Reduction of postsynaptic inhibition tolerated before seizure initiation: spinal cord

The reduction of postsynaptic inhibition tolerated before initiation of intrinsic spinal seizures was assessed using intracellular recording from lumbar motoneurons in spinal cats anesthetized by pentobarbital or alpha-chloralose or decerebrated and unanesthetized. The amplitude of antagonist group Ia and recurrent (Renshaw) IPSPs was monitored while incremental doses of the specific glycine antagonist, strychnine, were injected until seizures developed. Both kinds of IPSPs were reduced to less than 25% of control at seizure onset, independent of anesthesia. Assuming the recorded pathways were representative of all glycine-mediated spinal pathways, the results suggested that postsynaptic inhibition could be virtually eliminated before intrinsic spinal seizures were triggered. These results place a constraint on theories of spinal seizures initiation due to reduction of postsynaptic inhibition.