs (the submandibular and the pineal gland) remained unaffected. All sympathetic ganglia investigated--except the superior mesenteric ganglion--responded in a similar way to the immunization against 2.5 S NGF. These changes in the adrenergic cell bodies were largely reversible. The recovery of normal enzyme activities followed closely the decrease of the antibody titer after cessation of immunization boosting. This indicates that cell death is not caused by anti NGF-antibodies in ganglia of adult animals. Thus, in contrast to adrenergic neurons from newborn animals, which depend on NGF or a crossreacting NGF-like material for survival, differentiated adrenergic neurons need this factor for the maintenance of their normal function but not for survival.     

Relation of target encounter and neuronal death to nerve growth factor responsiveness in the developing mouse trigeminal ganglion

An aim of this study was to define precisely the period in the developmental history of primary sensory neurons during which nerve growth factor (NGF) exerts its growth-promoting effect. The mouse trigeminal ganglion and its peripheral projection were studied at closely staged intervals throughout development using light and electron microscopy, and the influence of NGF and anti-NGF antiserum on neurite outgrowth from ganglion explants was investigated at corresponding stages in culture. By embryonic day 9.5 (E9.5) peripheral fibers were first visible and increased in number until E13. Throughout this period in vitro neurites grew in the presence of anti-NGF. Peripheral fibers initially contacted the epithelium of the mandibular process by E10.5 and the maxillary process by E11. This coincided with the stage in vitro during which the magnitude of neurite outgrowth was significantly increased by NGF. The development of this response was independent of target encounter since it occurred in neurons which had not contacted their targets prior to explantation. There was an approximate one-to-one relationship between the number of neurons in the ganglion and peripheral fibers throughout development. A peak of some 44,400 fibers and 42,600 neurons was reached by E13 and fell to 20,800 and 19,000, respectively, by birth. Neurite outgrowth was elicited by NGF throughout the period of neuronal death. It is argued that the time course of the influence of NGF is consistent with a role as a selective maintenance factor but not as an agent directing initial outgrowth.     

Purification of adult rat sciatic nerve ciliary neuronotrophic factor

The ciliary neuronotrophic factor (CNTF), a protein required for the survival of cultured avian embryonic parasympathetic ciliary ganglionic neurons, was recently purified from extracts of selected chick intraocular tissues. Here we report the purification of a mammalian CNTF activity from extracts of adult rat sciatic nerve using a fractionation procedure similar to that employed for isolating chick eye CNTF. About 2 micrograms of CNTF protein can be obtained from each 1.5 g batch of nerve tissue. Like the chick CNTF, the mammalian factor displays trophic activity for dorsal root and sympathetic as well as ciliary ganglionic neurons. The nerve CNTF activity differs from its chick counterpart in molecular weight and chromatographic behavior on ion-exchange columns. Unlike purified nerve growth factor (NGF), nerve CNTF activity is insensitive to anti-NGF antibodies and is unable to support the survival of 8-day chick embryo dorsal root ganglion neurons.     

Effects of nerve growth factor on autonomic neurons in the chick embryo: A stereological study

Quantitative effects of nerve growth factor (NGF) on the sympathetic, Remak and ciliary ganglia in chicken embryos were investigated. Purified mouse beta NGF was injected (80 micrograms per day for three or four consecutive days) into the yolk sac at different stages (starting on days 6, 8, 10 and 13) of embryonic development. Ganglia were taken for fixation and embedding one day after the last NGF injection. The number of neurons belonging to the different size classes was determined by a computer aided stereological method based on unfolding of cell diameter frequencies. The volume of sympathetic ganglia was increased at all stages with a maximum of 8-fold occurring on day 10. The ganglion of Remak showed a 3-fold volume increase up to embryonic days 10 and 12. Ciliary ganglia did not exhibit any differences in volume or neuron size between the controls and the embryos injected with NGF. The number of neurons was increased in younger sympathetic and Remak ganglia in response to NGF, as was the recruitment of neurons to the larger size classes.     

Glia cell line‐derived neurotrophic factor mediates survival of murine sympathetic precursors

During embryonic development, neurons are first produced in excess, and final numbers are adjusted by apoptosis at later stages. Crucial to this end is the amount of target‐derived growth factor available for the neurons. By this means, the target size correctly matches the innervating neuron number. This target‐derived survival has been well studied for sympathetic neurons, and nerve growth factor (NGF) was identified to be the crucial factor for maintaining sympathetic neurons at late embryonic and early postnatal stages, with a virtual complete loss of sympathetic neurons in NGF knockout (KO) mice. This indicates that all sympathetic neurons are dependent on NGF. However, also different glia cell line‐derived neurotrophic factor (GDNF) KO mice consistently presented a loss of sympathetic neurons. This was the rationale for investigating the role of GDNF for sympathetic precursor/neuron survival. Here we show that GDNF is capable of promoting survival of 30% sympathetic precursors dissociated at E13. This is in line with data from GDNF KOs in which a comparable sympathetic neuron loss was observed at late embryonic stages, although the onset of the phenotype was unclear. We further present data showing that GDNF ligand and canonical receptors are expressed in sympathetic neurons especially at embryonic stages, raising the possibility of an autocrine/paracrine GDNF action. Finally, we show that GDNF also maintained neonatal sympathetic neurons (40%) cultured for 2 days. However, the GDNF responsiveness was lost at 5 days in vitro. © 2013 Wiley Periodicals, Inc.     

