A potent transient outward current regulates excitability of dorsal raphe neurons

Activity of neurons in the dorsal raphe nucleus of the rat was recorded intracellularly in a brainstem slice. The neurons had a high input resistance, a linear I-V curve in the hyperpolarizing direction and a long membrane time constant. Broad action potentials were followed by a large afterhyperpolarization (AHP). This AHP removes partial inactivation of a potent transient outward rectifier that is activated by a subsequent depolarization of the neuron; it clamps the cell membrane at a potential slightly below firing level and blocks generation of action potentials for up to 100 ms. The transient rectification was sensitive to 4-aminopyridine (4-AP) but not to tetraethylammonium (TEA). It appears to share similar properties with those of IA seen elsewhere and to function in the regulation of interspike intervals of dorsal raphe (DR) neurons in vitro.