MODIFICATION OF MUSCARINIC ACETYLCHOLINE-RECEPTORS IN THE RAT-BRAIN FOLLOWING CHRONIC IMMOBILIZATION STRESS - AN AUTORADIOGRAPHIC STUDY

The modifications of rat brain muscarinic acetylcholine receptors induced by chronic immobilization stress lasting 10 min/daily or 2 h/daily for 3, 7 or 21 days were analyzed by quantitative in vitro autoradiography. [H-3]N-Methylscopolamine ([H-3]NMS) was used as ligand. Chronic immobilization stress for 10 min/day did not produce any significant change in the properties of [H-3]NMS binding sites throughout the rat brain. In contrast, 2 h/day immobilization caused a significant increase in the maximal number of muscarinic receptors (B(max)) in several brain areas such as the cortical layers, the CA1 field of the hippocampus and caudate-putamen, among others. Affinity values (K(d)) were not modified. These results suggest that chronic immobilization stress induces supersensitivity of muscarinic receptors in certain cholinergic pathways in rat brain, the pattern of response being different to that previously found for acute stress.