Effects of iontophoretically applied norepinephrine and dopamine on fimbria-evoked activity in the lateral septum.

Norepinephrine (NE) and dopamine (DA) are present in the lateral septum and presumably modulate activity of neurons in this region. Iontophoretic techniques were used to study the actions of NE and DA on stimulation-evoked activity of neurons in the lateral septum. Stimuli were applied to the fimbria, and the effects of NE and DA on field and unitary responses were recorded. Norepinephrine strongly inhibited the monosynaptically driven negative field potential and associated unitary responses. Dopamine produced an inhibitory, excitatory, or bimodal pattern of changes in the monosynaptic responses. Ventrally in the lateral septum, where a later polysynaptic excitatory response to fimbria stimulation was also seen, NE and DA augmented the polysynaptic responses, while producing inhibitory (NE) or inhibitory-excitatory (DA) effects on the monosynaptic response. Effects of NE and DA may play a role in modulation of the relay of descending hippocampal input to the medial septum, which is relayed by way of neurons in the lateral septum. In this manner catecholamines may indirectly produce modulatory effects in the theta pace-making cells in the medial septum.