Voltage dependence of subthreshold resonance frequency in layer II of medial entorhinal cortex. Hippocampus

ABSTRACT: The resonance properties of individual neurons in ento-rhinal cortex (EC) may contribute to their functional properties in awake, behaving rats. Models propose that entorhinal grid cells could arise from shifts in the intrinsic frequency of neurons caused by changes in membrane potential owing to depolarizing input from neurons coding velocity. To test for potential changes in intrinsic frequency, we meas-ured the resonance properties of neurons at different membrane poten-tials in neurons in medial and lateral EC. In medial entorhinal neurons, the resonant frequency of individual neurons decreased in a linear man-ner as the membrane potential was depolarized between 270 and 255 mV. At more hyperpolarized membrane potentials, cells asymptotically approached a maximum resonance frequency. Consistent with the previ-ous studies, near resting potential, the cells of the medial EC possessed a decreasing gradient of resonance frequency along the dorsal to ventral axis, and cells of the lateral EC lacked resonant properties, regardless of membrane potential or position along the medial to lateral axis within lateral EC. Application of 10 lM ZD7288, the H-channel blocker, abol-ished all resonant properties in MEC cells, and resulted in physiological properties very similar to lateral EC cells. These results on resonant properties show a clear change in frequency response with depolariza-tion that could contribute to the generation of grid cell firing properties in the medial EC. VC 2012 Wiley Periodicals, Inc. KEY WORDS: grid cells; stellate cells; lateral entorhinal cortex; spatial navigation; oscillatory interferenc