DIFFERENTIAL-EFFECTS OF BUPRENORPHINE AND PENTAZOCINE ON THE REGIONALCEREBRAL METABOLIC-RATE FOR GLUCOSE IN THE CONSCIOUS RAT

The effects of buprenorphine (BNP, 10-200 mu g/kg, i.v.) and pentazoci ne (PTZ, 2.5-10 mg/kg, i.v.) on the regional cerebral metabolic rate f or glucose (rCMR(glc)) mere analyzed in nine anatomically discrete are as of the conscious rat brain by the simultaneous use of [C-14]2-deoxy glucose, the glucose analogue that can be phosphorylated in the brain, and [H-3]3-O-methylglucose, a nonmetabolizable glucose analogue. Orig inally, this method was developed by Gjedde and Diemer in the rat and in humans. The rCMR(glc) was significantly decreased by BNP (100 or 20 0 mu g/kg) in most of the brain regions investigated, except the cereb ellum. In contrast, PTZ (10 mg/kg) significantly increased rCMR(glc) i n the cerebral cortex and medulla. In the cerebral cortex and medulla, the direction of the effect on rCMR(glc) was opposite for BNP (22% de crease at the dose of 200 mu g/kg) and PTZ (22% increase at the dose o f LO mg/kg). These findings strongly suggest that the discrepancies be tween the marked effects of BNP (a partial mu agonist and kappa antago nist) and PTZ (a mu antagonist and kappa agonist) on rCMR(glc) reflect the selectivity of agonist action at the different types of opioid re ceptors, mu and kappa receptors, in the rat brain.