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McCall RB, Humphrey SJ. 
“Involvement of Serotonin in the Central Regulation of Blood Pressure: Evidence for a Facilitating Effect on Sympathetic Nerve Activity”. 
J. Pharmacol. Exp. Ther.. 1982;222:94-102.
The effects at serotonin (5-HT) receptor agonists and antagonists on sympathetic nervous discharge (SND) recorded from the external carotid and splanchnic nerves were studied in baroreceptor-denervated cats. Intravenous administration of the 5-HT antagonists methysergide (0.025-1.6 mg/kg), metergoline (0.01-0.32 mg/kg), cyproheptadine (0.05-1.6 mg/kg) and cinanserin (0.2-0.4 mg/kg) was associated with a prolonged dose-related inhibition at SND. Maximum reductions in SND produced by methysergide, metergaline, cyproheptadine and cinanserin were 90, 72, 71 and 50%, respectively. In contrast, a progressive increase in SND was observed in vehicle control animals. Methysergide, metergoline and cyproheptadine failed to reduce SND in cats pretreated with the 5-HT synthesis inhibitor p-cholorpheylalanine. Clonidine (20 mcg/kg i.v.) significantly inhibited SND (-73%) in p-cholorophenylalanine-treated cats. The selective 5-HT agonists 5-methoxydimethyltryptamine and lisuride also reduced also SND in a dose-dependent manner. The time course of the depressor effects of 5-methoxydimethyltryptamine and lisuride correlate well to their ability to inhibit 5-HT cell firing. These data indicate that 5-HT agonists which act presynaptically to inhibit 5-HT cell firing and antagonists which act postsynaptically to block the effect of synaptically released 5-HT both mediate a central reduction in SND. It is concluded that central 5-HT neurons facilitate transmission in central sympathetic pathways.
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