Long-lasting convulsant effect on the cerebral cortex of Naja naja venom.

1. A neurotoxic fraction has been prepared from Indian cobra venom (Naja naja) by column chromatography on CM Sephadex.2. When assayed for lethality in mice, or for neuromuscular blocking potency in the rat phrenic nerve-diaphragm preparation, this fraction was 2.4-2.9 times as potent as whole venom.3. Application of either whole venom (0.5-1.0 mg/ml) or the neurotoxic fraction (0.25-1.0 mg/ml) to the exposed cerebral cortex of the rat led to the appearance in the somatosensory evoked potential of abnormal negative waves, resembling in amplitude and latency those produced by the cortical application of strychnine or curare.4. This effect differed from that produced by strychnine or curare in that after washing off the toxin the abnormal responses persisted for as long as the experiment continued (8-9 hours).