Stimulation of growth of new axonal sprouts from lesioned monoamine neurones in adult rat brain by nerve growth factor

Nerve growth factor modulation of retinal ganglion cell physiology

Nerve growth factor (NGF) is an endogenous neurotrophin involved in the development, maintenance and regeneration of mammalian sympathetic and sensory neurons. Additionally, NGF is known to have trophic and differentiating activity on several populations of cholinergic neurons of the central nervous system (CNS), and to act as a differentiation factor in the development of the visual cortex. The paramount functions of NGF in the visual system are also highlighted by the presence of this neurotrophin and both its receptors TrkA and p75 in most intra-ocular tissues, including lens, vitreous, choroid, iris, and trabecular meshwork. In the retina, NGF is produced and utilized specifically by retinal ganglion cells (RGC), bipolar neurons and glial cells, and is thought to have crucial protective effects in several disease states. Studies on the role of NGF on RGCs survival following optic nerve transection, ischemic injury, ocular hypertension and glaucoma are discussed in this review.

Nerve growth factor increases activity of ornithine decarboxylase in rat brain

Intraventricular administration of nanogram quantities of nerve growth factor to adult rats results in a marked increase in the activity of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in the brain. The increase occurs in all major brain regions and the activity is maximal by 7.5 hr after administration. The enzyme response to nerve growth factor increases in magnitude during maturation; the relative increase in ornithine decarboxylase activity in adult animals is much greater than that in young. Neither insulin nor bovine growth hormone was able to increase ornithine decarboxylase activity to the same extent as did nerve growth factor. When brain was separated into neuronal- and glial-enriched fractions, induction of ornithine decarboxylase was found in both, but a greater increase was observed in the glial fraction.

Nerve growth factor and Alzheimer's disease

Nerve growth factor (NGF) is a well-characterized protein that exerts pharmacological effects on a group of cholinergic neurons known to atrophy in Alzheimer's disease (AD). Considerable evidence from animal studies suggests that NGF may be useful in reversing, halting, or at least slowing the progression of AD-related cholinergic basal forebrain atrophy, perhaps even attenuating the cognitive deficit associated with the disorder. However, many questions remain concerning the role of NGF in AD. Levels of the low-affinity receptor for NGF appear to be at least stable in AD basal forebrain, and the recent finding of AD-related increases in cortical NGF brings into question whether endogenous NGF levels are related to the observed cholinergic atrophy and whether additional NGF will be useful in treating this disorder. Evidence regarding the localization of NGF within the central nervous system and its presumed role in maintaining basal forebrain cholinergic neurons is summarized, followed by a synopsis of the relevant aspects of AD neuropathology. The available data regarding levels of NGF and its receptor in the AD brain, as well as potential roles for NGF in the pathogenesis and treatment of AD, are also reviewed. NGF and its low affinity receptor are abundantly present within the AD brain, although this does not rule out an NGF-related mechanism in the degeneration of basal forebrain neurons, nor does it eliminate the possibility that exogenous NGF may be successfully used to treat AD. Further studies of the degree and distribution of NGF within the human brain in normal aging and in AD, and of the possible relationship between target NGF levels and the status of basal forebrain neurons in vivo, are necessary before engaging in clinical trials.

Cellular localization of nerve growth factor-like immunoreactivity in adult rat brain: quantitative and immunohistochemical study

