Cardiovascular Effects of Neuropeptide Y in Rat Brainstem Nuclei

Central catecholaminergjc neurons are involved in cardiovascular regulation. Neuropeptide Y (NPY) coexists with adrenaline and noradrenaline in the rat brain, and interactions among these substances have been studied. The purpose of this study was to investigate the possible role of NPY in central cardiovascular control. Male Sprague-Dawley rats were anesthetized with urethane, and blood pressure was monitored intra-arterially. Intramedullary mkroinjection (60 nl) of NPY (0, 46.5 fmol, 465 fmol, 1.5 pmol, and 4.65 pmol) was made into the nucleus tractus solitarii (NTS), into the area postrema, and into the Cl area in the rostroventrolateral medulla. Injection site was identified by L-glutamate administration and confirmed histologi-cally. Unilateral injection of NPY into the NTS produced a prominent dose-related decrease in heart rate and systolic and diastolic blood pressure (-106±8 beats/min,- 5 6 ± 2 mm Hg, and- 3 3 ± 2 mm Hg, respectively after 4.65 pmol NPY, n=7, /><0.001). Maximal changes occurred at 30 seconds and recovered in 10 minutes for blood pressure and 20 minutes for heart rate. Injection into the area postrema produced an initial increase in heart rate and mean blood pressure (+23 ±2 beats/min and +18 ±2 mm Hg) followed by a prolonged decrease in heart rate and mean blood pressure (—14±4 beats/min and —15±2 mm Hg, respectively, n=7, /;<0.01). However, injection of NPY into the Cl area produced a dose-related increase in bloo