VISCEROENDOCRINE RESPONSES ELICITED BY NEUROPEPTIDE-Y IN THE NUCLEUS-TRACTUS-SOLITARIUS

Neuropeptide Y (NPY) has been shown to be of CNS regions, including th e nucleus tractus solitarius (NTS). In this meeting report, a brief ov erview is presented of recent studies from our laboratory examining th e role of NPY in NTS-mediated mechanisms of cardiorespiratory and visc eroendocrine regulation. Microinjections of NPY, NPY analogs, or C-ter minal NPY fragments were made into the subpostremal NTS of anesthetize d spontaneously breathing rats. NPY elicited pronounced dose-related d epressor responses, bradycardia, and reductions in respiratory minute volume. The overall cardiorespiratory response pattern elicited by NPY was mimicked by NPY13-36, a fragment of NPY exhibiting selective agon ist properties at presynaptic Y2 receptors, Whereas the Y1 receptor-se lective analog, [Leu31, Pro34]NPY, and the C-terminal inactive fragmen t, NPY26-36, Were found to be ineffective. In an effort to further cha racterize intrinsic NTS mechanisms mediating the NPY-evoked response p attern, NPY microinjections were similarly made in a group of rats wit h bilateral glossopharyngeovagotomy (G-vagotomy) and in a group of rat s decerebrated at the supracollicular level. The results showed that w hereas decerebration did not appreciably affect the NTS-mediated cardi orespiratory responses elicited by NPY, G-vagotomy enhanced the NPY-ev oked hypotension while at the same time abolishing the NPY-evoked brad ycardia and reductions in tidal volume. Taken together, these observat ions with G-vagotomized animals, along with the results from microinje ction studies using selective ligands for NPY receptors, suggest that NPY may modulate primary visceral afferent information via activation Of Y2 receptors distributed at presynaptic sites in the subpostremal N TS. On the other hand, the influence of reciprocal NPY-containing neur onal connections with rostral brain regions on NTS-mediated cardioresp iratory responses elicited by NPY appeared not to be consequential, at least in normal rats. However, when similar microinjections of NPY we re made into the same subpostremal NTS sites of intact rats which were diabetic, there was a dramatic attenuation in cardiorespiratory respo nsiveness to NPY. These results suggest that NPY-sensitive mechanisms in the NTS mediating cardiorespiratory responses may conceivably be in fluenced by the increased hypothalamic NPYergic activity that has been observed in diabetic rats. These observations, together with recent f indings from our laboratory showing that microinjection of NPY into th e same subpostremal NTS sites potently stimulates insulin secretion, p rovide support for the notion that NPY may play a crucial modulatory r ole in NTS-mediated visceroendocrine response patterns involved in car diorespiratory control and nutrient homeostasis.