To elucidate the role and the mechanism of action of nerve growth factor in the adult central nervous system, we investigated the localization of nerve growth factor-like immunoreactivity in adult rat brain, both quantitatively and immunohistochemically, using polyclonal anti-nerve growth factor immunoglobulin G. We raised rabbit polyclonal anti-mouse nerve growth factor antibody with an extremely high titer as 10(-9) determined by an enzyme immunoassay. The affinity-purified anti-nerve growth factor immunoglobulin G specifically recognized nerve growth factor with no cross-reaction to recombinant brain-derived neurotrophic factor and neurotrophin-3 evaluated by an enzyme immunoassay. We quantified nerve growth factor content in each layer of the adult rat cerebral cortex and in each small piece (0.225 mg wet weight tissue) of the diencephalon, brainstem and cerebellum with a highly sensitive two-site enzyme immunoassay. Nerve growth factor content was unevenly distributed in the cerebral cortex (dense in layers II/III and V/VI and sparse in layers I and IV). Moderate to high levels of nerve growth factor were registered in the habenular nuclei, zona incerta, ventral tegmental area, substantia nigra, locus coeruleus, ventral cochlear nucleus, trapezoid body, lateral vestibular nucleus, cerebellar nuclei and paraflocculus. Immunohistochemically, the nerve growth factor-like immunoreactivity was found in the cell bodies, dendrites and axons of adult rat central neurons, not only in the cerebral cortex, hippocampus and basal forebrain, but also in the diencephalon, brainstem and cerebellum. The population of neurons with nerve growth factor-like immunoreactivity was limited, but unexpectedly widespread, and the density of these cells correlated well with the content determined by an enzyme immunoassay in the present and a previous study [Nishio T. et al. (1992) Expl Neurol. 116, 76-84]. The monoamine neurons, including dopaminergic, noradrenergic and serotonergic neurons, showed intense nerve growth factor-like immunoreactivity, indicating that the central monoaminergic neuronal system may also be involved in the nerve growth factor trophic system. To visualize nerve growth factor transported in the axons and to enhance the immunostaining in the nerve growth factor-producing cells, we injected colchicine, a potent inhibitor of microtubule polymerization and a blocker of axoplasmic transport, into the lateral ventricle of adult Wistar rat brain. Colchicine treatment enhanced the intensities of nerve growth factor-like immunoreactivity in the axons and cell bodies, especially in the axon hillocks and the proximal axons of the nerve growth factor-producing neurons. This observation may suggest the existence of an orthograde axonal transport system for nerve growth factor in the central neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Development and distribution of noradrenergic and cholinergic neurons and their trophic phenotypes in the avian ceruleus complex and midbrain tegmentum

We investigated the development of noradrenergic and cholinergic neurons in the ceruleus complex and mesencephalic tegmentum in embryonic and posthatch chickens and compared the distribution of transmitter phenotypes with the expression of nerve growth factor receptor (NGFR) mRNA and fibroblast growth factor receptor (FGFR) mRNA. Noradrenergic and cholinergic neurons were visualized by using antibodies against dopamine-beta-hydroxylase (DBH) and choline acetyltransferase (ChAT), respectively. Expression of receptors for trophic factors was determined by using in situ hybridization techniques. Noradrenergic neurons concentrate in caudal parts of the locus ceruleus and nucleus subceruleus. Cholinergic ceruleus neurons are abundant in the nucleus mesencephalicus profundus, pars ventralis (MPv) as well as in the nucleus subceruleus and locus ceruleus. This cholinergic population resembles the cholinergic pontomesencephalotegmental complex of mammals. Both DBH and ChAT label is evident at and after six days of incubation (E6). The distribution and numbers of immunolabeled neurons are similar in the embryonic and posthatch chick. Initially, many tegmental and ceruleus neurons express substantial levels of NGFR mRNA (E7-E9). After E9, expression of NGFR mRNA decreases in most of these neurons, except for a distinct subpopulation of neurons in caudal parts of the ceruleus complex with increased levels of NGFR transcripts. These NGFR-positive neurons coincide in number and distribution with the noradrenergic subpopulation of the ceruleus complex (800-900 neurons). Expression of FGFR mRNA was first detected in ceruleus neurons at E13. Neurons with FGFR transcripts have the same number and distribution as the neurons with the cholinergic phenotype (2,000-2,300 neurons). Transmitter heterogeneity in the ceruleus complex is reflected by a heterogeneity of receptors for trophic factors, with NGFR expressed in the noradrenergic subpopulation, and FGFR expressed in the cholinergic subpopulation. These findings provide evidence for new chemoarchitectonic subdivisions of the avian ceruleus complex. The data showing onset of ChAT expression prior to the onset of FGFR expression argue against a role of FGFR in the determination of the cholinergic transmitter phenotype. Expression of NGFR in the noradrenergic ceruleus subpopulation reveals remarkable species differences as compared to mammals.

Expression of nerve growth factor (NGF) receptors in the brain and retina of chick embryos: comparison with cholinergic development

The expression of nerve growth factor receptor (NGFR) transcripts was investigated with in situ hybridization techniques in the CNS of chick embryos from 3 days of incubation (E3) to 14 days posthatch (P14). The time course and distribution of NGFR expression was compared with the development of the cholinergic phenotype. Cholinergic properties were assessed by immunolabeling for choline acetyltransferase (ChAT) and histochemistry for acetylcholinesterase (AchE) activity. NGFR transcripts are expressed transiently in the inner plexiform layer and ganglion cell layer of the retina (E4-P1), neostriatum and hippocampus (E18), infundibular hypothalamus (E7-18), spiriform complex (E9-15), layers 2, 3 (E9-18), and 10 (E11-18) of the optic tectum, nucleus mesencephalicus profundus, pars ventralis (E9-18), parvicellular isthmic nucleus (E7-P1), magnocellular isthmic nucleus (E9-E18), nucleus semilunaris (E7-18), isthmo-optic nucleus (E7-P14), rostral motor nuclei (E5-18), developing cerebellum (E7-15), internal granule cell layer (E11-18) and Purkinje cell layer (E15-P14) of the cerebellar cortex, and the inferior olivary nucleus (E9-15). A small number of neuronal populations with embryonic expression of NGFR remain strongly NGFR-positive in the posthatch animal:habenular nuclei (labeled after E5), nucleus subrotundus (after E9), mesencephalic trigeminal nucleus (after E5), caudal parts of locus ceruleus and nucleus subceruleus (after E7), medullar reticular nuclei (after E11), and motor nuclei IX, X, and XII (after E9). The majority of neuronal populations with NGFR expression show cholinergic properties in development, and NGFR expression always precedes the onset of ChAT immunoreactivity. Postnatal expression of growth factor receptors is largely confined to neurons of the reticular type. NGFR expression in avian CNS nuclei differs from that in mammals. Early loss of NGFR expression in the cholinergic basal forebrain (which remains strongly NGFR positive in mammals) and persistent NGFR expression in parts of the avian locus ceruleus indicate changes of growth factor receptor expression and growth factor requirements in phylogeny. Knowledge of the time and distribution of NGFR expression in the chick embryo will facilitate the assessment of specific functions of NGF and NGF-like molecules in an embryonic model with easy access for experimental manipulations.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects of axotomy on substance P-containing and nicotinic acetylcholine receptor-containing retinal ganglion cells: time course of degeneration and effects of nerve growth factor

The time course of degeneration of chick retinal ganglion cells was examined with Nissl stains and immunohistochemical methods for detection of substance P-like immunoreactive and nicotinic acetylcholine receptor immunoreactive neurons. Small lesions were made in the retinae, adjacent to the optic nerve head, and were subsequently sectioned parallel to the vitreal surface, permitting direct comparison of normal and axotomized retinal ganglion cells distal to the site of axon damage. At four and six days after surgery, a large number of degenerating cells with clear cytoplasm and pyknotic nuclei were seen. After eight, 10 and 14 days, many retinal ganglion cells displayed a chromatolytic response with dispersed Nissl granules, eccentric nuclei and the cells appeared crenulated. The number of apparently normal neurons in the ganglion cell layer in the axotomized region was reduced by about 50% six days following surgery, by about 70% on the 10th day and by about 75% on the 17th day. The remaining neurons in the ganglion cell layer were identified as displaced amacrine cells. From day 2 onwards, increased numbers of glial cells were present in the optic fibre, ganglion cell and inner plexiform layers. Many glial cells were enlarged and displayed extensive cytoplasmic processes, while others showed mitotic activity. Somata and proximal dendrites of retinal ganglion cells were intensely stained for substance P-like immunoreactivity at two and four days following surgery. At six, eight and 10 days, staining intensity was markedly reduced though still evident and at 14 and 17 days, substance P-like immunoreactivity had virtually disappeared. The persistence of limited substance P-like immunoreactive ganglion cells 10 days after surgery indicates that these cells have a relatively protracted response to axotomy. Nicotinic acetylcholine receptor-like immunoreactivity in the ganglion cells at two and four days following axotomy was substantially reduced. The majority of faintly stained nicotinic acetylcholine receptor-like immunoreactive ganglion cells, as visualized in counterstained sections, did not exhibit pyknosis in the immediate period following axotomy. Double label studies demonstrated that substance P-like immunoreactive ganglion cells were distinct from the nicotinic acetylcholine receptor-like immunoreactive ganglion cells. In a second set of experiments, nerve growth factor was then placed into the vitreous humor following intra-retinal axotomy. The somata, dendrites and proximal axons of lesioned substance P-like immunoreactive ganglion cells in these retinae were more intensely stained for a longer period of time and appeared more robust than cells from untreated retinae.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of nerve growth factor on the elongation of neurites from axotomized rat embryonic septal-basal forebrain neurons: an in vitro analysis

