THE 5-HT1A AGONIST 8-OH-DPAT INCREASES ATTACHMENT MAINTENANCE BUT DECREASES SUCKLING-RELATED INTAKE IN 17-18-DAY-OLD RAT PUPS

Deprived and nondeprived preweanling (17-18 days of age) Sprague-Dawle y rat pups were injected with 0, 0.03, 0.06, 0.1, or 0.5 mg/kg of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and observed in a suckling test using a milk replete anaesthetized dam, wi th milk let-downs being intermittently precipitated via IV infusions o f oxytocin. In experiment 1, the 0.5 mg/kg dose of 8-OH-DPAT was obser ved to increase the proportion of nondeprived animals which attached t o a nipple; no dose effect was seen in deprived animals, who generally all attached. Deprived pups given the 0.5-mg/kg dose exhibited a lowe r frequency of nipple disattachment/reattachment following milk let-do wns and had significantly lower percent body weight gains when compare d with saline controls. In experiment 2a, the 0.5-mg/kg dose of 8-OH-D PAT was observed to decrease the overall incidence of nipple disattach ment/reattachment as well as to suppress nipple shifting per se in bot h deprived and nondeprived l7-18-day-old rat pups; this dose also supp ressed body weight gains in both the deprived and nondeprived pups. Th e suppression in weight gain by 8-OH-DPAT does not appear to be primar ily related to a drug-induced reduction in nipple shifting. In experim ent 2b, where pups were given access to only one nipple, an 8-OH-DPAT- related reduction in body weight gain was still evident. These experim ents, which demonstrate that attachment maintenance and suckling inges tion are altered in opposite ways by 8-OH-DPAT, provide strong evidenc e that these two suckling-related phenomena are subject to different p hysiological controls.