AFFINITY CHANGES IN MUSCARINIC ACETYLCHOLINE-RECEPTORS IN THE RAT-BRAIN FOLLOWING ACUTE IMMOBILIZATION STRESS - AN AUTORADIOGRAPHIC STUDY

The modifications in rat brain muscarinic acetylcholine receptors induced by acute immobilization stress lasting 10 min or 2 h were analyzed by quantitative in vitro autoradiography. [H-3]N-Methylscopolamine ([H-3]NMS) was used as a ligand. Immobilization stress for 10 min did not produce any significant change in the properties of [H-3]NMS binding sites throughout the brain. In contrast, 2 h immobilization caused a significant increase in receptor affinity (K(d)) without modification in the maximal number of receptors (B(max)) in several brain areas such as the caudate-putamen, cortical layers and CA1 field of the hippocampus, among others. These results, found even in animals killed immediately after the end of the immobilization sessions, suggest that immobilization stress induces supersensitivity of muscarinic receptors in certain cholinergic pathways in rat brain.