Abstract: The activities of GABA-catabolizing enzymes (GABA-transaminase and succinic semialdehyde dehydrogenase), succinate dehydrogenase, alanine and aspartate amino transferases, the contents of GABA, glutamate, glutamine, alanine, aspartate and glycine were studied in rat brain regions after acute morphine administration. Intraperitoneal (i.p.) administration of 10 mg/kg morphine increased the glutamate level and decreased GABA and glycine levels in cortex. This may explain an excitable effect of morphine. When the higher doses of morphine were administered (20 and 40 mg/kg, i.p.), the most pronounced changes in the amino acids tested were observed in brain stem, possibly because of higher density of opiate receptors there. Decrease in glutamate level in the brain stem was accompanied by accumulation of its metabolic precursors glutamine and aspartate and decrease of inhibitory amino acids (GABA, glycine) leves, when the dose of 40 mg/kg was used. The data obtained indicate a dose-dependent relationship between the parameters studied and behavioral action of morphine.
Reference: Vinitskaya A.G., Kurbat M.N., Lelevich V.V., Kozlovsky A.V., GABA metabolism and contents of neuroactive amino acids in rat brain after acute morphine administration, Biomeditsinskaya khimiya, 2005, vol: