Induction of RSA-like oscillations in both the in-vitro and in-vivo hippocampus.

Although the medial septum is generally regarded as the 'pacemaker' of hippocampal Rhythmical Slow Activity (RSA) its precise role has recently been queried, as RSA-like activity can be recorded from in-vitro juvenile hippocampal slices. Here we demonstrate that a critical condition for in-vitro RSA generation in the adult slice is concurrent excitation (provided by bath application of either carbachol or glutamate) and disinhibition (bath application of picrotoxin). Furthermore, under similar conditions of excitation and disinhibition, the in-vivo adult hippocampus is also capable of generating RSA-like oscillations in the absence of septal influences. These findings suggest that, in-vivo, the medial septum may modulate an intrinsically generated hippocampal oscillation through its excitatory and disinhibitory efferents.