Researchers develop MRI technique to study brain anatomy in invertebrates
ATLANTA -- Scientists with the Center for Behavioral Neuroscience, a research consortium based at Georgia State University, have for the first time used a form of magnetic resonance imaging to reveal anatomical features of the nervous system in a live crayfish, a crustacean whose brain measures only 3 millimeters wide.
The technique, which is reported and highlighted in an accompanying commentary in the Dec. 15 issue of The Journal of Experimental Biology, provides a powerful new tool for understanding the neurobiology of behavior in invertebrate animal models.
Conventional MRI technology employs high-intensity magnetic fields to excite protons in the water molecules of soft tissue. Scanners detect the excitation and image cross-sectional slices of an organ, such as the brain. To image a live crayfish, whose physiology does not normally respond to magnetic fields, CBN researchers injected manganese, a contrast-enhancing agent that crayfish cells absorb, through a long tube into its circulatory system. The infusion took place while the animal was positioned inside the MRI scanner.
"Before injecting the manganese, we couldn't see the animal's brain at all," said Georgia State research scientist Jens Herberholz, the study's lead author. "But shortly after injecting it, we suddenly saw the brain light up like a Christmas tree and could easily discern its substructures."
Herberholz and his colleagues, including Georgia State professor Donald Edwards, Georgia State lab technician Christopher Mims, and Emory University's Xiaodong Zhang and Xiaoping Hu, developed manganese-enhanced MRI to study the crayfish brain. They discovered the technique also is effective in imaging other parts of the animal's body. In their pilot study, the scientists imaged a number of complex anatomical structures in the foregut that had never been seen in a live crayfish.
Crayfish serve as one of the best animal models for studying the neural bases of aggression and social hierarchies. During an initial encounter, two crayfish fight one another to establish dominant and subordinate roles. This interaction alters the physiology of each animal's brain at the cellular level.
Before manganese-enhanced MRI, researchers relied on dissections and electrophysiology to measure the neural changes associated with social behavior in crayfish. With the new technology, which is not harmful to crayfish, Herberholz said the same animal could be imaged repeatedly, enabling scientists to capture changes as they occur.
"This technique can be used to study invertebrate anatomy, but manganese also is a marker for neural activity," said Herberholz. "There are a wealth of potential applications for research on invertebrates, which serve as important model systems for understanding how neural circuitry produces behavior in all animals, including humans."
Georgia State University. December 2004.
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