Pharmacological characterization of medullary serotonin neurons.
In the present study we investigated the characteristics of medullary raphe serotonergic neurons. Specifically, we sought to examine further the similarities between medullospinal 5-HT neurons and the more extensively studied neurons of the dorsal raphe. Intravenous administration of 5-methoxy-dimethyltryptamine (5-MeODMT) produced a dose-related inhibition of the firing of midline medullary 5-HT neurons. Microiontophoretically applied 5-MeODMT also inhibited medullary 5-HT neurons. The inhibitory potency of 5-MeODMT was nearly identical to that observed for dorsal raphe 5-HT neurons. Microiontophoretic or intravenous administration of the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) did not alter the firing rate of medullary 5-HT neurons. Intravenous administration of the alpha 1-receptor antagonist prazosin resulted in an inhibition of the medullary 5-HT neuronal firing. The discharge of medullary 5-HT neurons increased during iontophoresis of norepinephrine. These data are discussed in relation to the identification and characterization of medullary 5-HT neurons. In addition, the data suggest that the firing rate of medullary 5-HT neurons is regulated in part by a tonic excitatory noradrenergic input.
Clement
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Cardiovascular Disease Research, Upjohn Company, Kalamazoo, MI 49001.
McCall
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D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D008526:Medulla Oblongata / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008732:Methoxydimethyltryptamines / Q000494:pharmacology; D009433:Neural Inhibition; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism*
D000662:Amphetamines; D008732:Methoxydimethyltryptamines; D012701:Serotonin; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine; D009638:Norepinephrine; D011224:Prazosin