Evidence for decreased calcium dependent potassium conductance in hippocampal CA3 neurons of genetically epilepsy-prone rats.

The genetically epilepsy-prone rat (GEPR) has become an important model to study genetic predisposition to epilepsy involving not only the brainstem but also forebrain structures. Previous work in CA1 hippocampal cells showed a reduction in spike frequency adaptation and only subtle changes in slow afterhyperpolarization (AHP). As important differences exist in calcium dependent potentials in the CA1 and CA3 hippocampal cells, we compared the membrane properties of hippocampal CA3 cells in GEPRs and Sprague-Dawley (SD) rats. There was no significant difference in the resting membrane potential, input resistance, charging time constant or rheobase between GEPRs and SD rat neurons. The action potential amplitude and the width at half maximal amplitude did not differ. A marked reduction in spike frequency adaptation accompanied by a very significant reduction in AHP was seen in the GEPR rats. Since calcium dependent potassium conductance produces both spike frequency adaptation and AHP, our results suggest that this conductance is reduced in the GEPR CA3 neurons.