July 21, 2003

Hu uses crayfish to leap ahead in brain imaging


By Poul Olson

A Center for Behavioral Neuroscience (CBN) research team led by Emory’s Xiaoping Hu and Georgia State’s Don Edwards has developed a magnetic resonance imaging (MRI) technique using manganese for identifying anatomical structures and neural pathways in the crayfish brain.

The technique, which was adapted from an imaging technique used on rodents, employs the paramagnetic element manganese to image neural activity in living crayfish, whose brains measure only 3 millimeters wide. Initial tests of the technique have yielded detailed anatomical images of the crayfish brain that have never before been seen. Hu is professor of biomedical engineering and a Georgia Research Alliance Eminent Scholar in Imaging at the School of Medicine. Edwards is professor of biology at Georgia State.

“Prior to the development of this technology, it would take weeks of histology to identify simple structures in the crayfish brain,” said CBN post-doctoral fellow Jens Herberholz. “Now we can generate these images in just a few hours.”

Neuroscientists have been studying crayfish, an invertebrate, for more than 50 years. The simple neural network and well-defined social hierarchies of the crayfish make the animals ideal models for behavioral research, especially studies of aggression. In an initial encounter, two crayfish typically will fight one another until dominant/subordinate roles are established. These roles remain stable between the two animals, but may change when they encounter other crayfish.

A signature behavior associated with crayfish aggression is the tail flip. One type of tail flip indicates aggressiveness, while others signify subordination and the intention to escape. In their research, Edwards and Herberholz use conventional methods of electrophysiology to determine the neural circuitry of the tail flip. However, this technique can only delineate single neural pathways. With manganese-enhanced MRI, the scientists hope to determine activation of multiple pathways simultaneously.

“Our goal is to use manganese as an activity marker for identifying entire patterns of brain activation in dominant and subordinate crayfish,” Herberholz said. “We also want to compare changes that occur before and after an aggressive encounter.”

MRI technology, which was developed for imaging the human brain, has rarely been used to study a brain of the crayfish’s small size. To overcome the limitations of the technology, Hu and Herberholz are working to improve the resolution of their small-animal MRI scanner and develop a more sensitive coil customized to the crayfish’s head.

Manganese can be rapidly infused into the crayfish brain and is well tolerated. For these reasons, Hu projected it will be possible to conduct longitudinal studies of an individual crayfish using MRI technology to assess changes that occur in its brain over an extended period.

Hu and Edwards said the development of manganese-enhanced MRI for studying the crayfish could not have happened without the CBN. Hu recalled an initial meeting last year when Edwards spoke of his need to image the crayfish brain.

“I had never before worked with crayfish,” Hu said. “Now we have a powerful new tool for studying the invertebrate brain.”

The CBN, a science and technology center funded by the National Science Foundation with additional support from the Georgia Research Alliance, is a consortium of eight universities in the Atlanta area. CBN researchers study four aspects of behavioral neuroscience: fear, aggression, affiliation and reproduction.