PIRTLE, T.J.*; SATTERLIE, R.A.: Ionic currents underlying the activity of swim interneurons of Clione limacina

The marine pteropod mollusk, Clione limacina is used as a model system to study the cellular basis of locomotor speed change. Clione swim by alternate dorsal and ventral flexion of wing-like parapodia. The swim central pattern generator is located in the pedal ganglia and consists of two groups of interneurons — one group of interneuron (d-interneurons) controls the dorsal bend of the wing and another group (v-interneurons) controls the ventral bend of the wing. The two antagonistic groups of interneurons interact through reciprocal inhibitory synapses. Thus, when one group of interneuron is active it simultaneously inhibits activity in the other group. Additionally, both d-interneurons and v-interneurons exhibit postinhibitory rebound (PIR). Jointly, the reciprocal inhibitory synaptic connections between d-interneurons and v-interneurons and PIR generate the basic motor rhythm. Here we describe preliminary data that suggests that isolated Clione swim interneurons exhibit three inward currents that include an inward current that generates PIR (I_PIR). In addition, Clione swim interneurons exhibit at least two outward currents — one that closely resembles a delayed rectifier type K⁺-current (I_K) and one that closely resembles the fast transitory K⁺-current (I_A). Changes in swimming speed are produced in part by serotonin’s modulation of the intrinsic properties of swim interneurons. We are currently investigating serotonin’s modulation of identified currents in Clione swim interneurons.