SEROTONERGIC MODULATION OF SWIMMING SPEED IN THE PTEROPOD MOLLUSK CLIONE-LIMACINA .2. PERIPHERAL MODULATORY NEURONS

A symmetrical cluster of serotonin-immunoreactive neurons in the pedal ganglia of Clione limacina has been described morphologically and phy siologically. At least five of the cluster neurons send axons to the i psilateral wing that branch throughout the entire wing area. Activatio n of these cells did not produce a motor effect in non-swimming prepar ations, but did enhance contractility in swimming preparations. Activi ty in the pedal neurons did not produce detectable central effects as neither swim interneuron nor swim motor neuron activities were altered . Most notable was a lack of a change in swim frequency, a characteris tic of swim acceleration. Activity in the pedal neurons did enhance th e size of muscle junctional potentials and spikelike responses, but on ly in slow-twitch muscles. The peripheral modulatory effect was blocke d by the serotonin antagonist mianserin.