Effect of bilateral decortication on nerve growth factor content in basal nucleus and neostriatum of adult rat brain

NGF, TrkA-P and neuroprotection after a hypoxic event in the developing central nervous system

A decrease in the concentration of oxygen in the blood and tissues (hypoxia) produces important, sometimes irreversible, damages in the central nervous system (CNS) both during development and also postnatally. The present work aims at analyzing the expression of nerve growth factor (NGF) and p75 and the activation of TrkA in response to an acute normobaric hypoxic event and to evaluate the possible protective role of exogenous NGF. The developing chick optic tectum (OT), a recognized model of corticogenesis, was used as experimental system by means of in vivo and in vitro studies. Based on identification of the period of highest sensitivity of developmental programmed cell death (ED15) we show that hypoxia has a mild but reproducible effect that consist of a temporal increase of cell death 6 h after the end of a hypoxic treatment. Cell death was preceded by a significant early increase in the expression of Nerve Growth Factor (NGF) and its membrane receptor p75. In addition, we found a biphasic response of TrkA activation: a decrease during hypoxia followed by an increase -4 h later- that temporally coincide with the interval of NGF overexpression. To test the NGF - NGF receptors role in hypoxic cell death, we quantified, in primary neuronal cultures derived from ED15 OT, the levels of TrkA activation after an acute hypoxic treatment. A significant decline in the level of TrkA activation was observed during hypoxia followed, 24 h later, by significant cell death. Interestingly, this cell death can be reverted if TrkA inactivation during hypoxia is suppressed by the addition of NGF. Our results suggest that TrkA activation may play an important role in the survival of OT neurons subjected to acute hypoxia. The role of TrkA in neuronal survival after injury may be advantageously used for the generation of neuroprotective strategies to improve prenatal insult outcomes.

A nerve growth factor mimetic TrkA antagonist causes withdrawal of cortical cholinergic boutons in the adult rat

Cholinergic neurons respond to the administration of nerve growth factor (NGF) in vivo with a prominent and selective increase of choline acetyl transferase activity. This suggests the possible involvement of endogenous NGF, acting through its receptor TrkA, in the maintenance of central nervous system cholinergic synapses in the adult rat brain. To test this hypothesis, a small peptide, C(92-96), that blocks NGF-TrkA interactions was delivered stereotactically into the rat cortex over a 2-week period, and its effect and potency were compared with those of an anti-NGF monoclonal antibody (mAb NGF30). Two presynaptic antigenic sites were studied by immunoreactivity, and the number of presynaptic sites was counted by using an image analysis system. Synaptophysin was used as a marker for overall cortical synapses, and the vesicular acetylcholine transporter was used as a marker for cortical cholinergic presynaptic sites. No significant variations in the number of synaptophysin-immunoreactive sites were observed. However, both mAb NGF30 and the TrkA antagonist C(92-96) provoked a significant decrease in the number and size of vesicular acetylcholine transporter-IR sites, with the losses being more marked in the C(92-96) treated rats. These observations support the notion that endogenously produced NGF acting through TrkA receptors is involved in the maintenance of the cholinergic phenotype in the normal, adult rat brain and supports the idea that NGF normally plays a role in the continual remodeling of neural circuits during adulthood. The development of neurotrophin mimetics with antagonistic and eventually agonist action may contribute to therapeutic strategies for central nervous system degeneration and trauma.

Analysis of c-Fos and glial fibrillary acidic protein (GFAP) expression following topical application of potassium chloride (KCl) to the brain surface

Application of high K+ concentrations to a limited area of the brain surface is known to trigger spreading depression. We used this model to observe the response of cortical areas, distant to the exposed site, at the cellular level. Immunostaining of glial fibrillary acidic protein (GFAP) and of the proto-oncogene c-Fos was analyzed in brain sections at different times after K+ application. Piriform and parietal cortices, as observed in coronal sections located 3 mm rostrally from the center of the stimulated area and ipsilateral to it, showed a dramatic increase in immunostaining for both markers. However, the time course for such increments was different. c-Fos protein(s) expression was high at 1.5 h and decreased at 24 h after K+ exposure and c-fos mRNA expression correlated with the immunohistochemical results. At these initial times GFAP immunoreactivity was still low but began to rise between 2 and 7 days after treatment in exactly the same areas where c-Fos expression had been up-regulated. No significant effect, for either marker, was evident in the contralateral piriform or parietal cortices. In addition, we studied the effects of the NMDA antagonist MK-801 (4 mg/kg i.p.) on the expression of mRNA for GFAP and c-fos and demonstrated a marked reduction in the upregulation of these genes.

Glial cell reaction to cis-dichlorodiammine platinum treatment in the immature rat cerebellum

In this study we have investigated changes in glial cells of the cerebellum of cis-dichlorodiammine platinum (cisDDP)-treated rats. The expression of S-100 protein and glial fibrillary acidic protein (GFAP), taken as markers of glial cell function, was evaluated using immunocytochemical methods. In parallel, immunoreactivity for calbindin, parvalbumin, and phosphorylated 200-kDa neurofilament protein was observed in Purkinje cells as markers for neuronal integrity and activity. Results showed that, although no difference in the immunostaining of S-100 protein between control and treated animals could be observed, an increase in the frequency of GFAP immunoreactive cells was present in cisDDP-treated rats. In Purkinje cells, immunocytochemical expression of calbindin and parvalbumin was decreased after drug treatment. In addition, following immunoreaction for phosphorylated 200-kDa neurofilament protein, the somata of Purkinje cells, which were negative in control animals, were stained in treated rats. These findings suggest that cisDDP does not significantly interfere with pathways of glial cell activity and that the increased number of GFAP positive astrocytes may be due to an activation of glial cells consequent upon neuronal death.

Differential expression of p140trk, p75NGFR and growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamus and adjacent cortex following neocortical infarction and nerve growth factor treatment

A loss of target-derived neurotrophic factors is hypothesized to be one of the major determinants of central nervous system neuronal degeneration. In order to obtain further insight into early neuronal responses to injury, lesion-induced alterations in the expression of high- and low-affinity nerve growth factor receptors, as well as growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamic and neocortical neurons were studied. For this purpose, unilateral cortical devascularization operations were conducted on adult rats. Animals received i.c.v. infusions of vehicle or nerve growth factor (12 micrograms/day) and were killed at one, three, seven and 15 days post-lesion. In situ hybridization studies using 35S-labelled oligonucleotide probes for p75NGFR, p140trk and growth-associated phosphoprotein-43 messenger RNAs reveals that these genes were differentially regulated following the lesion. In the nucleus basalis magnocellularis ipsilateral to the lesion, p140trk gene expression significantly decreased on days 3 and 7, while p75NGFR messenger RNA initially increased on day 3 and decreased on days 7 and 15 after lesion. GAP-43 messenger RNA levels were significantly increased in the nucleus basalis magnocellularis on post-lesion days 3 and 7. Moreover, in contrast to p75NGFR or 140trk, growth-associated phosphoprotein-43 messenger RNA levels were significantly increased in pyramidal neurons located in the remaining cortex adjacent to the cortical lesion at all time points. In the lateral and ventroposterior nuclei of the thalamus, growth-associated phosphoprotein-43 messenger RNA level was slightly increased on days 1 and 3 and was dramatically decreased, significantly below the levels in sham-operated controls, on post-lesion days 7 and 15. During nerve growth factor application, the level of p140trk messenger RNA in the lesioned nucleus basalis magnocellularis returned to values observed in the contralateral nucleus basalis magnocellularis while p75NGFR messenger RNA was increased above values noted in all animals not treated with nerve growth factor. Nerve growth factor treatment did not affect the expression of growth-associated phosphoprotein-43 messenger RNA in any of the areas studied. p140trk messenger RNA was not up-regulated during the time that nerve growth factor was applied, as observed for p75NGFR, but only eight days after interrupting nerve growth factor treatment. Three cell types, nucleus basalis magnocellularis, cortical pyramidal and thalamic neurons, were probably affected in different ways by the devascularization with respect to lesion extent. Consequently, the remaining number of synaptic contacts in each of these brain areas is most likely different which may lead to a differential regulation of growth-associated phosphoprotein-43 messenger RNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemotaxis and accumulation of nerve growth factor by microglia and macrophages

Astrocytes and microglia play a critical role in the reaction of the central nervous system (CNS) to trauma. Although both astrocytes and microglia can produce it, accumulation of immunoreactive nerve growth factor (the prototype neurotrophin important for the survival of several classes of neurons) was observed selectively in cultured microglia and macrophages, rather than in astrocytes. Furthermore, microglia were found to display chemotaxis toward a localized source of nerve growth factor and, as demonstrated by autoradiography, take up extracellular nerve growth factor. These findings suggest that microglia, the brain's own macrophages, participate in the regulation of nerve growth factor availability in a site-specific manner. This novel function may assume a general importance both in the CNS and the peripheral nervous system at critical times after trauma when this neurotrophin is needed for nerve cell survival.

Effects of the chemical denervation on the glial cells of the rat pineal gland: an immunocytochemical study during postnatal development

We have studied the postnatal evolution of the glial cells in the rat pineal gland after its chemical pre- and perinatal denervation, by the assessment of the immunocytochemical expression of three antigens characteristic of glial cells i.e., vimentin (VIM), glial fibrillary acidic protein (GFAP), and S-100 protein. The neurotoxic agents we applied consisted of 6-hydroxydopamine (6-OHDA) administered during the first 5 postnatal days, and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) injected to pregnant rats in the 15th gestational day. VIM immunoreactivity was detected in pineal glial cells from the first postnatal day, both in denervated and control groups. However, in denervated glands, the maturation process of the glial cells is considerably accelerated, since they appear completely detached of the connective tissue septa at day 15. From day 30, the number of VIM-positive structures progressively increases until adulthood, when a large number of immunoreactive cell processes produces a reticular appearance to the denervated pineal gland. The first GFAP and S-100 protein immunoreactive cells were observed earlier in denervated animals (5th postnatal day for S-100 protein, and 10th postnatal day for GFAP) compared with controls. In the experimentally denervated groups, the population of positive cells, as well as their size and the number of their cell processes, is considerably higher and progressively increased. They were always characteristically located in the proximal half of the gland. From day 45, this region of the gland shows a notable amount of hypertrophic positive cells with thick processes, showing a gliotic aspect.(ABSTRACT TRUNCATED AT 250 WORDS)

Degeneration of rat cholinergic basal forebrain neurons and reactive changes in nerve growth factor expression after chronic neurotoxic injury--II. Reactive expression of the nerve growth factor gene in astrocytes

Long-term consumption of ethanol both in human and rodent induces a process of chronic degeneration of cholinergic basal forebrain neurons which results in a cholinergic deafferentation of the cortical mantle. We have used quantitative northern blot analysis and in situ hybridization to demonstrate that these degenerative events in rat evoke an increase in the expression of the nerve growth factor gene in a number of brain areas, including the cholinergic basal forebrain nuclei and their cortical target regions. By combining non-radioactive in situ hybridization and immunohistochemistry activated astrocytes were identified as the major source of altered nerve growth factor gene expression. This increased nerve growth factor expression is paralleled by a dendritic remodelling of basal forebrain neurons, while the expression of choline acetyltransferase in surviving neurons remains the same. This failure of nerve growth factor to rescue the expression of choline acetyltransferase differs from the effects of exogenously administered nerve growth factor in acutely lesioned systems. The results indicate that under certain conditions of chronic neurodegeneration, the utilization of nerve growth factor might be impaired, which could be due to a defective nerve growth factor signalling mechanism.

Degeneration of rat cholinergic basal forebrain neurons and reactive changes in nerve growth factor expression after chronic neurotoxic injury--I. Degeneration and plastic response of basal forebrain neurons

The process of degeneration and dendritic reorganization of cholinergic neurons was investigated in the rat basal forebrain under the conditions of chronic neurotoxic injury induced by long-term consumption of ethanol. After 28 weeks of ethanol treatment (20% v/v), both the number of choline acetyltransferase-immunoreactive basal forebrain neurons and levels of biochemical measures of cholinergic neurons, such as the activity of choline acetyltransferase and the synthesis and content of acetylcholine, were decreased by about 60-80%. The number of cholinergic neurons showing a positive hybridization signal to choline acetyltransferase messenger RNA was decreased to a similar extent. On the contrary, the reduction in the number of neurons immunoreactive for nerve growth factor receptor p75, which in control brains is highly co-localized with the expression of choline acetyltransferase, was much less pronounced and reached only 20-30%. The loss of choline acetyltransferase expression was associated with a cellular hypertrophy. Neurons which had survived the neurotoxic damage, furthermore, showed a remodelling of the dendritic organization which was quantitatively investigated after Golgi impregnation. This process of dendritic reorganization was mainly characterized by an increase in number and length of terminal dendritic segments. The results indicate that under the conditions of the present paradigm of chronic neurodegeneration, a certain number of cholinergic neurons persists in a form where they lost their ability to express detectable amounts of choline acetyltransferase messenger RNA and the enzyme protein. Persisting neurons, however, show both expression of nerve growth factor receptor p75 and signs of perikaryal and dendritic growth. It might, therefore, be hypothesized that chronic degeneration of cholinergic basal forebrain neurons triggers reactive attempts of repair which involve the action of trophic factors such as nerve growth factor.

Dendritic reorganisation in the basal forebrain under degenerative conditions and its defects in Alzheimer's disease. II. Ageing, Korsakoff's disease, Parkinson's disease, and Alzheimer's disease

Changes in the dendritic arborisation of Golgi-impregnated basal forebrain neurones with respect to size, shape, orientation, and topology of branching were quantitatively investigated in ageing, Alzheimer's disease (AD), Korsakoff's disease (KD), and Parkinson's disease (PD). A reorganisation of the whole dendritic tree characterized by an increase in both the total dendritic length and the degree of dendritic arborisation as well as by changes in the shape of the dendritic field was found during ageing, in KD, PD, and AD. Dendritic growth under these conditions was related to the extent of cell loss in basal forebrain nuclei. There appeared to be major differences, however, with respect to the overall pattern of dendritic reorganisation between AD on one side and ageing, KD, and PD on the other side. In both ageing and KD, dendritic growth was largely restricted to the terminal dendritic segments, resulting in an increase of the size of the dendritic field (pattern of "extensive growth") In AD, however, dendritic growth mainly resulted in an increase of the dendritic density within the dendritic field without being accompanied by an increase in the size of the volume occupied by the dendritic tree (pattern of "intensive growth"). In AD, aberrant growth processes were frequently observed in the perisomatic area or on distal dendritic segments of basal forebrain neurones of the reticular type. Neurones with aberrant growth profiles were typically located in the direct vicinity of deposits of beta/A4 amyloid. Perisomatic growth profiles were covered by the low-affinity receptor of nerve growth factor p75NGFR. Aberrant growth processes were not present in ageing, KD, and PD. On the basis of the present study, it is concluded that under certain degenerative conditions, reticular basal forebrain neurones undergo a compensatory reorganisation of their dendritic arborisation, a process that has become defective in AD, thereby converting a physiological signal into a cascade of events contributing to the pathology of the disease.

