Glutamate receptors in the developing auditory system of chick

The main goal of this thesis was to identify differences in AMPA receptor subunit structure and function in auditory and nonauditory neurons. These data could then serve as a possible explanation for the unique properties possessed by AMPA receptors in the auditory systems. Initially, as the sequence of splice variants of chick AMPA receptors was unavailable, the first step thus involved cloning the flip and flop isoforms of GluRs 1-4. Next, enzymes that cut either the flip or the flop isoform were identified and used ascertain the relative abundances of flip and flop isoforms of AMPA receptor subunit mRNA. The study showed that chick AMPA receptors exist as flip and flop isoforms and are differentially distributed in the CNS chick. Multiple band obtained when GluR4 was amplified from the chick CNS, suggested that additional splice variants may be present. Sequencing confirmed that three additional variants were present, caused by splicing at a c-terminal site. One of these variants had been previously described in rat, whereas the other two were novel. The spatial and temporal distribution of these novel isoforms and their splice variants were examined. Additionally, the distribution of these variants in specific cell-types was examined. AMPA receptors on auditory neurons posses highly specialized physiological properties. We hypothesized that these unique physiological properties were a function of the molecular make-up of the receptor. The study showed that auditory AMPA receptors are enriched in GluRs 3 and 4 flop and deficient in GluR2. Additionally, auditory neurons are highly permeable to calcium and this permeability is not due to lake of expression of GluR2 or a lack of RNA editing at the Q/R site. It is hypothesized that the high calcium permeability may be due to differential incorporation of GluR2 into AMPA receptors on the surface of these neurons. The data in this thesis will be an invaluable tool not only to researchers who study the auditory system but to the neuroscience community at large, given the importance of AMPA receptors in the nervous system.