After 500 million years of evolution, what could the brains of a tobacco budworm moth and a mouse have in common? Very likely, it is something that humans share as well, which is why the National Institutes of Health (NIH) have recently given a $710,000 grant to Charles E. Linn, working in the lab of Wendell Roelofs, professor and chair of the Department of Entomology at Cornell's New York State Agricultural Experiment Station in Geneva, N.Y., and Neil Vickers, assistant professor in the biology department at the University of Utah. The three-year grant, "Discrimination of Complex Mixtures in Olfactory Signaling," involves microsurgery, behavioral testing and neurophysiological analysis of moths.
The scientists study the neurobiology and behavior of sex pheromone communication systems among insects. Pheromones are chemical signals produced by insects to attract mates in blends that are unique to that species. A major research problem is to understand how sensory information for individual chemicals is integrated in the brain and recognized as a specific pheromone blend. A key structural feature in the antennal lobe of insect brains, and in the olfactory bulb in mouse brains, are the olfactory glomeruli. The glomeruli route specific sensory inputs to different areas of the brain. In the antennal lobe of the male insect there is a specific macroglomerular complex -- a set of glomeruli involved in processing the pheromone signal. Each glomerulus in the complex receives sensory input of one specific pheromone component.
To find out how the routing occurs, Linn and Vickers are transplanting antennal imaginal disks between different moth species. The imaginal disks develop into the antennae of the donor species in the adult moth. At the experiment station, Kathy Poole, a technician in Roelofs' group, performs an interspecies transplant -- the first of its kind -- of the imaginal disks from larvae of two moth species, the tobacco budworm Heliothis virescens and the corn earworm Helicoverpa zea. Several weeks after the transplant, adult moths emerge. One day after they emerge, the moths are tested in a flight tunnel for response to each of the two species' pheromones. After testing they are shipped overnight to the University of Utah, where Vickers completes the neurophysiological component of the research the next day.
The project began as inter-race transplants in the European corn borer at Geneva, without Vickers' collaboration. Linn received a two-year seed grant from the National Science Foundation to allow development of the transplant procedure. After successfully developing the technique, Linn and Roelofs realized that future funding would require expertise in neurophysiology. It was at a pheromone conference in Europe that the collaboration with Vickers, who specializes in the study of the neural underpinnings of insect behavior and olfaction, was established. At this point, they also switched from the European corn borer to the tobacco budworm and corn earworm because of the depth of background information available for the two new moth species.
The NIH picked up on the project because of its underlying significance to their goal of understanding the sense of smell. It addresses questions relating to neuronal targeting, how the neurons' development and connections are directed. The olfactory glomeruli are particularly important because they play a very similar role in both invertebrates and vertebrates. "If you look at a flow diagram of a mouse brain and a flow diagram of a moth brain, the steps involved in the sensory detection -- first and second and third levels of processing -- are all completely analogous, so [NIH] is interested in glomerular organization in the same way we are," said Linn. Additionally, the moth brain is simpler and, as such, is a more attractive candidate for this type of study.
"Now that both labs have stable funding, we are looking forward a very productive period of research," said Linn. "Using a novel experimental paradigm that involves behavior, neuroanatomy and neurophysiology to address key problems that are relevant to a wide range of animal groups is very exciting and bound to produce a number of discoveries. Additionally, the more we learn about discrimination of pheromone blends, the better we can utilize pheromones in pest management strategies. And that is an equally important part of our research program at the experiment station."
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