Effects of neuropeptide Y on food intake and brain biogenic amines in the rainbow trout ( Oncorhynchus mykiss)

Abstract

Neuropeptide Y (NPY) is one of the most potent stimulants of food intake in mammals, but very little is known about NPY actions in fish. The present study investigated the role of NPY in food intake in the rainbow trout ( Oncorhynchus mykiss). Food intake was monitored at different times after intracerebroventricular administration of porcine NPY (4 or 8 μg). Both doses significantly increased food intake at 2 and 3 h, and this effect was dose-dependent. However, 50 h after administration of NPY, food intake was significantly lower than in control fish, and cumulative food intake had returned to levels similar to those seen in the control group. The NPY antagonist ( d-Tyr 27,36, d-Thr 32)-NPY (10 μg) inhibited food intake 2 h after icv administration, but did not block the orexigenic effect of NPY when administered jointly with 4 μg NPY. To identify the NPY receptor subtypes involved in the effects of NPY on food intake, we studied the effects of the Y 1 receptor agonist (Leu 31, Pro 34)-NPY (4 μg), the Y 2 receptor agonist NPY(3–36) (4 μg), and the highly specific Y 5 receptor agonist (cPP 1–7, NPY 19–23, Ala 31, Aib 32, Gln 34)-hPP (4 μg). Short-term (2 h) food intake was moderately stimulated by the Y 1 agonist, more strongly stimulated by the Y 2 agonist, and unaffected by the Y 5 agonist. We found that administration of NPY (8 μg icv) had no effect on aminergic systems in several brain regions 2 and 50 h after NPY administration. These results indicate that NPY stimulates feeding in the rainbow trout, and suggest that this effect is cooperatively mediated by Y 2- and Y 1-like NPY receptors, not by Y 5-like receptors.