Experiments were performed to evaluate the effects on the levels of aspartate, GABA and glutamate in the periaqueductal central gray matter, hypothalamus, midbrain reticular formation and cortex of mouse brain following various treatments. The results indicate that only glutamate among the 3 neurohumors is systematically altered relative to the experimental manipulations. Moreover, among the 4 brain areas examined, the data implicate only the periaqueductal central gray matter as a locus of morphine's antinociceptive action. Morphine also appears to produce a drug-specific effect in hypothalamus which, however, is not analgesia-related. There were no significant pain, stress or drug-related effects on the levels of glutamate in either the midbrain reticular formation or the cortex. © 1976.
Sherman, A. D., & Gebhart, G. F. (1976). Morphine and pain: Effects on aspartate, GABA and glutamate in four discrete areas of mouse brain. Brain Research, 110(2), 273–281. https://doi.org/10.1016/0006-8993(76)90402-9