## LSU Historical Dissertations and Theses

1998

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Richard C. Bruch

#### Abstract

The expression of 7 transmembrane domain receptors in olfactory receptor neurons of the channel catfish, Ictalurus punctatus was characterized. Due to disagreements in the literature as to how many odorant receptor genes are expressed in olfactory neurons, this study directly measured the number of odorant receptor gene transcripts expressed in single olfactory neurons. Individual olfactory receptor neurons can express more than one receptor, with some neurons expressing at least 3 to 4 receptors. These findings correlate with electrophysiological evidence but disagree with conclusions based on in situ hybridization. Receptors similar to odorant receptors are also expressed in taste buds, indicating a possible role for these receptors as detectors of taste stimuli. The odorant receptors may belong to a larger group of chemoreceptors that function as detectors of various signals depending on the cell in which they are expressed. The expression of metabotropic glutamate receptors (mGluR) in olfactory receptor neurons was also characterized. Two subtypes of these receptors, mGluR1 and mGluR3, were found in olfactory receptor neurons. These receptors were coexpressed with each other and with odorant receptors. Immunocytochemical analysis determined that these receptors were localized in the dendritic knobs and cilia of the neurons and electrophysiological evidence indicated that these receptors affected the response to the glutamate odorant. These findings support the hypothesis that mGluRs may have a function in olfaction. The last aim of this dissertation characterized the phosphorylation of the odorant and mGluRs by protein kinase C (PKC). An in vitro assay was used to determine if the PKCs known to be expressed in olfactory receptor neurons, PKC$\beta$ and PKC$\delta$, phosphorylate a consensus site found on both receptors. It was shown that mGluRs were phosphorylated by PKC$\beta$ and PKC$\delta$, with higher phosphorylation occurring by PKC$\beta$. PKC may thus function to desensitize mGluRs in vivo. The consensus site on the odorant receptor was only phosphorylated by PKC$\delta$. This site is located on extracellular loop 2 of the odorant receptor and when phosphorylated may function as a targeting signal during processing of the receptor.

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