OVARIAN HORMONES DO NOT AFFECT THE INITIATION AND MAINTENANCE OF INTRAVENOUS SELF-ADMINISTRATION OF HEROIN IN THE FEMALE RAT

The effect of ovarian hormones on the initiation and maintenance of he roin intravenous self-administration was studied in ovariectomized fem ale rats. In Experiment 1 (initiation), the behavior of groups of fema les (n = 8) ovariectomized (OVX), injected with 10 mu g estradiol benz oate (EB) every 3 days (OVX+EB), and intact, was compared with that of intact males (n = 7) exposed to an ascending series of doses of heroi n (6.125-50 mu g/kg per infusion) on a fixed ratio-FR-1-reinforcement schedule. Twelve 3-h sessions per dose were given, 2 per day in the da rk and 2 in the light period of a 12:12-h light:dark cycle. No differe nces in rate of responding between groups were observed at any of the heroin doses during acquisition or during tests given after acquisitio n on a descending series of doses. In Experiment 2 (maintenance), 7 OV X female rats were trained to self-administer heroin on an FR-1 reinfo rcement schedule. They were then switched to a progressive ratio sched ule, 4 sessions per day, 4 h each, and a regimen of EB and progesteron e (P) injections was initiated during which all animals were tested ov er a 5-day period (cycle) at each of four doses of heroin (50, 25, 12. 5, and 0.0 mu g/kg per infusion). Neither EB, given on Day 3, nor P, g iven on Day 5 of each cycle, affected the highest ratio achieved (brea kpoint) or number of heroin infusions taken. These results suggest tha t the sensitivity of female and male rats to the reinforcing effects o f heroin is not different, and that, in females, the reinforcing effec ts are not affected by circulating ovarian hormones.