Differential actions of serotonin antagonists on two behavioral models of serotonin receptor activation in the rat

Ligand binding studies have identified certain serotonin (5-HI) antagonists with selective affinity for 5-HI2 receptors and other serotonin antagonists with affinity for both 5-HI1 and 5-HI2 receptors. This study compared the actions of ketansenn and pipamperone, selective 5-HI2 receptor antagonists, with meter-goline and methysergide, nonselective 5-HI antagonists, on two behavioral responses in rats that are produced by the activation of 5-HI receptors: 1) the head shake response and 2) the 5-HI syndrome. Both the selective and the nonselective 5-HI antag-onists blocked the head shake response produced by 5-hydroxy-L-tryptophan. The order of relative potency was: metergoline> ketanserin> pipamperone> methysergide. All four antagonists also blocked the head shake response produced by the 5-HI agonist quipazine. In contrast, the symptoms of the 5-HI syn