| Abstract: | An examination was made of the effect of REM sleep deprivation (REMSD) on some forms of altered motor activity, such as akinesia and catalepsy, induced by intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration of morphine in adult, male Wistar rats. Administration of morphine (25 mg/kg i.p.) induced an akinetic-cataleptic syndrome and decreased spontaneous vertical motor activity (SVMA) in animals allowed undisturbed sleep. REMSD decreased the morphine-induced akinesia and catalepsy that are known to be mediated by an inhibitory mu-opiate system. The locomotor depressant action of morphine was converted to excitation (manifested as increased SVMA and hopping behavior) by REMSD. Similarly, decreased motor activity following i.c.v. administration of morphine (25 micrograms) was replaced by excitation in the form of jumping behavior after REMSD. Naltrexone (1 mg/kg i.p.) blocked the akinetic and cataleptic effects, but not the excitatory effects, of morphine. It is suggested that REMSD is associated with a functional insufficiency of an inhibitory mu-opiate system, thus unmasking the excitatory morphine effects. The proposed insufficiency of an endogenous opioid system might explain an increase in neuronal excitation during REMSD and the therapeutic effect of REM deficiency in some types of depression. |
