Interactions of septal evoked responses to stimulation of the fornix and medial forebrain bundle.

Gross and single unit septal evoked response to stimulation of the fornix and medial forebrain bundle (MFB) were studied in anesthetized, acutely prepared rats. Stimulation of the fornix and MFB produced short-latency antidromic and synaptic activation of localized groups of septal target cells. In addition, stimulation of either pathway produced inhibition of spontaneous single cell activity. The interactions of these responses were studied by delivering paired stimuli to the fornix and/or MFB. A prior stimulus to the fornix potentiated the responses of cell groups synaptically activated by subsequent fornical stimulation, but briefly depressed the sunaptic activation of septal cells by subsequent MFB stimulation. A prior stimulus to the MFB slightly potentiated the synaptic activation of septal cells by a subsequent MFB stimulus, but depressed the responses of cell groups synaptically activated by a subsequent stimulus to the fornix. These results were discussed in terms of their implications for septal organization and function.