Stimulating dopamine D1 receptors increases the locomotor activity of developing rats

To determine the role of dopamine D1 receptors in the locomotor activity of developing rats, male offspring were habituated to an animal activity monitor and were then injected with the dopamine D1 receptor antagonist, SCH 23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl- 2,3,4,5-tetrahydro-(1 H)-3-benzazepine), or vehicle and returned to the activity monitors. 30 min later, they were injected with the dopamine D1 receptor agonist, SKF 38393 (R(+)-1-phenyl-2,3,4,5-tetrahydro-(1 H)-3-benzazepine-7,8-diol), or vehicle and were again placed in the activity boxes where their locomotor activity was monitored individually for 1 h. The litter was used as the unit for statistical analyses. There was a significant increase in the locomotor activity of 10- and 21-day-old offspring injected with SKF 38393. This effect was antagonized by pretreatment with SCH 23390. These data provide the strongest evidence to date that stimulation of dopamine D1 receptors increases the locomotor activity of habituated developing rats.