[Effect of acetylcholine, noradrenaline and serotonin on septal neurons in vitro]

Effects of Ach, NE and 5HT, introduced into the bath medium, were investigated in 75 units recorded extracellularly in slices of the guinea pig septum. Equally high reactivity to the all three substances was observed (86-88% of reactive units). Ach evoked slowly developing moderate increase of spontaneous activity in 63% of the units; in 24% it enhanced, accelerated, or evoked rhythmic bursts (1-3,5 per s). NE evoked higher and rapidly developing activation in 73% of the units; 5HT increased or decreased the level of activity in equal proportions of the cells (45% each). Both NE and 5HT neither provoked nor intensified rhythmic burst activity. Activatory and inhibitory effects of NE, 5HT and Ach were not blocked in the medium with high Mg2+ concentration. Burst activity disappeared in this condition in some units, but was preserved in the others. It is concluded that in some of the septal units transmitter substances modulate the activity of endogenous pacemaker mechanism.