The administration of nerve growth factor (NGF) into the brain of a fornix-fimbria lesioned rat can rescue many cholinergic, septal-basal forebrain (SBF) neurons from imminent cell death. Unfortunately, it is unclear if NGF can stimulate regenerative growth from axotomized, SBF neurons. In the present study, we used an in vitro model system to determine if NGF could affect neurite outgrowth from nonaxotomized and/or axotomized, embryonic SBF neurons. Axotomized neurons were obtained by severing the neuritic fields surrounding embryonic day (E) 15 SBF explants maintained in primary culture. Acetylcholinesterase (AChE) histochemistry was used to assess the effects of NGF on cholinergic neurites. We report that 1) neurite outgrowth on type I collagen from E15 SBF neurons in primary culture (nonaxotomized neurons) was not affected by NGF. 2) NGF enhanced the outgrowth (regeneration) of axotomized, SBF neurons on a collagen substratum; however, neurons had to be treated with NGF both before and after axotomy to stimulate regeneration effectively. Application of NGF either before or after axotomy did not enhance regenerative neurite outgrowth. 3) SBF neurons had to be axotomized for NGF to facilitate neurite outgrowth. This is supported by the observation that SBF explants, initially maintained in NGF-supplemented medium in suspension culture, did not demonstrate enhanced neurite outgrowth in the presence of NGF when plated onto a substratum. 4) The regenerative growth of AChE-negative, as well as AChE-positive, neurites was facilitated by NGF treatment. In addition to data concerning neurite outgrowth, we also found that the NGF receptor, as recognized by the antibody 192-IgG, expands its distribution as time in culture progresses; i.e., staining, originally confined to cell bodies and proximal processes within the explant, later included neurites that emanated from the explant. Thus, our results demonstrate that NGF can stimulate regenerative growth from axotomized, but not nonaxotomized, embryonic SBF neurons. We hypothesize that, given the appropriate substratum for axon elongation in vivo, NGF can stimulate the regeneration of SBF neurons in the injured adult brain.

Sympathetic sprouting in the central nervous system: a model for studies of axonal growth in the mature mammalian brain

Sympathetic fibers innervate many peripheral tissues but are normally confined to extracerebral structures within the cranial cavity, e.g. blood vessels. The invasion of the central nervous system by vascular sympathetic axons is a unique example of neuronal plasticity which provides new information concerning the regulation and mechanisms of neuronal sprouting in both the peripheral and central nervous systems. In this paper, the principal findings concerning the conditions under which such sprouting occurs, the mechanisms which may be involved, and the question of its possible function are reviewed. Of special interest is the fact that a nerve growth factor-like brain factor may be involved in this growth response. The principles gleaned from studies of this sprouting phenomenon may be applicable to other models of neuronal plasticity and may have clinical relevance.

Entorhinal lesions result in increased nerve growth factor-like growth-promoting activity in medium conditioned by hippocampal slices

Nerve growth factor (NGF) is present in high concentrations in the rat hippocampal formation where it may be involved in sympathetic sprouting following septohippocampal denervation. In addition, recent evidence suggests that some forebrain cholinergic neurons, including septohippocampal neurons, are responsive to exogenous NGF. Since septohippocampal neurons have been shown to sprout in response to entorhinal lesions both in rats and, recently, in humans, we sought to determine whether endogenous NGF-like activity increases in the rat hippocampal formation following injury to the entorhinal cortex. We found that entorhinal lesions which result in extensive denervation of the dentate granule cells, and subsequent sprouting of septohippocampal axons, do result in greater NGF-like growth-promoting activity in medium conditioned by slices of the denervated tissue when compared to medium conditioned by control tissue. These results suggest that brain NGF may be involved in injury-induced sprouting of forebrain cholinergic neurons.

Evaluation of transected spinal cord regeneration in the rat

Rat spinal cords were subjected to a 200 g/cm force acceleration injury at T10. Ten days later, the cords were totally transected at T10 and the rats separated into two groups: group C (controls) had the spinal cord realigned end-to-end; group X had 3 mm trimmed from proximal and distal cord stumps and a semifluid collagen matrix (CM) bioimplant was inserted in the gap. The CM polymerized to a firm gel at body temperature within 2 h. All rats were maintained 90 days posttransection (dpt). At 90 dpt, they were examined for local spinal cord blood flows, somatosensory evoked potentials, and a neurological evaluation. After killing, the cords were processed for electron and light microscopy and monoamine histofluorescence. The results indicated that CM can support the growth of central neurites, fibroblasts, and an adequate anastomotic network of blood vessels. Control scar tissue does not promote the presence of nerve fibers and blood vessels to the extent observed in the CM. Somatosensory evoked potential early waveforms were present in CM-bioimplanted rats but not in controls. No rat regained walking ability at 90 dpt but muscle tone and strength appeared better in CM-implanted than in control rats. We conclude that a CM bridge can provide a well vascularized, relatively nonhostile environment for central neurites and catecholaminergic axons extending from the proximal spinal cord tissue across the CM bridge and into the distal stump.

