Title

Neurochemical and Sensory Regulation of Metamorphosis in a Gastropod Mollusc

Date of Award

5-23-2010

Document Type

Honors Thesis

Department

Biology

First Advisor

Anthony Pires

Language

English

Abstract

The signal transduction pathway that regulates metamorphosis in larvae of Crepidula fornicata remains incompletely understood. While it has been established that catecholamines modulate metamorphosis through uncharacterized dopaminergic pathways, recent evidence suggests that these pathways are more complex and are dependent on more factors-both internal and external-than originally hypothesized. Of particular interest is the interaction between the internal regulatory mechanisms and the sensory experience of the larvae, the understanding of which may explain the "spontaneous metamorphosis" (metamorphosis in the absence of any inducer) observed in older larvae. The present study had two goals: to establish an explicit link between the modulation of metamorphosis by catecholamines and the sensory experience of the larvae, and to further explore the pharmacological agents thought to affect the hypothesized metamorphic pathway. In both young competent and older competent larvae, brief, defined periods of mechanosensory stimulation potentiated metamorphosis in response to the natural inducer, a result that was synaptically mediated and indicative of a link between larval sensory experience and the internal regulatory pathway. Elevation of exogenous dopamine (DA) did not consistently potentiate metamorphosis, and pharmacological experiments showed that treatment with 10- 7-10-7 M Sch-23390, a D1 antagonist, significantly increased the frequencies of metamorphosis. These two results challeng previously published studies that correlated the elevation endogenous catecholamines to the enhancement of metamorphosis, and suggested a positive relationship between activation of dopamine receptors and the potentiation of metamorphosis. While DA had no effect on metamorphosis, the drug treatment suggested that dopamine receptors play an important role in the regulation of metamorphosis. Physiological differences in larval abilities to respond to DA or in larval age may have affected these data, which nonetheless indicate that aminergic regulation of metamorphosis in this organism is far from being resolved.

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