Tolerance to the behavioral effects of bromocriptine in cats.

Repeated daily administration of LSD and related hallucinogens produces tolerance to their behavioral effects. The objective was to test whether repeated administration of bromocriptine (BC) produced behavioral tolerance. Experiments began after 4 weeks of habituation and baseline measurements. Cats were then injected daily with BC (10 mg/kg i.p.) for 7 days. The frequency of 40 different behaviors and neurological signs were scored for 60 min after one h post-injection. There was a rapid tolerance to the 'emergent' behavior induced by BC. In the case of hallucinatory-like behavior/escape, tolerance to a second dose of BC one day after a first dose was virtually complete. A substantial tolerance to BC effects such as abortive grooming, increased investigatory-play behavior and grooming occurred within one day. The decrease in sleep produced by BC was absent at the fourth day. Limb flicks and body shakes decreased but persisted until the seventh day. There was also tolerance to emotional behavior (irritability, rage, threat, flight) but motor effects (circling, ataxia, hypokinesia) remained throughout the week. Autonomic reactions were unaffected by BC. The results indicated that the psychotomimetic effects (but not the motor or autonomic) of BC showed rapid and long-lasting tolerance. These studies suggest that BC-induced alterations in cats parallel parameters of action of hallucinogens in humans.