Behavioral sensitization to cocaine is not associated with changes in serotonin (5-HT) fiber immunoreactivity in rat forebrain

We investigated whether cocaine-induced behavioral sensitization is associated with changes in serotonin (5-HT) immunoreactivity. Male Sprague-Dawley rats were injected with either cocaine (15 mg/kg, IP) or saline twice daily for seven days. Their behavior was observed and rated for locomotor activation and stereotypy. One day after the final injection, the brains were processed for 5-HT immunohistochemistry. The intensity of 5-HT immunoreactive staining of 5-HT axons and terminal varicosities was blindly rated in cocaine-sensitized rats and found not to differ from saline-treated rats. The results support the hypothesis that unlike some amphetamine derivatives, repeated cocaine administration which results in behavioral sensitization is not neurotoxic to 5-HT axons and terminals in the forebrain.