Acute and short-term effects of intraventricular injection of somatostatin and LHRH on glutamate and GABA levels in rat brain.

Glutamate and GABA content in different regions of adult female rat brain were determined at 10 and 30 min following intraventricular injection of LHRH or somatostatin. Cerebral cortex, cerebellar and hypothalamic glutamate levels were significantly elevated at 30 min following injection of 1 micrograms somatostatin, whereas hypothalamic glutamate levels were elevated at 10 min following a 0.5 micrograms dose. LHRH at a dose of 1 micrograms elevated cerebellar and brain stem glutamate levels at 10 and 30 min, whereas a 0.5 micrograms dose significantly elevated cerebral cortex, cerebellar and hypothalamic glutamate levels at 30 min. Third ventricular injection of 1 micrograms somatostatin produced a significant decrease in hypothalamic GABA levels at 10 and 30 min, whereas a 0.5-microgram dose decreased brain stem GABA levels at 10 min. LHRH at a dose of 0.1 microgram significantly increased cerebral cortex and cerebellar GABA levels at 10 min and brain stem GABA levels at 10 and 30 min following injection. Intraventricular injection of LHRH at a dose of 0.5 microgram significantly elevated cerebral cortex, cerebellar and brain stem GABA levels at 30 min. Hypothalamic GABA levels were elevated at 10 and 30 min following 0.5 and 1 microgram intraventricular LHRH injection. The implications of these results are discussed in relation to probable interaction between these neuroactive amino acids and neuropeptides in the rat brain.