Abstract
Changes in levels of substance P-like immunoreactivity (SPLI) were observed in the rat dorsal raphe nucleus after cocaine treatment and were compared with concurrent cocaine-induced changes in 5-hydroxytryptamine (5-HT) content in the pons-medulla (PM). Acute administration of cocaine (15–30 mg/kg) consistently resulted in increases of SPLI, specifically in the area of the dorsal raphe nucleus, which were accompanied by significant decreases of PM 5-HT levels. Treatment of rats with 5-hydroxytryptophan (5-HTP), the 5-HT precursor, along with RO4-4602, the decarboxylase inhibitor, caused increments in PM 5-HT content with concurrent decreases in dorsal raphe nucleus SPLI. When cocaine and 5-HTP were administered simultaneously the changes in serotonin and SPLI were attenuated, suggesting that each substance antagonized the effect of the other. These data suggest a specific interaction between substance P and 5-HT in the dorsal raphe nucleus area.
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