By Leigh MacMillan
Dec. 15, 2000

Ensure—it's not just a dietary nutrition supplement anymore. Mice are crazy about it, and they will learn and correctly perform tasks just to get a lick or two of the sweet stuff.

Reward-based learning is central to some of the tests conducted in the Murine Neurobehavioral Laboratory, a new Vanderbilt University research resource devoted to testing neurological behaviors in mice. Michael P. McDonald, an assistant professor of pharmacology, fellow in the John F. Kennedy Center, and veteran rodent behavioral tester directs the core facility.

Mouse testing is in high demand as researchers use genetic manipulations to remove or add genes to the mouse genome, creating models to study gene functions and disease. The mouse is a good model organism because its genome is closely related to the human genome.

The new core facility offers testing rooms outfitted with specialized equipment to assess attention, impulsivity, anxiety, compulsive behavior, learning, memory, behaviors characteristic of autism, depression, schizophrenia and more.

"The degree of murine behavioral expertise available under one roof is extraordinary," said Randy D. Blakely, the Allan D. Bass Professor of Pharmacology and director of the Center for Molecular Neuroscience. "Before this core was established, many investigators had to work with collaborators outside of Vanderbilt."

Resources of the Murine Neurobehavioral Laboratory are also expected to play a key role in the analysis of mutant mice currently being developed by the Tennessee Mouse Genome Consortium. The TMGC, formed in 1998 to pool the state's resources and expertise for functional genomics—the analysis of genes and what they do—recently received a $12.7 million grant from the National Institute of Mental Health to develop and study mouse models for neurological diseases and disorders.

Of the series of testing rooms that make up the core facility, one is filled with "Skinner boxes"—named after the behaviorist B. F. Skinner who invented them. Each box, about the size of a 13" TV, is a sound-attenuated, light- and temperature-controlled chamber equipped with a testing cage and the electronics to operate cues like light and sound, to deliver the Ensure reward, and to record the mouse's actions.

Skinner boxes can be used to assess multiple behaviors, including attention, short-term memory, impulsivity, and behaviors related to depression and drug abuse. McDonald and graduate student Bill Siesser write the customized computer programs that operate the boxes.

Here's how a test for attention—using a Skinner box—works. A mouse is trained to poke its nose into a hole in the cage wall at the same time that a light is flashing there, in order to get a sweet reward. Nose-pokes replace the traditional lever-press because mice learn the tasks more quickly using this natural behavior, McDonald said.

Mice that serve as a model for attention deficit hyperactivity disorder (ADHD) do not respond as quickly and have more "misses" compared to normal mice.

To test impulsivity, a tone is added while the light flashes. The mouse learns that when the tone sounds, no reward is given. When normal mice hear the tone, they refrain from nose-pokes; the ADHD mice behave impulsively and poke whether the tone sounds or not.

In a similar test for children, a computer screen flashes letters, and the child is instructed to press the lever when he sees an "X."

"Children with ADHD miss more of the X's and press the lever more when they're not supposed to," McDonald said. "The mouse test is a very good analog."

In addition to the 30 tests currently set up, McDonald and Tsuyoshi Miyakawa, the research assistant professor of pharmacology who manages the core, offer advice and assistance to investigators interested in running different, specialized tests.

Some of the mice McDonald expects to analyze will come through the TMGC, which includes Vanderbilt, Meharry Medical College, the University of Tennessee (Knoxville and Memphis), St. Jude Children's Research Hospital, and Oak Ridge National Laboratory.

"The idea is for Oak Ridge to induce random mutations in mice, put them through a broad-based rapid screen, and pick out the mice with the most interesting phenotypes for further study," said McDonald.

The mutagenesis program supported by the new NIH grant will focus on creating random mutations in chromosomes thought to harbor culprit genes for psychiatric and neurological disorders. Dan Goldowitz, Ph.D., professor of Anatomy and Neurobiology at UT Health Science Center, is the principal investigator for the new grant.

McDonald has worked with Oak Ridge investigators to develop the initial behavioral screens, which will include rapid tests of locomotor activity, anxiety, sensory motor gating (related to autism and schizophrenia), depression, learning and memory. Vanderbilt and other consortium sites will carry out more extensive tests on selected mice.

"The consortium has possibilities for uncovering new models for behavioral and neurologic disorders," Blakely said. "It brings together the analytical power of multiple sites."

McDonald joined the Vanderbilt faculty in 1999 after working at the NIH, where he studied various models of Alzheimer's disease. While he was at the NIH, McDonald frequently assisted other investigators in setting up and conducting behavioral tests.

In his own research program, McDonald continues to focus on cognitive deficiencies in rodent models of Alzheimer's disease, ADHD and autism.

Mice that make too much of the amyloid precursor protein, one of the putative pathogenic agents of Alzheimer's, develop sticky plaques that resemble those seen in humans with Alzheimer's disease. McDonald's group is trying to reverse plaque formation and memory deficits in these mice by deleting a different gene for a protein called GD3 synthase. GD3 synthase participates in the synthesis of gangliosides, molecules that play a critical role in the formation of plaques in Alzheimer's brains.

If the experiments work, McDonald said, "it would suggest that partial removal of gangliosides in Alzheimer's patients, either genetically or with drugs, might be a promising avenue of therapy."

Murine Neurobehavioral Laboratory
http://bret.mc.vanderbilt.edu/mnl/index.htm

Tennessee Mouse Genome Consortium
http://tnmouse.org/index.html