Muscarinic cholinergic receptors subtypes in rat cerebellar cortex: light microscope autoradiography of age-related changes

Muscarinic cholinergic M1-M5 receptor subtypes were investigated in the cer ebellar cortex of Fischer 344 rats aged 6 (young), 15 (adult) and 22 months (senescent) by combined kinetic and equilibrium binding and light microsco pe autoradiography. In young rats the rank order of receptor density was M5 <M4<M3 and M3<M5<M4 in the molecular and granular layers, respectively. M1, M2, M4 and M5 receptors were also observed within Purkinje neurons. M1 rec eptor did not show age-related changes as well as the M2 receptor in the mo lecular layer. In this layer, M3-M5 receptors were increased in senescent c ompared to younger rats. In the granular layer the expression of M2 and M5 muscarinic receptors was similar in young and senescent rats and higher in adult rats. M3 and M4 receptors were more in adult and senescent rats compa red to young animals. In Purkinje neurons, a slight-to-moderate age-related increase of M1 and M5 receptor expression was observed. (C) 2001 Elsevier Science B.V. All right reserved.