Y2 receptors for neuropeptide Y in the nucleus of the solitary tract mediate depressor responses.

In anesthetized, spontaneously breathing rats, microinjections of selective agonists of neuropeptide Y (NPY) receptor subtypes were made into the medial region of the caudal nucleus of the solitary tract (NTS) at the level of the area postrema. This region of the rat NTS exhibits very high densities of NPY binding sites. Microinjections of the long C-terminal NPY fragment, NPY(13-36), a selective agonist at Y2 receptors, into the caudal NTS elicited pronounced, dose-related reductions in blood pressure and respiratory minute volume. Moreover, the specific pattern of cardiorespiratory responses elicited by NPY(13-36) was remarkably similar, over approximately the same dosage range, with the cardiorespiratory response pattern elicited by intact NPY. In contrast to the potent NTS-mediated responses evoked by NPY(13-36), similar microinjections conducted with either NPY(26-36), an inactive C-terminal NPY fragment, or [Leu31,Pro34]NPY, a NPY analog with specific agonist properties at Y1 receptors, into the same caudal NTS sites did not appreciably affect cardiorespiratory parameters even at 10-20-fold higher dosages. The present results with selective agonists for NPY receptor subtypes suggest that the depressor responses and reductions in minute volume elicited by microinjections of intact NPY and NPY(13-36) were mediated by Y2 receptors in the caudal NTS, likely distributed at presynaptic sites in the medial region of the subpostremal NTS.