Modelling the regulation of theta-rhythm by increasing afferent inflow in septal slices.

We recorded the neuronal activity of the medial region of the septum (MS-DB) intracellularly in guinea-pig septal slices. Electrical stimulation of the diagonal band (DB) evoked a low-threshold initial period of inhibition in the cells (20-280 msec in various cells). When the intensity of the stimulation was increased, this inhibitory phase shortened gradually or in a step-wise fashion, remaining unaltered in a portion of the cells with brief (40-50 msec) inhibition. The duration of the inhibition stabilized within a range of 30-60 msec. Many cells with single-spike background activity switched to generating post-inhibitory bursts at various levels of stimulation by current. Cells of the MS-DB with background rhythmical bursts always responded by phase locking to the stimulus. As a result, 58% of all of the cells of the MS-DB generated relatively short-latency, synchronized bursts when the level of afferent inflow was increased.