THE ROLE OF HIPPOCAMPAL 5-HYDROXYTRYPTAMINE(1A) (5-HT1A) RECEPTORS INTHE ANTICONFLICT ACTIVITY OF BETA-ADRENOCEPTOR ANTAGONISTS

The nonselective beta-adrenoceptor antagonists pindolol and cyanopindo lol, which bind to 5-HT1A and 5-HT1B receptors, showed an anticonflict effect by increasing the number of punished licks in the Vogel confli ct test in rats, when administered directly into the CAI region of the dorsal hippocampus (i.hp.). The maximum effect was observed after inf usion of 1 mu g of pindolol and 3 mu g of cyanopindolol. However, the selective beta(1)- and beta(2)-adrenoceptor antagonists betaxolol and ICI 118,551, respectively, which have a negligible affinity for 5-HT r eceptors, did not affect the punished responding, when administered i. hp. in doses up to 10 mu g. The anticonflict effect of pindolol(1 mu g ) was significantly reduced by (S)-WAY 100135, a selective 5-HT1A-rece ptor antagonist, administered i.hp. (0.1 mu g) or s.c. (10 mg/kg). Fur thermore, (S)-WAY 100135 injected i.hp. (0.3 mu g) significantly antag onized the anticonflict effect of pindolol injected i.p. (8 mg/kg). (S )-WAY 100135 given alone i.hp. (0.03-3 mu g) or s.c. (5-10 mg/kg) did not affect the punished responding in rats. These results indicate tha t the anticonflict effect of the beta-blockers which were tested, or a t least pindolol, depends on their agonist action on postsynaptic 5-HT 1A receptors located in the hippocampus.