Lesion induced expression of low-affinity NGF-binding protein (p75) immunoreactivity after neonatal and adult aspiration lesions of the rat dorsomedial prefrontal cortex

The present study was performed in order to examine whether or not NGF-mediated processes could be involved in the sparing of function observed after neonatal prefrontal cortex lesions. After unilateral neonatal aspiration lesions of the dorsomedial prefrontal cortex, fibers immunoreactive for the low-affinity NGF-binding protein (p75) with a deviant morphology were observed in the severed hemisphere only. The morphology of these fibers was characterized by their large caliber, their large, often bulbous varicosities, and their curly appearance. These fibers were present as soon as 24 h after the operation. Between 3 and 5 days after the operation, the greatest abundance of these fibers was found in the ventrorostral areas of the forebrain and along the pathways of cortical projections of the cholinergic cell groups. After 7 days, such fibers were no longer observed. After comparable lesions in adult animals, a similar type of fiber was observed in the lesioned hemisphere. However, in these cases a response comparable to that observed in the neonatal animals was not observed until 5 days after the operation, with fewer fibers. Furthermore, in contrast to what was observed after neonatal lesions, in adult animals no indications of retrograde transport of p75 immunoreactive material towards the cholinergic cells of the basal forebrain nuclei were found. From these findings it was concluded that the prompt upregulation of p75 expression in neonatal animals may contribute to the survival of the cholinergic cells of the basal forebrain, and may therefore be involved in the restoration of function of the medial prefrontal cortex.

Neocortical infarction in subhuman primates leads to restricted morphological damage of the cholinergic neurons in the nucleus basalis of Meynert

The aim of the present study was to investigate the long-term effect of cortical infarction on the subhuman primate (Cercopithecus aethiops) basal forebrain. The lesion, carried out by cauterizing the pial blood vessels supplying the left fronto-parieto-temporal neocortex, induced retrograde degenerative processes within the ipsilateral nucleus basalis of Meynert. The morphometrical analysis revealed that significant shrinkage of cholinergic neurons and loss of neuritic processes were localized within the intermediate regions of the nucleus basalis. The average cross-sectional areas of choline acetyltransferase-immunoreactive neurons in the intermedio-ventral (Ch4iv) and intermedio-dorsal (Ch4id) nucleus basalis were decreased to 62.5 +/- 9.5 and 58.0 +/- 8.6%, respectively, of the sham-operated values. Although an apparent loss of Nissl-stained magnocellular neurons in Ch4iv and Ch4id was found by applying a quantitative analysis based on a perikaryal-size criterion, data obtained by the quantification of immunostained material failed to reveal any significant decrease of cholinergic cell density. Results are discussed in view of future application of this ischemic model to study processes of retrograde degeneration following cortical target removal and to assess potential neurotrophic and neuroprotective properties of pharmacologic agents.

Increased levels of nerve growth factor (NGF) protein and mRNA and reactive gliosis following kainic acid injection into the rat striatum

After excitotoxic lesion of the rat striatum, the time courses of local nerve growth factor (NGF) and NGF mRNA contents were investigated using a sensitive immunoassay (ELISA) and reverse transcription coupled to polymerase chain reaction (RT/PCR). To investigate a possible correlation of increased NGF expression and excitotoxin-induced reactive gliosis, striata were also analysed by immunohistochemistry with glial markers. We found elevated striatal NGF protein after lesion over the whole observation period. NGF mRNA showed a biphasic increase 10 h and 10 days after lesion, the latter co-inciding with an increased astrogliosis. These results indicate that NGF accumulation after excitotoxin-induced neurodegeneration is partly due to local reactive astrocytes.

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.

Potentiation of nerve growth factor-induced alterations in cholinergic fibre length and presynaptic terminal size in cortex of lesioned rats by the monosialoganglioside GM1

The effect of monosialoganglioside GM1 and/or nerve growth factor treatment on the cholinergic innervation of the rat cortex was studied using both light- and electron-microscopic techniques assisted by image analysis. Adult male Wistar rats were unilaterally decorticated and received continuous infusions, via minipump, of vehicle, GM1 (1.5 mg/day) and/or nerve growth factor (12 micrograms/day) into the cerebroventricular space. Treatments were initiated immediately post-lesion and ended after seven days. Thirty days post-lesion (i.e. 23 days after the end of drug administration) brains were processed for choline acetyltransferase immunocytochemistry for either light- or electron-microscopic analysis. At this time-point choline acetyltransferase-immunoreactive neurons in the ipsilateral nucleus basalis magnocellularis were significantly reduced in size especially in the mid portion of this nucleus, in lesion vehicle-treated rats. Moreover, decreases in choline acetyltransferase immunoreactive fibre length (ranging from 31 to 50%) and varicosity number (ranging from 26 to 39%) occurred in all cortical layers within a portion of the remaining cortex of these animals. Monosialoganglioside GM1 or nerve growth factor treatment equally attenuated deficits in nucleus basalis magnocellularis cell size and cortical choline acetyltransferase immunoreactive fibre length. However, nerve growth factor, but not monosialoganglioside GM1 treatment also increased choline acetyltransferase-immunoreactive varicosity number above control levels. In lesioned rats which received both nerve growth factor and the monosialoganglioside GM1, the mean cross-sectional area of nucleus basalis magnocellularis cholinergic neurons did not differ significantly from control values. By contrast, cortical choline acetyltransferase-immunoreactive fibre length and varicosity number were significantly increased above control values and that induced by nerve growth factor treatment alone. Quantitative electron-microscopic analysis showed that cholinergic boutons in cortical layer V were considerably shrunken in lesioned vehicle-treated rats and that GM1 treatment failed to significantly attenuate this deficit. However, exogenous nerve growth factor provoked a significant increase (35% above control values) in cortical cholinergic presynaptic terminal size which was even further augmented by concurrent GM1 treatment (69% above control values). This trophic factor-induced increase in bouton size was confirmed using serial electron microscopy and computer-assisted three-dimensional reconstruction of the cholinergic varicosities. The number of synaptic contacts in cortical layer V was also found to be significantly reduced (45% of control values) in lesioned vehicle-treated rats but was maintained at control levels by exogenous GM1 treatment. In addition, a significant increase (95% above control levels) in the number of choline acetyltransferase-immunoreactive boutons with synaptic differentiations was noted in lesioned nerve growth factor-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Primate nucleus basalis of Meynert p75NGFR-containing cholinergic neurons are protected from retrograde degeneration by the ganglioside GM1

