Rats treated chronically with the dopamine agonist quinpirole (0.5 mg/kg, twice weekly X 10) met 5 criteria for performance of compulsive checking. Specifically, in a large open-field with single small objects in 4 of 25 locales, quinpirole rats revisited two places/objects excessively often and rapidly, compared with other locations in the environment or saline controls. They performed a ritual-like set of behavioral acts at these two places/objects and stopped in relatively few locales before returning to the preferred places/objects. Finally, they shifted their behavior to a new location when the object was moved there. Clomipramine (10 mg/kg, daily) postponed but did not prevent the development of the quinpirole effect. Quinpiroleinduced compulsive checking may be an exaggeration of normal checking of home site in rats.Results suggest an animal model of obsessive-compulsive disorder and a role for dopamine in this disorder.

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Infants of rats and other mammals respond to a novel environment by becoming immobile, and then showing a process of motorial expansion called "warm-up." Starting from immobility, new types of movement are incorporated into the stream of behavior according to rather strict rules of order. Once a new type of movement has been performed, the infant reverts to it repeatedly. As a result, the earlier portion of the behavior appears stereotyped, giving the impression of an automatism. Later, as new types of movement are added to the infant's repertoire, the movement becomes increasingly rich and unpredictable, giving the impression of "free" behavior. The same rules of order operate within "warm-up" sequences of movement, and across such sequences, day by day. Concurrently, there is an increase in the amplitude of movements, resulting in a gradual expansion of the portion of the environment explored by the infant. The same rules of order seem to operate in the development of locomotion in more primitive vertebrates. In rats under the action of psychoactive drugs, the "warm-up" sequence is performed in reverse.

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