Induction of depressive-like effects by subchronic exposure to cocaine or heroin in laboratory rats.

The effect of psychoactive drugs on depression has usually been studied in cases of prolonged drug addiction and/or withdrawal, without much emphasis on the effects of subchronic or recreational drug use. To address this issue, we exposed laboratory rats to subchronic regimens of heroin or cocaine and tested long-term effects on (i) depressive-like behaviors, (ii) brain-derived neurotrophic factor (BDNF) levels in reward-related brain regions, and (iii) depressive-like behavior following an additional chronic mild stress procedure. The long-term effect of subchronic cocaine exposure was a general reduction in locomotor activity whereas heroin exposure induced a more specific increase in immobility during the forced swim test. Both cocaine and heroin exposure induced alterations in BDNF levels that are similar to those observed in several animal models of depression. Finally, both cocaine and heroin exposure significantly enhanced the anhedonic effect of chronic mild stress. These results suggest that subchronic drug exposure induces depressive-like behavior which is accompanied by modifications in BDNF expression and increases the vulnerability to develop depressive-like behavior following chronic stress. Implications for recreational and small-scale drug users are discussed. In the present study, we examined the long-term effects of limited subchronic drug exposure on depressive-like symptoms. Our results demonstrate that short-term, subchronic administration of either cocaine or heroin promotes some depressive-like behaviors, while inducing alterations in BDNF protein levels similar to alterations observed in several animal models of depression. In addition, subchronic cocaine or heroin enhanced the anhedonic effect of chronic stress.