THE NONPEPTIDE NEUROPEPTIDE-Y Y-1 RECEPTOR ANTAGONIST BIBP3226 BLOCKSTHE [LEU(31),PRO(34)]NEUROPEPTIDE Y-INDUCED MODULATION OF ALPHA(2)-ADRENOCEPTORS IN THE NUCLEUS-TRACTUS-SOLITARII OF THE RAT

THE potential blockade of the neuropeptide Y (NPY) Y-1 receptor agonis t [Leu(31),Pro(34)]NPY-induced modulation of the characteristics of al pha(2)-adrenoceptor agonist [H-3]p-aminoclonidine binding sites by a s elective non-peptide NPY Y-1 receptor antagonist BIBP3226, was studied in the nucleus tractus solitarii of the rat by means of quantitative receptor autoradiography. [Leu(31),Pro(34)]NPY at a concentration of 1 0 nM significantly increased the K-d value of [H-3]p-aminoclonidine bi nding sites in the nucleus tractus solitarii without influencing the B -max, suggesting the existence of an antagonistic modulation by NPY Y- 1 receptors of alpha(2)-adrenoceptors in the nucleus tractus solitarii . BIBP3226 at 100 nM fully blocked the [Leu(31),Pro(34)]NPY-induced in crease in K-d of the [H-3]p-aminoclonidine binding sites. The present results therefore provide evidence, by use of a NPY Y-1 receptor antag onist, for the existence of a NPY Y-1/alpha(2), receptor interaction i n the nucleus tractus solitarii.