Evidence for the existence of serotonin type-2 receptors on cholinergic terminals in rat cortex

Levels of serotonin type-2 receptors and choline acetyltransferase (ChAT) were measured in various rat brain regions following unilateral lesions of the nucleus basalis magnocellularis (nBM). As expected, lesions of the nBM markedly decrease cortical ChAT activity. Moreover, [3H]ketanserin (serotonin type-2) binding is significantly decreased in lamina IV of the anterior and middle cortex on the lesioned vs control side. [3H]ketanserin binding in the striatum is not affected by lesions of the nBM. Autoradiograms of [3H]ketanserin binding in lesioned animals show similar results. This suggests that at least a certain proportion of serotonin type-2 receptor binding sites are located on cholinergic terminals in lamina IV of the rat cortex. Therefore, further investigations on cholinergic-serotonergic interactions in the cortex and their possible involvement in senile dementia of the Alzheimer's type appear to be highly relevant.