EFFECT OF HYPOXIA ON GLUTAMATE EFFLUX AND SYNAPTIC TRANSMISSION IN THE GUINEA-PIG HIPPOCAMPUS

Simultaneous assessment of synaptic activity and glutamate efflux in g uinea pig hippocampal brain slices was made before, during and after a 10-min period of hypoxia. Spontaneous glutamate efflux was assessed b y determining glutamate concentration in the superfusion medium at dis crete times using high performance liquid chromatography (HPLC). Synap tic activity was assessed using extracellular recording of the evoked population spike in the CA1 region following stimulation of the Schaff er collateral pathway. Hypoxia decreased (P < 0.05) the amplitude of t he population spike by 3 min and abolished it bk 5 min. This was accom panied by an increase (P < 0.05) in glutamate concentration in the sup erfusate at 10 min. Following re oxygenation, the population spike ret urned to baseline amplitude by 5 min and was greater (P < 0.05) than b aseline at 10 and 20 min of recovery. Glutamate concentration returned to baseline levels by 1 min of recovery. This experimental preparatio n can be used to explore the temporal relationship between glutamate e fflux and synaptic activity during hypoxia. The results of this study indicate that, in the hippocampal CA1 region, post-synaptic elements a re more sensitive than their presynaptic counterparts to hypoxia.