Effect of unilateral nucleus basalis lesion on cortical and striatal acetylcholine and dopamine release monitored in vivo with microdialysis

Cortical and striatal extracellular acetylcholine (ACh), choline (Ch), dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) levels were estimated in samples collected with microdialysis in halothane-anaesthetized rats which had received 0.6 microliter of ibotenic acid (5 micrograms/microliters) into the left nucleus basalis magnocellularis (microdialysis experiments were performed 3-4 weeks after the lesion). Samples were collected under basal (Ringer or Ringer including 10 microM neostigmine) and KCl (100 mM)-stimulated conditions. In the intact frontoparietal cortex and striatum, basal ACh (only detected under neostigmine perfusion) was in the 30 and 300 nM range, respectively. In the same conditions, Ch was in the 0.7 microM range in the cortex and in the 0.2 microM range in the striatum. The inclusion of KCl in the perfusion medium strongly enhanced cortical (greater than 7-fold) and striatal (greater than 10-fold) ACh. KCl only moderately increased striatal (65%) but not cortical Ch. In the lesion side, both basal and stimulated ACh were significantly reduced in the cortex (greater than 60%), but not in the striatum. Ch was not significantly changed in the cortex and striatum. The nucleus basalis lesion also produced a drop in extracellular levels of cortical and striatal DA (40% and 55%, respectively). Neither cortical nor striatal ACh levels were modified by a unilateral DA deafferentation (6-hydroxydopamine lesion into the medial forebrain bundle). However, the destruction of the intrinsic cortical ACh by injection of kainic acid into the frontoparietal cortex produced a 30% decrease in ACh.     

Evidence for nerve growth factor-ganglioside interaction in forebrain cholinergic neurons

Cholinergic neurons of the forebrain respond trophically to nerve growth factor (NGF) in some experimental circumstances. The cholinergic cell system of the nucleus basalis magnocellularis (NBM) which projects to the cortex shows signs of cellular degeneration following limited devascularizing cortical lesions, while no apparent damage is observed in the remaining ipsilateral cortex. These cholinergic cells possess receptors for NGF and the administration of this peptide into the cerebroventricular space prevents cell shrinkage and loss of activity of the biosynthetic enzyme for acetylcholine, choline acetyltransferase (ChAT). Analogous trophic responses can be elicited in this system with the application of the sialoganglioside GM1. In addition, GM1 can increase the effects of NGF on ChAT activity in lesioned neurons of the NBM-to-cortex model system described above. This cooperative interaction is observed even when ineffective doses of GM1 are administered. Furthermore, an interaction between these two putative neurotrophic substances has been noted over other cholinergic parameters such as cortical high affinity choline uptake (HACU). These studies confirm the idea that trophic factors can be utilized to rescue degenerating neurons of the CNS and, in addition, lend support to the concept that gangliosides can facilitate actions of endogenously produced trophic factors.     

Immunohistochemical and neurochemical correlates of learning deficits in aged rats

This study examined whether cholinergic and monoaminergic dysfunctions in the brain could be related to spatial learning capabilities in 26-month-old, as compared to three-month-old, Long-Evans female rats. Performances were evaluated in the water maze task and used to constitute subgroups with a cluster analysis statistical procedure. In the first experiment (histological approach), the first cluster contained young rats and aged unimpaired rats, the second one aged rats with moderate impairment and the third one aged rats with severe impairment. Aged rats showed a reduced number of choline acetyltransferase- and p75(NTR)-positive neurons in the nucleus basalis magnocellularis, and choline acetyltransferase-positive neurons in the striatum. In the second experiment (neurochemical approach), the three clusters comprised young rats, aged rats with moderate impairment and aged rats with severe impairment. Alterations related to aging consisted of reduced concentration of acetylcholine, norepinephrine and serotonin in the striatum, serotonin in the occipital cortex, dopamine and norepinephrine in the dorsal hippocampus, and norepinephrine in the ventral hippocampus. In the first experiment, there were significant correlations between water maze performance and the number of; (i) choline acetyltransferase- and p75(NTR)-positive neurons in the nucleus basalis magnocellularis; (ii) choline acetyltransferase-positive neurons in the striatum and; (iii) p75(NTR)-positive neurons in the medial septum. In the second experiment, water maze performance was correlated with the concentration of; (i) acetylcholine and serotonin in the striatum; (ii) serotonin and norepinephrine in the dorsal hippocampus; (iii) norepinephrine in the frontoparietal cortex and; (iv) with other functional markers such as the 5-hydroxyindoleacetic acid/serotonin ratio in the striatum, 3,4-dihydroxyphenylacetic acid/dopamine ratio in the dorsal hippocampus, 5-hydroxyindoleacetic acid/serotonin and homovanillic acid/dopamine ratios in the frontoparietal cortex, and 3,4-dihydroxyphenylacetic acid/dopamine ratio in the occipital cortex.The results indicate that cognitive deficits related to aging might involve concomitant alterations of various neurochemical systems in several brain regions such as the striatum, the hippocampus or the cortex. It also seems that these alterations occur in a complex way which, in addition to the loss of cholinergic neurons in the basal forebrain, affects dopaminergic, noradrenergic and serotonergic processes.     

