Exposure of animals to artificial gravity conditions leads to the alteration of the glutamate release from rat cerebral hemispheres nerve terminals

The biochemical basis underlying the effects of altered gravity on the process of nervous signal transmission is not clear. We have investigated the effect of hypergravity stress (created by centrifugation of rats at 10 g for I h) on the basal and stimulated release Of L[C-14]glutamate (a chemical transmitter of excitatory signals) from isolated rat brain nerve terminals (synaptosomes). It has been shown that the hypergravity stress exerted a different influence on the Ca2+-dependent and the Ca2+-independent component of neurotransmitter release. The Ca2+-dependent L-[C-14]glutamate release evoked by potassium chloride was equal to 14.4 +/- 0.7% of total synaptosomal label for control animals and 6.2 +/- 1.9% for animals, exposed. to hypergravity (P less than or equal to 0.05) and was more than twice decreased as a result of the hypergravity stress. We observed no statistically significant difference in the Ca2+-independent component Of L-[C-14]glutamate release. For control group and animals exposed to the hypergravity stress it was equal to 7.7 +/- 2.8% and 12.9 +/- 2.0%, respectively. We have also investigated the effect of the hypergravity stress on the activity of high-affinity Na(+)dependent glutamate transporters. K-m and V-max Of L-[C-14]glutamate uptake have been determined. The maximal velocity of glutamate uptake was decreased as a result of hypergravity loading, but no difference in the K. values between control rats and hypergravity exposed animals was observed. These findings indicate that hypergravity stress alters neurotransmitter reuptake and exocytotic neurotransmitter release processes. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.