Evidence that the 5-HT3 receptors of the rat, mouse and guinea-pig superior cervical ganglion may be different.
1. Using grease-gap recordings from the isolated superior cervical ganglion of mouse, rat and guinea-pig, we have compared the depolarization evoked by 5-hydroxytryptamine (5-HT) with that evoked by the selective 5-HT3 receptor agonist 2-methyl-5-HT (2-Me-5-HT). 2. The maximum depolarization induced by 2-Me-5-HT was smaller than that induced by 5-HT in all three species, and particularly in the guinea-pig. 3. The 5-HT2 receptor antagonist ketanserin (1 microM) caused a clear rightward shift of the dose-response curve to 5-HT on the guinea-pig ganglion, but not on the mouse or rat ganglion. Spiperone (0.03 microM) had a quantitatively similar action to ketanserin (0.1 microM) on the 5-HT dose-response curve of the guinea-pig ganglion. Ketanserin had no significant effect on the dose-response curve to 2-Me-5-HT on any of these ganglia. 4. Using 2-Me-5-HT as the agonist, we determined the pA2 values for two 5-HT3 receptor antagonists. The potency of ICS 205-930 varied by approximately 100 fold between the species and that of (+)-tubocurarine varied by over 1000 fold. The differences in the pA2 values of these compounds varied independently among the species. 5. We conclude that 5-HT3 receptors are present on the superior cervical ganglion from the rat, mouse and guinea-pig, but these receptors may be pharmacologically distinct from each other. In addition, the depolarization of the guinea-pig superior cervical ganglion by low concentrations of 5-HT is largely mediated by ketanserin-sensitive receptors.
Newberry
N R
NR
Merck, Sharp and Dohme Research Labs, Neuroscience Research Centre, Harlow, Essex.
Cheshire
S H
SH
Gilbert
M J
MJ
D000818:Animals; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D007211:Indoles / Q000494:pharmacology; D007650:Ketanserin / Q000494:pharmacology; D008297:Male; D051379:Mice; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology; D017783:Superior Cervical Ganglion / Q000187:drug effects* / Q000502:physiology; D000077526:Tropisetron; D014403:Tubocurarine / Q000494:pharmacology
D007211:Indoles; D011985:Receptors, Serotonin; D012701:Serotonin; D000077526:Tropisetron; C045918:2-methyl-5-HT; D007650:Ketanserin; D014403:Tubocurarine