Abstract

We studied the effects of intra-third cerebroventricular administration of neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) on the locomotor activity and the feeding and learning behavior of mice. NPY (0.3-10 micrograms), PYY (0.1-10 micrograms) and PP (3.0-10 micrograms) produced significant increases in locomotor activity. A significant decrease was then observed 15 min after administration of 10 micrograms of PYY. NPY, PYY and PP significantly increased food intake at 20 min and this effect continued for 2 to 4 hr at the high doses. The feeding response to PP family peptides were quite similar to that in locomotor activity with respect to dose-response, time course and peptide specificity. Learning behaviors were evaluated at three different stages of memory processing, acquisition, consolidation and retrieval, in a battery of step-down type passive avoidance tests. NPY and PYY had no effect on acquisition, but significantly improved consolidation at a dose of 0.03 and 0.3 microgram, respectively. NPY also improved retrieval at a dose of 0.03 microgram. The ranking order of potency in stimulating feeding and locomotor activity was PYY > NPY > PP, and in improving memory consolidation NPY > PYY > PP. These observations suggest that NPY and PYY influence different neural substrates in the brain involved in feeding and learning.