Devaluation of Sucrose Caused by Social Instability Stress in Adolescent Male Long-Evans Rats in the Presence of an Unfamiliar Peer
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Rats that undergo the Social Instability Stress procedure during adolescence (SS: daily 1-hour isolation + re-pairing with an unfamiliar cage partner for 16 days) display changes in reward-related behaviour. Specifically, SS rats spend less time in social interaction but more time in social approach compared to controls, indicative of an altered social repertoire; SS males also show increased aggression when competing for access to sweet substances. To investigate to what extent SS influences choice behaviour when social and sweet rewards are presented simultaneously, a Social Discounting test was conducted. The SS procedure was administered during either adolescence or adulthood to both male and female rats to investigate sex differences and to determine if SS effects were specific to administration during adolescence. Results showed that increasing concentrations of sucrose (0%, 2%, 5%, 10%) had no influence on time spent near a novel peer during the Social Discounting choice test, but rats drank less of 5% sucrose when in a social condition relative to when drinking alone. The only stress effect to emerge was in adolescent-stressed males tested immediately after the stress procedure; SS adolescent males spent significantly less time drinking sucrose overall compared to controls, indicative of a stress-induced anhedonia. The stress-induced devaluation of sucrose was not long-lasting as it was not found in adolescent males tested after a delay. Thus, Social Instability stress produces short-lasting behavioural changes in reward processing only in adolescent male rats.