The discriminative stimulus properties of EGb 761, an extract of Ginkgo biloba

Stimulus control was established in a group of nine rats using a dose of EG b 761 of 10 mg/kg, administered IF, 15 min before training. A two-lever ope rant task using a fixed-ratio 10 schedule of sweetened milk reinforcement w as used. Based upon a criterion for the presence of stimulus control of fiv e consecutive sessions during which 83% or more of all responses were on th e appropriate lever, a mean of 24 sessions was required to reach criterion performance. Subsequently, it was observed that EGb 761-induced stimulus co ntrol is significantly antagonized by the selective S-HT1A antagonist WAY 1 00635, but is unaffected by the 5-HT2 antagonist pirenperone. Furthermore, EGb 761 generalized to the selective 5-HT1A agonist, 8-hydroxy-dipropylamin otetralin [8-OH-DPAT], and this generalization was blocked by WAY-100635. T he present results indicate that EGb 761 is able to induce stimulus control when administered via the intraperitoneal route, and that its stimulus eff ects are mediated in part by activity at the 5-HT1A receptor. (C) 1999 Else vier Science Inc.