Regional distribution of Ginkgo biloba-induced c-Fos immunoreactivity

A growing literature supports the notion that Ginkgo biloba has cognitive enhancing and anxiolytic properties; however, its effects on neuronal populations have yet to be characterized. The present study used c-Fos immunoreactivity (Fos-IR) to characterize functional activity in selected brain regions following administration of a standardized Ginkgo biloba extract. Because Ginkgo is typically consumed orally, Exp 1 sought to identify patterns of neural activity induced by oral administration. To ensure that the alterations in functional neural activity observed in Exp 1 were not simply due to novel gustatory experience, Exp 2 characterized patterns of Fos-IR following intraperitoneal administration of Ginkgo. Rats were habituated to handling and experimental conditions. In Exp 1, rats self-administered 150 mg/kg Ginkgo or vehicle alone (strawberry jam) orally. In Exp 2, rats were injected with Ginkgo (2.5 or 25 mg/kg, i.p.) or vehicle (0.3% gum Arabic). Animals were anaesthetized and perfused transcardially. Brains were sectioned, immunostained using a c-Fos antibody, then the number of labelled cells was quantified microscopically in selected brain regions. In both experiments Ginkgo increased Fos-IR in numerous brain regions including the insular cortex and amygdala. Intraperitoneal administration induced Fos-IR in some additional regions including the nucleus accumbens and dentate gyrus. Results provide important preliminary data serving to identify several candidate neural sites involved in the cognitive enhancing and anxiolytic effects of Ginkgo biloba.