Effects of physostigmine on septo-hippocampal averaged evoked field potentials.

Field potentials were elicited in the CA3 field of freely-moving animals by paired-pulse stimulation of the ventral portion of the medial septum before and after exposure to physotigmine. Physostigmine had no effect on response components elicited by a single stimulus or by the first stimulus of a pulse pair. However, the amplitude of a late positive component elicited by the second stimulus of a pair was increased significantly following physostigmine. These results suggest that activity in a cholinergic portion of the septo-hippocampal pathway may serve to modulate the responsiveness of neurons in the CA3 field to subsequent stimulation.