Effect of a novel environment on locomotor hyperactivity of rats induced by apomorphine in the nucleus accumbens.

Bilateral local injections into the nucleus accumbens of apomorphine in doses between 0.125 and 20 micrograms produced a dose-dependent increase of locomotor activity in rats recorded over the first 5-min period after placing the animals in a novel environment 7 min after the injection. Continuous records over consecutive 5-min periods revealed that the locomotor effect of apomorphine (1 microgram, bilaterally) declines rapidly within less than 30 min. Progressively weaker locomotor hyperactivity in the first 5-min periods was observed after prolongation of the interval between intra-accumbens injection of apomorphine and the commencement of testing from 7 to 12, 17 and 22 min, respectively. Since no difference was found between locomotor activity of animals just placed in the novel environment and that of animals already present in this environment for one or more periods of record at fixed times after the injection, it is concluded that exploration does not contribute to locomotor hyperactivity induced by intra-accumbens injections of apomorphine.