Effect of serotonin on cholinergic septo-hippocampal reactions in the rabbit

In noncurarized and unanaesthetized rabbits, the unit activity and field potentials evoked by testing stimulation of the medial septum were studied before, during (3-10 min), and in different periods (up. to 0.5 h) after microiontophoretic serotonin (5-OT) application or n. Raphe stimulation. In most of the cases, just during 5-OT application or n. Raphe stimulation, cholinergic septo-hippocampal responses decreased. Trace facilitatory effect of native and exogenously applied 5-OT on these responses was found. Increase of efficiency of cholinergic excitatory input was considered as a confirmation of the role of the serotonergic system in hippocampal long-term posttetanic potentiation after the stimulation of the medial septum. On the whole the data obtained indicate a complex modulatory 5-OT influence on the cholinergic septo-hippocampal responses.