Effects of scopolamine treatment and lesion of the nucleus basalis upon various cholinergic markers in the rat brain cortex

Abstract

The effect of chronic scopolamine on muscarinic receptors in rat frontoparietal cortex was investigated by measuring the specific binding of [(3)H](?)quinuclidinyl benzilate and [ (3)H ](+)-cis- methyldioxolane . Administration of the muscarinic antagonist, scopolamine (10 mg/kg/day i.p.) for 21 days, produced a significant increase of the density of muscarinic receptors by 20% when using [(3)H](?)quinuclidinyl benzilate, without modifying the affinity for this ligand. However, this chronic treatment left the binding of [ (3)H ](+)-cis- methyldioxolane unchanged. After bilateral lesion with ibotenic acid at the level of nucleus basalis of Meynert, there was a significant decrease of about 50% in the high affinity uptake of choline and choline acetyltransferase activity in the frontoparietal cortex. Carnitine acetyltransferase activity in this region was significantly decrease by 15% in lesioned rats compared to sham control rats. Under these conditions, the specific binding of [ (3)H ](+)-cis- methyldioxolane was significantly decreased while the binding of [(3)H](?)quinuclidinyl benzilate was not modified. From these results, it would seem, on the one hand, that the muscarinic receptors labelled by [ (3)H ](+)-cis- methyldioxolane are located at least partially presynaptically and are regulated differently from those labelled by [(3)H](?)quinuclidinyl benzilate since they are insensitive to a chronic treatment with scopolamine. On the other hand, the results of cortical carnitine acetyltransferase obtained here suggest that this enzyme is partially localized to neurons arising from the region of the nucleus basalis.