Date of Award

4-22-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. Deborah Baro - Chair

Second Advisor

Dr. Susanna Greer

Third Advisor

Dr. Teryl Frey

Fourth Advisor

Dr. Paul Katz

Fifth Advisor

Dr. Charles Derby

Abstract

Neural circuit flexibility is fundamental to the production of adaptable behaviors. Invertebrate models offer relatively simple networks consisting of large, identifiable neurons that are useful for investigating the electrophysiological properties that contribute to circuit output. In particular, central pattern generating circuits within the crustacean stomatogastric nervous system have been well characterized with regard to their synaptic connectivities, cellular properties, and response to modulatory influences. Monoaminergic modulation is essential for the production of adaptable circuit output in most species. Monoamines, such as dopamine and serotonin, signal via metabotropic receptors, which activate intracellular signaling cascades. Many of the neuronal and network targets of monoaminergic modulation in the crustacean stomatogastric nervous system are known, but nothing is known of the signal transduction cascades that mediate the biophysical response. This work represents a thorough characterization of monoaminergic receptors in the crustacean stomatogastric nervous system. We took advantage of the close phylogenetic relationship between crustaceans and insects to clone monoaminergic receptors from the spiny lobster. Using a novel database mining strategy, we were able to identify several uncharacterized monoaminergic receptors in the Panulirus interruptus genome. We cloned one serotonin (5-HT2βPan) and three dopamine receptors (D1αPan, D1βPan, and D2αPan), and characterized them with regard to G protein coupling and signal transduction cascades. We used a heterologous expression system to show that G protein couplings and signaling properties of monoaminergic receptors are strongly conserved among vertebrate and invertebrate species. This work further shows that DAR-G protein couplings in the stomatogastric nervous system are unique for a given receptor subtype, and receptors can couple to multiple signaling pathways, similar to their mammalian homologs. Custom made antibodies were used to localize monoamine receptors in the stomatogastric ganglion, and in identified neurons. Pyloric neurons show unique receptor expression profiles, which supports the idea of receptor expression as an underlying mechanism for cell-type specific effects of a given modulator. Receptors are localized to the synaptic neuropil, but are not expressed in the membrane of large diameter processes or the soma. The localization of dopamine receptors in identified pyloric neurons suggests that they may respond to synaptic, paracrine or neurohormonal dopamine signals. This work also supports the idea that different types of signals can be generated by a single receptor.

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Biology Commons

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