Histochemical studies of sympathetic sprouting: fluorescence morphology of noradrenergic axons

The importance of distinguishing between central and peripheral noradrenergic axons is evident from recent observations that sympathetic fibers will invade the central nervous system following specific lesions. The present paper reviews the normal histofluorescence appearance of peripheral and central NE fibers in several species as well as their appearance following experimental manipulations. The most striking differences between these two types of NE neurons is their axonal fluorescence morphology which is apparently determined by the target tissue, and their responsiveness to nerve growth factor (NGF). The latter may account for the remarkable growth of sympathetic axons into regions of the central nervous system denervated of cholinergic fibers. The use of glyoxylic acid in studying such sprouting is also discussed.

Effect of nerve growth factor on regeneration of goldfish optic axons

Axonal outgrowth following a crush of the goldfish optic nerve was enhanced if nerve growth factor (NGF) was administered by intraocular injection or by local application to the lesion site. Various forms of NGF (beta, 2.5S and 7S) were effective, producing a 20-40% decrease in the time required for recovery of the startle reaction to a bright light. A corresponding increase in axonal outgrowth was revealed by histological examination of the optic nerves. The effect produced by a single intraocular injection given at the time of the lesion was not further increased by subsequent injections. Up to 14 days after the lesion, the size of the retinal ganglion cell bodies and the incidence of nucleoli detectable by light microscopy were not affected by the NGF treatment.

Nerve growth factor (NGF) stimulation of cholinergic telencephalic neurons in aggregating cell cultures

The addition of nerve growth factor (2.5S NGF) to serum-free aggregating cell cultures of fetal rat telencephalon greatly stimulated the developmental increase in choline acetyltransferase activity. Two other neuronal enzymes, acetylcholinesterase and glutamic acid decarboxylase, showed only slightly increased activities after NGF treatment whereas the total protein content of the cultures and the activity of 2',3'- cyclic nucleotide phosphodiesterase remained unchanged. The stimulation of choline acetyltransferase was dependent on the NGF media concentrations, showing a 50% maximum effect (120% increase) at approximately 3 ng/ml (10-10 M 2.5S NGF). NGF treatments during different culture periods showed that the cholinergic neurons remained responsive for at least 19 days. The continued treatment was the most effective; however, an initial treatment for only 5 days still caused a significant stimulation of choline acetyltransferase on day 19. The observed stimulation appeared to be specific to NGF. Univalent antibody fragments (Fab) against 2.5S NGF completely abolished the NGF-dependent increase in choline acetyltransferase activity, whereas Fab fragments of control IgG were ineffective. Furthermore, angiotensin II, added in high amounts to the cultures, showed no stimulatory effect. The present results suggest that certain populations of rat brain neurons are responsive to nerve growth factor.

Retinal ganglion cell response to axotomy and nerve growth factor antiserum treatment in the regenerating visual system of the goldfish (Carassius auratus): an in vivo and in vitro analysis

In vitro nerve growth factor (NGF) antiserum (anti-NGF) treatment was found to significantly depress retinal ganglion cell neurite outgrowth in goldfish explant culture. Goldfish retinas, conditioned by a 14-day prior optic nerve crush, demonstrated a significant dose response inhibition of neurite outgrowth if incubated with various concentrations of the antiserum (i.e. concentrations from full strength to 1:100) before explantation for tissue culture. NGF added to the incubation medium containing antiserum partially eliminated the inhibition of neurite outgrowth during the first 4 days of explant culture. Antiserum treatment at the higher concentrations (i.e. full strength and 1:1.5 dilution) caused a cessation of nerve growth from explants between culture days 3 and 4. However, controls at this time still exhibited vigorous neurite outgrowth. In vivo treatment with anti-NGF administered intraocularly at 7 days after optic nerve crush (i.e. 7 DPA) was found to significantly reduce the size and complexity of retinal ganglion cell nucleoli when analyzed morphometrically at 14 DPA. No other cell parameters measured (i.e. cell size, nuclear size, cell/nuclear ratios and mitochondrial, Golgi and RER densities) were found to be affected by the single antiserum treatment.

Retinal ganglion cell response to nerve growth factor in the regenerating and intact visual system of the goldfish (Carassius auratus)

Light and electron microscopic observations indicated that 1 microgram NGF injected into the goldfish eye at the time of optic nerve crush initiated significant retinal ganglion cell body, nuclear and nucleolar hypertrophy when compared to controls at 7 days post-axotomy (7 DPA). In addition, the ultrastructural morphometric values for NGF-treated retinal ganglion cells at 7 DPA were not significantly different from the normal hypertrophy found in 14 DPA controls. Therefore, it appears that NGF treatment caused an acceleration of the normal cell body response to axotomy by about a week. These responses were found to be specific for the NGF molecule and dose-dependent over a 100-1000 ng NGF concentration range. In contrast to the lesioned state, NGF treatment had no significant influence on intact, non-lesioned retinal ganglion cell morphology as measured by morphometric analysis. These results strongly indicate that the responsiveness of the goldfish retinal ganglion cells to NGF is initiated by the axotomy. Eyes treated with NGF in the same manner that elicited the dramatic retinal ganglion cell morphological changes at 7 DPA could also be shown to significantly increase neurite outgrowth from retinal explants cultured at the same post-operative period (i.e. 7 DPA).