Nerve growth factors (NGF, BDNF) enhance axonal regeneration but are not required for survival of adult sensory neurons

Largely on the basis of studies with nerve growth factor (NGF), it is now widely accepted that development of the peripheral nervous system of vertebrates is dependent in part on the interaction of immature sensory and autonomic neurons with specific survival factors that are derived from peripheral target fields. I have found, in marked contrast to an absolute requirement for NGF during development, that adult rat dorsal root ganglion sensory neurons are not dependent on NGF or other survival factors for long-term (3-4 weeks) maintenance in vitro. When dissociated and enriched, at least 70-80% of adult DRG neurons survived and extended long processes either in the absence of exogenously added NGF or upon the removal of any possible source of endogenous NGF or other neurotrophic activity (i.e., nonneuronal cells, in chemically defined culture medium, in the presence of an excess of anti-NGF antibodies, or when cultured as single neurons in microwells). Although not required for survival or expression of a range of complex morphologies, both NGF and brain-derived neurotrophic factor (BDNF) were found to stimulate the regeneration of axons from adult DRG neurons.     

Effects of long-term nerve growth factor deprivation on the nervous system of the adult rat: An experimental autoimmune approach

Adult rats immunized with 2.5S mouse nerve growth factor (NGF) produced antibodies which cross-reacted with rat NGF. By the criterion of ammonium sulfate precipitation followed by Sephadex G-200 chromatography, all serum anti-NGF activity was retained in the IgG fraction. Animals which developed and maintained chronic (5–6 months) serum titers of anti-NGF demonstrated a pronounced biochemical and morphological atrophy of the superior cervical ganglion which was accompanied by a 35–40% reduction in neuronal number. Norepinephrine was reduced by approximately 90% in heart and brown fat. The extent of biochemical atrophy correlated well with serum titers of anti-NGF. No effects were observed on the short adrenergic neurons of the vas deferens, adrenal medullary chromaffin cells, central adrenergic neurons, or peripheral sensory neurons. These results strongly suggest that mature peripheral sympathetic neurons remain dependent on NGF for survival as well as for maintenance.     

The role of NGF uptake in selective vulnerability to cell death in ageing sympathetic neurons

We have examined the hypothesis that differences in nerve growth factor (NGF) uptake and transport determine vulnerability to age-related neurodegeneration. Neurons projecting to cerebral blood vessels (CV) in aged rats are more vulnerable to age-related degeneration than those projecting to the iris. Uptake of NGF was therefore examined in sympathetic neurons projecting from the superior cervical ganglion (SCG) to CV and iris in young and old rats by treating the peripheral processes of these neurons with different doses of I125-NGF. Total uptake of I125-NGF was reduced in old CV-projecting, but not iris-projecting, neurons. Numbers of radiolabelled neurons projecting to each target were counted in sectioned ganglia. The data showed age-related reductions in numbers of labelled neurons projecting to CV, but no change in numbers of neurons projecting to the iris. Calculation of uptake of I125-NGF per neuron unexpectedly showed no major age-related differences in either of the two neuron populations. However, uptake per neuron was considerably lower for young and old CV-projecting, compared to iris-projecting, SCG neurons. We hypothesized that variations in NGF uptake might affect neuronal survival in old age. Counts of SCG neurons using a physical disector following retrograde tracing with Fluorogold confirmed the selective vulnerability of CV-projecting neurons by showing a significant 37% loss of these neurons in the period between 15 and 24 months. In contrast, there was no significant loss of iris-projecting neurons. We conclude that vulnerability to, or protection from, age-related neurodegeneration and neuronal cell death are associated with life-long low, or high, levels of NGF uptake, respectively.     

Effects of nerve growth factor on splenic norepinephrine and pineal N-acetyl-transferase in neonate rats exposed to alcohol in utero: Neuroimmune correlates

