Modulation of the excitability of septohippocampal terminals in the rat: relation to neuronal discharge rate.

The excitability of the axonal terminals of medial septal neurons projecting to the dentate gyrus has been studied in the anesthetized rat under various experimental conditions: spontaneous or drug-induced variations in neuronal soma discharge rate, conditioning stimulation of afferent pathways (perforant path, commissural pathway, fimbria-fornix). It has been observed that terminals excitability is inversely correlated to the level of neuronal ongoing activity. These effects were observed on virtually all septal neurons projecting to the dentate gyrus. Since about one half of the septohippocampal neurons are likely to be cholinergic, it follows that such a phenomenon is not transmitter specific.