Ketamine abolishes the tonic phase of the seizures evoked by sudden cooling of toad isolated spinal cords

Spinal seizures evoked by sudden cooling (SSSC) were used to investigate the anticonvulsant activity of ketamine (KET) injected either intralymphatically (i.l., 5-40 mg/kg) or intrathecally (i.t., 0.5-1.0 mumol/20 microliters) using isolated spinal cord-hindleg preparation. KET inhibited the tonic phase and prolonged the clonic phase in a dose-dependent manner. The cionic phase was depressed or totally blocked at KET doses of 80-160 mg/kg, i.l. or 2 mumol/20 microliters, i.t. This depression was not prevented by i.t. administration of concanavalin A. The latency of onset of seizures was also increased by KET. KET abolishes the tonic-extensor phase of SSSC in which activation of N-methyl-D-aspartate-receptors may play a role.