Rivastigmine antagonizes deficits in prepulse inhibition induced by selective immunolesioning of cholinergic neurons in nucleus basalis magnocellularis

Impairments of cortical cholinergic inputs from the nucleus basalis magnocellularis fundamentally alter information processing and attentional function, thereby advancing the severity of psychopathology in major neuropsychiatric disorders. It was previously shown in adult rats that bilateral 192 IgG saporin-induced selective immunolesioning of the cholinergic neurons in the nucleus basalis produces pronounced and long-lasting deficits in sensorimotor gating measured by prepulse inhibition of the startle reflex. This behavioral paradigm is considered a valid model of sensorimotor gating deficits in the psychotic spectrum and efforts to analyze the significance of the cholinergic basal forebrain in this context are of great interest. In the present study the predictive value of the selective cholinergic immunolesioning model was tested by examining the ability of the cholinesterase inhibitor rivastigmine to restore prepulse inhibition in immunolesioned rats. We report here a pronounced restoring effect of acute (0.75 or 1.5 mg/kg s.c.) as well as repeated (0.75 mg/kg s.c. b.i.d., for 10 days) treatment with rivastigmine in this model of disrupted prepulse inhibition. Intra-nucleus basalis magnocellularis infusions of 192 IgG saporin resulted in extensive loss of basal-cortical cholinergic neurons as shown by the marked decrease in basal telencephalic choline acetyltransferase immunopositive neurons and cortical choline acetyltransferase activity. In this condition, rivastigmine was found to significantly increase cortical acetylcholine extracellular levels in lesioned animals measured by in vivo microdialysis. Taken together, our results strengthen the proposal that the nucleus basalis represents a critical station of the startle gating circuitry. In addition, our findings strongly indicate that even after dramatic decrease of cholinergic neurons, inhibition of acetylcholinesterase restores the cholinergic synaptic function to a point approaching normalization of experimentally induced psychopathology.     

Atrophy of cholinergic neurons within the rat nucleus basalis magnocellularis following intracortical AF64A infusion

The rat nucleus basalis magnocellularis (nBM) was morphometrically analyzed following multiple intracortical AF64A infusions. At 3 weeks post-infusion, brains were histochemically double-stained for acetyl-cholinesterase and Nissl substance following diisopropylfluorophosphate pretreatment. Intracortical AF64A induced significant atrophy, but not degeneration, of nucleus basalis cholinergic cell bodies. These results suggest that retrograde cellular atrophy is associated with inhibition of presynaptic high-affinity choline transport on cortical terminals of nBM cholinergic neurons.     