The effects of unilateral devascularizing lesions of the neocortex in primates (Cercopithecus aethiops) on the immunoreactivity of choline acetyltransferase and the low-affinity nerve growth factor receptor (p75NGFR) were investigated in cell bodies of the nucleus basalis of Meynert. Choline acetyltransferase enzymatic activity was measured in the dissected ipsi- and contralateral nucleus basalis of Meynert as well as in the remaining cortex adjacent to the lesion. Cortically lesioned animals displayed a shrinkage of p75NGFR-immunoreactive cholinergic cell bodies in only the intermediate portion of the nucleus basalis of Meynert as well as a depletion of choline acetyltransferase activity in this cellular complex. In contrast, cortically lesioned monkeys treated with monosialoganglioside did not reveal a significant loss of choline acetyltransferase activity or shrinkage of nucleus basalis of Meynert cholinergic neurons, but rather a modest hypertrophy. These results are discussed in relation to a possible use of putative trophic agents in the repair of the damaged central nervous system.

Perisomatic sprouts immunoreactive for nerve growth factor receptor and neurofibrillary degeneration affect different neuronal populations in the basal nucleus in patients with Alzheimer's disease

Aberrant morphological profiles, most likely reflecting a process of perisomatic sprouting, have been detected in Alzheimer's disease (AD) on neurons of the basal nucleus of Meynert by means of Golgi impregnation. Using the mouse monoclonal antibody, ME 20.4., perisomatic profiles were shown to be immunoreactive for nerve growth factor receptor (NGFR). Double label studies using either thioflavin S or anti-neurofibrillary tangle (NFT) antibody B5 in combination with ME 20.4 demonstrated that neurons with aberrant growth profiles failed to express neurofibrillary tangle-bearing material, which otherwise could be detected in large amounts throughout the basal forebrain. The results indicate that in AD, neurons in the basal forebrain, not affected by neurofibrillary degeneration, respond to an increased trophic influence. Dendritic sprouting in AD might, therefore, more likely be regarded as an attempt by the nervous system to repair itself following damage rather than as an abnormal process with primary pathologic significance leading to cellular degeneration.

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.

MK-801 affects the potassium-induced increase of glial fibrillary acidic protein immunoreactivity in rat brain

Exposure of a limited brain surface to a high potassium (K+) concentration produces an injury limited to the underlying cortex, without apparently affecting other brain areas. Such a treatment produces an increased expression of glial fibrillary acidic protein (GFAP) in astrocytes, as assessed by immunohistochemical techniques, throughout the cortex ipsilateral to K+ exposure. This effect is evident 2 days after treatment and persists up to, at least, day 7. Thirty days after K+ exposure GFAP immunostaining is similar in both hemispheres. Administration of the non-competitive NMDA antagonist MK-801 (4 mg/kg i.p.) prior to the injury prevented the rise in GFAP immunoreactivity (IR) at 2 but not 7 days after the treatment. Administration of MK-801 after the injury appeared to have no effect on GFAP expression. This work confirms that brain injury, associated with spreading depression, can induce a glial response far from the lesion site. Furthermore, the fact that this phenomenon can be modified by an NMDA receptor antagonist suggests that glutamate may play a role, in vivo, in the regulation of astrocytic response to injury and introduces the possibility that brain injury-induced gliosis may be pharmacologically manipulated.

Multiple sclerosis patients express increased levels of beta-nerve growth factor in cerebrospinal fluid

We describe the measurement of beta-nerve growth factor (NGF) content in cerebrospinal fluid (CSF) from multiple sclerosis (MS) patients compared with CSF from age-matched normal subjects using a specific sandwich immunoassay (ELISA). During acute attacks patients exhibit a significant increase of NGF content compared to controls. In contrast during remission the mean NGF levels in CSF markedly decrease. These results strongly indicate that increased NGF production in CSF is a characteristic feature of the MS inflammatory response.

In vivo activated brain astrocytes may produce and secrete nerve growth factor-like molecules

The cellular localization of the nerve growth factor-like immunoreactivity (NGF-LIR) has been studied in the septum and hippocampus of the rat brain 7 days following partial electrolytic lesion (2 mA, 30 s) of the septohippocampal pathways or after single intraventricular administration of 15 U of interleukin-1 beta (IL-1 beta). A double immunostaining technique which allowed a simultaneous localization of NGF-LIR and that of astroglia marker glial fibrillary acidic protein was used. Our data show that after both treatments, apart from neuronal localization of NGF-LIR typical for normal brain, many astrocytes both in the septum and hippocampus became NGF-like immunoreactive. Besides, NGF-LIR often formed a "halo" reaction around astrocytes. These results support the notion that activated in vivo brain astrocytes may, just as astrocytes growing in vitro, synthesize and secrete NGF-like molecules. Our findings may be of importance in considerations concerning trophic support to the cholinergic neurons of the basal forebrain nuclei whose impaired function is essentially responsible for some cognitive deficits in neurodegenerative diseases such as Alzheimer disease.

