Serotonin increases the frequency of light-elicited discrete waves in type-B photoreceptors of Hermissenda.

Serotonin (5-HT) produces both short- and long-term enhancement of generator potentials in identified type B-photoreceptors of Hermissenda. The actions of 5-HT have been shown to modulate both light- and voltage-dependent conductances. To further examine light-dependent processes we studied spontaneous and light-elicited discrete waves in the presence of 5-HT. Serotonin significantly increased the frequency of light-elicited discrete waves without initially increasing spontaneous discrete waves recorded in the dark. The increase in discrete wave frequency produced by 5-HT could not be described by a simple Poisson process, since the observed interval distribution after 5-HT application deviated significantly from the predicted exponential interval distribution.