Sleep and waking in 5,7-DHT-lesioned or (-)-pindolol-pretreated rats after administration of buspirone, ipsapirone, or gepirone.

The effects of partial 5-HT1A receptor agonists buspirone (0.010-4.0 mg/kg), ipsapirone (0.010-6.0 mg/kg), and gepirone (0.025-4.0 mg/kg) on sleep and waking were studied in vehicle-treated and 5,7-dihydroxytryptamine (5,7-DHT)-injected rats. 5,7-DHT-treated animals showed a marked and significant serotonin and 5-HIAA depletion in the raphe regions of the pons and upper brain stem, cerebral cortex, hippocampus, and striatum. Subcutaneous administration of the partial agonists to both the vehicle-infused and the 5,7-DHT-treated animals significantly increased waking (W) and reduced light sleep (LS), slow-wave sleep (SWS), and REM sleep (REMS). Pretreatment with (-)pindolol (2.0 mg/kg) reversed the effects of buspirone and gepirone on W and non-REM sleep (LS + SWS) whereas REMS remained suppressed. (-)-Pindolol failed to reverse the effects of ipsapirone on sleep and W. The present results tend to indicate that increased W after acute administration of buspirone, ipsapirone, or gepirone depends upon the activation of postsynaptic 5-HT1A receptors. The well-known anxiolytic action observed after chronic administration of the azapirones seems to be related to mechanisms other that these involved in their stimulant effect.