The Function of Antennal Lobe Interneurons in Olfactory Behavior in Drosophila melanogaster. A.J. Alldredge , J.S. de Belle. Biological Sciences, University of Nevada,Las Vegas, Las Vegas, NV.

   Recent success in finding odor receptors in Drosophila emphasizes the need to understand how olfactory input is processed in the brain. It is thought that antennal lobe (AL) glomeruli are the initial encoding stations that receive sensory input from the antennal nerve (AN). Approximately 2000 AN neurons, which transmit sensory information from an infinite number of different odors and concentrations in the flies' environment, converge onto the forty-three glomeruli in each AL. This suggests that odor quality and concentration is processed in a combinatorial fashion, requiring communication among glomeruli. Interneurons that project into the glomeruli provide the means for inter-glomerular communication. The resulting code can then be directed to and interpreted by other areas of the brain. Removing interneurons by hydroxyurea (HU) ablation during a specific time point in development prevents communication among the glomeruli, creating a system for looking at the degree to which inter-glomerular communication is required for odor discrimination in the antennal lobe. Because HU ablation removes mushroom body Kenyon cells as well as the AL interneurons, it is necessary to identify the AL as the exclusive center for preliminary odor discrimination. This can be accomplished by testing progeny of flies that express tetanus toxin crossed to GAL4 lines specific to other areas of the brain and flies with known structural mutants for the ability to respond properly to given odors. An understanding of this system provides a model for the brain's capacity to take a specific stimulus from the environment and encode information that is meaningful for higher brain structures.