Unilateral decortication affects muscarinic cholinergic receptor binding in rat basal forebrain

The distribution of muscarinic acetylcholine receptors (including the M(1)-receptor subtype), beta-adreno receptors, and noradrenaline uptake sites was studied in cholinergic basal forebrain nuclei (medial and lateral septum, ventral and dorsal limb of the diagonal band, substantia innominata and nucleus basalis of Meynert) of adult rats 25 days after unilateral decortication, using quantitative receptor autoradiography. Unilateral neocortex suction lesion resulted 25 days postoperatively in significant enhancements of [(3)H]quinuclidinyl benzilate binding to the total population of muscarinic acetylcholine receptors in both sides of the substantia innominata (> 55%) and of the nucleus basalis of Meynert (> 45%) compared to sham-operated control rats. Additionally, increased binding levels in the medial septum (59%) and dorsal limb of the diagonal band (48%) were found in unilaterally decorticated rats. [(3)H]pirenzepine binding to M(1)-receptors was increased only in the nucleus basalis of Meynert (by 35%), in both sides, as a consequence of hemi-decortication. Unilateral decortication did not affect either [(3)H]dihydroalprenolol binding to beta-adreno receptors, or [(3)H]desipramine binding to noradrenaline uptake sites, in any of the basal forebrain regions studied. It is suggested that the enhanced binding to muscarinic acetylcholine receptors in the substantia innominata, medial septum and dorsal limb of the diagonal band following cortical damage may reflect an adaptive response to the morphological changes seen in cholinergic neurons of the nucleus basalis of Meynert after cortical lesion, whereas the receptor binding changes in the nucleus basalis of Meynert itself cannot be easily related to the morphological alterations observed there.