Antagonism studies with BMY-7378 and NAN-190: Effects on 8-hydroxy-2-(di- n-propylamino)tetralin-induced increases in punished responding of pigeons

The purported serotonin (5-HT)(1A) antagonists BMY-7378 and NAN-190 were examined in pigeons for their potential to block the effects of the prototypical 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH- DPAT) on punished ('conflict') and unpunished behavior and for their binding affinity at the 5-HT(1A) receptor site labeled by [³H]-8-OH-DPAT. Although BMY-7378 and NAN-190 both displayed high affinity for the 5-HT(1A) receptor (IC₅₀ values of 0.8 and 7.5 nM, respectively), their effects, when administered alone, as well as in combination with 8-OH-DPAT, were distinct. 8-OH-DPAT (0.3-3.0 mg/kg) produced large increases in punished responding at doses that did not affect or that decreased unpunished responding. Administration of NAN-190 (1.0-3.0 mg/kg) did not increase punished responding, whereas BMY-7378 (1.0-5.6 mg/kg) slightly increased behavior suppressed by punishment. Pretreatment with BMY-7378 attenuated the rate- increasing effects of 8-OH-DPAT on punished responding; however, these effects were accompanied by dose-dependent enhancement of the rate-decreasing effects of 8-OH-DPAT on unpunished responding. In contrast, NAN-190 blocked the rate-increasing effects of 8-OH-DPAT on punished responding and also reversed the rate-decreasing effects of 8-OH-DPAT on responding that was not punished. Pretreatment with NAN-190 failed to block increases in punished responding produced by 0.1 to 1.0 mg/kg of the benzodiazepine midazolam. These data suggest that NAN-190 may be characterized as an antagonist and BMY-7378 a partial agonist with respect to 5-HT(1A)-induced behavioral changes observed in the conflict procedure with pigeons.