5-HT(1A)-MEDIATED LOWER LIP RETRACTION - EFFECTS OF 5-HT(1A) AGONISTSAND ANTAGONISTS

This study investigated the production of lower lip retraction (LLR) i n the rat by the 5-hydroxytryptamine1A (5-HT1A) agonist 8-hydroxy-2-(d i-n-propylamino)-tetralin (8-OH-DPAT) and the effect of the putative 5 -HT1A antagonists pindolol and oxy-phenyl)-4-[4-(2-phthalimido)-butyl] -piperazine (NAN190). 8-OH-DPAT (0.125-1.0 mg/kg, IP) caused a dose-re lated increase in LLR. Pindolol (10-40 mg/kg, IP) and NAN190 (2.5-10 m g/kg, IP) produced a dose-related block of 8-OH-DPAT-induced LLR. Pind olol (10-40 mg/kg, IP) when administered alone was also found to cause LLR, suggesting that pindolol behaves as a partial agonist in this mo del. This was not the case with NAN 190 (2.5- 10 mg/kg, IP), which fai led to produce LLR; however, NAN190 (2.5-10 mg/kg, IP) produced a dose -related block of the pindolol-induced LLR. These results clearly demo nstrate that the LLR model can be used to detect 5-HT1A agonists, part ial agonists, and antagonists.