In order to characterize the thermoregulatory actions of brain neuropeptide Y (NPY), the effects of intra-third ventricular (I3V) injection of NPY on temperatures of colon (Tco), brown adipose tissue (TBAT) and tail skin (Ts) were observed at ambient temperatures (Ta) of 19 and 8 degrees C. 2. The injection of NPY in a dose of 8 mcg/100 g body wt evoked a fall of Tco by about 2 degrees C in both neutral and cold environments. NPY (4 and 8 mcg/100 g body wt) induced dose-dependent Tco falls in rats at thermoneutral environment. The thermolytic reactions induced by I3V administration of NPY were associated with a fall in TBAT but no changes in Is were observed. 3. The results suggest that NPY may mediate hypothermic response in neutral and cold environments mainly by its effects on the brown adipose tissues in the rat.
