THE EFFECTS OF 5-HT1A RECEPTOR AGONISTS, 5-HT1A RECEPTOR ANTAGONISTS AND THEIR INTERACTION ON THE FEAR-POTENTIATED STARTLE RESPONSE

The present study investigated whether the anxiolytic effect of 5-HT1A receptor agonists on the fear-potentiated startle response could be a ntagonized by 5-HT1A receptor antagonists. Therefore, control and fear -potentiated startle amplitudes were measured after co-administration of vehicle, flesinoxan (10 mg/kg PO) or 8-OH-DPAT (0.3 mg/kg SC) and D U 125,539 (0, 1, 3 and 10 mg/kg SC), (+/-)-pindolol (0, 3, 10 and 30 m g/kg SC) or WAY 100,635 (0, 0.1, 0.3 and 1 mg/kg SC). Unexpectedly, th e three antagonists themselves as measured in the vehicle-pretreatment groups dose-dependently decreased startle potentiation. Further, DU 1 25,530 and WAY 100,635 were able to reverse the attenuating effect of 8-OH-DPAT, while no antagonism of the flesinoxan effect on startle pot entiation was found. In contrast, both the flesinoxan- and 8-OH-DPAT-i nduced lower lip retraction were antagonized by DU 125,530 and WAY 100 ,635, but not by (+/-)-pindolol. The findings of the present study sug gest that drugs acting on 5-HT1A receptors differentially affect lower lip retraction and startle potentiation probably mediated by differen t neuronal populations.