Potentiation of yawning responses to the dopamine receptor agonists B-HT 920 and SND 919 by pindolol in the rat.

Subcutaneous injection of B-HT 920, a dopamine D2-receptor agonist, in doses ranging from 5 to 100 micrograms/kg, induced yawning behavior in rats. Yawning was also elicited by low doses (25-500 micrograms/kg sc) of SND 919, a newly synthesized dopamine receptor agonist. The yawning evoked by B-HT 920 or SND 919 was increased by the beta-adrenoceptor antagonist pindolol (20 mg/kg ip) which alone did not induce yawning. Stereotyped behavior did not appear after B-HT 920 or SND 919 given alone or in combination with pindolol. The results suggest that SND 919 as well as B-HT 920 has stimulatory activity at dopamine D2-receptors, and that pindolol may exert its enhancement of the yawning response to dopamine receptor agonists via blockade of beta-adrenoceptors.