Effects of repeated administration of d-amphetamine on agonistic behaviour of isolated male mice

Insufficient research has been carried out on the effects of repeated treatments with psychostimulants on agonistic behaviour. These effects were studied in mice using different schedules of administration and employing a low dose of amphetamine (1.5 mg/kg) which did not produce significant motor disruptions. After two injections, with a 5-day interval between them, antiaggressive effects (decreases in attack and increases in avoidance/flight behaviour) were found, which were similar to those observed after acute administration, in addition to an increase in defence. With a higher number of injections but with shorter intervals (daily treatment) the effects diminished and even disappeared. Tolerance to the antiaggressive as well as to motor effects (digging and non-social exploration) was found after 7 daily injections. The appearance of avoidance, defensive and flight behaviours in this model supports the inclusion of agonistic behaviour in rodent models of psychoses and highlights the importance of analysing the effects of different characteristics of the repeated treatment.