Three day old male Wistar rats were injected intracerebroventricularly (ICV) with 6-hydroxydopamine - 6-OHDA (133.4 µg, base form), 5,7-dihydroxytryptamine - 5,7-DHT (50 (g, base form) or with a control vehicle - 0.9% NaCl with 0.1% ascorbic acid (10 µl). After the animals had attained adulthood, quinpirole (the dopamine D2/D3 agonist) in doses of 0.0125 - 0.2 mg/kg IP was used to induce yawning behavior. In addition to the level of striatal dopamine, 5-hydroxytryptamine and their metabolites (DOPAC, 5-HIAA) were also measured by HPLC technique. Pretreatment with 5,7-DHT had no influence on quinpirole-induced yawning behavior as compared to control animals. 6-OHDA strongly diminished the effect of quinpirole. Results support previous findings that central DA D3 receptors seem to be presynaptic in nature.

Keywords: 6-hydroxydopamine, 5,7-Dihydroxytryptamine, Quinpirole, Yawning, biogenic amines, striatum