Peed in the Pteropod Na Rvous System and Wings

been describ neurons and neuromuscu 1989b; Satte Spencer, 1985; Satterlie et al. 1985, 1990). The pattern generator is relatively simple, producing a two-phase output that is translated into dorsal and ventral flexions of a pair of wing-like parapodia. Two forms of swimming, slow and fast, have been described which reflect plasticity in the organization of the pattern generator since the change from slow to fast swimming involves the activation of additional interneurons (Arshavsky et al. 1985d, 1989b). All but one type of swim interneuron and all swim motor neurons are restricted to the pedal ganglia. The swim musculature includes slow-twitch fatigue-resistant and fast-twitch fatigable fibers, the former being activated by a population of small motor neurons during slow swimming, while the latter are recruited into activity by a pair of large motor neurons during fast swimming (Satterlie, 1991a, 1993; Satterlie et al. 1990). This change of swimming be abr ddition w or fa wimmi to the almost entirely restricted to the pedal ganglia, the two-speed organization of the neuromuscular system, and our current anatomical and physiological understanding of swim system components, the Clione limacina swimming system represents an excellent model system for investigation of neuronal mechanisms of control and modulation of locomotory speed. One trigger for acceleration of swimming in Clione limacina is bath application or local application of serotonin (5hydroxytryptamine, 5-HT), which produces both an increase in the frequency of swimming movements and an increase in the force of wing contractions (Arshavsky et al. 1985a; Satterlie, 1989; Kabotyansky and Sakharov, 1990). These behavioral changes are characteristic of fast swimming, suggesting that serotonergic inputs to the swimming system may be involved in at least some forms of swim acceleration. Similarly, serotonin The Journal of Exp Printed in Great B