Prenatal alcohol exposure (FAE) has been associated with multiple anomalies, including a selective developmental delay of sympathetic innervation in lymphoid organs. Sympathetic neurons require nerve growth factor (NGF) for their development and maintenance, and recent evidence has suggested that alcohol impairs the synthesis and/or biological activity of NGF in selected central and peripheral neurons. Thus, the present study examined the hypothesis that NGF administration to FAE rats during early postnatal development would reverse some of the peripheral sympathetic deficits. Neonate rats, FAE and the corresponding control cohorts, received daily treatments of NGF or cytochrome C (0.3 mg/kg; s.c.) for various time intervals, and were killed 24hr or 10 days after the last treatment. The measured parameters included norepinephrine (NE) concentrations in the spleen and heart, which receive noradrenergic innervation from the coeliac ganglion and the superior cervical ganglion (SCG), respectively. In addition, we measured the activity of pineal N-acetyltransferase (NAT), the rate-limiting enzyme of melatonin biosynthesis, which depends on sympathetic innervation from the SCG. The data show that chronic, but not acute, NGF treatments reversed the FAE-related deficits in splenic NE concentrations as well as in pineal NAT activity in a time- and age-dependent manner. Sympathetic neurons play an important role in immune modulation. Thus, the altered splenic NE levels and pineal NAT activity may play a role in immune deficits associated with exposure to alcohol in utero.     

Regulation of myelinated nociceptor function by nerve growth factor in neonatal and adult rats

The role of nerve growth factor (NGF) as a survival factor for sensory neurons during embryonic life has been well documented. Here we examine the actions of NGF or antisera against NGF (anti-NGF) on physiologically identified sensory neurons with myelinated axons later in life, after the dependence on NGF for survival ends. We find that the effects of NGF and anti-NGF are specific for sensory neurons which are nociceptors. Treatments were found to affect the biophysical properties, the development, or the physiological function of myelinated nociceptors. They also affect the animal's behavioral response to noxious stimulation, depending upon when the treatments were given: neonatally, from 2–5 weeks of age, or chronically, beginning at birth. Thus, we find that the actions of NGF are specific for nociceptors but that the function of this neurotrophic factor changes according to the developmental age of the animal.     

Remodeling of adult sensory axons in the superior cervical ganglion in response to exogenous nerve growth factor

In previous studies, we found that a 2-week in vivo intracerebroventricular infusion of nerve growth factor (NGF) elicited a sprouting response by sympathetic perivascular axons associated with the intradural segment of the internal carotid artery. We hypothesized that NGF infused into the ventricular system would be internalized by responsive sympathetic cerebrovascular axons, retrogradely transported to parent cell bodies in the superior cervical ganglion (SCG), and subsequently released into the local ganglionic environment. Because fibers exhibiting immunoreactivity for calcitonin gene related peptide (CGRP) have been localized in the SCG, we used immunohistochemical methods to investigate whether a response by CGRP-immunoreactive axons in the SCG occurred following the proposed transport to and release of exogenous NGF in the ganglion. In consecutive tissue sections of the SCG stained for either CGRP or NGF, we found CGRP pericellular 'baskets' surrounding identified NGF-immunoreactive cell bodies. Nerve growth factor infusion resulted in a significant increase both in the number of CGRP pericellular baskets and in NGF-immunoreactive cell bodies. A significant positive correlation (r=0.95, P<0.05) between the pericellular baskets and NGF-immunoreactive cell bodies was observed, suggesting that intracranial projection neurons in the SCG released infused NGF (or possibly a converted signal) into the local ganglionic environment to elicit remodeling of CGRP fibers to form pericellular baskets. These findings were confirmed in sections double labeled for NGF and CGRP immunoreactivity. This remodeling suggests that exogenous NGF may mediate retrograde transneuronal plasticity, allowing for future in vivo examinations of the mechanisms involved in neurotrophin transport and release.     

Destruction of the sympathetic nervous system in neonatal rats and hamsters by vinblastine: prevention by concomitant administration of nerve growth factor

If the primary mechanism by which nerve growth factor (NGF) gains access to the cell body is a specific uptake and retrograde transport from the periphery, then an inhibitor of axoplasmic transport would be expected to produce cell death. Such an inhibitor was administered to neonatal and adult rats and hamsters. A single injection of vinblastine (0.25–0.5 mg/kg s.c.) to 2-day-old rats produced massive cell death in the superior cervical ganglia (SCG). The levels of tyrosine hydroxylase in the SCG were reduced 80% at doses of 0.4 mg/kg, a dose which was uniformly fatal. Doses of 0.25 mg/kg at two days of age resulted in a 50% mortality rate and the survivors showed a permanent, partial sympathectomy. The adrenal medulla and sensory neurons did not appear to be affected. Administration of a single injection of vinblastine at maximally tolerated doses did not destroy sympathetic neurons in animals 14 days of age or older. Chronic administration of vinblastine (0.5 mg/kg every other day for two weeks) to adult rats did not destroy sympathetic neurons. Similar results were obtained in hamsters.Concomitant administration of NGF appeared to completely prevent the cytotoxic effects of vinblastine assessed by both morphological and enzymatic criteria. Several explanations are discussed which might explain these results.The similarities in the effects of vinblastine, other drugs, and axonal crush on sympathetic neurons are noted. It is proposed that all drugs which destroy sympathetic neurons (guanethidine, 6-hydroxydopamine, vinblastine) as well as anti-NGF and axonal ligation destroy the neurons by depriving the cell body of NGF from the periphery.