Mechanism of epileptogenesis of the Mongolian gerbil, a gnetical animal model of epilepsy.

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The Mongolian gerbil (Meriones unguiculatus), a genetical animal model of epilepsy, shows the epileptic motor manifestations elicited by several kinds of stimulation. We found that the rhythmical movement of the pinnae occurring after posture change, a strong inducer of the seizure, was the first detectable sign of the stimulus-induced behaviors which would develop into adult-type seizure manifestations. Electrophysiological study showed that the movement of the pinnae was induced when an area of the sensorimotor cortex was stimulated electrically. This area was overlapped spatially with the vestibular cortex determined by electrical stimulation of the vestibular organ. Neurotracing analysis showed that the thalamic area projecting to the cortical area for the movement of the pinnae seemed to correspond to that thought to project to the vestibular cortex in other animal species. Since vestibular stimulation is a presumptive extrinsic factor involved in the posture change, these results and other electrophysiological and morphological observations seem to support our hypothesis that the vestibular stimulation induces progressively increasing number of afterdischarge in a cortical area which is responsible to the formation of epileptic manifestations starting from the movement of the pinnae. In the neurons of the gerbil, there was a protein like P70, a70 kDa protein considered to be involved in the epiletogenesis of cobalt-treated rat. This protein may be a genetically determined factor to lower the threshold of the neurons of this animal species.