D2 receptor blockade in the dorsal raphe increases quinpirole-induced locomotor excitation.

The D2/D3 dopamine receptor agonist quinpirole (QNP) produces biphasic effects on locomotion and can induce oral behaviour. To determine whether or not these behaviours result from actions of QNP at D2 receptors located in the dorsal raphe, nucleus (DRN), rats were pretreated intra-DRN with the selective dopamine D2 receptor antagonist, raclopride (0, 1 or 2 microg) prior to an acute peripheral injection of QNP (0 or 0.5 mg/kg, s.c.). Intra-DRN raclopride did not affect QNP-induced oral activity or QNP-induced locomotor inhibition. However, the high dose of raclopride potentiated QNP-induced locomotor excitation. These data suggest that D2 receptor activation in the DRN suppresses QNP-induced locomotor excitation, an effect that may be related to D2 receptor-mediated alterations in serotonin transmission.