Excitatory and inhibitory amino acids in the cerebral cortex of nucleus basalis magnocellularis lesioned rats

The effect of quisqualic acid-induced lesions of the nucleus basalis magnocellularis on latent inhibition

Latent inhibition (LI) is a reduction in the rate of acquisition of a Pavlovian conditioned response that results from prior nonreinforced preexposure to a conditioned stimulus (CS). LI has been suggested to reflect the operation of mechanisms involved in stimulus selection for subsequent cognitive processing. The present experiment was conducted to assess the effect of bilateral lesions of the nucleus basalis magnocellularis (NBM) on LI employing a conditioned emotional response paradigm. Bilateral lesions of the NBM were produced by administration of 0.12 M quisqualic acid and resulted in decreased cortical acetylcholinesterase staining, as well as a 40% reduction in cortical choline acetyltransferase activity. Following lever press training, preexposed animals received 40 presentations of a 60-s tone CS. Nonpreexposed animals received no tone presentations. Acquisition of conditioned suppression was then assessed over the course of 4 tone-shock (0.6 mA, 0.5 s) pairings. Control, preexposed animals displayed a retarded rate of acquisition in comparison to nonpreexposed controls, thereby demonstrating that the parameters used in the present experiment produced LI. In contrast, lesioned animals preexposed to the CS acquired conditioned suppression as readily as nonpreexposed lesioned animals. However, the acquisition of conditioned suppression in both lesioned groups was found to be similar to that displayed in the preexposed control group. This pattern of results was interpreted as being attributable to a lesion-induced impairment in the ability to maintain stimulus processing, rather than a deficit in the ability to filter a stimulus.

Transplants to the cerebral cortex of nucleus basalis magnocellularis-lesioned rats: effects on deficits in latent inhibition

Bilateral quisqualic acid-induced lesions of the nucleus basalis magnocellularis (nbm) in rats disrupted the expression of latent inhibition, a phenomenon thought to be dependent upon selective attention processes. Since grafts of adrenal chromaffin cells to the cerebral cortex of nbm-lesioned rats have been shown to ameliorate other lesion-induced cognitive deficits, we tested here whether expression of latent inhibition could be reinstated by graft placement. Interestingly, grafts of either chromaffin cells or cells from kidney or liver that have been used previously as control grafts, were able to restore latent inhibition in lesioned animals. These results suggest that it may be a host response to graft placement rather than a factor supplied by the grafted tissue itself that is responsible for the amelioration of lesion-induced deficits of latent inhibition.

Ibotenic acid lesion of nucleus basalis magnocellularis differentially affects cholinergic, glutamatergic and GABAergic markers in cortical rat brain regions

The present study was undertaken to study the effect of reduced cortical cholinergic activity on gamma-aminobutyric acid (GABA)ergic and glutamatergic mechanisms in cholinoceptive cortical target regions which are assumed to play an important role for realizing cognitive functions. The densities of cortical muscarinic cholinergic receptor subtypes and corresponding receptor genes m1 through m4, N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) and kainate glutamate receptor subtypes as well as GABAA and benzodiazepine receptors were measured in rats 1 week after unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (Nbm) applying quantitative receptor autoradiography and in situ hybridization. Ibotenic acid lesion resulted in a striking loss of acetylcholinesterase (AChE) staining in the lesioned Nbm which is associated with a 60% decrease in AChE staining and a 30% reduction in [3H]hemicholinium-3 binding in frontal and parietal cortical regions as well fore- and hindlimb areas ipsilateral to the lesion, being more prominent in the more rostral cortical regions. M1-muscarinic cholinergic receptor binding was not changed in any of the cortical regions studied 1 week after lesion. M2-muscarinic receptor binding levels are slightly increased in the parietal cortex only. The lesion-induced increase in parietal cortical M2-muscarinic receptor binding is complemented by an increase in the hybridization signal for the corresponding m4-mRNA transcript. In cortical regions displaying a reduced activity of AChE and decreased levels of high-affinity choline uptake sites due to forebrain cholinergic lesion, NMDA receptor binding was markedly reduced in comparison to the unlesioned brain side whereas AMPA and kainate binding has been significantly increased in these regions. Muscimol binding to GABAA receptors was increased in the rostral portions of frontal and parietal cortices as compared with the unlesioned brain side. Binding levels of benzodiazepine receptors were not affected by the lesion in any of the cortical regions studied. The differential changes in glutamate and GABA receptor subtypes following lesion might be regarded as the consequence of a cortical reorganization compensating for the reduced cholinergic presynaptic input. The data further suggest that presynaptic cortical cholinergic deficits might affect both glutamatergic and GABAergic functions with different intensity and different directions.