Chronic fluoxetine-induced desensitization of 5-HT1A and 5-HT1B autoreceptors: regional differences and effects of WAY-100635.
Desensitization of 5-HT(1A) and 5-HT(1B) autoreceptors is thought to be the mechanism underlying the therapeutic effects of fluoxetine and other selective serotonin reuptake inhibitors when these are administered chronically. The blockade of 5-HT(1A) autoreceptors occurring on administration of a selective serotonin reuptake inhibitor together with a 5-HT(1A) autoreceptor antagonist is responsible for the acute increase in 5-hydroxytryptamine (serotonin, 5-HT) levels observed under these circumstances. The effects of repeated administration of selective serotonin reuptake inhibitors together with 5-HT(1A) receptor antagonists have not been widely studied. In this work, we found that the effects of fluoxetine (5 mg/kg, i.p., daily for 12 days) to desensitize 5-HT(1B) autoreceptors in the frontal cortex, as measured by the effect of the locally administered 5-HT(1B) receptor agonist, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93129), and to desensitize 5-HT(1A) autoreceptors as measured by the action of the 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 50 microg/kg, s.c.) to reduce 5-HT levels in cortex, were prevented by concomitant administration of the 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide (WAY-100635; 0.3 mg/kg, s.c.). 5-HT(1B) receptor activity in the hypothalamus, as measured by the effects of locally administered CP 93129, and 5-HT(1A) autoreceptor activity, as determined by the effects of subcutaneous 8-OH-DPAT to reduce 5-HT levels in hypothalamus, were not altered either by fluoxetine alone or by fluoxetine in the presence of WAY-100635. The data suggest that the regulation of extracellular levels of 5-HT in the cortex and hypothalamus is subject to different autoregulatory mechanisms.
Newman
Michael E
ME
Biological Psychiatry Laboratory, Department of Psychiatry, Hadassah-Hebrew University Medical Center, PO Box 12000, Jerusalem 91120, Israel. newman@hadassah.org.il
Shalom
Galit
G
Ran
Avigail
A
Gur
Eitan
E
Van de Kar
Louis D
LD
D000818:Animals; D017660:Autoreceptors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D004334:Drug Administration Schedule; D005473:Fluoxetine / Q000008:administration & dosage*; D008297:Male; D010879:Piperazines / Q000494:pharmacology*; D011725:Pyridines / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D044282:Receptor, Serotonin, 5-HT1A / