NGF treatment potentiates c-fos expression in the rat nucleus basalis upon excitotoxic lesion with quisqualic acid

The induction of the c-fos gene in the rat brain by NGF was studied in a model of acute cholinergic hypofunction, i.e., the lesion of the nucleus basalis magnocellularis (NBM) with quisqualic acid. Choline acetyltransferase and Fos immunoreactivity (IR) in the NBM were analyzed at different times after the excitotoxic lesion. NGF treatment induced a potentiation of Fos expression 4 and 24 h after lesion. The possibility is discussed that c-fos induction is one of the early mechanisms of the neuroprotective action of NGF.     

C-fos expression in the rat nucleus basalis upon excitotoxic lesion with quisqualic acid: a study in adult and aged animals

Summary. A unilateral quisqualic acid lesion was placed in the nucleus basalis magnocellularis of 3- and 24-month-old rats, and the animals were sacrificed at different times post-surgery. The morphology and the number of the cholinergic neurons of the nucleus basalis were analyzed by means of immunohistochemistry for cholineacetyltransferase, in order to evaluate the size and severity of the lesion. Immunohistochemistry for the immediate early gene c-fos was also performed in order to clarify its role in the process of neurodegeneration following the excitotoxin injection. The DNA laddering and TUNEL techniques were used to define the type of cell death involved. At short times (4 hr) the lesion induced alterations in the morphology of cholinergic neurons of the nucleus basalis. Subsequently, a significant decrease in the number of neurons was found in comparison to the contralateral unlesioned side. In the older animals the loss of cholineacetyltransferase immunoreactivity had an earlier onset (4 hr) than in the young (24 hr). C-fos expression was induced by the lesion and not by saline injection in the nucleus basalis and in neighbouring areas of the brain as early as 4 hr after surgery. The c-fos protein was no longer present by 24 hr. Furthermore, the c-fos gene product was consistently absent from the nuclei of cholinergic cells. The aged animals exhibited a slower and smaller increase in c-fos as measured by counting the labelled nuclei in the injected area. Analysis of DNA fragmentation did not provide any evidence for apoptosis as the type of cell death involved in the cholinergic degeneration. These results indicate that the c-fos protein might have a protective role in the response to excitotoxic lesions. Furthermore, we have shown that the aged brain displays a reduced ability to produce a c-fos-mediated plastic response to the lesion. Received December 17, 1997; accepted February 17, 1998     

Behavioral impairments after lesions of the nucleus basalis by ibotenic acid and quisqualic acid

Ibotenic acid (IBO) or quisqualic acid (QUIS) was infused into the region of the nucleus basalis magnocellularis (NBm) in F344 rats in order to behaviorally and biochemically characterize the effects of these two neurotoxins. QUIS infusion resulted in a slightly higher depletion of choline acetyltransferase (ChAT) activity in both anterior and posterior regions of cortex than did lesions caused by infusion of IBO. Both QUIS- and IBO-treated rats demonstrated significantly longer latencies than controls to find a hidden platform in a Morris water maze task. In addition, QUIS-treated rats performed significantly better than IBO-treated rats in the water maze. Analysis of swim speed and open field behavior did not show significant differences in general motor activity. Passive avoidance retention was unaffected by either neurotoxin. Cortical amino acid levels, [3H]neurotensin binding, dopamine, norepinephrine, and serotonin levels were unaffected by either neurotoxin. The levels of HVA and 5-HIAA in the IBO and QUIS groups were significantly reduced compared to controls, but were not significantly different from each other. Histological examination showed greater damage to non-NBm structures with IBO than with QUIS, including the basolateral nucleus of the amygdala and the reticular formation of the thalamus. The greater behavioral deficit seen after IBO lesions may be due to damage to other areas rather than differences in the extent of depletion of corticai ChAT, amino acids, catecholamines or indolamines.     

