Age-related changes of noradrenergic-NPY interaction in rat brain: norepinephrine, NPY levels and α-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 α-adrenergic binding was investigated in brainstem in young (4 months) and old (34 months) Wistar rats. NE concentration was the same in senescent rats, whether NPY concentration was decreased both in brainstem and hypothalamus compared to levels in young rats. [³H]prazosin binding to α₁-adrenoceptors was not modified, but [³H]rauwolscine binding to α₂-adrenoceptors was altered with age. In fact, the density of α₂-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 [³H]rauwolscine binding to α₂-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.