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 EGb 761 of 10 mg/kg, administered i.p., 15 min before training. A two-lever operant task using a fixed-ratio 10 schedule of sweetened milk reinforcement was used. Based upon a criterion for the presence of stimulus control of five consecutive sessions during which 83% or more of all responses were on the appropriate lever, a mean of 24 sessions was required to reach criterion performance. Subsequently, it was observed that EGb 761-induced stimulus control is significantly antagonized by the selective 5-HT1A antagonist WAY-100635, but is unaffected by the 5-HT2 antagonist pirenperone. Furthermore, EGb 761 generalized to the selective 5-HT1A agonist, 8-hydroxy-dipropylaminotetralin [8-OH-DPAT], and this generalization was blocked by WAY-100635. The present results indicate that EGb 761 is able to induce stimulus control when administered via the intraperitoneal route, and that its stimulus effects are mediated in part by activity at the 5-HT1A receptor.