Chronic stress and social isolation regulate motivation and hedonic value differently

Chronic exposure to stress allows the expression of a wide spectrum of atypical behaviors in the organism. Several factors contribute to the phenotypic variability of responses to stress, including biological sex, type of stressor, and stress duration. The combination of these elements is associated with different phenotypes (physiological, morphological, behavioral). We used 66 male and female Wistar rats, divided into 6 groups: Unpredictable stress battery (CUSB), social isolation post-weaning (PWSI), and No-stress. The stress exposure began on postnatal day (PND) 30 and continued until PND65, and then they were tested on PND90. We evaluate the changes in hedonic value for caloric content (evaporated milk) in an open-choice task and non-caloric content using the saccharin preference test. The subjects were exposed to evaluate the effort-dependent motivation, and we used the progressive ratio paradigm. The male rats exposed to CUSB and PWSI decreased their caloric and noncaloric consumption, which showed evidence of anhedonia. However, we didn’t find differences in the female rats exposed to stress. On the other hand, the males exposed to CUSB significantly decreased the response rate in the progressive ratio trials (lower motivation); however, there were no differences in the PWSI group. We found a divergence in the palatable substance intake after exposure to the CUSB and PWSI in the Wistar rat. We observe an anhedonic effect in males only. Besides, CUSB produced changes in the hedonic value and motivation, whereas the subjects exposed to PWIS got an anhedonic effect, but not in motivation.