Figure 7.

Schematic drawing depicting how the synergy of direct and indirect cholinergic septo-hippocampal pathways may coordinate the firing of principal cells in hippocampal subfield CA3. The solid black line indicates the membrane potential of a representative CA3 principal cell across time, the gray dotted line indicates the resting membrane potential, when no pathway is active, and the green vertical lines indicate the occurrence of action potentials. A, If no pathway is active, the membrane potential of the majority of CA3 principal cells shows only small deviations from the resting membrane potential and a regular spiking activity. B, Activation of the direct pathway hyperpolarizes the majority of CA3 principal neurons, which results in a strongly reduced spiking rate. C, In contrast, activation of the indirect pathway results in a rhythmic disinhibition of the majority of CA3 principal cells, which results in increased spiking activity. D, The synergistic action of both the direct and indirect cholinergic septo-hippocampal pathways results in reduced but phase-coupled spiking activity.