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Conditioned taste aversion (CTA) is a unique form of classical conditioning whereby an animal learns to associate a novel taste stimulus with negative visceral effects. Acquisition of CTA results in reduced intake of future presentations of the conditioned novel taste stimulus. Here I investigated both behavioral and neural characteristics of CTA expression in two experiments: 1) taste specificity and learned safety of short-term CTA expression, and 2) whether the same neurons that are activated during CTA expression against conditioned sucrose (the CS) are re-activated by LiCl injection (the US). In the first experiment, we tested whether short-term CTA expression shares with long-term CTA expression the well-defined features of taste specificity to the conditioned taste and learned safety (reduced association of a taste with a toxic effect by prior non-toxic experience with the conditioned taste). We found that short-term expression of CTA was not taste specific and could be attenuated by prior exposure to the conditioned taste only. The second experiment investigated activation at the neural level. CTA acquisition results in expression of c-Fos in the intermediate zone of the nucleus tractus solitaris (NTS) following presentation of the conditioned taste. These patterns of c-Fos expression are similar to what is seen following administration of LiCl. By administering the conditioned taste 3 hours prior to the administration of LiCl, we were able to double-label for c-Fos vii protein (induced by the taste and persisting after mRNA degradation ) and c-fos mRNA (induced by the toxin prior to protein synthesis) and thus measure dual activation of cells by the taste and the toxin. We found that approximately 40% of cells expressing c-Fos were double-labeled for protein and mRNA.