Regional decreases of cortical choline acetyltransferase after lesions of the septal area and in the area of nucleus basalis magnocellularis

Choline acetyltransferase and [³H]choline uptake have been measured in neocortical regions and hippocampus one week after lesions which destroyed the septum bilaterally, and after unilateral lesions in the area of nucleus basalis magnocellularis. Lesions of the septal area, which severely decreased choline acetyltransferase in hippocampus, only moderately decreased choline acetyltransferase in a posterior cortical region and had no effect in frontal and parietal regions. In contrast, lesions which included nucleus basalis magnocellularis decreased choline acetyltransferase markedly in frontal and parietal regions and had less of an effect in the posterior cortical regions. Lesion-induced decreases of [³H]choline uptake paralleled those of choline acetyltransferase. Lesions which included nucleus basalis magnocellularis had no effect on choline acetyltransferase in hippocampus, nucleus accumbens, olfactory tubercle, midbrain or pons-medulla.These results suggest the existence of topographically distinct cholinergic inputs to neocortex. In agreement with previous studies, cholinergic projections from the peripallidal region of nucleus basalis magnocellularis are predominantly to frontal and parietal neocortex. In contrast to previous suggestions, cholinergic projections to neocortex from the septal area are limited to the posterior regions of neocortex.     

Recovery of cortical acetylcholine output after ganglioside treatment in rats with lesion of the nucleus basalis

The changes in acetylcholine release from the cerebral cortex induced by a unilateral electrolytic lesion of the nucleus basalis and by a treatment with GM1 monosialoganglioside (30 mg/kg i.p. for 20 days) were investigated. Acetylcholine release was measured using the cortical cup technique in rats transected at midpontine level. In the lesioned rats treated with saline an ipsilateral 38% decrease in acetylcholine release was observed. GM1 treatment prevented the decrease and brought about a 30% contralateral increase. These results indicate that GM1 induces a functional recovery of the cholinergic neurons ascending to the cortex.     

Serotonergic input to cholinergic neurons in the substantia innominata and nucleus basalis magnocellularis in the rat.

The aim of the present study was to determine, at the light microscopic level, whether the serotonergic fibers originating from the dorsal raphe nucleus (B7), median raphe nucleus (B8) and ventral tegmentum (B9) make putative synaptic contacts with cholinergic neurons of the nucleus basalis magnocellularis and substantia innominata. For this purpose, we utilized: (i) the anterograde transport of Phaseolus vulgaris leucoagglutinin combined with choline acetyltransferase immunohistochemistry; (ii) choline acetyltransferase/tryptophan hydroxylase double immunohistochemistry; and (iii) the FluoroGold retrograde tracer technique combined with tryptophan hydroxylase immunohistochemistry. Following iontophoretic injections of Phaseolus vulgaris leucoagglutinin in the dorsal raphe nucleus, labeling was observed primarily in the ventral aspects of the nucleus basalis magnocellularis and in the intermediate region of the substantia innominata. When Phaseolus vulgaris leucoagglutinin was combined with choline acetyltransferase immunohistochemistry, a close association between the Phaseolus vulgaris leucoagglutinin-positive fibers and cholinergic neurons was observed, even though the majority of the Phaseolus vulgaris leucoagglutinin-immunoreactive terminals seemed to establish contact with non-cholinergic elements. Following Phaseolus vulgaris leucoagglutinin injection in the median raphe nucleus, very few labeled fibers with no evident close contact with nucleus basalis magnocellularis and substantia innominata cholinergic neurons were observed. After tryptophan hydroxylase/choline acetyltransferase double immunohistochemistry, a plexus of serotonergic (tryptophan hydroxylase-positive) fibers in the vicinity of choline acetyltransferase-immunoreactive neurons of the substantia innominata and nucleus basalis magnocellularis was observed, and some serotonergic terminals have been shown to come into very close contact with the cholinergic cells. Most of the tryptophan hydroxylase-immunoreactive terminals seem to establish contacts with non-cholinergic cells. Following FluoroGold injection in the nucleus basalis magnocellularis and substantia innominata, the majority of retrogradely labeled neurons was observed mainly in the ventromedial cell group of the dorsal raphe nucleus. In this area, a minority of the FluoroGold-positive neurons was tryptophan hydroxylase immunoreactive. These findings show that serotonergic terminals, identified in very close association with the cholinergic neurons in the substantia innominata and nucleus basalis magnocellularis, derive primarily from the B7 serotonergic cell group of the dorsal raphe nucleus, and provide the neuroanatomical evidence for a direct functional interaction between these two neurotransmitter systems in the basal forebrain.     

