Administration of 0.5-2.5 mg/kg SX-3228 to rats during the light phase induces a significant reduction of rapid-eye-movement sleep (REMS) (P<0.05) during the third recording hour. Administration of SX-3228 (0.5-2.5 mg/kg) at the beginning of the dark period significantly and dose-dependently reduces waking (W) and increases slow wave sleep (SWS) during the 6-h recording period (P<0.05-0.01); however, significant changes during the last recording hour are restricted to the 2.5 mg/kg dose (P<0.01)[1].