Heterogenous Properties of Potassium Glutamate Neurones in the Ventral and Dorsal Zones of the CA1 Hippocampus

A comparative study of the electrophysiological characteristics of pyramidal (PC) neurons of the dorsal and ventral parts of the CA1 zone of the hippocampus of mice was conducted using the patch-clamp method in the “whole cell” configuration. The potassium load was used as a parameter for cell type discrimination (an increase in K+o from 3.0 to 8.5 mM in the medium). It has been established that two types of cells with different sensitivity to potassium are registered in both parts of the CA1 zone. In PC-A type cells, the burst activity caused by a step of current I (from 10 to 200 pA) is potentiated by potassium with an increase in K+o to 8.5 mM, whereas in PC-I type cells at currents I 100 pA there is no effect of potassium loading, and at currents ≥ 125 pA, suppression of burst activity is observed. The ratio of the number of PC-A/PC-I cells in the ventral and dorsal parts is 16 : 5 and 8 : 8, respectively. Potassium potentiation of burst activity is higher in ventral PC-A cells than in dorsal cells. Only in PC-A cells with potassium loading, the threshold current (Ith) decreases by 2.5 times and a spontaneous burst (pacemaker) activity is manifested. The Sag potential and the adaptation index of induced impulse activity are higher in the ventral PC-A cells than in the dorsal ones. The potassium load reduces the Sag potential. An analysis of the voltage characteristics shows that incoming and outgoing (predominantly) slow potassium currents are activated under potassium load. The currents in the ventral neurons of both types are 1.5–2.0 times lower than in the dorsal ones (at –100 mV and +20 mV). Taken together, these data suggest that K+ o-sensitive ventral PC-A cells can play an important role in hyper-excitation of neural networks and induction of epileptogenesis.