Induction of ornithine decarboxylase by renin-free nerve growth factor

Renin-free nerve growth factor causes the induction of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) in superior cervical ganglia from neonatal rats but not in the brain of mature rats. Less pure preparations of nerve growth factor induce the enzyme in both brain and ganglia. The induction of ornithine decarboxylase in the central nervous system appears to be due to renin, not to nerve growth factor itself.

[Role of cell-milieu interactions in the differentiation of nerve cells]

In this review some aspects of nerve cell development are studied from the point of view of the role of the environment on differentiation processes. In the first part, attention is focused on the early stages, with special emphasis on the commitment of the cells coming from the neural crest to acquire and keep a specialized phenotype. In the second part, attempts were made to understand the mechanisms of action of specific growth factors, the Nerve Growth Factor (NGF) being taken as a model molecule. Information presently available is presented on factors that may be implicated in the development of cell types other than those NGF-sensitive, with considerations as to whether the notion of specific growth factors can be generalized to all nervous cell types or not.

Role of nerve growth factor in ethylnitrosourea-induced neural carcinogenesis

The sensitivity of the rat nervous system to malignant transformation by ethylnitrosourea (ENU) is a function of age at treatment. From late gestation, nervous structures decrease in sensitivity with age as non-neural structures increase in susceptibility. There is a decrease in the proportion of neural tumors induced by ENU and an increase in survival time when nerve growth factor (NGF) levels are elevated in the fetal or neonatal stage. If antibodies directed against mouse beta-NGF (anti-NGF) are administered prior to neonatal ENU treatment, neural tumors appear earlier, although in the same proportion as with treatment by ENU alone. This effect is not observed if the ENU is administered first. This phenomenon seems to be attributed to an increased number of trigeminal nerve neurinomas, which have a shorter latent period than other nervous system tumors. The induced neurological tumors in rats treated neonatally with anti-NGF prior to ENU seem to be almost exclusively neurinomas in the peripheral nervous system. Fetal anti-NGF treatment leads to an increased number of intracerebral gliomas and a longer survival time, which corresponds to the longer latent period of these tumors. The role of NGF in the sensitivity of the rat nervous system to carcinogenesis by ENU and its possible implications in the development of the nervous system discussed.

Retinal ganglion cell response to axotomy and nerve growth factor antiserum in the regenerating visual system of the newt (Notophthalmus viridescens): an ultrastructural morphometric analysis

One 3.0 mg dose of the nerve growth factor antiserum (anti-NGF) injected into the vitreous chamber of the eye at the time of optic nerve transection elicits significant changes in the normal newt (Notophthalmus viridescens) retinal ganglion cell body response to axotomy at 7 and 14 days postaxotomy (DPA). Light microscopic observations indicate that anti-NGF treatment significantly reduces the per cent of retinal ganglion cells demonstrating nuclear chromatin reactivity (ie., homogeneous to a more heterogeneous state) from 33.36 +/- 3.02 to 22.82 +/- 2.98%. In addition, the per cent of retinal ganglion cells demonstrating prominent nucleoli is dramatically decreased from 32.08 +/- 1.64 to 18.20 +/- 1.79% at 7 DPA. It is also important to note that the number of prominent nucleoli in the 7 DPA group is reduced to such an extent by anti-NGF treatment that the value is not significantly different from that of intact controls. Intact controls will routinely exhibit approximately half the number of prominent nucleoli that are normal for the untreated 7 DPA group. A definite dose-response relationship can be shown to exist between the per cent of nuclear reactive ganglion cells demonstrating prominent nucleoli and various anti-NGF concentrations at 14 DPA. There does not appear to be a dose-response relationship between various anti-NGF concentrations and the per cent of retinal ganglion cells demonstrating nuclear reactivity at 14 DPA. However, the degree of nuclear chromatin reactivity appears to be less at the higher anti-NGF concentrations (ie., greater than or equal to 3.0 mg/eye) at 14 DPA. Electron microscopic morphometric analysis reveals that anti-NGF treatment significantly reduces the cell perikaryal area at 7 and 14 DPA while the nuclear area remains unchanged. Therefore, there is a significant decrease in the cytoplasmic/nuclear ratios at both 7 and 14 DPA in response to anti-NGF treatment which appears more pronounced by 14 DPA. Anti-NGF treatment also significantly reduces the mitochondrial and nucleolar densities, as well as the nucleolar areas of cells at 7 and 14 DPA. There are no significant changes in Golgi field densities in response to anti-NGF treatment.

