The effect of chronic fluoxetine on social isolation-induced changes on sucrose consumption, immobility behavior, and on serotonin and dopamine function in hippocampus and ventral striatum

Abstract

This study examined the effect of fluoxetine, a selective serotonin (5-HT) reuptake inhibitor, on isolation-induced changes on sucrose consumption and preference, spontaneous open-field activity, forced swimming behavior, and on tissue levels of 5-HT and dopamine (DA) in hippocampus and ventral striatum (VS). Male Sprague–Dawley rats were reared in social isolation or group housing from postnatal day 28. Thirty-two days later, half of the isolated animals were orally treated with fluoxetine (10 mg/kg/day) during the following 34 days. At the end of this period, behavior was assessed and afterward ex-vivo tissue samples were obtained. It was found that fluoxetine restored isolation-increased sucrose consumption and immobility behavior, without affecting locomotor activity, which appeared slightly increased in isolated groups both treated and untreated. In the hippocampus, isolation rearing depleted 5-HT contents and increased 3,4-dihydroxyphenylacetic acid (DOPAC) levels, as well as 5-HT and DA turnover. These neurochemical alterations were reversed by fluoxetine. In VS, treated and untreated isolated rats showed higher 5-HT levels than grouped congeners. Although fluoxetine did not affect 5-HT and DA contents in this region, it slightly reversed the alterations in the 5-HT and DA turnover observed in isolated rats. Overall, social isolation impaired incentive and escape motivated behaviors. At the neurochemical level, isolation rearing affected 5-HT rather than DA activity, and this differential effect was more noticeable in hippocampus than in VS. The chronic treatment with fluoxetine during the last month of rearing somewhat prevented these behavioral and neurochemical alterations. Our data suggest that isolation rearing is an appropriate procedure to model some developmental-related alterations underlying depression disorders.