Story posted August 26, 2010
The first reaction is usually disbelief. But when people figure out that Katie DuBois’11 is perfectly serious about how she spent the summer, skepticism quickly turns to fascination.
DuBois, a biology major, has been peering inside an open black cube where a baseball-sized Styrofoam ball is perched, spinning erratically, atop an air blower. The spinning ball has a highly unusual power source, says DuBois: "It's a cricket."
DuBois is one of seven student researchers who have been working with Bowdoin Associate Professor of Biology and Neuroscience Hadley Horch this summer to develop new ways of studying auditory systems in crickets. With the help of Laboratory Instructor Steve Hauptman, she helped to build the spinning device, best described as a cricket "treadmill," which is giving the researchers important new data on the cricket's remarkable ability to regenerate damaged auditory neurons.
DuBois demonstrates how the device works:
She carefully places a cricket on the ball, securing it with a tiny helmet-like dollop of non-toxic epoxy that she will later remove. At first, the cricket walks quickly, spinning the ball as it moves. Then it stands suddenly still. DuBois leans in and blows on the cricket from one side. The cricket starts walking in the opposite direction. A sensor underneath the air chamber records the data, including the cricket’s speed and direction, which appear on a nearby computer screen.
Eventually, these data will be used to analyze the cricket’s response to external auditory cues. The researchers will play the sound of a male cricket to a female, as well as the sound of a predatory bat. Using their auditory systems, the female will determine if the sounds are threatening or appealing and respond accordingly—walking away from or toward the sound.
It sounds straightforward, except that the crickets in Horch’s lab are different than the average basement-dwelling variety: They don’t have fully functioning auditory systems.
Each cricket has had one of its ears removed—located on its foreleg. In most organisms this would be irreparable damage, but, as Horch explains: "It turns out that the cricket is doing something highly unusual in response to injury, something very few other animals do—regenerating its auditory nerves."
Dendrites (branches that extend out from a neuron) typically respect the midline and stay on one side of the body. When one of the cricket’s ears is removed, however, the dendrites of those auditory neurons grow across the midline and communicate with the auditory neurons of the opposite ear. " This is one of the most elegant and complex examples of neuronal regeneration known," says Horch.
The processes by which this regeneration occurs are only just beginning to be understood. As DuBois's co-researcher Alex Pfister ’10 puts it: "We know the dendrites grow, but we don’t know much more.”
And they don’t know how the injured crickets will respond to the auditory cues. “If we can use the motion-tracking behavior as an assay to confirm when the animal has recovered from injury," observes Horch, "we can start disrupting certain molecules within the cricket and asking what kind of behavioral effects these manipulations have.”
Pfister has spent the summer trying to devise another way of viewing the actual regenerative process. She anaesthetizes the cricket and injects an AN-2 neuron (an auditory neuron) with fluorescent dye that can be viewed using a confocal microscope. “We don’t know if there’s variation in the regeneration,” she says. “We don’t know why the nerves regenerate or what roles genes or proteins play in regeneration.”
The researchers are particularly curious about the role that semaphorin, a protein involved in dendrite development. Previous studies of adult mammals have found that the level of semaphorin surges in response to injuries to the nervous system. If semaphorin or some other molecule is the key to the cricket’s ability to regenerate damaged nerves after an injury, the findings could reach far beyond the cricket treadmill.
“By investigating the exceptional case we may learn something that could be therapeutically useful for other organisms—including humans,” says Horch.
DuBois and Pfister's summer research fellowships were supported by a grant from the Maine IDeA Network of Biomedical Research Excellence (INBRE).
All photos by Michele Stapleton.