Differential effects of thirst and satiety on conditioned taste aversion acquisition, retrieval, and memory extinction.

Thirst is an essential motivational component that could modulate the strength of conditioning; pioneer studies show that the rats' sexual dimorphism observed in the rate of aversive memory extinction of conditioned taste aversion (CTA) is affected by the state of fluid deprivation. On the other hand, previous evidence suggests that fluid intake volume and temporal context before and during conditioning may influence CTA. Furthermore, although CTA has been demonstrated using various types of stimuli, neural processing and homeostatic regulation of water and nutritional balance may differ depending on the stimulus used and the conditioning stages. Therefore, this study explored the effects of state motivated by thirst and satiation, using saccharin, as a non-caloric sweet stimulus, during CTA and the aversive memory extinction process under similar contextual and temporal conditions. First, we implemented an ad libitum water protocol in male and female adult rats to evaluate saccharin aversive memory formation; we compared this with a traditional CTA with liquid deprivation in the same context and temporal consumption conditions. Furthermore, we evaluated whether liquid satiety affects the acquisition or the aversive memory retrieval differentially. Our results show that the ad libitum liquid regimen allows reliable quantifications of basal water consumption, monitored every hour for more than five days. We observed a reliable CTA, where the magnitude of aversive memory and its extinction is significantly higher in both male and female rats; the strong CTA observed is substantially due to the satiety state during taste aversion memory retrieval. Our data show that although liquid deprivation does not affect CTA acquisition, it does induce weakness in the magnitude of aversive retrieval expression and fast aversive memory extinction, similarly in male and females. Overall, the results indicate that the need to satiate the demand for liquids during retrieval prevails over the conditioned aversion learned, suggesting, that thirst is a source of temporary variables dominating the aversive responses during CTA retrieval.