Denervation of dopaminergic neurons with 6-hydroxydopamine increases nerve growth factor content in rat brain

Denervation of dopaminergic neurons by intra nigral injection of 6-hydroxydopamine (6-OHDA) increased nerve growth factor (NGF) content in the cortex and hippocampus, both of which are innervated by cholinergic neurons. The increase continued during an observation period of 0.5-28 days after the lesion. The time course of changes in NGF content was quite different from that of cholinergic neuron denervation. The decreased dopamine content produced in the striatum by 6-OHDA injection was not recovered during the observation period. These results suggest that dopaminergic neuron damage may affect NGF synthesis.

Glial fibrillary acidic protein immunoreactivity following cortical devascularizing lesion

Disruption of a restricted area of the pia-arachnoid compromises vascular irrigation of the underlying cortex, leading to infarction of the tissue. This study was undertaken to examine the effects of such brain injury on glial cells. Adult male Wistar rats were processed for glial fibrillary acidic protein immunoreactivity at 1, 4, 7, 15 and 30 days after undergoing cortical devascularization. One day post-lesion, glial fibrillary acidic protein-positive cells were observed only at the lesion site. Glial fibrillary acidic protein-positive cells were present in the ipsilateral remaining cortex, distant from the wound, between days 4 and 15, and were also evident in the thalamus beginning 4 days post-lesion. These diverse temporal patterns of GFAP immunoreactivity in different brain structures suggest that various mechanisms can mediate increased GFAP immunostaining following injury.

Immunohistochemical localization of nerve growth factor in the rat pineal gland

Sympathetic nerve fibers arising from the superior cervical ganglia are the main innervation of the rat pineal gland. Since most organs innervated by these ganglia contain nerve growth factor (NGF), the hypothetical existence of NGF in the pineal gland was investigated. The peroxidase anti-peroxidase technique was applied for the immunohistochemical demonstration of NGF using a polyclonal antiserum on Bouin-fixed, paraffin-embedded pineal glands from adult, young and 6-hydroxydopamine (6-OHDA)-treated rats. Few immunopositive cells were observed in the adult pineal gland. A more conspicuous population of immunoreactive cells was noted in young animals (20-45 days old), especially in those chemically denervated with 6-OHDA. NGF immunoreactive cells displayed a stellate shape resembling the interstitial or glial cells previously described in the rat pineal gland. Since NGF plays a trophic effect on sympathetic neurons during development and adulthood, we postulate that its presence in the pineal gland may exert a trophic role on its sympathetic innervation.

Regulation by dopaminergic neurotransmission of dopamine D2 mRNA and receptor levels in the striatum and nucleus accumbens of the rat

The effect of dopamine depletion or pharmacological blockade of dopamine receptors on striatal and accumbens dopamine D2 mRNA and receptor levels was assessed by in situ hybridization histochemistry and receptor autoradiography. The time course of pharmacological blockade with haloperidol demonstrates a complex mode of regulation of dopamine D2 mRNA and receptor levels. By day 8 of haloperidol treatment, D2 mRNA and receptor levels were decreased (up to 20%) in the medial and anterior aspects of the caudate-putamen (mCPU and aCPU) and the nucleus accumbens (NAc). However, by day 21 of haloperidol treatment, D2 mRNA and receptor were increased relative to vehicle-injected controls. Likewise, unilateral dopamine depletion due to 6-hydroxydopamine (6-OHDA) lesions of mesencephalic dopaminergic neurons resulted in decreased levels of D2 receptor mRNA by day 8 post-lesion in the ipsilateral mCPU, aCPU and the NAc. However, at days 14 or 21 post-lesion, there was a reversal of the effect with increases of up to 22% in all brain regions ipsilateral to the lesion. Although no decreases in receptor level were observed at day 8, significant increases in receptor level in all three brain regions were detected at days 14 and 21 post-lesion. The results demonstrate that midbrain dopaminergic innervation exerts tonic effects on the levels of dopamine D2 receptor and mRNA in the caudate-putamen and the nucleus accumbens of the rat. Changes in receptor level are frequently accompanied by comparable changes in mRNA level, indicating a mass action relationship between receptor level and receptor biosynthesis in these forebrain regions in the rat.

