Multitiered strategy for behavioral phenotyping of transgenic and knockout mice

A. Holmes and J.N. Crawley

Experimental Therapeutics Branch, National Institute of Mental Health, NIH, Bethesda, MD, U.S.A.

The emergence of techniques that permit the manipulation of the brain at the genetic level has provided neuroscience with a valuable research tool. Studying the behavioral phenotypes of transgenic mice (which have additional gene products) and gene knockout mice (in which a gene is inactivated) can be a powerful means to understand the neural basis of behavior and the pathophysiology of neurological and neuropsychiatric disorders. There are also important caveats and limitations to the gene mutation approach to studying behavior. One central concern is the potential for general deficits in health and neurological function, or impaired sensory and motor abilities, to impact performance in behavioral tests.

In our laboratory we have employed a multitiered strategy for behavioral phenotyping of transgenic and knockout mice to explain any specific behavioral phenotype in the broader context of sensory, motor and neurological function, and thus reduce the potential for false positive/negative interpretations of mutant phenotypes. Preliminary observations begin with direct monitoring of home cage behavior for any abnormal hyperactivity, aggressive behavior, sleeping and nesting patterns, or poor feeding. Next mice undergo a comparison with wild-type littermates on indices of general health, such as the condition of the fur, skin and whiskers, limb tone, body weight, and core body temperature. Sensory and neurological functions are measured using a battery of simple tests for basic eye, ear, and whisker reflexes, acoustic startle responses, nociceptive responses, and visual perception. Lastly, muscular strength and motor abilities are tested by use of the wire hang test, accelerating rotarod, ring test for catalepsy, and locomotor activity in a novel open field. A mutant mouse that appears to be in good health and which has grossly intact neurological function is a suitable subject for more sophisticated tests which focus on a particular behavioral domain. For example, to test for a learning and memory phenotype, the Morris water maze, T-maze, Barnes maze and social transmission of food preferences are examples of hippocampally-mediated tests. As an important complement to these spatial memory tasks, the cued and contextual fear conditioning paradigm is a popular means to test for amygdala-dependent memory function in mutant mice.

Using the multitiered strategy, we have recently examined the behavioral phenotype of transgenic mice overexpressing galanin, a neuropeptide that has been linked with Alzheimer's disease pathology and cognitive deficits. GAL-tg mice were found to be healthy and normal across the range of neurological, sensory and motor tests described. Against this background, testing for learning and memory in the Morris water maze revealed a highly specific deficit in spatial memory in adult and aged GAL-tg mice.

Paper presented at Measuring Behavior 2000, 3rd International Conference on Methods and Techniques in Behavioral Research, 15-18 August 2000, Nijmegen, The Netherlands

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