EFFECTS OF PUTATIVE DOPAMINE D-3 RECEPTOR AGONISTS, 7-OH-DPAT, AND QUINPIROLE, ON YAWNING, STEREOTYPY, AND BODY-TEMPERATURE IN RATS

7-OH-DPAT ((+/-)-2-(dipropylamino)-7-hydroxy-1,2,3,4-tetrahydronaphthalene) was recently identified as a dopamine receptor agonist having a > 100-, 1,000- and > 10,000-fold higher affinity for dopamine D-3 than for D-2, D-4 and D-1 receptors, respectively. Quinpirole (LY 171555) has also been reported to have a 113-fold greater affinity for dopamine D-3 receptors than for D-2 receptors. Therefore, we investigated the effects of these putative dopamine D-3 receptor agonists on yawning, stereotypy and rectal temperature in rats (N = 424). 7-OH-DPAT and quinpirole administered subcutaneously (SC) at respective low doses of 10-250 mu g/kg and 25-500 mu g/kg elicited yawning behavior. The yawning induced by these agents was blocked by spiperone (0.5 mg/kg, SC) and scopolamine (0.5 mg/kg, SC) but was increased by intraperitoneal (IP) administration of pindolol (20 mg/kg). The yawning was also potentiated after treatment with reserpine. 7-OH-DPAT and quinpirole at respective high doses of 0.25 mg/kg (SC) and 0.5 mg/kg (SC) evoked slight stereotypy such as sniffing and licking, and this effect was enhanced by a selective dopamine D, receptor agonist, SK&F 38393 (1-phenyl-2,3,4,5,-tetrahydro-(1H)-3-benzazepine-7,8-diol). 7-OH-DPAT (0.5 mg/kg, SC) and quinpirole (0.5 mg/kg, SC) decreased, but SK&F 38393 (10 mg/kg, SC) increased body temperature. However, the hyperthermia induced by SK&F 38393 was interestingly enhanced by 7-OH-DPAT and quinpirole. The present results demonstrate that 7-OH-DPAT and quinpirole evoke yawning at low doses and stereotypy at high doses, and that these agents reduce body temperature but enhance the hyperthermia induced by the dopamine D-1 receptor agonist SK&F 38393.