Kurian_1992_Neurobiol.Aging_13_521

It is well established that muscarinic cholinergic receptors are linked to phosphoinositide hydrolysis in brain. Previous studies of muscarinic responses used Li+ to increase inositol phosphate accumulation and suggested little or no change during aging. Li+ disrupts certain aspects of the inositol phosphate metabolism and inhibits the formation of inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4]. Ins(1,3,4,5)P4 appears to have second messenger functions. To investigate the effects of aging on agonist stimulated Ins(1,3,4,5)P4 formation, young (6-8 months) and old (28-30 months) Fischer 344 rat cerebral cortical or hippocampal slices were challenged with various agonists known to stimulate phosphoinositide hydrolysis in brain using a recently developed assay that does not use Li+. Carbachol and quisqualate stimulated [3H]inositol trisphosphate ([3H]InsP3) and [3H]Ins(1,3,4,5)P4 formation in young and old rat cerebral cortical slices. Norepinephrine, 5-hydroxytryptamine, and vasopressin failed to stimulate [3H]Ins(1,3,4,5)P4 or [3H]InsP3 formation in either young or old rat cerebral cortical slices. In old rat cerebral cortical slices, the carbachol-stimulated [3H]Ins(1,3,4,5)P4 formation was reduced by 44%. Angiotensin II stimulated [3H]InsP3 was increased (219%) in old rats. There was no influence of aging either on the basal level or on the maximal response to carbachol or quisqualate in hippocampal slices. These studies suggest region-specific changes in phosphoinositide hydrolysis during aging.