title: Serotonin and thyrotropin-releasing hormone do not augment their effects on gastric motility on their microinjection into the nucleus raphe obscurus of the rat.
abstract: The existence of an interaction between serotonin (5-HT) and thyrotropin-releasing hormone (TRH) in the nucleus raphe obscurus (NRO) of the rat in their excitatory effects on gastric motor function was examined using two different approaches. First, 5-HT and TRH were microinjected into the NRO alone at two different doses and then as a mixture in the same animals. In a second group of animals, both agents were microinjected in a rapid (20-30-sec interval) sequential order. These experiments were performed in alpha-chloralose-anesthetized rats intragastric pressure and pyloric and greater curvature motility were monitored. Both 5-HT at a dose of 6 nmol and TRH at doses of 0.6 and 15 pmol evoked significant increases in intragastric pressure. Microinjection of a mixture of 5-HT at a low dose of 0.6 nmol and TRH at doses of 0.6 pmol (low) and 15 pmol (high) resulted in significant increases in intragastric pressure that did not differ from the effects of TRH microinjected alone. A mixture of 5-HT at a low dose of 0.6 nmol and TRH at a high dose of 15 pmol evoked increases in pyloric motility that did not differ from the effects of TRH alone and increases in greater curvature motility that were significantly lower than the effects of TRH alone at the same dose. Microinjection of a mixture of 5-HT at a high dose of 6 nmol and TRH at a low dose of 0.6 pmol evoked increases in intragastric pressure that did not differ from the effect of 5-HT alone. Rapid sequential microinjection of TRH at either a low dose of 0.6 pmol or the larger dose of 15 pmol after 5-HT (0.6 nmol) resulted in increases in intragastric pressure that did not differ from the response to either dose of TRH microinjected after vehicle. Similarly, the intragastric pressure response to 5-HT (0.6 nmol) given after either dose of TRH was not significantly different from the response to 5-HT after vehicle. In summary, our study demonstrates that 5-HT and TRH do not augment their excitatory effects on gastric motor function on dual or sequential micro-injections in the NRO of the alpha-chloralose-anesthetized rats.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans, USA.
authors.forename: Z K
authors.initials: ZK
authors.lastname: Krowicki
authors.forename: P J
authors.initials: PJ
authors.lastname: Hornby
mesh_terms: D000818:Animals; D004357:Drug Synergism; D005769:Gastrointestinal Motility / Q000187:drug effects*; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D008845:Microinjections; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000494:pharmacology*; D013270:Stomach / Q000187:drug effects / Q000502:physiology; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D012701:Serotonin; D013973:Thyrotropin-Releasing Hormone; C027979:L-pyroglutamyl-L-histidyl-3,3-dimethylprolinamide; D011761:Pyrrolidonecarboxylic Acid