EVIDENCE THAT 5-HT1D RECEPTORS MEDIATE INHIBITION OF SYMPATHETIC GANGLIONIC TRANSMISSION IN ANESTHETIZED CATS

In anaesthetized cats, 5-carboxamidotryptamine (5-CT) or 5-hydroxytryp tamine (5-HT) (0.3-300 mu g kg(-1),i.v.) inhibited the postganglionic compound action potential evoked by preganglionic electrical stimulati on (0.5 Hz) with a similar potency in the stellate and splanchnic gang lia. In the 5-HT experiments transmission thorough the inferior mesent eric ganglia was also recorded. The maximal inhibitory effect of 5-HT was greater on the stellate and splanchnic ganglia (60 +/- 4 and 52 +/ - 5%) than on the inferior mesenteric (15 +/- 2%). The effects of 5-HT were unaffected by pretreatment with antagonists (1 mg kg(-1);i.v.) f or 5-HT2 (BW501C67), 5-HT1A (WAY-100635) and 5-HT3 receptors (ondanset ron). However, responses to both 5-HT and 5-CT were attenuated signifi cantly by GR127935 (I mg kg(-1)) except the responses to 5-HT at the i nferior mesenteric ganglia. These results are consistent with the invo lvement of 5-HT1D receptors mediating inhibition of sympathetic gangli onic transmission in vivo.