Separate and combined effects of morphine and amphetamine on quantitative electroencephalogram and regional cerebral...

The effects of morphine (5 mg/kg) and amphetamine (5 mg/kg) were examined on relative regional cerebral glucose uptake (RrCGlu), surveyed in 20 brain areas in the rat. No relationship was found between drug effects on the cortical RrCGlu and the quantitative electroencephalogram (QEEG) measured from frontal and occipitoparietal cortices. Discriminant function analysis revealed that the two drugs produced identifiably different QEEG changes and that the combination engendered an unique metastate that most closely resembled amphetamine's effect with no morphine characteristics. The two drugs evoked qualitatively similar RrCGlu changes at most sites surveyed, with certain exceptions which are discussed. Both increased RrCGlu at the substantia nigra. Morphine, but not amphetamine, increased RrCGlu at the periaquaeductal gray. Since amphetamine is known to potentiate morphine analgesia and to ameliorate many of the opiate's depressant effects, the finding that the combination evokes cortical QEEG changes that more closely resemble amphetamine may have implications for understanding the increased psychotoxicity of chronic combined abuse.