Nerve growth factor and the neostriatum

Chronic alcohol intoxication in rats leads to a strong but transient increase in NGF levels in distinct brain regions

Nerve growth factor (NGF), a member of the neurotrophin family, is an essential mediator of neuronal activity and synaptic plasticity of basal forebrain cholinergic neurons. In this study NGF-protein levels were determined in areas of the basal forebrain cholinergic system, its projection areas as well as the striatum and the cerebellum after long-term exposure (6 and 9 months) to ethanol and a phase of withdrawal in male Sprague-Dawley rats. 6-month alcohol treatment led to an increase of NGF to 650-850% of controls in the basal forebrain and the septum and to a 210-485% increase in the cholinergic projection areas (anterior cortex, hippocampus and olfactory bulb). After 9 months exposure to ethanol, a decrease of NGF by 16% in the frontal cortex was observed compared to controls. In the other brain regions no differences in NGF expression were detectable at this time-point. These results support the idea of an endogenous neuroprotective mechanism acting through a transient NGF induction followed by a decrease in NGF-levels during the course of further neuronal degeneration.

Effects of ethanol on neurotrophic factors, apoptosis-related proteins, endogenous antioxidants, and reactive oxygen species in neonatal striatum: relationship to periods of vulnerability

The developing central nervous system is extremely sensitive to ethanol, with well-defined temporal periods of vulnerability. Many brain regions are particularly susceptible to ethanol during the early neonatal period, corresponding to the human third trimester, which represents a dynamic period of growth and differentiation. For this study, neonatal rats were acutely exposed to ethanol or control conditions at a neonatal age when the developing striatum has been shown to be vulnerable to ethanol (postnatal day 3 [P3]), and at a later age (P14), when this developing region is relatively ethanol-resistant. We then analyzed basal levels of neurotrophic factors (NTFs), and ethanol-mediated changes in NTFs, apoptosis-related proteins, antioxidants, and reactive oxygen species (ROS) generation, which may underlie this differential temporal vulnerability. Sequential analyses were made following ethanol exposure on these two postnatal days, with assessments of NTFs nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4); apoptosis-related proteins Bcl-2, Bcl-xl, Bax, Akt and c-jun N-terminal kinase (JNK); antioxidants superoxide dismutase, glutathione reductase and catalase; and ROS. The results indicated that basal levels of BDNF, and to some degree NGF, were greater at the older age, and that ethanol exposure at the earlier age elicited considerably more pro-apoptotic and fewer pro-survival changes than those produced at the later age. Thus, differential temporal vulnerability to ethanol in this CNS region appears to be related to differences in both differential levels of protective substances (e.g. NTFs), and differential cellular responsiveness which favors apoptosis at the most sensitive age and survival at the resistant age.

The neurotrophin receptors trkA, trkB and trkC are differentially regulated after excitotoxic lesion in rat striatum

In the present work, we examined the time-dependent changes in trkA, trkB and trkC mRNA levels induced by the injection of glutamate receptor agonists into the striatum. Changes in trk mRNAs induced by quinolinate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), kainate or 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) were analyzed by a ribonuclease protection assay. All high-affinity neurotrophin receptors showed differential regulation after intrastriatal injury. Up-regulation of trkA expression was observed in kainate- or ACPD-injected striata at 10 and 24 h, respectively, whereas quinolinate injection induced down-regulation between 4 and 6 h after injury. Interestingly, all the excitatory amino acid receptor agonists induced up-regulation of trkB-kinase mRNA levels. This increase was maximal between 2 and 4 h after injection except in kainate injected striata, which showed the peak of expression at 10 h. In contrast, no changes in trkC mRNA expression were observed after striatal excitotoxic injury. In conclusion, our results show that trk receptor mRNA levels are differentially regulated by excitatory amino acid receptor agonists in the striatum, suggesting that changes in the levels of neurotrophin receptors might be involved either in synaptic plasticity processes or in neuronal protection in the striatal excitotoxic paradigm.

Nerve growth factor preserves a critical motor period in rat striatum

We previously found the occurrence of a critical motor period during rat postnatal development where circling training starting the 7-day schedule at 30 days-but not before or after-induces a lifetime drop in the binding to cholinergic muscarinic receptors (mAChRs) in striatum. Here, we studied whether nerve growth factor (NGF) participates in this restricted period of muscarinic sensitivity. For this purpose, we administered mouse salival gland 2.5S NGF (1.4 or 0.4 microg/day, infused by means of ALZA minipumps) by intrastriatal unilateral route between days 25 and 39, and then trained rats starting at 40 days. Under these conditions, NGF induced a long-term reduction in the striatal [3H] quinuclidilbenzylate (QNB) binding sites despite the fact that motor training was carried out beyond the natural critical period. Thus, at day 70, measurement of specific QNB binding in infused striata of trained rats showed decreases of 42% (p < .0004) and 33% (p < .02) after administration of the higher and lower NGF doses, respectively, with respect to trained rats treated with cytochrome C, for control. Noncannulated striata of the NGF-treated rats also showed a decrease in QNB binding sites (44%; p < .0001) only at the higher infusion rate. This effect was not found in the respective control groups. Our observations show that NGF modulates the critical period in which activity-dependent mAChR setting takes place during rat striatal maturation.

Differential regulation of the expression of nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 after excitotoxicity in a rat model of Huntington's disease

In the present study we have evaluated changes in nerve growth factor (NGF), brain-derived neurotrophic factor, and neurotrophin 3 (NT-3) mRNA expression induced by different glutamate receptor agonists injected into the neostriatum. Up-regulation of NGF expression was observed at 24 h after intrastriatal quinolinate injection, an N-methyl-D-aspartate receptor agonist, and this increase was maintained up to 7 days after lesion. NGF up-regulation was also apparent in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) treatment from 6 to 16 h postinjection. Instead, BDNF was up-regulated only at 6 h after kainate or AMPA excitotoxicity. Interestingly, NT-3 mRNA was down-regulated from 10 to 16 h following AMPA lesion, while 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid injection enhanced NT-3 mRNA levels at 10 h. Our results show a specific neurotrophin response induced by stimulation of each glutamate receptor. These activity-dependent changes might be involved in neuronal plasticity processes and may underlie the differential vulnerability of striatal neurons observed in neurodegenerative disorders.

Large neostriatal neurons in humans and their possible role in neuronal networks

The Golgi method was used to study the structure of large neostriatal neurons in adult humans. Four types of large interneurons were found (spider cells, hairy cells, asymmetric fan cells, and giant stretched cells), along with two types of large projection cells (large reticular cells with spines and giant reticular cells with smooth dendrites). The structural features and possible mediators of these cells are discussed, along with their roles in neostriatal neuronal networks and in the development of pathological symptoms in chorea and progressive supranuclear paralysis.

Systemic administration of anti-NGF antibodies to neonatal mice impairs 24-h retention of an inhibitory avoidance task while increasing ChAT immunoreactivity in the medial septum

Neonatal mice received subcutaneous injections of either antibody against murine NGF raised in goat (3 mg, injection volume 50 microliters) or preimmune serum on postnatal days 2, 4, 6, 8, 10, and 12. They were tested on postnatal days 15-16 or 20-21 for learning and 24-h retention of a passive avoidance step-through task. Immunostaining for choline acetyltransferase (ChAT) was measured in two cholinergic forebrain areas (septum and caudate-putamen) on postnatal day 16 or 21. Locomotor activity and exploratory behavior in an open-field test were also assessed on day 17 or 22, following a single administration of either scopolamine (2 mg/kg) or saline solution. While anti-NGF treatment did not affect acquisition on day 15, impairment in retention was evident on day 16. On days 20-21, no effects were found either on acquisition or on retention capabilities. Analysis of ChAT immunostaining revealed a significant increase of ChAT-immunopositive cells in the medial septal area in 16-day-old but not in 21-day-old mice. Behavior in the open-field test and age-typical response to scopolamine were not altered by anti-NGF at either of the two ages considered. These data support the view that immunological neutralization of endogenous NGF specifically affects the maturation of retention capabilities in altricial rodents, and confirm the involvement of forebrain cholinergic mechanisms in early memory processes.

