Cortical Cortical Choline Acetyltransferase Research Articles

Synergistic effects of tetrahydroaminoacridine and lithium on cholinergic function after excitotoxic basal forebrain lesions in rat.

Effects of lithium and tetrahydroaminoacridine (THA), either alone or in combination, were tested in an animal model of excitotoxic cholinergic deafferentation of the cerebral cortex. Rats received ibotenic acid lesions of cholinergic basal forebrain nuclei resulting in a 30% to 40% depletion of both cortical choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity. Lithium as well as THA, given separately either prior or subsequently to the development of the lesion, had small but significant effects on the recovery of cortical ChAT and AChE activity. Applied in combination, these drugs clearly showed synergistic effects. These potentiating actions might be due to neuroprotective/ neurotrophic mechanisms as well as to effects on acetylcholine turnover and muscarinic receptor-coupled phosphoinositide turnover. Similar approaches of combination therapy might prove useful for the management of mental disorders associated with cholinergic dysfunction.

Nucleus basalis lesions: Implication of basoamygdaloid cholinergic pathways in memory

Previous studies have shown a lack of association between cortical choline acetyltransferase (ChAT) activity and severity of memory impairment following excitotoxic lesions of the nucleus basalis magnocellularis (NBM). It recently has been proposed that the differential effects of NBM injections of various excitotoxins on amygdaloid and cortical ChAT may explain this result. The present study evaluated the mnemonic effect of unilateral intra-NBM infusions of the excitotoxins phthalic acid and quisqualic acid, which decrease ChAT activity primarily in the amygdala and cortex, respectively. Rats were trained in a double Y-maze, lesioned, and allowed to recover for 1 week prior to memory assessment. Behavioral results showed impaired working but not reference memory following phthalic acid lesions, and no significant effect following quisqualic acid lesions. Biochemical analysis in a second group of subjects confirmed that phthalic acid lesions produced a large decrease in basolateral amygdaloid ChAT, but had little effect on cortical ChAT activity. Conversely, quisqualic acid lesions produced a large decrease in cortical, but not basolateral amygdaloid, ChAT activity. These results suggest that the NOM amygdalopetal cholinergic pathways play a role in mnemonic functioning.

Mnemonic deficits in the double Y-maze are related to the effects of nucleus basalis injections of ibotenic and quisqualic acid on choline acetyltransferase in the rat amygdala

Many researchers have reported that the magnitude of decrease in cortical choline acetyltransferase (ChAT) following excitotoxic lesions of the nucleus basalis magnocellularis (nbm) is unrelated to the degree of cognitive impairment. Recently, an explanation has been offered for this lack of correlation: different excitotoxins, when injected into the nbm, differentially affected cholinergic projections to the cortex and amygdala, and those excitotoxins previously reported to produce the greatest mnemonic deficits produced the largest decreases in amygdaloid ChAT. The present study evaluated the role of amygdalofugal cholinergic projections in memory by comparing the effects of intra-nbm ibotenic and quisqualic acid on cortical and amygdaloid ChAT and on mnemonic performance in the double Y-maze. Rats were trained in the double Y-maze until working and reference memory choice accuracy stabilized to a criterion of ≥ 78% correct. Rats then were given either bilateral quisqualic acid (60 nmol in 0.5 μl), bilateral ibotenic acid (50 nmol in 0.5 μl), or sham (0.9% saline in 0.5 μl) lesions of the nbm, and again were tested on the maze. Quisqualate produced a selective impairment of working memory, a large (51%) decrease in cortical ChAT and a small (17%) decrease in amygdaloid ChAT; ibotenate, on the other hand, produced a greater impairment of working memory, an impairment of reference memory, a similar (51%) decrease in cortical ChAT, but a greater (30%) decrease in amygdaloid ChAT. These results suggest that the cholinergic projections from the nbm to the cortex and amygdala play an important role in memory. They suggest that excitotoxins producing greater depletions of amygdaloid ChAT produce greater mnemonic deficits.

The Cerebrovascular Effects of Physostigmine Are Not Mediated through the Substantia Innominata

This study sought to determine whether the cortical cholinergic projections from Meynert's nucleus are actually the target of the cholinesterase inhibitor physostigmine, which presents the ability to increase cortical blood flow. To this aim, the multiregional cerebrovascular effects of physostigmine in rats with and without lesion of the substantia innominata (SI), the equivalent of Meynert's nucleus of primates, were investigated. Unilateral SI lesions were made using ibotenic acid in three groups of rats. Four to 11 days later, the cortical choline acetyltransferase (ChAT) activity was measured in one group to assess the efficacy of the lesion. In the two other groups, the regional cerebral blood flow was measured using the [ 14C]iodoantipyrine technique, under physostigmine (0.2 mg/kg/h iv) or control conditions. SI lesion induced 27-59% fall in cortical ChAT activity in the ipsilateral hemisphere with the frontal area most affected. Despite these large biochemical differences, the lesion had little cerebrovascular effects. Side-to-side blood flow differences did not exceed 11% and did not strictly overlap the ChAT depletion. Physostigmine increased flow (38-66%) in all cortical areas, with no frontal predominance. Despite these considerable vasodilations, there were no significant differences between the lesioned and the intact hemisphere, nor any significant interaction between physostigmine and SI lesion. Thus, physostigmine does not actually activate the SI neuron terminals. This result suggests that cholinesterase inhibitors cannot be used as presynaptic markers of the cholinergic activity of this nucleus and casts doubts on their specificity as enhancement therapeutic agents in Alzheimer's disease.

Lesions of the nucleus basalis magnocellularis in immature rats: Short- and long-term biochemical and behavioral changes

Short- and long-term effects of unilateral lesions of the nucleus basalis magnocellularis (NBM) on cortical choline acetyltransferase (ChAT) activity and passive avoidance conditioned responses were examined in immature rats. The lesions were made by stereotaxic injection of quisqualic acid on postnatal days 14 (P14), 17 (P17), and 21 (P21). A marked loss of ChAT activity was found 7 days after surgery in all age groups of lesioned rats. Unoperated P14 rats were unable to perform the passive avoidance conditioned responses. Acquisition began on P17. Lesions made on P17 and P21 strongly impaired the acquisition and retention of the task, evaluated 7 days postoperation. No biochemical but a partial behavioral recovery was observed 3 months after surgery in rats lesioned on P14. On the contrary, despite a persistent decrease in cortical ChAT activity, rats lesioned on P21 were able to acquire and retain the passive avoidance conditioned response. These results indicate that destruction of NBM cholinergic neurons shortly after birth is not compensated for by the developmental plasticity of the residual neurons but results in permanent cholinergic hypofunction. They also demonstrate that cholinergic NBM neurons play an important role in the acquisition and retention of a passive avoidance task; nevertheless, a behavioral recovery may take place 3 months after the lesion, even in the presence of a persistent cholinergic hypofunction.

Basic Fibroblast Growth Factor Ameliorates Learning Deficits in Basal Forebrain-Lesioned Mice

The effect of basic fibroblast growth factor (bFGF) treatment on memory and learning performance ability was investigated in basal forebrain (BF)-lesioned mice. Eight-week-old male ddY mice underwent bilateral BF lesions by delivery of radiofrequency current. Basic FGF (5 or 50 ng/side) was microinjected into the same location immediately after lesioning. From fifteen days after the treatment, a step-through type passive avoidance test was performed daily for 10 days. Lesioned animals showed severe impairment in the acquisition process in this task, but not in the retention process. Basic FGF improved the step-through performances; step-through latency was elongated in a dose-dependent manner on the first test trial day and the mean time required to reach the acquisition criterion was shorter than in the vehicle-treated control group. However, bFGF did not alter the cortical choline acetyltransferase (ChAT) activity decrement induced by BF lesion. These results suggest that bFGF ameliorates the memory deficit without affecting the cortical ChAT activity.

