AGE-DEPENDENT CHANGES IN 2ND MESSENGER AND ROLIPRAM RECEPTOR SYSTEMS IN THE GERBIL BRAIN

Age-related alterations in binding sites of major second messengers and a selective adenosine 3',5'-cyclic monophosphate (cyclic-AMP) phosphodiesterase (PDE) in the gerbil brain were analysed by receptor autoradiography. [H-3]Phorbol 12,13-dibutyrate (PDBu), [H-3]inositol 1,4,5-trisphosphate (IP3), [H-3]forskolin, [H-3]cyclic-AMP, and [H-3]rolipram were used to label protein kinase C (PKC), IP3 receptor, adenylate cyclase, cyclic-AMP dependent protein kinase (PKA), and Ca2+/calmodulin-independent cyclic-AMP PDE, respectively. In middle-aged gerbils (16 months old), [H-3]PDBu binding was significantly reduced in the hippocampal CA 1 sector, thalamus, substantia nigra, and cerebellum, compared with young animals (1 month old). [3H]IP3 binding revealed significant elevations in the nucleus accumbens, hippocampal CA1 sector, dentate gyrus, and a significant reduction in cerebellum of middle-aged gerbils. [H-3]Forskolin binding in middle-aged animals was significantly increased in the nucleus accumbens and hilus of dentate gyrus, but was diminished in the substantia nigra and cerebellum. On the other hand, in middle-aged animals, [H-3]cyclic-AMP binding revealed a significant elevation only in the hippocampal CA 3 sector, whereas [H-3]rolipram binding showed a significant reduction in the thalamus and cerebellum. Thus, the age-related alteration in these binding sites showed different patterns among various brain regions in middle-aged gerbils indicating that the binding sites of PKC, IP3, and adenylate cyclase are more markedly affected by aging than those of PKA and cyclic-AMP PDE and that the hippocampus and cerebellum are more susceptible to these aging processes than other brain regions. The findings suggest that intracellular signal transduction is affected at an early stage of senescence and this may lead to neurological deficits.