[Control of ingestive behavior and rumination by neuropeptides]

In sheep as in other species, intracerebroventricular (ICV) administration of picomolar doses of several peptide hormones affects food intake and rumination, suggesting that these hormones play a role in the physiological control of feeding behavior. Their effects depend on their duration (short vs long-term) and/or their nature (orexigenic vs anorexigenic). Among the short-term satiety factors, CCK8, CRF and calcitonin, administered ICV, decrease food intake by reducing the rate (CCK8) or the duration (CRF, calcitonin) of ingestion; in contrast, the gastrin group of peptides (gastrin 17, penta or tetragastrin) reduces food intake by promoting an early period of rumination. Opioid peptides such as Met-enkephalin and Dynorphin initiate food intake in satiated sheep and are supposed to be active in the short-term regulation of food intake in these ruminants. In contrast both calcitonin gene-related peptide (CGRP) and growth hormone-releasing factor (GRF) increase the daily food intake, when ICV injected, but their centrally mediated orexigenic effects depend on the regimen and the digestive status. These results confirm the species differences observed in food intake regulation and the major role of the C.N.S. in controlling feeding behavior and energy balance in ruminants.