Which GABA Receptors Are Expressed in the Zebrafish Lateral Line?

The presence of the neurotransmitter GABA in the mammalian inner ear is well established, yet its role in regulating inner ear cell function is less clear. We seek to understand the role of the GABA in the inner ear using the model organism zebrafish. Zebrafish possess a sense that humans do not: they can detect water movement with their lateral line system. Zebrafish sense water movement with cells that project out from the body of the fish into the environment. These so-called hair cells are remarkably similar to the sensory cells of the cochlea and semi-circular canals. Because they are on the outside of the zebrafish, and not behind a bony skull, lateral line hair cells are easily accessible to study. Therefore, we are determining if we can use the lateral line system to understand more about GABA in the inner ear. We have used RNA extraction and RT-PCR to detect the expression of 27 GABA-related genes in zebrafish. We have also identified a novel alternative exon in one isoform. Overall, our results suggest that the genes expressed in the lateral line are orthologs of genes expressed in the mammalian inner ear, and thus zebrafish appear to be an appropriate model organism with which to further study GABA function in the inner ear

Is the Zebrafish a Good Model Organism to Study the Role of GABA in the Inner Ear?

A key part of sound perception requires cells in the inner ear to adjust their sensitivity based on background noise—consider how startling a loud clap is in a quiet classroom versus a rock concert. This adjustment is thought to occur by neurons from the brain communicating with ear cells via chemical neurotransmitters. Our lab seeks to understand how one neurotransmitter in particular, GABA, adjusts the sensitivity of ear cells. Although the presence of GABA in the inner ear has been known for decades, its role in regulating inner ear cell function is only beginning to be understood. Our goal is to determine if we can use the zebrafish model organism to further understand the role of GABA. We plan to accomplish this by determining if the GABAergic system in zebrafish is similar to what is found in mammals. Zebrafish have a sixth sense that humans do not possess – they can sense water movement with their lateral line sensory system. The sensory cells within the lateral line, called hair cells, project out from the body of the fish in order to respond to the movement of water. These hair cells are remarkably similar to the cells within the human inner ear that sense sound waves and head position. Because they are located on the outside of the zebrafish body, as opposed to behind a bony skull, lateral line hair cells are easily accessible for study. Therefore, we are determining if we can use the lateral line system to understand more about the mammalian inner ear with respect to GABA signaling. We have used RNA extraction and RT-PCR to look for the expression of 27 genes in zebrafish that are important for GABA signaling. Our results suggest that the genes expressed in the lateral line are orthologs of genes expressed in the mammalian inner ear, and therefore the zebrafish is an appropriate model organism with which to further study the role of GABA in the inner ear