CAIN, SD; BALTZLEY, MJ: The Distribution of Neurotransmitters Controlling the Foot Cilia of the Sea Slug Tritonia diomedea

The nudibranch mollusc Tritonia diomedea, which is known to orient to water currents and the Earth’s magnetic field, primarily locomotes using ciliary action of cells that cover the surface of the foot. The activity of these cilia is controlled by central neurons, a few of which have been individually identified (i.e., Pd5, Pd6 and Pd21). In addition, two neurotransmitters, TPep and 5HT, have been shown to stimulate beating of the ciliated foot epithelial cells. To further determine the types and spatial relationships of neural regulatory pathways controlling cilia beating, we investigated the distribution of four different neurotransmitters (TPep, 5HT, dopamine and acetylcholine) within the foot epithelium as well as the CNS. Although TPep and 5HT colocalize in a few cells in the CNS, no colocalization was detected in the foot epithelium. Because both of these transmitters have been shown to stimulate ciliary beating, our results suggest that two independent pathways exist to stimulate the rate of ciliary transport and hence the rate of crawling in Tritonia. In addition, choline acetyl-transferase (ACh) colocalized with TPep in Pd5 and Pd6 and foot tissue. Dopamine was present in the foot as revealed by anti-tyrosine hydroxylase staining. Preliminary studies indicated that the role of dopamine might be to cause rapid ciliary arrest, a function not previously identified in Tritonia. These transmitter systems represent the motor output of the behavioral pathways controlling directed movement, and provide a platform for investigating the interactions of these pathways in controlling orientation behavior.