Comparison of the effects of acute and chronic ibotenic and quisqualic acid nucleus basalis lesioning

The present study examines the effects of acute (1 month recovery) and chronic (8 month recovery) bilateral quisqualic (quis) and ibotenic (ibo) acid nucleus basalis (NB) lesioning on the activity of cholinergic neurons and on passive avoidance (PA) and water-maze (WM) performance. Our data demonstrate that A: The activity of choline acetyltransferase (ChAT) in cortical tissue and the number of ChAT positive neurons in the NB were decreased 1 and 8 months after quis or ibo NB lesioning. B: Ibo NB lesioning produced a greater nonspecific subcortical cell loss than quis NB lesioning. C: PA retention was impaired by acute and chronic quis and ibo NB lesioning. D: Acute ibo NB lesioning impaired acquisition and reversal learning in WM performance whereas chronic ibo NB lesioning impaired only reversal WM learning. Acute and chronic quis NB lesioning impaired reversal WM learning. The present results suggest that NB cholinergic neurons do not recover spontaneously from excitotoxin-induced damage and that they may be importantly involved in inhibitory avoidance and spatial reversal learning performance.     

NGF receptor gene expression is decreased in the nucleus basalis in Alzheimer's disease

Basal forebrain neuronal atrophy in Alzheimer's disease (AD) may be caused by a deficit in the NGF responsiveness of magnocellular cholinergic neurons which project to the cerebral cortex and hippocampal formation. We have used in situ hybridization to show that NGF-receptor (NGF-R) mRNA-positive neurons are lost within all divisions of the nucleus basalis of Meynert (Ch4 cell group) in AD patients as compared to normal aged controls. The posterior division of the nucleus basalis showed the largest decrease in NGF-R mRNA hybridization in the disease, with no overlap in neuronal number between AD cases and normal controls. Northern (RNA) blotting showed decreased levels of NGF-R mRNA in the nucleus basalis in the disease. No differences in the number of NGF-R mRNA-positive neurons between normal aged and AD patients were detected within the NGF-responsive cell groups of the medial septum (Ch1) and nucleus of the vertical limb of the diagonal band (Ch2). These results show that NGF-R gene expression is selectively reduced within basal forebrain neuronal populations which exhibit degenerative changes in AD.     

beta-amyloid neurotoxicity is mediated by a glutamate-triggered excitotoxic cascade in rat nucleus basalis

Whereas a cardinal role for beta-amyloid protein (Abeta) has been postulated as a major trigger of neuronal injury in Alzheimer's disease, the pathogenic mechanism by which Abeta deranges nerve cells remains largely elusive. Here we report correlative in vitro and in vivo evidence that an excitotoxic cascade mediates Abeta neurotoxicity in the rat magnocellular nucleus basalis (MBN). In vitro application of Abeta to astrocytes elicits rapid depolarization of astroglial membranes with a concomitant inhibition of glutamate uptake. In vivo Abeta infusion by way of microdialysis in the MBN revealed peak extracellular concentrations of excitatory amino acid neurotransmitters within 20-30 min. Abeta-triggered extracellular elevation of excitatory amino acids coincided with a significantly enhanced intracellular accumulation of Ca2+ in the Abeta injection area, as was demonstrated by 45Ca2+ autoradiography. In consequence of these acute processes delayed cell death in the MBN and persistent loss of cholinergic fibre projections to the neocortex appear as early as 3 days following the Abeta-induced toxic insult. Such a sequence of Abeta toxicity was effectively antagonized by the N-methyl-D-aspartate (NMDA) receptor ligand dizocilpine maleate (MK-801). Moreover, Abeta toxicity in the MBN decreases with advancing age that may be associated with the age-related loss of NMDA receptor expression in rats. In summary, the present results indicate that Abeta compromises neurons of the rat MBN via an excitotoxic pathway including astroglial depolarization, extracellular glutamate accumulation, NMDA receptor activation and an intracellular Ca2+ overload leading to cell death.     

Learning disturbances following excitotoxic lesion of cholinergic pedunculo-pontine nucleus in the rat

Compared to brain anterior cholinergic systems such as the septo-hippocampal and nucleus basalis-cortical pathways, posterior cholinergic groups have received little attention with respect to their involvement in learning and memory. In this study, the effect of lesion of the cholinergic pedunculo-pontine cell bodies (PPN) by the excitotoxin quisqualic acid was investigated on spontaneous locomotor activity and learning in rats. Behavioral tasks designed to test both reference memory (cross maze and water maze) or working memory (radial maze) were used. PPN lesion had no effect on initial nor on nocturnal locomotor activity in a circular corridor. The lesion disrupted learning in the water and radial mazes, but was without influence on acquisition in the cross maze. The difference in results obtained in the two tasks designed to test reference memory (cross maze and water maze) indicated that the disturbance depended on task difficulty rather than on a particular memory component. It is suggested that the PPN is involved in the sustained attention required to perform correctly in water and radial mazes. The PPN cannot therefore be considered as a uniquely extrapyramidal structure. In addition to its descending outputs, the PPN has ascending connections to the neocortex, either directly or indirectly via the thalamus, and so pathological changes in this region may be partly responsible for the cognitive disorders of aging or those observed in various neurodegenerative conditions.     

