| When consumption of a novel tasting substance is followed by administration of a chemical agent that produces physiological changes indicative of malaise, animals will reduce their consumption of the substance during subsequent encounters. This learned response is traditionally referred to as a conditioned taste aversion (CTA). Studies have shown that the hormone estradiol is capable of producing this learned gustatory aversion. In addition, estradiol produces reductions in food intake and body weight, a phenomenon that is referred to as its anorectic effects. As a consequence of this anorectic effect, we question whether estradiol truly can induce CTA learning. Therefore, one of the purposes of the experiments presented in this dissertation was to test the dissociability of estradiol CTA and estradiol anorexia. The second purpose of this thesis was to examine the neural basis of estradiol CTA and estradiol anorexia. Four approaches were adopted to test the ability of estradiol to condition independent of its ability to produce reductions in eating. First, we show that estradiol can produce a CTA in the absence of its anorectic effects. Second, we demonstrate that a low dose of estradiol that produces reductions in eating does not produce CTA. Next, we show that contingent pairing is necessary for a CTA since non-contingent pairing does not result in the gustatory aversion. Finally, we dissociate the conditioning effect of estradiol from its anorectic effect by showing that both excitotoxic and electrolytic lesions of the lateral parabrachial nucleus (PBN) either attenuated or blocked an estradiol CTA, while leaving estradiol anorexia unaffected. Together, all of the data suggest that estradiol can condition a gustatory aversion. The data also suggest that estradiol elicits a CTA based on its aversion inducing properties since lesions of the lateral PBN, an area that processes visceral information, blocked the CTA. Third, the data show that the lateral PBN is necessary for estradiol CTA. Finally, the studies show that although the lateral PBN is involved in different types of anorexia, it is not involved in estradiol anorexia. |
