低周波および高周波ネットワーク・オシレーションを介した新皮質‐海馬間相互作用

抄録

The neocortex and the hippocampus are connected by way of the entorhinal cortex and the subiculum. To examine the ongoing network interactions among these cortical areas during neocortical slow (<1 Hz) oscillations and hippocampal fast (80-250 Hz) oscillations, we recorded intracellular potentials in single neocortical, entorhinal, subicular, and hippocampal neurons, together with hippocampal field potentials and multi-unit activity in adult rats, anesthetized with urethane and ketamine. We have found that 1) most entorhinal and subicular neurons displayed slow oscillations, including bimodal depolarizing (up) and hyperpolarizing (down) states, in synchrony with neocortical slow oscillations, 2) no bimodal up-down distribution of the membrane potential was present in hippocampal CA3 and CA1 neurons, 3) while hippocampal granule cells were directly driven by the up state (by way of the entorhinal input), CA3 and CA1 neurons discharged during both up and down states, 4) gamma (30-80 Hz) and fast (ripple) oscillations were observed in the hippocampal CA1 area irrespective of the up-down transition, 5) hippocampal ripples and neocortical slow oscillations correlated only weakly and at a long (sec) time scale. These observations suggest that entorhinal and subicular regions are "neocortex-like" and distinct from hippoocampal circuits that lack the necessary mechanisms for the maintenance of slow oscillations; hippocampal networks can generate self-organized gamma and ripple activities independent of the neocortical/entorhinal slow oscillations. [J Physiol Sci. 2006;56 Suppl:S14]