Early exposure to low levels of estradiol (E2) mitigates E2-induced conditioned taste aversions in prepubertally ovariectomized female rats

Abstract

17 beta-Estradiol (E2) can serve as a potent unconditioned stimulus in producing a conditioned taste aversion to saccharin in rats, with the effect being greater in males than in females. To determine whether the female's lower susceptibility to such conditioning is due, in part, to early experience with estrogen, we performed the following experiment. First, we pretreated groups of prepubertally ovariectomized female rats with either sesame oil (control group) or low doses of E2 (0.3, 0.75, or 1.50 microgram). Second, in subsequent conditioning sessions, we presented a 0.2% saccharin solution to the rats prior to the injection of 100 micrograms of E2 (the unconditioned stimulus). Third, we tested the magnitude of the conditioned aversion to the saccharin solution and its tendency to extinguish during the following week. The E2-pretreated animals evidenced significantly weaker taste aversions and extinguished them more rapidly than did the oil-pretreated controls, even at the lowest E2 pretreatment dose, suggesting that prior experience with low levels of estrogen can significantly mitigate, in female rats, the magnitude of a conditioned taste aversion produced by a high dose of estrogen.