THE EFFECT OF HYPOXIA ON NEUROTRANSMITTER PHENOTYPE OF FOREBRAIN CHOLINERGIC NEURONS

The effect of hypoxia on the neurotransmitter phenotype of rat forebrain cholinergic neurons was analyzed using a dissociated fetal rat culture system. The aims of this study were to examine the feasibility of using choline acetyltransferase (ChAT) activity as a measure of cell injury and/or recovery, to measure the time course of hypoxic effects on ChAT activity, to determine how changes in ChAT activity at 48 h post-injury relate to microscopic changes and LDH release into the medium during that time, and finally to explore the possible mechanisms of hypoxic injury in this model. At exposure to 0.5-1.5% O2 there was a time-dependent decrease in ChAT activity when cells were harvested 48 h after exposure. Forty-eight hours after 8-9 h hypoxic exposure ChAT activity was 50-60% that of controls without any alteration in morphology of neurons. An 8 h exposure to hypoxic conditions caused a post-exposure time-dependent decrease in ChAT activity to 20% of control level at 72 h. Thereafter there was spontaneous recovery of phenotype to 60% of control which remained stable between 5 and 7 days post-exposure. Loss of neurotransmitter phenotype was not well correlated with other measures of cytotoxicity including morphological changes and LDH release. The loss of phenotype observed with hypoxia was mimicked by glutamate and kainate but not by NMDA. Consistent with these observations, neither APV nor AP3 significantly altered the effect of hypoxia on forebrain cholinergic neurons, while the addition of APV and CNQX in combination protected the phenotype of these neurons only if there was 50% or less loss of phenotype following hypoxia. However both APV and CNQX independantly provided significant protection from hypoxia in mixed cortical-basal forebrain cultures supporting a role for afferent input from cortex in both NMDA and non-NMDA receptor mediated injury.