Movement-related glutamate levels in rat hippocampus, striatum, and sensorimotor cortex

Changes in brain extracellular glutamate during movement stress were studie d using in vivo microdialysis. Male Long-Evans rats were placed in a clear cylinder designed to elicit behavioral activation while undergoing microdia lysis sampling from either the hippocampus, striatum or sensorimotor cortex . Glutamate levels were determined by high performance liquid chromatograph y with fluorescence detection in the dialysates taken before, during, and a fter exposure to the cylinder. Animals were in a behaviorally quiescent sta te before exposure to the cylinder, but they demonstrated increases in rear ing, locomotion, and turning while in the cylinder. Dialysate glutamate lev els were significantly enhanced in the samples taken while the rat was in t he cylinder compared with samples taken before or after exposure to the cyl inder. In a second study, rats were implanted with bilateral probes in the forelimb sensorimotor cortex, and one forelimb was immobilized by means of a plaster of paris cast. Glutamate, aspartate, serine, and taurine levels w ere quantified in casted animals. In casted animals, dialysate glutamate le vels were lower on the side contralateral to the immobilized limb during bo th quiescence and movement stress. Aspartate and taurine, but not serine le vels increased during movement stress in both the side contralateral and th e side ipsilateral to the immobilized limb. These results suggest that ther e is extracellular overflow of glutamate and other neuroactive amino acids during spontaneous movement, and chronic disuse can suppress extracellular glutamate levels. (C) 1999 Elsevier Science Ireland Ltd. All rights reserve d.