NGF deprivation of adult rat brain results in cholinergic hypofunction and selective impairments in spatial learning

Cholinergic hypofunction has often been correlated with a variety of behavioural impairments. In the present study, adult Wistar rats were intraventricularly infused with antibodies to nerve growth factor (anti-NGF) to examine the effects on cholinergic neurons of the basal forebrain, and on behavioural performance. Immunocytochemical techniques indicated that chronically infused anti-NGF penetrates into the basal forebrain, cortex, striatum, corpus callosum and hippocampus, confirming previous findings after a single injection. Treatment with anti-NGF for 1 or 2 weeks resulted in a significant decrease of 27-33% in density of choline acetyltransferase immunostaining of the cholinergic cell bodies in the medial septum and vertical diagonal band, and a 26% reduction in choline acetyltransferase enzyme activity in the septal area. An array of spatial learning Morris water maze tasks was used to distinguish between acquisition skills and the flexible use of learned information in novel tests. Rats subjected to the spatial learning paradigm received anti-NGF infusion for 2 weeks prior to and for another 2 weeks during the behavioural testing. The anti-NGF-treated animals were found to be no different from those receiving control serum in the Morris water maze acquisition task, either in the latency to find the platform or in the time spent searching in the training quadrant when the platform was removed. However, in consecutive extinction trials, anti-NGF rats continued to search in the empty training quadrant, suggesting the occurrence of perseveration; control rats expanded their search over other areas of the pool.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral asymmetries and recovery in rats with different degrees of unilateral striatal dopamine depletion

A detailed behavioral analysis during the first postoperative week was performed in rats which had sustained various degrees of unilateral neostriatal dopamine (DA) lesions by administration of the neurotoxin 6-hydroxydopamine into the substantia nigra. These animals were assigned to different groups according to their residual DA levels in the damaged neostriatum (as percentage of the intact side). On the first day after toxin injection into the substantia nigra, turning asymmetries (tight turns) toward the side of the lesion were observed in animals with a mean residual DA level of 32% or less. Out of these, the strongest asymmetries were observed in animals with a mean residual DA of 3%. After one week, the asymmetry in tight turns had totally recovered except in those groups with mean residual DA levels of 17% or less. Partial recovery was found in animals with mean residual DA of 9 and 17%, whereas no indication for recovery was found in animals with the most severe lesions (mean residual DA 3%). Measurement of thigmotactic scanning also revealed an asymmetry for the side of the lesion on the first post-operative day. This asymmetry was observed over a wider range of DA lesion than that observed in turning, namely up to a mean residual DA level of 78%. Furthermore, recovery to symmetry was observed in all lesion-groups except in those with more severe lesions (mean residual DA 17% or less). In contrast to turning, the strongest asymmetries were not displayed by the animals with the most severe lesions. Furthermore, locomotor activity was affected by the lesion, since on the first postoperative day locomotion was reduced in animals with mean residual DA of 39% or less. On day 7, this lesion-dependent deficit had recovered to control levels. Finally, the analysis of net turns allowed the prediction of lesion size in animals with residual DA levels of less than 15%. These results are discussed with respect to mechanisms of recovery, the role of lesion size, and the value of different behavioral measures to predict the degree of DAergic lesion.

Differential expression of immediate early genes in distinct layers of rat cerebral cortex after selective immunolesion of the forebrain cholinergic system

The aim of this study was to show whether reduction or loss of cortical cholinergic activity results in any particular change in the expression of the proto-oncogenes c-fos and/or c-jun. To produce cortical cholinergic hypofunction, the monoclonal antibody, 192IgG, to the low-affinity nerve growth factor receptor p75NGFR coupled to a cytotoxin, saporin, was used as an efficient and selective immunotoxin for cholinergic neurons in rat basal forebrain. Brain sections of adult rats that had received an intracerebroventricular injection of 4 micrograms of the 192IgG-saporin were subjected to in situ hybridization using oligonucleotides to detect c-fos and c-jun mRNA. Autoradiographs obtained were evaluated by quantitative image analysis. Seven days following injection of the immunotoxin there was a dramatic loss in acetylcholinesterase staining in frontal, parietal, piriform, temporal, and occipital cortices, hippocampus, and olfactory bulb, but not in the striatum and cerebellum. In situ hybridization revealed a considerable increase in the level of c-fos mRNA in the lateral septum following the cholinergic lesion, whereas in the medial septum both c-fos and c-jun mRNA were elevated. Immunolesioning led to a distinct and specific increase in the level of c-jun but not c-fos mRNA in the parietal and occipital cortex that was restricted to cortical layer IV. These data suggest that reduced cortical cholinergic activity differentially regulates expression of c-fos/c-jun genes in distinct cortical regions of the rat brain.

