BRAUBACH, O.R.*; DICKINSON, A.J.G.; EVANS, C.E.; CROLL, R.P.; Dalhousie University, Halifax, NS; Whitehead Institute, Cambridge, MA; Ottawa Health Research Institute, ON; Dalhousie University, Halifax, NS: Neural Control of the Velum in Larvae of the Gastropod, Ilyanassa obsoleta.

A ciliated velum is a common feature of molluscan development and is used by larvae to execute swimming and feeding behaviors. Here we examined the role of neural elements in the velum of the caenogastropod, Ilyanassa obsoleta. Through immunohistochemistry we showed putative innervation of velar cilia and muscles by monoaminergic and peptidergic fibers. Photoelectric recordings were then used to study the effects of the tentatively identified neurotransmitters upon ciliary beating on isolated pieces of velum. Under control conditions, the pre-oral cilia beat at 8.89 Hz (&plusmn 2.810). Serotonin increased, while catecholamines (both dopamine and norepinephrine) inhibited beating of the pre-oral cilia in dose-dependent manners. Catecholamines also significantly increased the frequency of momentary, isolated ciliary arrests, which occurred with no accompanying muscular contractions. The neuropeptides, FMRFamide and leu-enkephalin, had no detectable effects on ciliary beat frequency nor on the numbers of isolated ciliary arrests along the pre-oral band. However, applications of both neuropeptides induced numerous muscular contractions, which were accompanied by sustained ciliary arrests. In contrast to the pre-oral cilia, the post-oral cilia were recorded to beat at a frequency of 13.34 (&plusmn 2.109) Hz, even after application of catecholamines in concentrations that completely suppressed beating of the pre-oral cilia. This study has thus revealed elaborate neural control of velar effectors and information from this account lays the groundwork for future investigations aimed at understanding neural function in larval Gastropoda.