Estrogen-induced suppression of intake is not mediated by taste aversion in female rats

Estrogen treatment can suppress the intake of a previously presented gustat ory conditioned stimulus (CS). This finding has been interpreted as an estr ogen-induced conditioned taste aversion. However, a distinction must be mad e between taste aversion and taste avoidance. In particular, tastes are onl y considered aversive if they elicit a stereotypic behavioral response, oth erwise the reduction in intake is classified as an avoidance. Although aver sive orofacial responses have been reported in male rats after taste-estrog en pairings, they have not been examined in ovariectomized female rats. The goal of the present investigation, then, was to use similar procedures to determine whether conditioned aversion also mediates the estrogen-induced r eduction of intake in female rats. Animals were introduced to a novel 0.1% saccharin solution and immediately thereafter were given a subcutaneous inj ection of vehicle or estradiol benzoate (10 mug). Responses were assessed u sing a two-bottle preference test, a one-bottle acceptance test, and a tast e reactivity (TR) test. The results confirmed previous reports of a reduced preference for saccharin after saccharin-estradiol pairing using the two-b ottle test. The reduction in intake during the one-bottle test, however, wa s not accompanied by stereotypic aversive responses, such as gaping. Surpri singly, a similar reduction in intake also occurred when using a backward c onditioning procedure in which estrogen was injected before, rather than af ter, CS access. Thus, the present results show that the suppressive effects of estrogen reflect an avoidance, rather than aversion and, moreover, that the reduced intake may be due to an unconditioned, rather than a condition ed, response. (C) 2001 Elsevier Science Inc. All rights reserved.