Location of nicotinic and muscarinic cholinergic and mu-opiate receptors in rat cerebral neocortex: evidence from thalamic and cortical lesions.

In vitro receptor binding techniques were used to identify the cellular location of nicotinic and muscarinic cholinergic and mu-opiate receptors in the fronto-parietal region of rat cerebral neocortex. Changes in the normal pattern of receptor binding of ligands for these 3 receptors were examined in a series of adjacent sections after unilateral thalamic fiber or cortical cell lesions. Thalamocortical fibers were destroyed by making either electrolytic lesions or kainic acid injections centered in the region of the thalamic ventrobasal complex. These lesions reduced cortical labeling of nicotinic ([3H]nicotine) and mu-opiate ([3H]DAGO) receptors while they did not affect cortical muscarinic ([3H]quinuclidinyl benzilate ([3H]QNB)) labeling. Intracortical injections of quinolinic acid (QA) were used to destroy cortical neurons and spare extrinsic fibers. Cortical QA lesions markedly reduced muscarinic and mu-opiate labeling, but had no significant effect on nicotinic binding at short survivals. Our results suggest that a subset of nicotinic receptors is located presynaptically on the specific thalamo-cortical fibers, while muscarinic receptors are located primarily on cortical neurons. Receptors of the mu-opiate type appear to be located both presynaptically on thalamo-cortical terminals and on intrinsic cortical neurons. The differences in the location of these receptor types suggest that each one modulates discrete aspects of cortical processing.