Neural control of the velum in larvae of the gastropod,Ilyanassa obsoleta

Abstract

SUMMARY Larval molluscs commonly use ciliated vela to swim and feed. In this study we used immunohistochemistry to demonstrate innervation of velar cilia and muscles by monoaminergic and peptidergic fibres in the caenogastropod, Ilyanassa obsoleta. Photoelectric recordings from pre-oral cilia on isolated pieces of velum revealed that serotonin increased, whereas catecholamines (dopamine and norepinephrine) decreased beat frequency at concentrations of 10-6 to 10-9 mol l-1. Catecholamines also increased the frequency of momentary, isolated arrests of pre-oral cilia, but failed to suppress beating of the post-oral cilia at these concentrations. The neuropeptides, FMRFamide and Leu-enkephalin, did not affect the frequency of ciliary beating or of isolated ciliary arrests, but did induce numerous muscular contractions, which were accompanied by sustained ciliary arrests. In terms of whole animal behaviour, serotonin caused larvae to concentrate toward the top of a water column and to increase feeding,whereas catecholamines caused larvae to concentrate toward the bottom of a water column and decrease feeding. Monoamine analogues which facilitated or opposed the effects of synthetic transmitters on larval behaviour, further suggested that these transmitters are released endogenously to control velar function. Finally, applications of peptides to whole larvae caused increased frequency of locomotory arrests. Together these findings demonstrate several potential roles for the nervous system in controlling larval behaviour in gastropods.

Nitric oxide signaling differentially affects habitat choice by two larval morphs of the sea slugAlderia willowi: mechanistic insight into evolutionary transitions in dispersal strategies.

“…In other gastropods, L-DOPA leads to an increase in dopamine production, either changing larval response to natural cues (Pires et al, 2000) or the timing of metamorphosis. Serotonin generally has an opposite effect to that of dopamine (Braubach et al, 2006;Yamamoto et al, 1999;Zega et al, 2005). Dopamine and serotonin had the expected opposing effects on metamorphosis in A. willowi, but functioned the same way in selective and non-selective larvae.…”

“…The neurotransmitters dopamine and serotonin typically have opposing effects on swimming and metamorphosis of molluscan larvae (Leise et al, 2004;Braubach et al, 2006;Yamamoto et al, 1999;Zega et al, 2005). Larvae were exposed to the dopamine precursor L-DOPA and to serotonin by diluting stock solutions to final concentrations of 10 ; assays were performed in the dark to prevent photochemical degradation of L-DOPA.…”

Evolutionary and Structural Diversification of the Larval Nervous System Among Marine Bryozoans

“…Recent developments in ubiquitous probes, confocal microscopy techniques, and three-dimensional image analyses have resulted in what has been called a new "golden age of morphology" (Harrison, 2002). Beyond the increased cytological detail provided by these techniques, functional inferences based on the details of neuronal connections and pathways have greatly improved our understanding of the stimuli received by larval sensory structures and their control over effector organs (Braubach et al, 2006). Regardless of the divergent morphologies observed between feeding and nonfceding larval forms, many marine invertebrate larval types are subject to convergent selective pressures due to the functional constraints of swimming in the plankton (Chia et al, 1984;Emlet, 1994), responding to external stimuli during active settlement behaviors before metamorphosis (Santagata, 2004a), and the remodeling of larval tissues during metamorphosis (Santagata, 2002;Heyland and Moroz, 2006).…”

Neurophysiological control of swimming behaviour, attachment and metamorphosis in black-footed abalone (Haliotis iris) larvae

“…While this is the first evidence of such an effect on larval behavior for this species, previous studies have investigated the neuronal control of larval ciliary movement in a number of mollusc species and considerable efforts have been made to characterize and map the neural circuit architectures involved (Jékely et al 2008). Results from these studies frequently reveal that patterns of cilia-based locomotion, velar ciliary beat frequency and the rate and duration of ciliary arrests are under dual innervation by excitory serotonergic and inhibitory dopaminergic mechanisms ( Croll & Dickinson 2004;Braubach et al 2006;Croll 2009). Our results demonstrate that swimming of H. iris larvae is quickly down-regulated by dopamine within the first two days, which infers a similar inhibitory dopaminergic role.…”