GLUTAMATE IMMUNOREACTIVITY IN RAT CEREBRAL-CORTEX IS REVERSIBLY ABOLISHED BY 6-DIAZO-5-OXO-L-NORLEUCINE (DON), AN INHIBITOR OF PHOSPHATE-ACTIVATED GLUTAMINASE

Glutamate (Glu) immunocytochemistry has been widely used to identify presumed gluergic neurons and synapses, but several problems related to the fact that Glu is both a synaptic transmitter and a compound used for metabolic purposes are still unsolved. One of these concerns the intense perikaryal staining observed in perfusion-fixed tissue. Phosphate-activated glutaminase, a key enzyme for the synthesis of releasable glutamate, is inhibited by the diazoketone 6-diazo-5-oxo-L-norleucine (DON), which greatly reduces glutamate release. In the present experiments, DON was either injected intraparenchymally or applied epipially to the sensorimotor cortex of adult Sprague-Dawley rats at concentrations of 0.25-1 mM. Both intraparenchymal and epipial applications of the chemical abolished Glu immunoreactivity in neuron