THE use of insulin-induced hypoglycemic coma, though no longer as widespread as formerly (LAQUEUR and LA BURT, 1960) is nevertheless still successfully employed in the treatment of certain types of mental illness. The effect of this and of other hypoglycemic agents on the biochemistry of the brain is therefore of practical as well as theoretical interest. Several investigators have studied the influence of insulin on amino acid levels in the brain. DAWSON (1950) was the first to observe the fall in glutamic acid in rat brain during insulin hypoglycemia and CRAVIOTO, MASSIEU and IZQUIERO (1951) to demonstrate the considerable increase in brain aspartic acid levels that occurs under these conditions. Other workers have since confirmed these findings ( DAWSON, 1953; OKUMURA, OTSUKI and NASU, 1959;JACOBSON, 1959). It has also been shown (JACOBSON, 1959) that the increase in aspartic acid in insulin-treated rats is not due to its liberation from N-acetyl-L-aspartic acid, the presence of which in the brain was first demonstrated by TALLAN, MOORE and STEIN (1956). Other effects on brain amino acids produced by insulin are a decrease in the level of y-aminobutyric acid (GABA) and of glutamine (CRAVIOTO et al., 1951).The aim of the present study was to extend these observations. The levels of ten components in the brain, namely glutamic acid (Glu), aspartic acid (Asp), GABA, glutamine (Glu-NH,), alanine (Ala), taurine (Tau), glycine (Gly), ethanolamine (EtOH-NH,), phosphoethanolamine (P.eth), and glutathione (GSH), were determined in brains of rats treated with four different hypoglycemic agents: insulin, tolbutamide, hypoglycin A, and the ketoacid derived from hypoglycin A (2-methylenecylopropanepyruvic acid). Attention was directed to the relationship between blood sugar levels and the change in brain amino acid patterns. The role played by N-acetyl-L-aspartic acid in the rise of aspartic acid in insulin-treated rats was also studied.
M A T E R I A L S A N D M E T H O D S
Injecfion of rats.Wistar rats (male, 250 @ were fasted 24 hr and injected intraperitoneally Hith the material under investigation dissolved in normal saline. The dose level used is reported in the section on results. Insulin (Zinc) was obtained from Novo, tolbutamide from the Upjohn Company, and crystalline hypoglycin A was prepared from the seeds of Blighiu supidu (DE ROPP el a/.. 1958).
2-Methylenecyclopropanepyruvicacid was prepared from natural hypoglycin by the treatment of the amino acid with L-amino acid oxidase. Each treatment was applied to a group of five rats and most experiments were repeated two or more times.Preparation of brain exfrucfs. Animals were killed by decapitation, their brains removed at once and frozen with powdered dry ice, the operation taking about 40 sec. Brains from each of the five rats receiving a given treatment were pooled and treated either by a modification of the alcohol procedure of ROBERTS and FRANKEL (1950) or by the picric acid extraction procedure used by TALLAN, MOORE. and SITIN (1954). For alcohol extract...
