Meeting Abstract

P1.72  Monday, Jan. 4  Regulation of Metamorphosis by Mechanosensory Stimulation and Catecholamines in a Gastropod PIRES, A.*; LEWIS, E.L.; Dickinson College; Dickinson College pires@dickinson.edu

Larvae of many marine invertebrates metamorphose in response to chemical cues in the environment. However, the chemosensory induction of metamorphosis may be modulated by other sensory experience, or by the biochemical context in which metamorphic signal transduction occurs. We report that in the caenogastropod Crepidula fornicata, brief exposure to the catecholamine precursor L-DOPA (10^-5 M, 30 min) resulted in 5-fold elevation of endogenous dopamine and potentiated metamorphosis in response to the natural cue, a pheromone derived from conspecific adults. Likely dopaminergic cells, localized by tyrosine-hydroxylase (TH) immunohistochemistry, were widely distributed in central ganglia and peripheral tissues. Among these cells were numerous peripheral somata with sensory morphology characterized by short apical processes leading to the epithelial surface, located around the mouth and in the tentacles and foot. Other TH-immunopositive cells with somata in the pedal ganglia innervated epithelia of the foot. Motivated by the hypothesis that mechanosensory activation of such cells may modulate metamorphosis, we stimulated larvae by gentle vortexing (10 Hz, 5 min) or repeated passage through a standardized pipet (aperture=1.5 x larval diameter, 50 cycles). Vortexing potentiated metamorphosis in response to natural cue in competent (13 d) larvae, and both treatments did so in younger (8 d) larvae that were becoming competent for metamorphosis. Mg⁺⁺ anesthesia during vortexing abolished the potentiation of metamorphosis, suggesting that the effect of mechanical stimulation was synaptically-mediated and not a consequence of tissue damage.