STRESS-INDUCED 5-HT1A, RECEPTOR DESENSITIZATION - PROTECTIVE EFFECTS OF GINKGO-BILOBA EXTRACT (EGB-761)

The effects of sub-chronic cold stress on the functioning of hippocamp al 5-HT1A receptors in old isolated rats and the possible protective e ffects of Ginkgo biloba extract (EGb 761) were investigated. Cold expo sure during five days, produced a significant reduction of the inhibit ory effect of 8-hydroxy-2-(di-n-propylamino) tetraline (X-OH-DPAT) on forskolin-stimulated adenylyl cyclase activity. In contrast, neither t he affinity nor the density of hippocampal [H-3]8-OH-DPAT binding site s were affected indicating that the reduced sensitivity of 5-HT1A rece ptors induced by stress is probably due to a modification of their cou pling mechanisms to adenylyl cyclase. The stress-induced desensitizati on of 5-HT1A receptors was prevented by the administration of EGb 761 (50 mg/kg per os/14 days). These results clearly indicate that 5-HT1A receptors are desensitized by stress and point out the reduced capacit y of old rats to cope with the adverse effects of a chronic stressor. EGb 761 appears to restore the age-related decreased capacity to adapt to a chronic stressor.