Alterations of muscarinic cholinergic receptors in the hippocampal formation of stressed rat: in vitro quantitative autoradiographic analysis.

Alterations in muscarinic cholinergic (mACh) binding sites in the hippocampal formation of rats after immobilization stress (IM-stress) lasting 0.5 or 3 h were quantitated using a computer-assisted image analysis system on autoradiograms following labeling of frozen sections with [3H]quinuclidinyl benzilate (QNB). The concentration of acetylcholine (ACh) in the rat hippocampus after IM-stress was also measured and showed no significant change compared to control. IM-stress for 0.5 h produced significant increases in the concentration of mACh binding sites in the whole hippocampal formation and in two subdivisions studied (CA1 plus CA2 and dentate gyrus); after 3 h of stress, the increase remained significant only in the dentate gyrus. These findings suggest that IM-stress induce a hypersensitivity of the septo-hippocampal cholinergic system and the 'up-regulation' of postsynaptic mACh receptors is more lasting in the dentate gyrus than in the hippocampus as a whole.