In vitro recording of raphe unit activity: evidence for endogenous rhythms in presumed serotonergic neurons.

The spontaneous activity of single neurons in the nucleus raphe dorsalis was recorded in vitro in mouse brain slices. The neurons displayed the slow and regular discharge pattern characteristic of raphe neurons recorded in vivo. When magnesium ion was added to increase the medium concentration to 20-30 mM for the purpose of inhibiting all synaptic transmission, raphe neurons continued to display the same discharge pattern and rate. The data suggest that the steady rhythmic firing of nucleus raphe dorsalis neurons is generated by an intracellular pacemaker mechanism.