Nerve growth factor: effects on D-amphetamine-induced activity and brain monoamines

Adult male rats were given 6-hydroxydopamine lesions of the nucleus accumbens, followed immediately by injections of saline or nerve growth factor (NGF; 125 B.U.) near the substantia nigra. Such lesions were previously reported to attenuate the locomotor response to D-amphetamine. NGF-treated rats showed an enhanced response to D-amphetamine (1.5 mg/kg) when tested 15 days postoperatively. Levels of dopamine and norepinephrine in the striatum and nucleus accumbens were equivalently depressed in the two lesion groups, indicating that the apparent recovery of the NGF-treated rats was probably not due to catecholaminergic neuronal regrowth. Intracerebral NGF administeration enhanced the response to D-amphetamine 15 days later in rats without lesions, and also appeared to result in increased turnover of brain norepinephrine and serotonin at 3, but not 15, days postadministration. NGF might increase dopamine turnover at 15 days, but the evidence obtained did not convincingly confirm or negate this possibility. The results in brain-damaged and intact rats, and also modify the apparent turnover of brain monoamines.

Retinal ganglion cell response to axotomy and nerve growth factor in the regenerating visual system of the newt (Notophthalmus viridescens): an ultrastructural morphometric analysis

Nerve growth factor (NGF) treatment, given as a single 200 BU intraocular injection at the time of optic nerve transection, was found to significantly accelerate the retinal ganglion cell response to axotomy in the newt (Notophthalmus viridescens). In the control series the per cent of neurons in the retinal ganglion layer demonstrating nuclear reactivity (i.e. chromatin changes) reaches a peak by 14 days post axotomy (14 DPA), plateaus through 21 DPA and falls thereafter, returning to control levels by 90 DPA. NGF treatment is shown to significantly accelerate the entrance of responding retinal ganglion cells into the reactive nuclear phase between 1 and 7 DPA, and by 7 DPA nuclear reactivity has reached a peak, in contrast to 14 DPA for control values. Consequently, NGF treatment causes retinal ganglion cells to be in the nuclear reactive state a week longer than controls but reactivity diminishes after 21 DPA as in controls. Electron microscopic morphometric analysis further substantiates these observations by demonstrating that NGF treatment can elicit certain cellular organelle changes a week earlier (i.e. at 7 DPA) than they would normally occur (i.e. at 14 DPA) in response to axotomy. In addition to eliciting cellular hypertrophy at 7 DPA, NGF treatment significantly increases Golgi field densities in the neuronal perikaryal cytoplasm as well as a doubling of the number of nucleoli per nucleus and stimulating a significant increase in nucleolar cross-sectional areas. A dose-response relationship exists between the per cent of retinal ganglion cells demonstrating nuclear reactivity at 7 DPA and various NGF concentrations which compares favorably with the dose response study involving the number of regenerating axons per nerve cross-section at 14 DPA. Studies to determine if the NGF mediated responses were a specific effect elicited by this protein molecule or whether they are also produced by other peptides which share some properties in common with NGF demonstrate that only NGF is capable of eliciting these responses.

Short-latency drinking and increased Na appetite after intracerebral microinjections of NGF in rats

NERVE GROWTH FACTOR (NGF) is a polypeptide trophic factor for peripheral sympathetic and sensory neurones(1,2). Apparent NGF(3-5) and NGF receptors(6,7) have also been identified in the brain, and intracerebral administration of NGF in the adult rat produces marked biochemical(8) and morphologica(9,10) changes in brain tissue. These findings, taken together with the observations that central injections of NGF facilitate behavioural recovery from brain damage(11,12), indicate that this polypeptide may have an important role in brain function. It has been observed that rats given intraventricular injections of up to 2.3 microg NGF drink copiously (M.E.L. and G. Guroff, unpublished observations). Perkins et al.(13) reported that diencephalic application of crystalline NGF (1-15 microg) resulted in an intense polydipsia. The present report confirms the observations of M.E.L. and Guroff, and extends the findings of Perkins et al.(13) by using solutions of NGF instead of crystals. It also describes for the first time a second phenomenon produced by intracranial administration of NGF, namely an intense appetite for aversive concentrations of sodium solutions.

