Cortical somatosensory evoked potentials of seizure-sensitive and seizure-resistant gerbils

The Mongolian gerbil is known as an animal model that often exhibits spontaneous seizures that are characteristic of human epilepsy. Whereas there is much more information available relating this phenomenon to anatomical and electrophysiological characteristics of the hippocampal formation, the somatosensory cortex has rarely been the focus of attention. Given the existence of the fine grain cortical barrels developed in an orderly matrix, the vibrissa ascending system was thought the best sensory channel in which the gerbil neocortical excitability was to be tested. In the present study, we compared cortical evoked potentials to electric stimulation of vibrissa (whisker) follicle between the seizure-sensitive (SS) and seizure-resistant (SR) gerbils. Whereas our standard stimulation of the whisker follicle elicited a positive-negative biphasic somatosensory cortical potential in SR animals, it evoked only a positive monophasic potential in SS animals. Although the amplitude of positivity was generally larger in SR animals, the latency to reach this peak was significantly smaller than in the SS animals. Apparently there was no group difference in the laminar profile or the size of barrels that represent, in one-to-one fashion, the array of whisker follicles. It was suggested that an altered level of excitability in the absence of gross anatomy differentiates the seizure-sensitive gerbils from the seizure-resistant counterparts. Possible functional differences between the cortices of the two groups were discussed in light of the known synaptic electrophysiology.