Effects of chronic infusion of nerve growth factor (NGF) in rats with nucleus basalis magnocellularis lesion

We attempted to evaluate the effects of bilateral injection of ibotenic acid (IA) into the nucleus basalis magnocellularis (nbm) of rats as well as the potential recovery mediated by the infusion of nerve growth factor (NGF). The lesion caused an impairment of learning and memory processes. Also, a severe depletion of choline acetyl transferase activity was detected in cortical areas. After the NGF administration, a significant reversion of these functional changes was observed. Thus, IA-lesioned rats might serve as a model for the evaluation of neurotrophic factors actions on basal forebrain damaged neurons.     

Effects of chronic infusion of nerve growth factor (NGF) in rats with nucleus basalis magnocellularis lesion

We attempted to evaluate the effects of bilateral injection of ibotenic acid (IA) into the nucleus basalis magnocellularis (nbm) of rats as well as the potential recovery mediated by the infusion of nerve growth factor (NGF). The lesion caused an impairment of learning and memory processes. Also, a severe depletion of choline acetyl transferase activity was detected in cortical areas. After the NGF administration, a significant reversion of these functional changes was observed. Thus, IA-lesioned rats might serve as a model for the evaluation of neurotrophic factors actions on basal forebrain damaged neurons.     

Comparison of quisqualic and ibotenic acid nucleus basalis magnocellularis lesions on water-maze and passive avoidance performance

The present study compares water-maze (WM) (reference and working memory) and passive avoidance (PA) (acquisition and retention) deficits induced by ibotenic (ibo) and quisqualic (quis) acid nucleus basalis magnocellularis (NBM) lesions. Ibo lesions produced a large subcortical cell loss and a decrease in frontal cortex (FR) choline acetyltransferase (ChAT) activity. Ibo lesions impaired WM acquisition and PA acquisition and retention performance. Quis NBM lesions were restricted to the ventromedial pallidum, but ChAT activity was decreased in FR. Quis NBM lesions impaired PA acquisition and retention, but had no effect on the reference or working memory WM performance.     

Effects of quisqualic acid nucleus basalis lesioning on cortical EEG, passive avoidance and water maze performance

The study examines the effects of unilateral quisqualic acid nucleus basalis (NB) lesioning on cortical EEG and learning behavior. Lesions produced both gliosis in the ventral pallidum and a marked reduction in the cortical ChAT activity. Normal cortical EEG activity was abolished on the side of NB lesion, i.e., slow wave activity and the incidence of high voltage spindles was higher on the side of lesion compared with the control side. NB lesioning impaired passive avoidance retention, but not spatial learning ability. These results suggest that EEG and passive avoidance deficits induced by NB quisqualic acid lesion may result from the damage specifically to cholinergic neurons. Thus, the restoration of EEG and passive avoidance performance defects in quisqualic-lesioned rats may be used as an index of the efficacy of the cholinergic replacement therapies.     

Effects of excitatory amino acid lesions upon neurokinin B and acetylcholine neurons in the nucleus basalis of the rat

The nucleus basalis magnocellularis (NBM) contains cholinergic neurons that project to the neocortex and is densely innervated by excitatory amino acid-containing terminals. A dysfunction in the balance of excitatory inputs or an alteration in the sensitivity of NBM cells to glutamate may underlie the selective vulnerability to aging. Some large NBM neurons contain neurokinin B (NKB) mRNA. The present study investigated whether α-2-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) orN-methyl-d-aspartate (NMDA) differentially destroy NKB-containing, NKB-receptive, or cholinergic NBM cells, and whether this vulnerability is altered by aging. Injections of AMPA or NMDA significantly decreased neocortical ChAT activity, as compared to control levels, across all three age groups, with no interaction between lesion and age group. The results of in situ hybridization histochemistry and NKB receptor studies suggest that NKB-containing neurons in the NBM, and the neurons they innervate, are not vulnerable to NMDA or AMPA in either young or old rats. While NKB mRNA-positive cells were diffusely distributed throughout the basal forebrain, only a small proportion of the large NBM cells contained NKB mRNA. The results suggest that NKB does not extensively colocalize with acetylcholine within the basal forebrain of rats and that NBM NKB neurons do not directly innervate cholinergic cells.     

