Effects of caloric or non-caloric sweetener long-term consumption on taste preferences and new aversive learning

Sugar consumption induces the consummatory suppression of sugary ethanol: Differential effects of sugar restriction according to sex and age

Sweet foods activate the reward system that is essential in processing natural reinforcers. Maturation changes in this system during adolescence are linked to heightened impulsivity and risk-seeking behavior, including the use of drugs like ethanol. This usually starts with the consumption of sugary mixtures. However, the influence of sugar exposure on ethanol consumption remains inconclusive. The present research examines the effect of long-term sugar exposure on sugary ethanol (S-EtOH) preference and net intake, exploring the implications of sex, age, accessor restriction of sugar, and its effect during the transition into adulthood. Wistar rats of both sexes were given 24-hour access to a sugar solution for 21 days during adolescence or adulthood. Subsequently, four preference tests of S-EtOH vs. water were carried out every other day, with or without sugar access between each preference test. Our results demonstrate that continuous acute and long-term sugar access induces a consummatory suppression effect on S-EtOH intake, particularly in adult rats, irrespective of sex. This effect becomes more pronounced with more extended periods of exposure to sugar, leading to a higher prevalence of low consumers. Notably, when sugar access was restricted after high familiarization, the suppression effect in adolescent male rats was reduced. Under these conditions, the rats appeared to be more susceptible to developing a preference for S-EtOH consumption. Furthermore, our longitudinal observations reveal that sugar access or restriction conditions during the transition from adolescence to adulthood play a crucial role in shaping S-EtOH consumption patterns in adulthood.

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.

Differential changes in GAP-43 or synaptophysin during appetitive and aversive taste memory formation

Association between events in time and space is a major mechanism for all animals, including humans, which allows them to learn about the world and potentially change their behavior in the future to adapt to different environments. Conditioning taste aversion (CTA) is a single-trial learning paradigm where animals are trained to avoid a novel flavor which is associated with malaise. Many variables can be analyzed with this model and the circuits involved are well described. Thus, the amygdala and the gustatory cortex (GC) are some of the most relevant structures involved in CTA. In the present study we focused in plastic changes that occur during appetitive and/or aversive taste memory formation. Previous studies have demonstrated that memory consolidation, in hippocampal dependent paradigms, induces plastic changes like increase in the concentration of proteins considered as markers of neuronal plasticity, such as the growth associated protein 43 (GAP-43) and synaptophysin (SYN). In the present experiment in male rats we evaluated changes in GAP-43 and SYN expression, using immunofluorescence, induce by the formation of aversive and appetitive taste memory. We found that taste aversive memory formation can induce an increase in GAP-43 in the granular layer of the GC. Furthermore, we also found an increase in SYN expression in both layers of the GC, the basolateral amygdala (BLA) and the central amygdala (CeA). These results suggest that aversive memory representation induces a new circuitry (inferred from an increase in GAP 43). On the other hand, an appetitive taste learning increased SYN expression in the GC (both layers), the BLA and the CeA without any changes in GAP 43. Together these results indicate that aversive memory formation induces structural and synaptic changes, while appetitive memory formation induces synaptic changes; suggesting that aversive and appetitive memories require a different set of cortical and amygdala plastic changes.