Regional brain glucose utilization during and following chronic naltrexone administration: preliminary observations in rat brain

Experiments were conducted to determine some of the metabolic correlates of tonic opioid activity in the central nervous system under conditions previously examined for changes in monoamine levels. The glucose metabolic rates in seven brain regions were determined by autoradiographic visualization of 14C-deoxyglucose incorporation in female rats after 8 days of chronic exposure to naltrexone pellets and 10 days after pellet removal. Autoradiographs were analyzed on a region-by-region basis to correspond to areas previously dissected and analyzed for changes in monoamine content under similar experimental conditions. Chronic administration of naltrexone resulted in a significant decrease in the metabolic activity of neurons in the striatum. Other brain areas examined under this condition were not significantly affected. Ten days following pellet removal, 14C-deoxy-glucose incorporation was indistinguishable from that determined in placebo treated rats in all brain regions examined. These results indicate that tonic opioid input is an important determinant of metabolic activity in the striatum. In addition, these results indicate that conditions previously shown to alter regional content of monoamines do not necessarily produce concomitant changes in regional glucose utilization.