Asphyxia induced by umbilical cord occlusion alters glutamatergic and GABAergic synaptic transmission in neurons of the superior colliculus in fetal rats

Using optical recordings, we studied the effects of asphyxia on intracellular Cl⁻ and Ca²⁺ concentrations (Cl⁻]i; Ca²⁺]i) in the superior colliculus of fetal rats, which were connected via the umbilical cord to the dam. Acute asphyxia was induced by umbilical cord occlusion. The number of fetal superior colliculus neurons showing GABA-mediated increases in Cl⁻]i (leading to hyperpolarization) following local synaptic electrical stimulation had decreased by 3 h post-asphyxiation, while the number showing GABA-mediated decreases in Cl⁻]i (leading to depolarization) increased. Ca²⁺]i rise, which occurred after acute asphyxiation, was antagonized by both non-NMDA and NMDA receptor antagonists. The increase in Ca²⁺]i following focal superior colliculus stimulation was markedly attenuated at 3 h post-asphyxiation.