The string test: an early behavioral change in thiamine deficiency.

Thiamine deficiency is a useful animal model of the interaction between biochemistry and behavior. Although numerous biochemical changes have been detected in thiamine deficiency, studies of behavioral changes are relatively scarce. We have modified and quantitated the string test, originally described by Miquel and Blasco, for application to thiamine-deficient rats. The string test is reproducible with time, and control rats have a narrow range of scores. 50% of rats treated with thiamine-deficient diet and pyrithiamine, a centrally-acting thiamine antagonist, have persistently decreased string test scores. This decrease is already present on day 5 of treatment, long before the onset of weight loss or neurological symptoms. Rats treated with oxythiamine, a peripherally acting thiamine antagonist, do not have decreased string test scores, even when anorectic and moribund. These findings suggest that impaired string test performance is a central system effect of thiamine deficiency, and that it may also be a useful behavioral parameter to follow in other animal models of metabolic encephalopathies.