The Journal of Neurophysiology Vol. 82 No. 3 September 1999, pp. 1147-1155
Copyright ©1999 by the American Physiological Society

Changes in the Calcium Dependence of Glutamate Transmission in the Hippocampal CA1 Region After Brief Hypoxia-Hypoglycemia

Playfair Neuroscience Unit, Toronto Hospital Research Institute, Department of Medicine (Neurology), Bloorview Epilepsy Program, University of Toronto, Toronto, Ontario M5T 2S8, Canada

Ouanonou, A., Y. Zhang, and L. Zhang. Changes in the Calcium Dependence of Glutamate Transmission in the Hippocampal CA1 Region After Brief Hypoxia-Hypoglycemia. J. Neurophysiol. 82: 1147-1155, 1999. Using the model of hypoxia-hypoglycemia (HH) in rat brain slices, we asked whether glutamate transmission is altered following a brief HH episode. The HH challenge was conducted by exposing slices to a glucose-free medium aerated with 95% N₂-5% CO₂, for ~4 min, and glutamate transmission in the hippocampal CA1 region was monitored at different post HH times. In slices examined 8 h post HH, CA1 synaptic field potentials are comparable in amplitude to controls, but are less sensitive to experimental manipulations designed to attenuate intracellular Ca²⁺ signals, as compared with controls. Reducing calcium influx, by applying a nonspecific calcium channel blocker Co²⁺ or lowering external Ca²⁺, attenuated CA1 synaptic potentials much less in challenged slices than in controls. Buffering intracellular Ca²⁺ by bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM) attenuated CA1 synaptic potentials in control but not in slices post HH. Furthermore, minimally evoked excitatory postsynaptic currents displayed a lower failure rate in post-hypoxic CA1 neurons compared with controls. Based on these convergent observations, we suggest that evoked CA1 glutamate transmission is altered in the first several hours after brief hypoxia, likely resulting from alterations in intracellular Ca²⁺ homeostasis and/or Ca²⁺-dependent processes governing transmitter release.