5-HT 1A-mediated lower lip retraction: Effects of 5-HT 1A agonists and antagonists

Abstract

This study investigated the production of lower lip retraction (LLR) in the rat by the 5-hydroxytryptamine 1A (5-HT 1A) agonist 8-hydroxy-2-( di- n-propylamino)-tetralin (8-OH-DPAT) and the effect of the putative 5-HT 1A antagonists pindolol and (1-(2-methoxy-phenyl)-4-[4-(2-phthalimido)-butyl]-piperazine (NAN190). 8-OH-DPAT (0.125–1.0 mg/kg, IP) caused a dose-related increase in LLR. Pindolol (10–40 mg/kg, IP) and NAN190 (2.5–10 mg/kg, IP) produced a dose-related block of 8-OH-DPAT-induced LLR. Pindolol (10–40 mg/kg, IP) when administered alone was also found to cause LLR, suggesting that pindolol behaves as a partial agonist in this model. This was not the case with NAN190 (2.5–10 mg/kg, IP), which failed to produce LLR; however, NAN190 (2.5–10 mg/kg, IP) produced a dose-related block of the pindolol-induced LLR. These results clearly demonstrate that the LLR model can be used to detect 5-HT 1A agonists, partial agonists, and antagonists.