Central administration of corticotropin releasing factor in the pig: Effects on operant feeding, drinking and plasma cortisol

Abstract

Four experiments were carried out to investigate the effects of corticotropin releasing factor (CRF) on ingestive behaviour and cortisol secretion in the prepubertal pig. In Experiment 1, 19-hr food-deprived animals were given intracerebroventricular (ICV) injections of 2.5, 10 or 20 μg CRF, or saline vehicle, 5 min after the start of a 30-min operant-feeding session. The total number of food reinforcements obtained in the posttreatment period did not change after 2.5 or 10 μg CRF, although the latter dose reduced intake in the final 5 min of the test; overall food consumption, however, was reduced after 20 μg CRF. In Experiment 2, pigs were treated intravenously with 20 μg CRF, or saline, using the same test situation as in Experiment 1; neither treatment significantly affected operant feeding. In Experiment 3, 19-hr water-deprived pigs were given ICV injections of 20 μg CRF, or saline, 15 min before the start of a 30-min operant-drinking session. Water intake was increased in the 5-min period directly after CRF injection, but there was no overall reduction in drinking. In Experiment 4, blood samples were taken at 15-min intervals for 30 min before and 90 min after ICV injection of 20 μg CRF, or saline, in food and water replete animals. Both treatments appeared to increase plasma cortisol levels, as determined by radioimmunoassay, but the effect was more pronounced after CRF.