The effect of SB-269970, a 5-HT(7) receptor antagonist, on 5-HT release from serotonergic terminals and cell bodies.
1. The presence of 5-HT(7) receptor mRNA and protein in 5-HT neurons suggests that this receptor may act as a 5-HT autoreceptor. In this study, the effect of the 5-HT(7) receptor antagonist, SB-269970 ((R)-1-[3-hydroxy phenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine), was investigated on 5-HT release in the guinea-pig and rat cortex and the rat dorsal raphe nucleus (DRN), using the techniques of in vitro [(3)H]-5-HT release or fast cyclic voltammetry, respectively. 2. Cortical slices were loaded with [(3)H]-5-HT and release was evoked by electrical stimulation. 5-CT inhibited the evoked release of [(3)H]-5-HT in a concentration-dependent manner. SB-269970 had no significant effect on [(3)H]-5-HT release while the 5-HT(1B) receptor antagonist, SB-224289 significantly potentiated [(3)H]-5-HT release. In addition, SB-269970 was unable to attenuate the 5-CT-induced inhibition of release while SB-224289 produced a rightward shift of the 5-CT response, generating estimated pK(B) values of 7.8 and 7.6 at the guinea-pig and rat terminal 5-HT autoreceptors respectively. 3. Rat DRN slices were electrically stimulated and the evoked 5-HT efflux detected by voltammetric analysis. 8-OH-DPAT inhibited evoked 5-HT efflux and was fully reversed by WAY 100635. SB-269970 had no effect on either 5-HT efflux per se or 8-OH-DPAT-induced inhibition of 5-HT efflux. In addition, 5-CT inhibited 5-HT efflux in a concentration-dependent manner. SB-269970 was unable to attenuate the 5-CT-induced inhibition of 5-HT efflux. 4. In conclusion, we were unable to provide evidence to suggest a 5-HT autoreceptor role for 5-HT(7) receptors. However, investigations with more selective 5-HT(7) receptor agonists are needed to confirm the data reported here.
Roberts
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C
Department of Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AW. Claire_Roberts-1@sbphrd.com
Allen
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L
Langmead
C J
CJ
Hagan
J J
JJ
Middlemiss
D N
DN
Price
G W
GW
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D020645:Mediodorsal Thalamic Nucleus / Q000187:drug effects / Q000378:metabolism; D010636:Phenols / Q000494:pharmacology*; D010881:Piperidones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013141:Spiro Compounds / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology*; D014316:Tritium
D010636:Phenols; D010881:Piperidones; D011985:Receptors, Serotonin; C108518:SB 22489G; C404922:SB 269970; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013141:Spiro Compounds; D013449:Sulfonamides; C104425:serotonin 7 receptor; D014316:Tritium; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C047087:5-carboxamidotryptamine