AGE-RELATED-CHANGES OF NORADRENERGIC NPY INTERACTION IN RAT-BRAIN - NOREPINEPHRINE, NPY LEVELS AND ALPHA-ADRENOCEPTORS

Noradrenergic-neuropeptide Y interaction, which is implicated in diffe rent physiological functions, was studied in senescent rats. Norepinep hrine (NE) and neuropeptide Y (NPY) levels were measured in brainstem and hypothalamus, and a-adrenergic binding was investigated in brainst em in young (4 months) and old (34 months) Wistar rats. NE concentrati on was the same in senescent rats, whereas NPY concentration was decre ased both in brainstem and hypothalamus compared to levels in young ra ts. [H-3]prazosin binding to alpha1-adrenoceptors was not modified, bu t [H-3]rauwolscine binding to alpha2-adrenoceptors was altered with ag e. In fact, the density of alpha2-adrenoceptors (B(max)) was lower, wh ile the binding affinity (K(d)) Was increased in old compared to young rats. These results suggest that the decrease of NPY levels could be one of the possible reasons for changes in [H-3]rauwolscine binding to alpha2-adrenoceptors in old rats. The G-protein-adenylate cyclase sys tem, which is impaired in senescent rats, could be involved in the dis organization of noradrenergic-NPY interaction.