The nucleus basalis magnocellularis: The origin of a cholinergic projection to the neocortex of the rat

The cells of origin of a neocortical cholinergic afferent projection have been identified by anterograde and retrograde methods in the rat. Horseradish peroxidase injected into neocortex labelled large, acetylcholinesterase-rich neurons in the ventromedial extremity of the globus pallidus. This same group of neurons underwent retrograde degeneration following cortical ablations. The region in which cell depletion occurred also showed significant decreases in the activities of choline acetyltransferase and acetylcholinesterase. Discrete electrolytic and kainic acid lesions restricted to the medial part of the globus pallidus each resulted in significant depletions of neocortical choline acetyltransferase and acetylcholinesterase. Hemitransections caudal to this cell group did not result in such depletions. Taken together these observations suggest that the acetylcholinesterase-rich neurons lying in the ventromedial extremity of the globus pallidus, as mapped in this study, constitute the origin of a major subcortical cholinergic projection to the neocortex. The utility of acetylcholinesterase histochemistry in animals pretreated with di-isopropylphosphorofluoridate in identifying cholinergic neurons is discussed in the light of this example; specifically, it is proposed that high acetylcholinesterase activity 4–8 h after this pretreatment is a necessary, but not sufficient, criterion for the identification of cholinergic perikarya.The neurons in question appear to be homologous to the nucleus basalis of the substantia innominata of primates, and are thus termed ‘nucleus basalis magnocellularis’ in the rat. No evidence was obtained to support the hypothesis that nucleus of the diagonal band projects to neocortex. However, striking similarities in size and acetylcholinesterase activity were observed among the putative cholinergic perikarya of the nucleus basalis magnocellularis, the nucleus of the diagonal band, and the medial septal nucleus.Kainic acid lesions of the neocortex produced uniform and complete destruction of neuronal perikarya. These lesions decreased neocortical glutamic acid decar?ylase activity, suggesting that there are GABAergic perikarya in the neocortex. However, the same lesions did not affect neocortical choline acetyltransferase. This observation suggests that there are no cholinergic perikarya in the neocortex, a conclusion that is consistent with the absence of intensely acetylcholinesterase-reactive neurons in the neocortex.     

Limited neocortical devascularizing lesions causing deficits in memory retention and choline acetyltransferase activity--effects of the monosialoganglioside GM1

In mature rats with unilateral cortical lesions, choline acetyltransferase activity was found to decrease by 40% in the ipsilateral nucleus basalis magnocellularis, compared with control animals. Intraventricular administration of the monosialoganglioside GM1 (5 mg/kg per day), via minipumps, over a period of 14 days prevented this fall in choline acetyltransferase activity. The activity of this enzyme in the sham operated subjects was not significantly different from that in the unoperated group. This biochemical data is in full agreement with regards to the protective action of monosialoganglioside GM1 on forebrain cholinergic neurons. In this study the behavioral effects of these cortical lesions were investigated for the first time. Results show that these lesions, with their associated retrograde neuronal degenerative effects, altered a variety of sensorimotor and memory-based behaviors. In particular, the limited unilateral devascularization of the neocortex increased baseline locomotor activity above control; affected motor coordination; impaired passive avoidance retention and reacquisition; and decreased the retention of learnt Morris water-maze information. Infusion of the monosialoganglioside into the ventricles, whilst having no effect on the increased motor activity or motor coordination deficit, did enhance the reacquisition of information in both memory-related tasks.     

Delayed treatment with nerve growth factor improves acquisition of a spatial task in rats with lesions of the nucleus basalis magnocellularis: evaluation of the involvement of different neurotransmitter systems.

