IN-SITU DETERMINATION OF M(1) AND M(2) MUSCARINIC RECEPTOR-BINDING SITES AND MESSENGER-RNAS IN YOUNG AND OLD RAT BRAINS

Changes in M(1), M(2) receptor binding and mRNA in aged (25-26 months) rat brains were examined to determine whether decreases in receptors are due to declines in expression of corresponding mRNA levels. With a ging, the M(2) muscarinic receptor binding sites and m(2) receptor mRN A were significantly decreased in the medial septum and diagonal band of Broca. In addition, M(2) receptor binding was also reduced in the b asal ganglia, CA3 held of the hippocampus, deeper layers of cortex, me dial and central nuclei of amygdala, and thalamic nuclei. However, M(1 ) binding was decreased in the basal ganglia, superficial layers of co rtex, CA3 field of hippocampus and lateral nuclei of amygdala. There w as no change in m(1) receptor mRNA expression between any brain region of young and old rats. These studies suggest the reduction of the M(2 ) receptor subtype during the transcriptional process, and alterations of M(1) subtypes during translational or post-transcriptional periods .