CHANGES IN MUSCARINIC CHOLINERGIC, PCP, GABA(A), D-1, AND 5-HT2A RECEPTOR-BINDING, BUT NOT IN BENZODIAZEPINE RECEPTOR-BINDING IN THE BRAINSOF AGED RATS

We used in vitro quantitative autoradiography to investigate changes i n neurotransmitter receptor binding, including muscarinic cholinergic, PCP, GABA(A), benzodiazepine, D-1 and 5-HT2A receptor, in the brains of aged rats, compared with such binding in young rats. Scatchard anal ysis revealed that the maximal number of binding sites for [H-3]quinuc lidinyl benzilate (QNB) in the caudate/putamen and accumbens was signi ficantly decreased in aged rats compared with young rats, while its af finity remained unchanged. The specific binding of [H-3]N-(1-[2-thieny l]cyclohexyl)3,4-piperidine (TCP) for the ion channels coupled with N- methyl-D-aspartate receptors in the caudate/putamen and hippocampus wa s significantly decreased in aged rats compared with young rats. The [ H-3]muscimol binding in aged rats was decreased in all brain regions e xamined compared with that in young rats, whereas [H-3]flunitrazepam b inding was not changed in any brain regions. The [H-3]SCH23390 binding for dopamine D-1 receptors was significantly increased in the parieta l cortex, but decreased in the caudate/putamen and accumbens of aged r ats compared with that in young rats. The [H-3]ketanserin binding for 5-HT2A receptors in the cortex and accumbens was significantly decreas ed in aged rats compared with young rats. These results suggest that u neven changes in receptors for various neurotransmitters throughout th e brain may be responsible for the decline of brain function in aged r ats.