ROLE OF 5-HT1A RECEPTORS IN THE ANTINOCICEPTIVE ACTION OF 8-HYDROXY-2(DI-N-PROPYLAMINO)TETRALIN IN THE RAT

The role of 5-HT1A receptors in the antinociceptive action of 8-hydrox y-2-(di-n-propylamino)tetralin (8-OH-DPAT) was investigated by using t he shock titration test in rats. A subcutaneous injection of 300 mu g/ kg 8-OH-DPAT significantly raised the threshold for flinching, jumping and vocalization whereas 100 mu g/kg only inhibited the flinch respon se. l-Propranolol and butyl-3-4-(2-methoxyphenyl)piperazin-1-yl-2-phen yl propanamide dihydrochloride], (+)-WAY100135, two antagonists at 5-H T1A receptors at 10 mg/kg s.c. antagonized the effect of 300 mu g/kg 8 -OH-DPAT on all measures. The effect of 300 mu g/kg 8-OH-DPAT on the t hree measures was unmodified in rats which had received 150 mu g 5,7-d ihydroxytryptamine intracerebroventricularly 10 days before testing. T he results suggest that 8-OH-DPAT inhibits nociceptive responses by st imulating postsynaptic 5-HT1A receptors.