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KMID : 0385219920020020160
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Korean Journal of Gerontology
1992 Volume.2 No. 2 p.160 ~ p.166
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Change in Muscarinic Receptors of Aged Rat Brain
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Kim Ok-Nyu
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Abstract
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The purpose of this study was to observe the effect of aging on the muscarinic cholinergic receptors in brain. We used two different brain preparations from young(3 months) and old(22-25 months) rats. We observed the effect of aging on whole brain intact cell aggregates using two different radioactive ligands for muscarinic receptor assay, and we also determined the specific binding capacities of brain regional homogenates for the expanded studying. The results of this experiment were followings; 1. Effect of aging in brain intact cell aggregates The Bmax of [3H]NMS was significantly reduced in old group but binding profiles for [3H]QNB was not altered with age. Scatchard plots were linear suggesting the interaction of two ligands with homogeneous population of muscarinic receptor in young and old group in this preparation. 2. Effect of brain regional homogenates The reductions of specific bindings of [3H]NMS and [3H]QNB for diencephalon homogenates in old group were significantly observed as same degree, but little decrease of Bmax for [3H]QNB was shown in cerebral cortex homogenates. The binding profiles of [3H]NMS were explained the linear interaction with muscarinic receptors in cerebral cortex and diencephalon, but the binding affinity of [3H]QNB were not the same patterns of [3H]NMS. Form above results, we found that the central muscarinic receptor densities for old group were significantly decreased in intact cell aggregates preparation and in some regional homogenates of rat brain. The differences of the binding capasities between [3H]NMS and [3H]QNB in intact cell aggregates were attributed to the different specificities(hydrophilic and lipophilic, respectively) of both ligands for labeling the relative population of muscarinic receptors densities in rat brain. As the specific binding values of [3H]NMS of old group was lesser than that of young group in contrast with the patterns of [3H]QNB in intact cell aggregates, we have assumed that the population or sites of central muscarinic receptors in cerebral cortex not labeled in aged group might be cited on or near the surface receptor of outer neuronal membrane or be changed their confirmational structure where [3H]NMS cam easily access, but we still wondered whether the reduction of both binding capacities of [3H]NMS and [3H]QNB in diecephalon of aged rat was attributed to the age-ralated decrease of numbers(density) of muscarinic receptors.
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KEYWORD
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aging, [3H]NMS, [3H]QNB, brain intact cell aggregates, brain regional homogenates, central muscarinic cholinergic receptors
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