Thyroxine increases nerve growth factor concentration in adult mouse brain

The effects of thyroxine and propylthiouracil on nerve growth factor concentrations in cerebral cortex, cerebellum, and brainstem of adult male mice were assessed by using a sensitive radioimmunoassay for the beta-subunit of mouse nerve growth factor. Thyroxine administration significantly increased the concentration of nerve growth factor in all three brain areas compared to control values, whereas propylthiouracil was without effect. These results suggest that thyroid hormones stimulate nerve growth factor synthesis in the mature central nervous system, and raise the possibility that the influence of thyroid hormones on central nervous system development might be mediated or influenced by nerve growth factor.

Studies on the mechanism of sprouting of noradrenergic terminals in rat and mouse cerebellum after neonatal 6-hydroxydopa

The effect of various pharmacologic agents on the noradrenergic innervation of rat cerebellum was observed. It was found that the neurotoxin 6-hydroxydopa (6-OHDOPA), when given to rats at birth, caused a 46% reduction at 5 weeks of age in tyrosine hydroxylase activity in the locus coeruleus, the nucleus of origin for noradrenergic fibers innervating the cerebellum. At the same time, however, both tyrosine hydroxylase activity and NE content were elevated by 50% in the cerebellum. By treating gravid mice with the 6-OHDOPA, which crosses the placental barrier to affect the brains of developing pups, a dissociation has been shown between the elevated cerebellar NE levels and reduced telencephalic NE content. None of the other assorted pharmacological agents--namely amphetamine, metaraminol, apomorphine, alpha-methyl-p-tyrosine. L-dihydroxyphenylalanine and tyramine--when given at birth, caused a permanent elevation in cerebellar NE content. This series of studies suggests that a reduced number of noradrenergic perikarya are providing a greater innervation of the cerebellum than in control rats. Also, alteration of the telencephalic noradrenergic fibers, which are also derived from the locus coeruleus, does not appear to be a necessary event for the initiation of sprouting of noradrenergic fibers in the cerebellum. Because none of the acute-acting pharmacological agents caused a permanent elevation of NE in the cerebellum, it appears that damage, and not mere stimulation or blockade, is a necessary event for initiation of sprouting.

Effects of nerve growth factor on behavioral recovery following caudate nucleus lesions in rats

Rats with bilateral lesions of the caudate nucleus received intracaudate injections of either nerve growth factor protein (NGF) on inert buffer immediately following surgery. NGF-treated animals demonstrated a faster recovery of normal appetitive behavior and perseverated less than their buffer-treated counterparts on a spatial reversal task, but both groups were impaired relative to sham controls on acquisition of an active avoidance response. Glia to neuron ratios were significantly increased in both lesion groups when compared with sham controls. However, this increase was less in the NGF-treated animals than in the buffer-treated animals. NGF treatment had no effect on steady-state caudate dopamine levels, measured six months after surgery.

Evaluation of the effects of nerve growth factor and anti-nerve growth factor on the development of central catecholamine-containing neurons

Intracisternal NGF or anti-NGF has been found to produce no long-term major alterations in central norepinephrine (NE) or dopamine levels when administered to neonatal rats. While NGF and anti-NGF were found to produce significant changes in brain NE content within one week of treatment, changes in central NE were no longer detectable at 30 days of age. Modification of the growth response of the central adrenergic neurons following 6-OHDA treatment was also not affected by NGF or anti-NGF when evaluated 3 weeks after treatment. However, centrally administered anti-NGF did induce a loss of peripheral NE terminals, which was attributed to leakage of the anti-NGF from the central injection site.

An explanation of axonal regeneration in peripheral nerves and its failure in the central nervous system

Nerve fibres severed within peripheral nerves are able to regenerate and reinnervate the structures they formerly supplied. Most axons severed within the mammalian central nervous system (CNS) do not regenerate in this way. Regenerative axonal growth begins to occur in the CNS but ceases about two weeks after injury. Five earlier theories purporting to explain this difference are reviewed and found not to account satisfactorily for many experimental observations. A new hypothesis is advanced in which it is held that in order for regeneration to take place, the growing tips of the axons must be surrounded by extracellular fluid containing proteins (of specified identity) derived from the blood plasma. Such proteins are thought to be imbibed by the tips of the fibres and transported retrogradely to the neuronal cell-bodies. With this hypothesis it is possible to explain the success of axonal regeneration in peripheral nerves and its failure in the CNS. It is also possible to account for the exceptional circumstances in which axons do regenerate in the CNS. Various experiments are suggested for testing the validity of the new hypothesis.