DIMINISHED POTASSIUM-STIMULATED GABA RELEASE IN-VIVO IN GENETICALLY EPILEPSY-PRONE RATS

This experiment was conducted to assess the physiological relevance of observed changes in transmitter amino acid content in severe seizure genetically epilepsy-prone rats (GEPR-9s) by use of microdialysis. Adu lt male GEPR-9s and non-epileptic control rats were implanted with gui de cannulae, and 6 mm (loop) dialysis probes were inserted unilaterall y into rostral caudate and perfused with artificial cerebrospinal flui d. Each subject was perfused in the awake state with 100 or 150 mM Kfor 80 min in separate counterbalanced sessions, and 20-min fractions collected. High K+ perfusion increased extracellular fluid GABA and gl utamate (GLU) in a concentration-dependent manner in both GEPR-9s and non-epileptic control rats. However, in the presence of 150 mM K+ GABA release was decreased in GEPR-9s relative to controls throughout the stimulation interval. In contrast, the increase in extracellular fluid GLU after high K+ was not different in the two groups. These results suggest an important role for mechanisms underlying GABA release in th e seizure susceptibility observed in GEPR-9s.