Nerve growth factor mRNA-containing cells are distributed within regions of cholinergic neurons in the rat basal forebrain

It has been proposed that nerve growth factor (NGF) provides critical trophic support for the cholinergic neurons of the basal forebrain and that it becomes available to these neurons by retrograde transport from distant forebrain targets. However, neurochemical studies have detected low levels of NGF mRNA within basal forebrain areas of normal and experimental animals, thus suggesting that some NGF synthesis may actually occur within the region of the responsive cholinergic cells. In the present study with in situ hybridization and immunohistochemical techniques, the distribution of cells containing NGF mRNA within basal forebrain was compared with the distribution of cholinergic perikarya. The localization o NGF mRNA was examined by using a 35S-labeled RNA probe complementary to rat preproNGF mRNA and emulsion autoradiography. Hybridization of the NGF cRNA labeled a large number of cells within the anterior olfactory nucleus and the piriform cortex as well as neurons in a continuous zone spanning the lateral aspects of both the horizontal limb of the diagonal band of Broca and the magnocellular preoptic nucleus. In the latter regions, large autoradiographic grain clusters labeled relatively large Nissl-pale nuclei; it did not appear that glial cells were autoradiographically labeled. Comparison of adjacent tissue sections processed for in situ hybridization to NGF mRNA and immunohistochemical localization of choline acetyltransferase (ChAT) demonstrated overlapping fields of cRNA-labeled neurons and ChAT immunoreactive perikarya in both the horizontal limb of the diagonal band and magnocellular preoptic regions. However, no hybridization of the cRNA probe was observed in other principal cholinergic regions including the medial septum, the vertical limb of the diagonal band, or the nucleus basalis of Meynert.(ABSTRACT TRUNCATED AT 250 WORDS)

Kainic acid-induced seizures stimulate increased expression of nerve growth factor mRNA in rat hippocampus

The influence of kainic acid (KA)-induced limbic seizure activity on the expression of mRNA for nerve growth factor (NGF) in adult rat brain was studied using in situ hybridization and S1 nuclease protection techniques with RNA probes complementary to murine and rat NGF mRNA. Within hippocampus, intracerebroventricular injection of 0.5 microgram KA caused a dramatic bilateral increase in hybridization of the 35S-labeled cRNA within stratum granulosum. This increase was first evident 1 h post-KA, appeared maximal at approximately 20-fold control levels at 2-3 h post-injection, and declined to control levels by 48 h post-injection. During the period of maximal hybridization, all but the deepest cells within stratum granulosum appeared to be autoradiographically labeled. Hybridization of the NGF cRNA probe was also increased within superficial layers of piriform and entorhinal cortex and, to much lesser extent, within scattered neurons of layers II and III of neocortex in KA-treated rats. In olfactory cortical areas, hybridization was maximally elevated 15.5-24.5 h after KA injection. In contrast to these effects, KA treatment did not consistently influence the density of hybridization, or number of neurons labeled, within the dentate gyrus hilus or the hippocampus proper (CA1-CA3). In agreement with the in situ hybridization results, S1 nuclease protection assay detected KA-induced increases in hybridization within pooled dentate gyrus/CA1 samples, but not hippocampal CA3 samples. These data support the conclusion that seizure activity stimulates a transient increase in NGF expression by select populations of forebrain neurons and indicates that experimental seizure paradigms might be further exploited for analyses of the mechanisms of NGF regulation and processing in the adult brain.

Nerve growth factor and the neostriatum

1. The present review summarizes evidence describing the expression, immunoreactivity, binding, transport, development, aging, and functions of NGF in the mammalian neostriatum. 2. Neostriatal NGF binding sites and intrinsic cholinergic neurons are co-localized, increase at a similar rate during ontogeny, and are lost to an equal extent following age- or injury-induced loss of neostriatal neurons. 3. Exogenously administered NGF augments ChAT activity in the intact caudate-putamen, nucleus accumbens, and following mechanical or excitotoxin-induced cholinergic injury. NGF antibodies lower ChAT in the intact caudate-putamen. 4. Neostriatal cholinergic interneurons are lost in the aged rat but also in Alzheimer's disease, Parkinson's disease, supranuclear palsy, and Huntington's chorea. Future studies need to address the extent to which these losses result from an abbreviation of NGF production, binding, or transport and whether rhNGF administration may retard or reverse these cholinergic losses.

Three-dimensional reconstruction and quantitative evaluation of devascularizing cortical lesions in the rat

The use of a reconstruction method suitable for three-dimensional (3-D) representations of the cortex for the quantitative evaluation of unilateral devascularizing cortical lesions is reported, demonstrating that 3-D reconstructions can be used for quantitative evaluation of the extent of cortical lesions, in addition to simply visualizing shapes. The procedure allowed the definition of precise quantitative parameters characterizing the volumes and surface areas of the cortical regions involved. It was shown that digitized serial sections from atlases can be utilized for multiple correlation studies by superimposing morphological and biochemical parameters. More specifically, the enzymatic activity of choline acetyltransferase (ChAT) in the nucleus basalis magnocellularis (NBM), and morphological parameters (number and cross-sectional areas) of the ChAT-positive immunoreactive cholinergic neurons, were related to the numerical values for the volume and surface area of the cortical lesions. The applicability of this method goes beyond the scope illustrated in this study. For example, various morphological anomalies in the brain could be quantified; changes in various cortical and subcortical structures could be followed during development; and the 3-D size, shape and position of a graft could be related to the number of viable foetal cells.

Interleukin-1 beta and tumor necrosis factor-alpha synergistically stimulate nerve growth factor (NGF) release from cultured rat astrocytes

Nerve growth factor (NGF) may mediate responses to brain injury. To examine regulation of NGF gene expression with respect to neural trauma we examined the effects of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) on NGF production in cultures of rat astroglial cells. Purified neocortical astrocytes in serum-free medium were treated with IL-1 beta, TNF-alpha or both. Whereas IL-1 beta and TNF-alpha alone elicited only small effects, simultaneous addition elicited within 48 h a large (3- to 6-fold) increase in NGF content in culture supernatants. Our data are consistent with a role for cytokines in NGF synthesis and release in the injured central nervous system (CNS).

