Characteristics of unlimited access to self-administered stimulant infusions in dogs.

When drug-naive dogs were given unlimited access to response-contingent intravenous infusions of either d-amphetamine, phenmetrazine, or methylphenidate, a regular cycle of drug intake interspersed with periods of voluntary abstinence was seen. During the drug self-administration phases there was a marked increase in locomotor behavior and stereotypy along with a decrease in body weight; the rest periods were characterized by minimal activity. These results are similar to those observed when humans engage in high-dose intravenous abuse of psychomotor stimulants.