Rats received bilateral lesions of the nucleus basalis magnocellularis by infusion of ibotenic acid. Fourteen days later, osmotic minipumps releasing human recombinant nerve growth factor (0.3 micrograms/day) were implanted subcutaneously. Starting one month after the lesion, spatial learning of the animals was tested using the Morris water maze. Acquisition of the task was impaired by the lesion, but treatment with nerve growth factor reduced the average latency to find the platform by approximately 9 s, which represents 28% of the lesion-induced behavioral deficit. Retention of this task and spatial acuity, tested in a trial in which the platform was not present, did not show a statistically significant improvement. Lesions of the nucleus basalis magnocellularis reduced the choline acetyltransferase activity in the neocortex, but not in the hippocampus. Treatment with nerve growth factor increased the choline acetyltransferase activity in the neocortex but not in the hippocampus. There was no significant difference in the levels of norepinephrine, dopamine, serotonin or their metabolites in the cortex or hippocampus between nerve growth factor-treated animals and lesioned control animals. There was no significant correlation between any of these neurochemical changes and behavioral performance (acquisition and spatial acuity). Treatment with nerve growth factor did not increase the number or the size of nerve growth factor receptor-immunoreactive neurons in the nucleus basalis magnocellularis. These data suggest that delayed treatment with nerve growth factor results in an improvement of spatial learning in rats with lesions of the nucleus basalis magnocellularis. A possible role for cholinergic mechanisms in this effect is discussed.     

NGF prevents further atrophy of cholinergic cells of the nucleus basalis due to cortical infarction in adult post-hypothyroid rats but does not restore cell size compared to euthroid rats

We have tested the hypotheses that nerve growth factor treatment in adult post-hypothyroid rats can: (1) restore cross-sectional area of cholinergic cells of the nucleus basalis and (2) prevent further atrophy of these neurons following cortical infaction. In addition, we assessed the expression of p75^NGFR and p140^trkA mRNAs in the nucleus basalis cells of post-hypothyroid rats. Rats were rendered hypothyroid by the addition of propylthiouracil to their diet beginning on embryonic day 19 until the age of 1 month. At this time both the pups and their dams continued to receive 0.05% propylthiouracil in their diet and the pups were thyroidectomized. At 60 days, propylthiouracil treatment was interrupted and thyroxine levels were restored to normal by daily subcutaneous administration of physiological levels of thyroxine. Morphometric analysis identified atrophied nucleus basalis magnocellularis cholinergic cells at two ages, days 75 and 105, identified by in situ hybridization for p75^NGFR and p140^trkA mRNAs in methylene blue stained cells (day 75) and choline acetyltransferase immunostaining (day 105). The mean number of silver grains (pixels) per μm² (mean±S.E.M.) of cell body cross-sectional area for p75^NGFR mRNA in the nucleus basalis magnocellularis of euthyroid rats was 3.43±0.89, which was not statistically different from post-hypothyroid animals (4.02±1.07). A similar finding was noted for p140^trkA mRNA: mean number of grains in the euthyroid group was 5.54±0.96 and was not statistically different from the post-hypothyroid group (6.32±1.45). Nerve growth factor treatment in adulthood (between days 75 and 82) did not restore cross-sectional area from early thyroid deprivation. However, it prevented further atrophy of nucleus basalis magnocellularis neurons following cortical devascularization inflicted in adulthood (day 75).     

Effect of unilateral decortication on acetylcholine release from the nucleus basalis

Acetylcholine (ACh) is released from the rat nucleus basalis magnocellularis (nbM) following tissue depolarization with 35 mM K+. In the present study, we report that cholinergic neurons within the nbM undergo retrograde changes resulting in a significant reduction in K+-evoked ACh release following cortical lesions.     

Independent effects of age and nucleus basalis magnocellularis lesion: maze learning, cortical neurochemistry, and morphometry.

The effects of age and lesion of the cholinergic nucleus basalis magnocellularis (NBm) were assessed behaviorally, morphologically, and biochemically. Groups consisted of rats lesioned 1 month before testing, rats lesioned 13 months before testing, and their respective age-matched controls. Both age and lesion independently induced behavioral deficits in performance on two water maze tasks. The combined effect of these two factors produced behavioral deficits equal to the sum of the individual impairments. NBm lesion produced a 28% decrease in anterior cortical choline acetyltransferase activity and a 20% decrease in synaptophysin immunoreactivity in the neocortex that was stable over a 12-month period. Neither neuritic plaque nor neurofibrillary-tanglelike structures were found in the brains of 18-month-old control rats, nor were they found in NBm-lesioned rats examined 15 months postlesion. There was an age-related decrease in homovanillic acid levels in both control and NBm groups, which suggests a decrease in dopamine turnover. These results show a lack of biochemical and behavioral recovery after NBm lesion and suggest that the effects of age on behavior are independent of NBm-cortical dysfunction.     