Immunoelectron microscopic evidence of nerve growth factor receptor metabolism and internalization in rat nucleus basalis neurons

Nerve growth factor receptor (NGFr) immunoreactive neurons of the adult rat nucleus basalis magnocellularis were examined by electron microscopy. Prominent NGFr immunoreactivity (IR) was consistently present along the perikaryal cell membrane and frequently in intracellular sites of protein synthesis and modification such as the rough endoplasmic reticulum and Golgi apparatus, respectively. Immunoperoxidase reaction product was also seen along the nuclear membrane. Membrane-bound aggregates of immunoreactive vesicles were scattered throughout the perikaryon, being more concentrated in the perinuclear region and in the proximal neurites. These may represent either aggregates of receptor-containing vesicles on their way to/from the cell membrane or secondary lysosomes where NGFr reaction product is degraded. Immunostained cytoplasmic vesicles which possessed an electron-dense coat and were adjacent to or contiguous with the plasmalemma probably represented internalized receptor. This ultrastructural study of the subcellular distribution of NGFr-IR in basal forebrain neurons therefore demonstrates sites of receptor metabolism and potential receptor-ligand interaction.

Activating the damaged basal forebrain cholinergic system: tonic stimulation versus signal amplification

The hypothesis that the cognitive decline in senile dementia is related to the loss of cortical cholinergic afferent projections predicts that pharmacological manipulations of the remaining cholinergic neurons will have therapeutic effects. However, treatment with cholinesterase inhibitors or muscarinic agonists has been, for the most part, largely unproductive. These drugs seem to disrupt the normal patterning of cholinergic transmission and thus may block proper signal processing. An alternative pharmacological strategy which focuses on the amplification of presynaptic activity without disrupting the normal patterning of cholinergic transmission appears to be more promising. Such a strategy may make use of the normal GABAergic innervation of basal forebrain cholinergic neurons in general, and in particular of the inhibitory hyperinnervation of remaining cholinergic neurons which may develop under pathological conditions. Disinhibition of the GABAergic control of cholinergic activity is assumed to intensify presynaptic cortical cholinergic activity and to enhance cognitive processing. Although the extent to which compounds such as the benzodiazepine receptor antagonist beta-carboline ZK 93,426 act via the basal forebrain GABA-cholinergic link is not yet clear, the available data suggest that the beneficial behavioral effects of this compound established in animals and humans are based on indirect cholinomimetic mechanisms. It is proposed that an activation of residual basal forebrain cholinergic neurons can be achieved most physiologically via inhibitory modulation of afferent GABAergic transmission. This modulation may have a therapeutic value in treating behavioral syndromes associated with cortical cholinergic denervation.

Correlative decrease of large neurons in the neostriatum and basal nucleus of Meynert in Alzheimer's disease

A quantitative investigation was performed on the large neurons in the neostriatum and basal nucleus of Meynert (bnM) in patients with Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). The degree of decrease of the large neurons in the neostriatum was quite similar to that in the bnM; these decreases were significantly correlative in AD, but not in PSP. These findings indicate that the large neurons in the neostriatum and bnM, which are considered to be cholinergic and to exclusively possess nerve growth factor receptors in the cerebrum, degenerate simultaneously in an equal ratio in AD.

Nerve growth factor increases in adult rat brain after hypoxic injury

Brain injury increases the synthesis of many growth and trophic factors. We have measured nerve growth factor (NGF) content in brain of adult rats with bilateral carotid artery occlusion exposed to 7% O2. Five days after hypoxia the NGF content was increased in neostriatum, hippocampus and cerebral neocortex, areas exhibiting focal neuronal degeneration and inflammation. The increase was not related to changes in choline acetyltransferase activity that was only reduced in heavily damaged cortex. The findings may indicate that the increase in NGF content was due to enhanced NGF synthesis by inflammatory cells including stimulated glia.

NGF in CNS: experimental data and clinical implications

The presence of beta-nerve growth factor (NGF) and its cell surface receptor (NGF-R) in the brain has been well established by a variety of experimental techniques in recent years. In particular, the molecular cloning of NGF and NGF-R as well as the development of sensitive two-site ELISA techniques for determining the levels of NGF and antibodies to NGF-R suitable for immunohistochemistry have led to rapid accumulation of data in this field from many laboratories. A main finding is the function of NGF in the cholinergic neurons of the basal forebrain, expressing NGF receptors and responding to the factor by increased activity of choline acetyltransferase, and the production of NGF in cortical areas and hippocampus comprising terminal areas for the cholinergic projections from the basal forebrain. In addition, findings suggest that additional neurons in the brain and spinal cord may utilize NGF, notably during development and possibly also after lesion of the adult CNS. Moreover, observations indicate that endogenous levels of NGF are lowered in the aged rat brain concomitant with losses of NGF-dependent neurons in the basal forebrain. The involvement of NGF in human neurodegenerative diseases is not established but the application of NGF to degenerating cholinergic neurons in Alzheimer patients may prove useful. A promising approach to achieve this goal is the production of biologically active, recombinant NGF.