Effect of Alpha-adrenoceptor Blockade on Sleep and Wakefulness in the Rat

Three alpha-adrenoceptor antagonists with different subtype selectivity were administered IP at the beginning of the light period of the illumination cycle to rats whose sleep-wake pattern was subsequently recorded for 12 hours. Yohimbine (1 mg/kg) initially increased active wakefulness but did not affect REM sleep. Phentolamine (10 mg/kg) and prazosin (0.5 and 1.0 mg/kg) increased the amount of REM sleep during the latter half of the light period. The mechanism of this delayed increase in REM sleep may be related to a greater extent of alpha-receptor binding as well as an optimal, moderate concentration of prazosin and phentolamine in the brain during the latter half of the light period.