Protective effects of the alpha 2-adrenoceptor antagonist,dexefaroxan, against degeneration of the basalocortical cholinergic system induced by cortical devascularization in the adult rat

It has been hypothesized [Colpaert, F.C., 1994. In: Briley, M., Marien, M. (Eds.), Noradrenergic Mechanisms in Parkinson's Disease. CRC Press, Boca Raton, FL, pp. 225-254] that a deficiency in the noradrenergic system originating from the locus coeruleus is a decisive factor in the progression of central neurodegenerative disorders including Alzheimer's disease, and that treatments which boost noradrenergic transmission (e.g. via blockade of alpha(2)-adrenoceptors) could provide both symptomatic and trophic benefits against the disease. Studies in the rat in vivo demonstrating that the selective alpha(2)-adrenoceptor antagonist dexefaroxan increases acetylcholine release in the cortex, improves measures of cognitive performance and protects against excitotoxin lesions, support this concept. As a further test of the hypothesis, we investigated the effect of dexefaroxan in a rat model of unilateral cortical devascularization that induces a loss of the cortical cholinergic terminal network and a retrograde degeneration of the cholinergic projections that originate in the nucleus basalis magnocellularis. Lesioned and sham-operated rats received a 28-day subcutaneous infusion of dexefaroxan (0.63 mg/rat/day) or vehicle, delivered by osmotic minipumps implanted on the day of the cortical devascularization procedure. In lesioned rats, the dexefaroxan treatment was associated with a significantly higher number and size of vesicular acetylcholine transporter-immunoreactive boutons in comparison to the vehicle treatment; this effect was most marked within cortical layer V. Dexefaroxan also significantly reduced the atrophy of cholinergic neurons within the nucleus basalis magnocellularis. Dexefaroxan had no observable effect on any of these parameters in sham-operated cohorts. These results show that systemically administered dexefaroxan mitigates cholinergic neuronal degeneration in vivo, and provide further evidence for a therapeutic potential of the drug in neurodegenerative diseases such as Alzheimer's disease, where central cholinergic function is progressively compromised.     

Lesions of the nucleus basalis magnocellularis in the rat: morphological, biochemical and behavioral reparative effect of nerve growth factor and ganglioside GM1

Three- and fifteen-month old rats with a unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (NBM) were used. In 3-month old rats, 4 days after the lesion a 34 and 33% decrease in high affinity choline uptake (HACU) rate was found in the ipsilateral frontal and parietal cortices, respectively. Twenty-one days later the lesioned rats showed a loss in the NBM choline acetyltransferase (ChAT)-positive cells, a marked decrease in ipsilateral cortical ChAT activity and an impairment of the acquisition of a passive avoidance conditioned response. If the lesioned rats received nerve growth factor (NGF) (10 micrograms i.c.v.) twice a week or daily administration of ganglioside GM1 (GM1) (30 mg/kg i.p.), beginning immediately after surgery, the decreases in the HACU rate and ChAT activity were significantly smaller and the behavioral performance was normal. A potentiation by GM1 of NGF effects on the cholinergic neurons of the NBM occurred since no differences were detected between sham-operated rats and rats trated with NGF plus either the active (30 mg/kg) or inactive (10 mg/kg) dose of GM1. The loss in the number of NBM ChAT-positive neurons was reduced by GM1 or prevented by NGF administrations, indicating that the two drugs prevent the cholinergic deficit by protecting the cholinergic neurons of the NBM from ibotenic acid neurotoxicity. GM1 had no effect on ChAT activity decrease and behavioral impairment in 15-month old rats. The latter finding indicates an age-related loss of the ability of GM1 to enhance neurotrophic activity in the NBM.     