Quisqualate lesions of rat NBM: Selective effects on working memory in a double Y-maze

Some authors have reported that quisqualic acid lesions of the nucleus basalis magnocellularis (NBM), although producing large cortical cholinergic losses, have little effect on memory. The purpose of the present study was to investigate the effects of quisqualic acid lesions of the NBM on working and reference memory in a double Y-maze. Each trial started with placement into one of the two end arms of the first Y-maze, and the correct response was to go down the stem (reference memory). Access was then given to the second Y-maze, the correct response being conditional upon the side of the first Y-maze from which that trial had begun (working memory). Rats were trained to an 88% correct criterion and were then given either bilateral quisqualic acid (60 nM, 0.5 μl) or sham lesions (0.9% saline, 0.5 μl) of the NBM. One week postsurgery, rats were tested on the double Y-maze task with delays of 0, 5 or 30 seconds being introduced prior to both the working and reference memory choice. NBM lesions produced a 63.2 ± 6.2% decrease of cortical choline acetyltransferase (ChAT) compared to unoperated controls. Delays affected only the working memory of the sham group. Rats with lesions showed a significant impairment of working memory at all delays, but no change in reference memory. Results indicate that quisqualic acid lesions of the NBM that produce significant reductions in cortical ChAT selectively impair working memory.

Effects of Unilateral Lesion of the Nucleus Basalis of Meynert on Brain Glucose Utilization in Callosotomized Baboons: A PET Study

Prior work has demonstrated that unilateral lesions of the nucleus basalis of Meynert (NbM) in baboons induce a marked reduction in glucose utilization of the ipsilateral cerebral cortex, linearly proportional to the depression in cortical choline acetyltransferase (ChAT) activity achieved. Unexpectedly, there was also marked hypometabolism of the contralateral cerebral cortex, and glucose utilization recovered gradually on both sides despite persistent deficit in cortical ChAT activity. To investigate the role of the corpus callosum (CC) in this bilateral metabolic effect and subsequent recovery, three baboons were subjected to unilateral electrolytic NbM lesion greater than 3 months following section of the anterior CC. Brain glucose utilization was sequentially studied by positron emission tomography; ChAT activity was measured and histological sections obtained after death. In these animals, the NbM lesion also induced significant metabolic depression over the ipsilateral cortex, proportional to the reduction in ChAT activity. Corpus callosotomy did not prevent the contralateral metabolic effects, suggesting that the latter do not normally operate through the CC. However, there was no significant recovery of glucose utilization, suggesting that, following unilateral NbM lesion, the CC normally mediates, at least in part, the recovery of cortical glucose utilization.

Comparative effects of ibotenic acid- and quisqualic acid-induced lesions of the substantia innominata on attentional function in the rat: further implications for the role of the cholinergic neurons of the nucleus basalis in cognitive processes

Two experiments examined the effects of excitotoxic lesions of the substantia innominata on cholinergic activity in the neocortex and on performance in a paradigm measuring selective attention in the rat. In Expt. 1, ibotenate-induced lesions produced approximately 30% reductions in cortical choline acetyltransferase (ChAT) activity, and damage to wide regions of the substantia innominata and ventral pallidum. The rats were impaired in their ability to localize brief visual targets in a serial reaction time task, as measured by reduced choice accuracy. This impairment was particularly evident at short stimulus durations, but the lesioned rats did not exhibit evidence of primary visual sensory dysfunction and exhibited only minor deficits when the stimuli were presented unpredictably. The deficit was exacerbated when distracting white noise was interpolated into the task. The rats with lesions were also slower to respond correctly, probably resulting partly from the adoption of a speed/error trade-off strategy, and were slower to collect earned food pellets, although they made no more errors of omission than controls. In Expt. 2, quisqualate-induced lesions produced fewer signs of non-specific damage and 50% reductions in cortical ChAT activity. This lesion produced generally qualitatively similar, but weaker effects to those of ibotenate-induced lesions. It was notable that many of the deficits following either ibotenate- or quisqualate-induced lesions lasted for several months after surgery. The results are discussed in terms of the cholinergic hypothesis of cognitive dysfunction. It is argued that lesions of the substantia innominata, including the magnocellular cholinergic neurons of the nucleus basalis of Meynert, produce deficits in attentional processing, which may not result from damage specifically to cholinergic cells. However, the longevity of the effects makes these preparations suitable for further exploration of the restorative effects of cholinergic treatments.

