MICROINJECTIONS OF SUBPICOMOLAR AMOUNTS OF NPY(13-36) INTO THE NUCLEUS-TRACTUS-SOLITARIUS OF THE RAT COUNTERACT THE VASODEPRESSOR RESPONSESOF NPY(1-36) AND OF A NPY-Y(1) RECEPTOR AGONIST

Microinjections of neuropeptide Y (NPY) (1-36) and of the NPY Y1 agoni st [Leu31,Pro34]NPY into the caudal dorsomedial part of the nucleus tr actus solitarius (Sol) in the anaesthetized rat led to the development of dose-related vasodepressor and bradycardic responses. The threshol d dose of the NPY Y2 agonist NPY(13-36) (50 fmol) significantly counte racted the vasodepressor actions of a close to ED50 dose of NPY(1-36) (2.5 pmol) and of the NPY Y1 agonist (5 pmol). These results indicate that NPY Y1 receptor activation in the Sol leads to the development of a vasodepressor response, which can be counteracted by NPY Y1 recepto r activation in the Sol. The results support the existence of a Y2/Y1 receptor-receptor interaction in the Sol, via which NPY Y2 receptors m ay reduce transduction over NPY Y1 receptors.