Nerve growth factor and basic fibroblast growth factor protect cholinergic neurons against quinolinic acid excitotoxicity in rat neostriatum

In the present work we have characterized a possible mechanism leading to the early survival of neostriatal cholinergic neurons after quinolinic acid injection. Different doses of quinolinic acid were injected in rat neostriatum and two different parameters were analysed 7 days after the lesion: choline acetyltransferase (ChAT) activity and nerve growth factor (NGF) levels. We have observed that ChAT activity decreased (until 68 nmol quinolinic acid) and NGF levels increased (until 34 nmol quinolinic acid) in a dose-dependent manner. In order to characterize the time-course of the lesion on NGF levels and ChAT activity, and the possible protective effect of NGF and basic fibroblast growth factor (bFGF) on cholinergic neurons, we have used the quinolinic acid dose (68 nmol) at which the first decrease of ChAT activity was observed. ChAT activity and NGF levels showed different patterns of response to quinolinic acid injection, since the maximal effect was reached at 1 day for ChAT activity and at 2 days for NGF levels. NGF or bFGF simultaneously injected with quinolinic acid (68 nmol) completely prevented the decrease in ChAT activity in a dose-dependent manner but NGF was more effective than bFGF. Furthermore, differences observed in ChAT activity after NGF but not bFGF treatment were correlated with changes in the number of ChAT immunoreactive cells. Finally, we have also observed that, although bFGF alone was not able to modify NGF levels, bFGF simultaneously injected with quinolinic acid produced an increase of NGF levels higher than that observed after quinolinic acid injection alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral stimulation or removal of rat vibrissae: analysis of nerve growth factor and tyrosine hydroxylase mRNA in the brain

Previous work has shown that unilateral manipulation of vibrissae in the rat can lead to behavioral asymmetries and to neuronal changes in the basal ganglia: in brief, vibrissae stimulation led to increases in neostriatal dopamine release, whereas unilateral removal of vibrissae led to asymmetries in striatal afferents and to bilateral changes in mesencephalic dopamine mechanisms which were related to the occurrence of behavioral asymmetries and the later recovery therefrom. In the present study, the analysis of neuronal mechanisms possibly affected by vibrissae manipulation was extended to the nerve growth factor and the expression of tyrosine hydroxylase mRNA. Unilateral stimulation or removal of the vibrissae did not lead to significant changes in tissue levels of nerve growth factor in the neostriatum, parietal cortex (including the barrel cortex) or the hippocampus. In contrast, tyrosine hydroxylase mRNA in the substantia nigra and ventral tegmental area was affected by vibrissae removal but not by stimulation, as a bilateral increase in labeling was observed on the level of individual neurons. This effect was only observed in animals tested 4 h after vibrissae removal but not after 10 days. The results are discussed with respect to the interaction of vibrissae function with the basal ganglia, the neurotransmitter dopamine and mechanism of functional recovery.

Growth factors in Parkinson's disease

The etiology of Parkinson's disease, one of the most frequent neurodegenerative disorders in human, is unknown. New hopes concerning satisfactory therapies include transplants of autologous adrenal medullary chromaffin tissue, fetal mesencephalic dopaminergic neurons, and local application of growth factors with a neurotrophic capacity. A large body of evidence supports the notion that neurons require trophic support not only during a limited period of ontogenesis, but during their whole lifespan. Relevant molecules promote survival, transmitter synthesis and other differentiated properties, and become crucially important when a neuron is metabolically or toxically impaired. Several molecules, most of which occur in the striatum and the substantia nigra, have been identified that protect lesioned dopaminergic nigrostriatal neurons in culture or in animal models of Parkinson's disease. These include members of the neurotrophin, fibroblast growth factor, and insulin-like growth factor families as well as epidermal growth factor/transforming growth factor alpha, interleukins and ciliary neurotrophic factor. Whether their effects are merely pharmacological, or reflect a physiological role in the nigrostriatal system, is unclear as yet. This article reviews experiments that document the trophic effects of these factors on dopaminergic neurons and discusses their possible physiological and therapeutic relevance.

Excitatory amino acid regulation of the enkephalin phenotype in mouse embryonic spinal cord cultures