NGF increases cortical acetylcholine release in rats with lesions of the nucleus basalis.

Rats received a unilateral lesion of the nucleus basalis by infusion of ibotenic acid. Two weeks after the lesion, osmotic minipumps were implanted, that infused 1 microgram human recombinant nerve growth factor (NGF) or cytochrome-C per day into the lateral ventricle. After four weeks of treatment, release of acetylcholine was measured in the frontal neocortex by means of in-vivo microdialysis. Release was decreased by 75% on the lesioned side; perfusion with 100 mM KCl increased release on the intact side by 130% and on the lesioned side by 80%. Treatment with NGF increased release on the lesioned side twofold, but had no effect on release on the intact side.     

Behavioral training-induced c-Fos expression in the rat nucleus basalis of Meynert during aging

The present study investigated the behavioral training-induced c-Fos expression in the nucleus basalis of Meynert (nbM) in differently aged rats. This study demonstrated that the c-Fos expression in nbM was significantly increased and the peak occurred at 2 h after dark-avoidance training. Although the increase of c-Fos expression was also observed after pseudotraining, the number of Fos-like immunoreactive neurons in pseudotrained rats was significantly less than that in dark-avoidance trained rats at each time-point. This result suggested that c-Fos expression might be involved in learning and memory processes. In addition, all the pseudotraining-, training- and memory arousing-induced c-Fos expression was decreased with increasing age, and the decrease was more notable in trained and memory aroused rats. This suggested that the total number of nbM neurons and/or the sensitivity of nbM neurons to experimental manipulations, especially learning and memory performance, might reduce during aging.     

Specific retrograde transport of nerve growth factor (NGF) from neocortex to nucleus basalis in the rat

[¹²⁵I]labeled NGF injected in very small quantities into the frontal or dorsal anterior occipital cortex of adult rats, was specifically taken up and transported retrogradely to large, presumably cholinergic neurons in the nucleus basalis region (lateral preoptic nucleus, anterior lateral hypothalamic nucleus, substantia innominata, ventral globus pallidus and internal capsule), as revealed by light microscopic autoradiography. Cells projecting to the injection site in the frontal cortex were localized ipsilaterally in the more caudal parts of the nucleus basalis region, whereas cells projecting to the dorsal anterior occipital cortex could be found throughout the entire extent of the nucleus basalis and also in the vertical and horizontal limb of the nucleus of the diagonal band of Broca. Other nuclei known to project to the cortex (locus coeruleus, substantia nigra, nucleus raphe, thalamus) were consistently found to be unlabeled. In contrast to [¹²⁵I]NGF, injection of [¹²⁵I]cytochrome C failed to label any cell bodies in the basal forebrain nuclei by retrograde transport. This high selectivity for uptake and retrograde transport of NGF indicates the presence of membrane receptors for NGF or a closely related molecule on these cholinergic neurons of the basal forebrain innervating the cerebral cortex.     

Drug discrimination learning in rats with excitotoxic lesions of nucleus basalis and ventral globus pallidus.

Rats can readily acquire conditional discriminations in which mixtures of drugs serve as compound internal discriminative stimuli. Excitotoxic lesions in the region of the nucleus basalis have been shown to impair the acquisition of conditional discriminations based upon external visual stimuli, but nothing was known about their effects on discrimination of internal stimuli. A baseline of undiscriminated bar-pressing for food reinforcers was established prior to surgery. Lesions were made by infusing either ibotenic or quisqualic acid bilaterally into the basal forebrain (the ibotenate-induced lesions had been shown previously to impair cortical cholinergic function and to produce non-specific damage). After surgery, rats were trained to discriminate effects of drug mixtures using a standard, two-bar operant conditioning procedure. The ibotenate, but not the quisqualate, lesion impaired the acquisition of a discrimination of a mixture of (+)-amphetamine plus pentobarbitone, while neither lesion impaired acquisition with a mixture of (-)-nicotine plus midazolam. The ibotenate lesions also reduced overall rates of responding in both experiments. Thus, the deficit in the acquisition of drug discrimination in rats with ibotenate lesions had some pharmacological specificity, but could not be related easily to disturbances in neocortical cholinergic function. In comparisons with other published data, the results suggest a possible dichotomy in the processing of interoceptive and external information in the basal forebrain, a major target of ventral striatal overflow.     

