Effect of the opioid antagonist naloxone on the regional metabolic rate for glucose in the conscious rat brain

The effect of naloxone, a potent and specific opioid antagonist, on cerebra l glucose utilization was investigated in conscious rat. For quantitative e valuation of the functional activity in brain, the regional cerebral metabo lic rate for glucose (rCMR(glc)) was measured by the double tracer techniqu e, using [C-14]2-deoxyglucose and [H-3]3-o-methylglucose. Intravenous admin istration of naloxone significantly increased rCMR(glc) in the medulla and thalamus at a dose of 1 or 10 mg/kg, and in the cerebral cortex, midbrain a nd cerebellum at a dose of 10mg/kg. Our findings strongly suggest that nalo xone by itself affects the cerebral functional activity within 10 min of ad ministration.