Spatial learning in rats: Correlation with cortical choline acetyltransferase and improvement with NGF following NBM damage

Rats display an acquisition deficit in a circular water maze following excitotoxic lesions of the nucleus basalis magnocellularis (NBM). Experiments were therefore performed to determine if acquisition behavior on this task could predict the degree of cortical cholinergic deafferentation and if the acquisition deficit could be pharmacologically reversed. Performance on acquisition was highly correlated with the lesion-induced reduction in cortical choline acetyltransferase (ChAT) activity. Accuracy of spatial behavior was highly correlated to percentage ChAT depletion ( r = 0.75). Neither lesioned rats nor controls displayed a retention deficit after a 9-day interval, nor did either group display a passive-avoidance retention deficit. To test the causal relationship between cholinergic dysfunction and spatial behavior, the central nervous system cholinergic enhancer nerve growth factor (NGF) was intraventricularly infused for 4 weeks. NGF infusion resulted in improved acquisition of the water maze task compared to NBM-lesioned rats receiving vehicle infusion and untreated rats with NBM lesions. These studies indicate that the decrease in cortical ChAT activity is likely to be responsible for the observed acquisition deficit and that pharmacological manipulations can be successfully used to improve behavior following NBM lesions.

A pathological study of the association between Lewy body disease and Alzheimer's disease.

The possibility of an association between Parkinson's disease and Alzheimer's disease has been examined by studying the age-specific prevalence of Lewy bodies in the substantia nigra in a group of 273 control cases without Parkinson's disease and 121 cases of Alzheimer's disease. The substantia nigra was also studied in 14 cases of Down's syndrome, 13 of which had cortical Alzheimer pathology. Twelve (7.8%) of the controls aged over 60 years showed nigral Lewy bodies. There was mild nerve cell degeneration and/or an extranigral distribution of Lewy bodies, suggestive of presymptomatic Parkinson's disease. Twenty five (22.5%) of the Alzheimer's disease cases over 60 years showed Lewy bodies, but only 14 (14.0%) of these had mild nigral cell loss consistent with presymptomatic Parkinson's disease. No case of Down's syndrome had Lewy bodies. Counts of tangles and plaques in hippocampus, frontal and temporal cortex were lower in cases of Alzheimer's disease with Lewy bodies compared with those without, but cortical choline acetyltransferase (ChAT) activities were similar. This suggests that Lewy body degeneration in the nucleus basalis of Meynert contributes to the deficit of cortical ChAT, but not to the cortical Alzheimer pathology. The relatively small difference in the prevalence of Lewy bodies between controls and Alzheimer's disease could be explained by the additive effects of Lewy body and tangle pathology causing dementia, rather than a greater than chance association between Parkinson's disease and Alzheimer's disease.

Effects of excitotoxic lesions of the substantia innominata, ventral and dorsal globus pallidus on visual discrimination acquisition, performance and reversal in the rat

