Sniffing, rearing and locomotor responses to the D-1 dopamine agonist R-SK&F 38393 and to apomorphine: differential interactions with the selective D-1 and D-2 antagonists SCH 23390 and metoclopramide.

The D-1 agonist R-SK&F 38393 induced non-stereotyped sniffing, rearing and locomotor responses that were blocked by the D-1 antagonist SCH 23390. The D-2 antagonist metoclopramide failed to block sniffing but blocked rearing and locomotion. Stereotyped sniffing and locomotion induced by apomorphine were each blocked by both antagonists. Either the criteria by which compounds are designated as D-1 or D-2 selective agents require revision, or else D-1 and D-2 mechanisms are able to reciprocally interact to influence the expression of behaviour initiated by stimulation of either receptor subtype.