Abstract

Rats prepared with chronic electrodes for recording the direct and voltage-integrated cortical electroencephalogram (EEG) as well as the integrated electromyogram were made dependent on morphine by its administration through chronic indwelling i.v. cannulas. Injections of morphine sulfate were given automatically at an initial dose of 1.25 mg/kg/hr for 24 hours. This dose was increased on successive days to 2.5, 5, 10 and 20 mg/kg/hr. respectively. After maintenance of the rats on the highest dose for two days, the injections were discontinued. EEG and electromyogram recordings monitored continuously revealed a suppression of rapid eye movement (REM) sleep during morphine administration at the progressively increasing doses; on the second day of the 20 mg/kg/hr dose, however, the duration of REM sleep returned to the control base-line value. The mean EEG voltage output of REM sleep episodes within these two days showed a slight but significant reduction. Within the first four to six hours after the withdrawal of morphine, the duration of REM sleep was significanty enhanced. After this initial elevation, both the duration and the mean EEG voltage output of REM sleep episodes declined to minimal levels during the remainder of the first day of withdrawal and remained below the control base-line values up to the third day. A significant rebound then occurred in both pamareters, during which the REM EEG voltage output was significantly elevated until the sixth or ninth day after withdrawal, while the rebound in REM time remained evident up to the 12th day. The increases in REM sleep time during this period of morphine abstinence extended to twice the REM rebound normally expected to follow REM deprivation by other means.