The GABAA receptor antagonist picrotoxin attenuates most sleep changes induced by progesterone

Progesterone has been shown to exert benzodiazepine-like effects on sleep, which suggests that they are mediated by an agonistic modulation of GABAA receptor functioning. To assess the involvement of GABAA receptors, we investigated the sleep responses to one dose of the GABAA antagonist picrotoxin (1.5 mg/kg) and progesterone (90 mg/kg), administered IP to eight rats alone and in combination, during the first 4 post-injection hours. Compared with vehicle, picrotoxin significantly delayed the latency to non-rapid eye movement sleep (non-REMS) and thereby decreased all sleep states, but barely affected the EEG activity within non-REMS. Progesterone significantly shortened non-REMS latency, increased pre-REMS, depressed low-frequency EEG activity (≤8 Hz) and augmented EEG activity in the higher frequencies within non-REMS. Except for the changes in high-frequency EEG activity, picrotoxin attenuated all effects of progesterone. These findings support the notion that GABAA receptors play an important role in the sleep effects of progesterone.