(full paper is archived in the Miller Library)
Title: Serotonergic modulation of the neuronal pattern generator for swimming in Melibe leonina
Student Author(s): Morris, Shannon R.
Location: Final Papers Biology 175H
Date: June 1990
Abstract: The modulation of the central pattern generator for swimming in Melibe leonina by serotonin is the focus of this paper. Changes in behavior and neuronal firing patterns were monitored during the application of serotonin in order to elucidate how a neural circuit can be modified by a chemical transmitter. Behavioral observations indicate that micromolar concentrations of serotonin cause an increase in swimming frequency immediately after application in a whole animal preparation. Recordings from Interneuron 1 in the swimming circuit show that serotonin causes a decrease in burst duration and an increase in both instantaneous frequency and spikes/second/burst immediately upon applicaiton. These three parameters are all consistent with a transient acceleration and tightening of the burst firing pattern of Interneuron 1. After washout, a second application of serotonin to the same ganglia results in no significant changes in the firing pattern of Interneuron 1. Similar results were seen in a whole animal preparation; after 1-3 applications of serotonin no changes in swimming frequency occurred upon additional application. Two possible mechanisms are given to explain the effects of serotonin. One explanation is that serotonin works as hormones affecting all the cells within the swimming neural circuit. The other explanation is that serotonin works as a neurotransmitter at specific synapses between the cells of the circuit.