Young age and low temperature, but not female gender delay ATP loss and glutamate release, and protect Purkinje cells during simulated ischemia in cerebellar slices

Excessive activation of glutamate receptors contributes to Purkinje cell (PC) damage during brain ischemia, but the mechanisms of glutamate release are contentious. Age, gender and temperature all strongly influence ischemic brain damage, but the mechanisms underlying their influence are not fully understood. We determined how age, gender and temperature influence ATP loss, glutamate release, glutamate receptor activation and PC damage during cerebellar ischemia. We used voltage-clamped PCs to monitor glutamate release during simulated ischemia in slices of cerebellum of different ages and genders, and at different temperatures. While gender did not affect ischemic glutamate release, both young age and low temperature dramatically delayed the onset of glutamate release without affecting its magnitude. Glutamate receptor and transporter density were similar around young and old PCs, but the rate of ATP decline during ischemia was dramatically slowed in young animals and by lowered temperature. Bypassing the ischemia-induced loss of ATP, and disrupting ionic gradients directly by pharmacologically inhibiting the Na⁺/K⁺-ATPase, reduced the difference in timing of glutamate release in newborn and mature cerebellum. Ischemic damage in newborn and mature cerebellum paralleled ATP loss and glutamate release, but blocking glutamate receptors did not prevent ischemic damage. Thus, protection against brain ischemia provided by young age or lowered temperature is due to slower consumption and hence delayed loss of ATP, with a corresponding delay in glutamate release and other undetermined damage mechanisms. The protection afforded by female gender must occur downstream of ATP decline, glutamate release, and activation of glutamate receptors on PCs.