EXCESS EXTRACELLULAR AND LOW INTRACELLULAR GLUTAMATE IN POORLY DIFFERENTIATING WOBBLER ASTROCYTES AND ASTROCYTE RECOVERY IN GLUTAMINE-DEPLETED CULTURE-MEDIUM

The wobbler mouse develops an inherited motoneuronal degeneration of u nknown origin in the spinal cord. Primary cultures of adult wobbler sp inal cord astrocytes display abnormal morphological characteristics wi th fewer processes and paucity of cell-cell contacts. We have searched for a possible involvement of glutamate and glutamine intra- and extr acellular accumulations in vitro in the abnormal differentiation of mu tant astrocytes. We have found significantly higher glutamate and glut amine concentrations in the culture media of mutant astrocytes over a 3-day period compared with normal control astrocytes. Moreover, intrac ellular glutamate concentrations decreased substantially in mutant ast rocytes, but intracellular glutamine concentrations remained unchanged . Furthermore, decreasing initial glutamine concentrations in the cult ure medium (glutamine-depleted medium) led to the recovery of normal e xtra- and intracellular concentrations of glutamate and recovery of qu asi-normal morphological differentiation and increased cell-cell conta cts, leading to an essentially normal looking astrocyte network after 3 days of culture. Under these conditions, which lead to recovery, the only remaining abnormality was the higher glutamine extracellular con centration attained in the originally depleted glutamine media. These findings suggest that mechanisms regulating glutamate/glutamine synthe sis and/or influx/efflux are defective in wobbler astrocytes, leading to metabolic imbalance and possible cytotoxic effects characterized by disturbed intercellular networks and poor differentiation.