SKF 38393 potentiates yawning induced by LY 171555: further evidence against the autoreceptor hypothesis of yawning.

The effect of concurrent D-1 receptor stimulation by SKF 38393 on the expression of yawning elicited by D-2 receptor stimulation with LY 171555 was studied in the rat. A low dose of SKF 38393 (2.5 mg/kg SC), while failed to elicit yawning, potentiated the effectiveness of LY 171555 in eliciting yawning at all the doses tested (12.5, 25 and 50 micrograms/kg SC) and this effect was abolished by SCH 23390 (0.012 mg/kg SC). The results indicate that in analogy with typical post-synaptic dopaminergic effects (hypermotility-stereotypy), yawning elicited by a D-2 agonist is facilitated by concurrent stimulation of D-1 receptors and therefore is consistent with previous evidence that yawning in response to a D-2 agonist is not mediated by autoreceptors.