Senile dementia and Alzheimer's disease: lack of changes of the cortical content of quinolinic acid

The content of Quinolinic Acid (QUIN) was fragmentographically measured in the frontal, parietal and temporal cortex obtained at autopsy from patients affected by Alzheimer's disease-senile dementia Alzheimer type (AD/SDAT) or matched controls. The density of large cholinergic neurons in the nucleus basalis magnocellularis and the density of plaques in the hippocampal formation, parietal and frontal cortex of these patients was also evaluated in order to obtain a quantitative estimation of the Alzheimer type changes. In the three cortical areas studied, the content of QUIN was similar in AD/SDAT patients and age matched controls. The AD/SDAT patients had an important reduction of the number of large cholinergic neurons in the nucleus basalis magnocellularis and a much higher density of plaques in cortex and in hippocampus than age matched controls. The data reported here do not support the possibility than an accumulation of QUIN plays a role in the neuronal degeneration occurring in the cortex of patients affected by AD/SDAT.     

The selective cyclooxygenase-2 inhibitor rofecoxib suppresses brain inflammation and protects cholinergic neurons from excitotoxic degeneration in vivo

Brain inflammatory processes underlie the pathogenesis of Alzheimer's disease, and non-steroidal anti-inflammatory drugs have a protective effect in the disease. The aim of this work was to study in vivo whether attenuation of brain inflammatory response to excitotoxic insult by the selective cyclooxygenase-2 inhibitor, rofecoxib, may prevent neurodegeneration, as a contribution to a better understanding of the role inflammation plays in the pathology of Alzheimer's disease. We investigated, by immunohistochemical methods, glia reaction, the activation of p38 mitogen-activated protein kinase (p38MAPK) pathway with an antibody selective for the phosphorylated form of the enzyme and the number of choline acetyltransferase-positive neurons and, by in vivo microdialysis, cortical extracellular levels of acetylcholine following the injection of quisqualic acid into the right nucleus basalis of adult rats. Seven days after injection, a marked reduction in the number of choline acetyltransferase-positive neurons was found, along with an intense glia reaction, selective activation of p38MAPK at the injection site and a significant decrease in the extracellular levels of acetylcholine in the cortex ipsilateral to the injection site. The loss of cholinergic neurons persisted for at least up to 28 days. Rofecoxib (3 mg/kg/day, starting 1 h prior to injection of quisqualic acid) treatment for 7 days significantly attenuated glia activation and prevented the loss of choline acetyltransferase-positive cells and a decrease in cortical acetylcholine release. The prevention of cholinergic cell loss by rofecoxib occurred concomitantly with the inhibition of p38MAPK phosphorylation. Our findings suggest an important role of brain inflammatory reaction in cholinergic degeneration and demonstrate a neuroprotective effect of rofecoxib, presumably mediated through the inhibition of p38MAPK phosphorylation.     

Effects of nerve growth factor and GM1 ganglioside on the number and size of cholinergic neurons in rats with unilateral lesion of the nucleus basalis

Four groups of rats with a unilateral ibotenic acid lesion of the nucleus basalis were treated with saline, nerve growth factor (NGF) 10 micrograms administered intracerebroventricularly twice per week, sialoganglioside GM1 30 m/kg daily i.p. and NGF twice per week plus GM1 10 mg/kg i.p. daily, respectively, beginning immediately after lesioning. Twenty-one days later the rats treated with saline showed a marked impairment in negotiating a 'step through' passive avoidance conditioned response, a 32% decrease in the number of choline acetyltransferase (ChAT)-positive neurons in the lesioned nucleus basalis and a 12% decrease in their areas. The rats treated with NGF and NGF plus GM1 showed no difference from sham-operated rats. In the GM1-treated rats a 12% decrease only in the number of ChAT-positive neurons was detected while performance and neuronal areas were normal. These findings indicate that NGF and GM1 prevent the cholinergic deficit by protecting the cholinergic neurons of the nucleus basalis from ibotenic acid neurotoxicity.     

Lesion of the nucleus basalis magnocellularis does not affect cerebral cortical blood flow in rats.

The effects of a unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (NBM) on blood flow of the cerebral cortex and striatum were studied at 2, 4, 8 and 16 weeks after the lesion in conscious rats. In the cerebral cortex, no side-to-side difference in blood flow was observed, though cholinergic enzyme activity was markedly reduced on the side of the lesion. The results suggest that NBM lesion produces disturbance of cholinergic neurons in the cerebral cortex without significant alteration of blood flow.