Estradiol enhances the acquisition of lithium chloride-induced conditioned taste aversion in castrated male rats

Abstract

The present study examined the effects of short-term treatment with ovarian hormones on the acquisition of conditioned taste aversion (CTA). Adult male rats were castrated and randomly divided into LiCl- and saline-treated groups. Nineteen days after castration, all of the animals were subjected to 23.5-h daily water deprivation for seven successive days (day 1 to day 7). On the conditioning day (day 8), the rats received either a 4 ml/kg of 0.15 M LiCl or the same dose of saline injection immediately after administration of a 2 % sucrose solution during the 30-min water session. Starting from day 6, rats in both groups received one of the following treatments: daily subcutaneous injection of (1) estradiol alone (30 μg/kg; estradiol benzoate (E) group), (2) estradiol plus progesterone (500 μg; E + progesterone (P) group), or (3) olive oil. From day 9 to day 11, all of the rats were given daily two-bottle preference tests during the 30-min fluid session. The estradiol and estradiol plus progesterone treatments in the LiCl groups resulted in significantly lower preference scores for the sucrose solution compared with the olive oil treatment groups, but no difference in preference score was seen between these two groups. These results indicate that both the estradiol and estradiol plus progesterone treatments in the LiCl groups enhanced the acquisition of CTA learning and suggest that estradiol affects the acquisition of CTA mediated by an activational effect in male rats, whereas progesterone treatment does not influence the effects of estradiol on the acquisition of CTA.

Genetic and environmental influences on one‐trial conditioned context aversion in mice

“…Circulating levels of estrogen have been found to influence conditioned disgust behaviors in rats, as evidenced by the rats' increased aversive responses to the reinforced context during the period of proestrus compared to diestrus 58 . It also has been reported that nausea, malaise, and conditioned aversive responses in animals are enhanced by estrogen 64 . Estradiol has been found not only to cause a shift in the palatability of a sucrose solution but also induce taste avoidance when paired with a novel sucrose taste 65 .…”

“…58 It also has been reported that nausea, malaise, and conditioned aversive responses in animals are enhanced by estrogen. 64 Estradiol has been found not only to cause a shift in the palatability of a sucrose solution but also induce taste avoidance when paired with a novel sucrose taste. 65 These results indicate that susceptibility to malaise‐inducing agents in females is caused by endogenous levels of gonadal hormones.…”

Social neuroscience of disgust

“…Results of prior studies have shown that estradiol can produce conditioned taste avoidance when paired with a novel sucrose solution, as well as conditioned aversion consisting of disgust responses to the sucrose taste . Estradiol has also been shown to enhance the acquisition of LiCl‐induced taste aversion in castrated male rats, possibly due to estradiol's illness inducing properties. In addition, the formation of conditioned taste aversion and reduction of food intake seen after administration of agonists for ERα, ERβ and GPER‐1 is likely associated with the nausea and potentially disgust related responses elicited by estrogens, .…”