Acute and continuous morphine administration on the γ-aminobutyric acid system in the mouse

Abstract

1. 1. Effects of acute and continuous morphine administration on γ-aminobutyric acid (GABA) and glutamate levels and activities of L-glutamate-1-carboxylase (GAD) and GABA-α-ketoglutarate aminotransferase (GABA-T) in whole or discrete areas of mouse brain have been investigated. 2. 2. Acute morphine administration resulted in a significant increased brain GABA content and decreased glutamate level. Neither brain GAD nor GABA-T activity were affected. 3. 3. Continuous morphine administration, on the other hand, caused no significant change in brain glutamate level. However, there were significant decreases in both GABA level and GAD activity. 4. 4. The rate of brain GABA accumulation, induced by aminooxyacetic acid (AOAA) in tolerant mice, was slower than in non-tolerant animals. 5. 5. Both acute and continuous morphine administration caused distinct effects on the GABA system in cerebral cortex, brain stem, hypothalamus and the remaining areas of the brain except cerebellum. These data may indicate that the CNS GABA system is linked with morphine analgesia, tolerance and physical dependence.