Involvement of 5-HT1B receptors in the anticonflict effect of m-CPP in rats.

The anticonflict activity of m-CPP, a non-selective agonist of 5-HT receptors, was studied in the drinking conflict test in rats. m-CPP administered in doses of 0.125-0.5 mg/kg increased the number of punished licks, the maximum effect having been observed after a dose of 0.25 mg/kg. The anticonflict effect of m-CPP (0.25 mg/kg) was antagonized by the non-selective 5-HT antagonist metergoline (1-4 mg/kg) and by the beta-adrenoceptor blocker SDZ 21009 (2 and 4 mg/kg) with affinity for 5-HT1A and 5-HT1B receptors. On the other hand, the 5-HT1A receptor antagonist NAN-190 (0.5 and 1 mg/kg), the 5-HT2 receptor antagonist ritanserin (0.25 and 0.5 mg/kg), and the beta-blockers betaxolol (8 mg/kg) and ICI 118,551 (8 mg/kg) with no affinity for 5-HT receptors did not affect the effect of m-CPP. The effect of m-CPP was not modified, either, in animals with the 5-HT lesion produced by p-chloroamphetamine. These results suggest that the anticonflict effect of m-CPP described above results from stimulation of 5-HT1B receptors--most probably these which are located postsynaptically.