Quisqualic acid-induced lesion of the nucleus basalis of Meynert in young and aging rats: plasticity of surviving NGF receptor-positive cholinergic neurons.

Previous studies have demonstrated that cholinergic neurons in the adult rat forebrain, i.e., septal region, are able to respond and regenerate after damage followed by exogenous treatment with beta-nerve growth factor. Furthermore, it has been shown that an age-related loss of NGF-receptor (NGFr) immunoreactivity occurs in cholinergic septal neurons. Since the regenerative capacity of cholinergic neurons is of importance for potential therapeutic strategies during the course of age-related neurodegenerative diseases, we have compared NGFr positive neurons in young adult (3 months old) and in aging (18-24 months old) rats in their ability to produce a physiological plasticity response after surviving an excitotoxic lesion of the nucleus basalis of Meynert (NBM). In aging control rats, NGFr immunoreactivity within NBM neurons was significantly reduced, in analogy to data obtained earlier from studies about septal neurons in aged rats. After lesion with quisqualic acid, a severe cell loss as well as atrophy of remaining cholinergic neurons was observed in both groups. Investigation of the NBM at various times after the lesion demonstrated signs of axonal or dendritic sprouting and local regeneration, with a maximum seen 3 months after the lesion. No age-related differences in the response could be found. However, despite local fiber growth, no reinnervation of the frontal and parietal cortex could be noted, as demonstrated by acetylcholinesterase histochemistry. Our findings suggest that, despite a relatively early onset of NGFr decline during lifetime, cholinergic cells keep the capacity for a plastic response, although they ultimately fail to reinnervate the neocortex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spread of acetylcholine sensitivity in the neocortex following lesion of the nucleus basalis

Neuronal responses to the iontophoretic application of acetylcholine, carbachol and nicotine were studied in rats, 2 or 3 weeks following bilateral lesions of the nucleus basalis region, and compared to those obtained in normal animals. The percentage of cortical neurons excited by acetylcholine and their individual sensitivity were higher in lesioned animals. Furthermore, the laminar distribution of the responses to acetylcholine and the proportion of responses to carbachol and nicotine were also modified.     

Decrease of somatostatin receptor binding in the rat cerebral cortex after ibotenic acid lesion of the nucleus basalis magnocellularis: a quantitative autoradiographic study

The specific binding of¹²⁵I-Tyr¹¹-somatostatin-14 (¹²⁵I-Tyr¹¹-SS-14) was measured in different cortical regions after unilateral ibotenic acid lesion of the rat nucleus basalis magnocellularis (NBM). A marked loss of acetylcholinesterase-positive fibers was observed in the frontal, parietal, temporal and occipital cortices ipsilateral to the lesion. The loss of cholinergic cell bodies in the NBM was further investigated with cholineacetyltransferase (ChAT) immunohistochemistry which indeed demonstrated a loss of ChAT-positive magnocellular perikarya. Autoradiographic analyses of specific binding of¹²⁵I-Tyr¹¹-SS-14 demonstrated a significant reduction in binding density in the denervated parts of the neocortex. The decrease in specific binding was most pronounced (40–50%) in the superficial layers (I–III) of the frontal, parietal and temporal cortices 2 and 4 weeks after lesion. A significant loss in¹²⁵I-Tyr¹¹-SS-14 binding in the deeper layers was only observed in the frontal cortex after 2 and 4 weeks. In the occipital cortex a significant decrease was measured in the superficial layers only after 4 weeks. The specific binding in all cortical regions returned to normal after 6 weeks. The results suggested that¹²⁵I-Tyr¹¹-SS-14 binding sites are localized on cholinergic afferents in the rat neocortex and that an up-regulation of number of binding sites, alternatively an increased binding affinity occured with time after lesion.