Expression of the preproenkephalin gene in developing spinal cord-dorsal root ganglia (SC-DRG) cultures was determined by Northern analysis following treatments with different agonists and antagonists of the glutamate receptor. Cultures (10-12 days old) were treated with various concentrations (10(-7)-10(-3) M) of N-methyl-D-aspartate (NMDA), quisqualate, kainic acid (KA), 2-amino-5-phosphonovaleric acid (APV) and 5-methyl-10,11-dihydro-5H-dibenzo[a, d]cyclohepten-5,10-imine maleate (MK801) either with or without blocking spontaneous electrical activity with 1 microM tetrodotoxin (TTX). In electrically active cultures, treatments with NMDA and KA increased preproenkephalin transcripts (mRNAppENK), showing maximum effects at 1 microM (4-fold and 2-fold, respectively), while treatments with quisqualate and MK801 caused concentration-dependent down-regulation in mRNAppENK. The most effective concentrations of NMDA (1 microM) and quisqualate (10 microM) altered mRNAppENK levels within 4 h of treatment and peaked after 24 h for NMDA and 48 h for quisqualate treatment. Co-treatment with APV completely blocked the NMDA-induced rise of mRNAppENK. During electrical blockade, none of the concentrations of NMDA tested showed any effect on enkephalin expression, neither could NMDA pre-treatment prevent the TTX-induced down-regulation of mRNAppENK. Our results indicate that the activity-dependent establishment of the enkephalin phenotype is modulated through the selective activation of the NMDA-glutamate receptor.

Distribution of nerve growth factor-like immunoreactive neurons in the adult rat brain following colchicine treatment

Using immunohistochemical techniques, we have previously localized nerve growth factor (NGF)-like immunoreactivity in the normal adult rat central nervous system (CNS) exclusively in the hippocampal mossy fiber region and within basal forebrain cholinergic neurons--a cell population believed to be primary NGF consumers within the CNS. In the present investigation, we have attempted to identify potential producers of NGF by pretreating animals with colchicine. Such a treatment would be expected to block microtubule-assisted neuritic transport mechanisms, thus preventing the accumulation of antigens normally obtained by retrograde transport and forcing the accumulation of cell products normally exported anterogradely. Forty-eight hours after colchicine administration within their innervation territories, basal forebrain cholinergic neurons showed a marked loss of NGF-like immunoreactivity. Conversely, following colchicine treatment, many new populations of NGF-like immunoreactive cells were detected, several of which have been previously observed with in situ hybridization techniques for NGF mRNA. Many NGF-like immunoreactive populations, however, were not previously recognized by in situ hybridization methods, including cells of the striatum, reticular thalamic nucleus, paraventricular hypothalamic nucleus, supraoptic nucleus, lateral and medial septum, substantia innominata, and nucleus basalis. Furthermore, evidence is provided that colchicine-blocked, NGF-like immunoreactive neurons within the basal forebrain are not cholinergic, thus reinforcing the hypothesis that trophic support for these NGF-dependent neurons may be derived from distant and local sources. The distinctive distribution of NGF-like immunoreactive cells observed in this study strongly correlates with the reported distribution of NGF mRNA in CNS neurons, thus suggesting that our antibodies are uniquely recognizing NGF and not other related neurotrophins.

Recovery of cholinergic phenotype in the injured rat neostriatum: roles for endogenous and exogenous nerve growth factor

Polyclonal antibodies against recombinant human nerve growth factor (rhNGF) potently inhibited PC12 neurite outgrowth, blocked high-affinity 125I-rhNGF binding but not its receptor, and cross-reacted with rat, mouse, and human nerve growth factor (NGF) but not with brain-derived neurotrophic factor, neurotrophin-3, ciliary neurotrophic factor, insulin-like growth factor, epidermal growth factor, or activin A. Immunocytochemistry revealed many NGF-positive neurons in the rat neostriatum. The NGF-positive neurons disappeared by 3 days after mechanical injury to the neostriatum and were replaced by intensely NGF- and glial fibrillary acidic protein-positive astrocytes. Enzyme-linked immunosorbent assay measurements revealed that the NGF content of the injured striatum was elevated by eightfold 3 days postinjury and by twofold 2 weeks later. The high-affinity choline uptake (HACU) into cholinergic nerve terminals was decreased by 23% at 2 and 4 weeks postinjury, yet choline acetyltransferase (ChAT) activity in these neurons was unchanged at 2 weeks and decreased by 14% at 4 weeks. Daily infusion of 1 microgram of rhNGF into the injury area did not alter the loss of HACU. However, this treatment elevated ChAT activity by 23-29% above intact neostriatal levels and by 53-65% relative to HACU at both survival times. Thus, lesion-induced increases in NGF levels within astrocytes are associated with maintenance of striatal ChAT activity at normal levels following cholinergic injury, even with decreases in HACU. Pharmacologic doses of rhNGF can further augment ChAT activity in damaged cholinergic neurons, showing the usefulness of exogenous NGF even when endogenous NGF is elevated in response to injury.