CARDIOVASCULAR EFFECTS OF 5-HT1A RECEPTOR AGONISTS INJECTED INTO THE DORSAL RAPHE NUCLEUS OF CONSCIOUS RATS

The aim of this study was to investigate the cardiovascular effects of the 5-HT1A receptor agonists, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), flesinoxan and 5-carboxamidotryptamine (5-CT) following injection into the dorsal raphe nucleus of conscious rats. 8-OH-DPAT (0.5-2.5 μg), flesinoxan (2.5-5.0 μg) and 5-CT (0.05 μg) caused hypotension, bradycardia and flat body posture. In contrast, injection of 8-OH-DPAT (0.5 μg) into the median raphe nucleus caused no cardiovascular changes or flat body posture. (-)Pindolol (0.5 μg dorsal raphe nucleus) had little effect on cardiovascular parameters, but significantly attenuated the cardiovascular effects of 8-OH-DPAT (0.5 μg dorsal raphe nucleus). N-Methylatropine (1 mg/kg i.v.) antagonised the cardiovascular effects of 8-OH-DPAT (0.5 μg dorsal raphe nucleus), suggesting these were vagally mediated. Both pretreatments also appeared to reduce 8-OH-DPAT-induced flat body posture. The results suggest that 8-OH-DPAT activates 5-HT1A receptors in the dorsal raphe nucleus to cause hypotension and bradycardia. © 1990.