Rats received infusions of ibotenic acid into the substantia innominata, in the region of the nucleus basalis of Meynert (nbM), before and after training on simple (simultaneous) and conditional visual discriminations. The ibotenate infusions reduced cortical choline acetyltransferase (ChAT) levels by about 20%, destroyed many ChAT-immunoreactive neurons in the nbM, but also caused the loss of many neurons in the substantia innominata and adjacent areas. These lesions did not impair the acquisition and performance of a simple visual discrimination, but did impair reversal of the discrimination and the performance of a conditional visual discrimination. However, the degree of impairment was unrelated to the degree of cortical ChAT loss. Ibotenic acid lesions to the dorsal globus pallidus also impaired reversal of discrimination but left acquisition and performance unaffected. Striatal dopamine depletion produced by 6-hydroxydopamine (6-OHDA) infusions into the mid-ventral caudate nucleus impaired performance of the simultaneous visual discrimination. Cortical noradrenaline depletion produced by 6-OHDA lesions of the dorsal noradrenergic bundle either alone or in combination with ibotenic acid lesions of the substantia innominata had no effect on acquisition of the discrimination. It is concluded that ibotenic acid lesions of the substantia innominata or to the dorsal globus pallidus affect learning and performance of conditional visual discrimination performance and impair reversal learning without affecting the capacity to discriminate visual events. These results are compared to those following cortical noradrenaline depletion or striatal dopamine loss.

Reactive microglia in patients with senile dementia of the Alzheimer type are positive for the histocompatibility glycoprotein HLA-DR

HLA-DR is a class II cell surface glycoprotein of the human histocompatibility complex usually expressed on the surface of cells that are simultaneously presenting foreign antigen to T-lymphocytes. Using immunohistochemical procedures with two specific monoclonal antibodies to HLA-DR, HLA-DR-positive reactive microglia were found in gray matter throughout the cortex of postmortem brains of patients with senile dementia of the Alzheimer type (SDAT) and were particularly concentrated in the areas of senile plaque formation. Double immunostaining with antibodies to glial fibrillary acidic protein (GFAP) showed that the HLA-DR-positive cells were different from the reactive astrocytes although the occasional positively staining giant astrocyte was also seen. Small numbers of resting microglia were HLA-DR-positive in white matter of both normal and SDAT brains. The SDAT cases also had reduced cortical choline acetyltransferase (ChAT) levels. In the 11 brains studied, the number of hippocampal HLA-DR-positive cells was positively correlated with the numbers of plaques and negatively correlated with average cortical ChAT.

Neocortical Cholinergic Enzyme and Receptor Activities in the Human Fetal Brain

In the human fetus, obtained postmortem at estimated gestational ages of 8-22 weeks, biochemical activities of cortical choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were comparable to those of adult brain tissue. In contrast cholinergic receptor binding, including muscarinic M1 and M2 subtypes (measured by displacement of [3H]N-methylscopolamine with, respectively, pirenzepine and carbachol) and [3H]nicotine (putative nicotinic) binding were undetectable before 13-14 weeks and even at 22 weeks were substantially (three- to fourfold) below the respective adult values. Cortical ChAT activity decreased significantly with gestational age whereas binding to the three receptors, including the proportion M1/M2, increased significantly. AChE was present at all ages investigated as the two molecular monomeric (G1) and tetrameric (G4) forms. The proportion of G4, which was much more soluble in fetal compared with adult cortex, increased approximately threefold. Histochemically AChE, although intense in the nucleus of Meynert, was generally confined to subcortical white matter at early fetal developmental periods, appearing later in the cortex localized to nerve fibres and occasional cell bodies. These observations suggest that during the second trimester of human fetal development, cortical cholinergic function may be preceded by relatively high ChAT activity and paralleled not only by increasing receptor binding but also by a proportional increase in the tetrameric form and histochemical reactivity of AChE.

Lack of correlation between cortical levels of choline acetyltransferase and learning scores in rats with globus pallidus lesions

Previous work has shown that rats with lesions of the globus pallidus (GP) exhibit a generalized learning impairment. Data are presented suggesting that this impairment is not due to inadvertent damage to the nucleus basalis magnocellularis. Rats with GP lesions evidenced a significant visual discrimination learning loss and a significant reduction in cortical choline acetyltransferase (ChAT) activity. However, there was no significant correlation between the severity of the learning loss and the amount of reduction of cortical ChAT activity.