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

Noradrenergic-neuropeptide Y interaction, which is implicated in different physiological functions, was studied in senescent rats. Norepinephrine (NE) and neuropeptide Y (NPY) levels were measured in brainstem and hypothalamus, and a-adrenergic binding was investigated in brainstem in young (4 months) and old (34 months) Wistar rats. NE concentration was the same in senescent rats, whereas NPY concentration was decreased both in brainstem and hypothalamus compared to levels in young rats. [H-3]prazosin binding to alpha1-adrenoceptors was not modified, but [H-3]rauwolscine binding to alpha2-adrenoceptors was altered with age. In fact, the density of alpha2-adrenoceptors (B(max)) was lower, while 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 system, which is impaired in senescent rats, could be involved in the disorganization of noradrenergic-NPY interaction.