Exposure to estradiol before but not during acquisition of LiCl-induced conditioned taste avoidance accelerates extinction.

Estradiol accelerates extinction of LiCl-induced conditioned taste avoidance when it is present continuously before and during acquisition. We have suggested that the effect of estradiol on extinction is due to its illness-associated, rather than learning-associated, properties. If this were the case, then one would expect estradiol to act before but not during acquisition. This expectation is based on previous work showing attenuation of learned taste avoidance when rats are given distal preexposure (greater than 24 h before conditioning) or proximal preexposure (less than 24 h before conditioning) to the illness-inducing agent LiCl before acquisition of a LiCl-induced conditioned taste avoidance. In three separate experiments, estradiol was administered during three different time periods via subcutaneous implantation of a 10-mm estradiol-filled capsule. In each experiment, the extinction of estradiol-treated females was compared to that of females implanted with empty capsules. In the first experiment, female rats were given distal exposure to estradiol before acquisition. Capsules were implanted 11 days before acquisition and were removed 2 days before acquisition. In the second experiment, female rats were given proximal exposure to estradiol before acquisition. Capsules were implanted 2.5 h before LiCl was paired with a sucrose solution and were removed 16.5 h later. In the third experiment, female rats were given exposure to estradiol during acquisition. Capsules were implanted at the same time as LiCl administration and were removed 18 h later. The only estradiol-treated females to show accelerated extinction were those given distal preexposure to estradiol in Experiment 1. These data do not support a learning-associated hypothesis and only partially support an illness-associated hypothesis. The failure to find accelerated extinction following proximal preexposure may reflect an inappropriate choice of the parameters used in the experiment or a difference in the stimulus properties of LiCl and estradiol that allow each to serve as conditioning and preexposure agents in conditioned taste avoidance paradigms [corrected].