The trained circling rat: a model for inducing unilateral caudate dopamine metabolism

Despite considerable knowledge about brain dopamine in drug-induced and pathological states, the dynamic relationship of dopamine to voluntary motor behaviour is not established. In an effort to produce selective, lateralized changes in brain dopamine metabolism associated with movement, we have now developed an animal model in which normal rats were trained to circle for a sucrose/water reward. Turning direction was randomly assigned. The effect of circling on dopamine metabolism was studied by killing animals during the reinforcement period and measuring caudate dopamine and dihydroxyphenylacetic acid (DOPAC) concentrations in both sides of brain. Prior to turning, caudate dopamine and DOPAC levels were the same bilaterally. By contrast, animals killed after 20 min of circling showed a 67% increase in dopamine and a 46% increase in DOPAC concentrations in the caudate contralateral to the turning direction while the ipsilateral caudate showed no concentration changes. Such a rapid, massive unilateral increase in caudate dopamine metabolism suggests that dopamine neurones in contralateral caudate are selectively activated during circling behaviour. This model should be useful for further study of the relationships between neurotransmitter activity, regional brain physiology and voluntary movement, without the need for drugs or brain lesions.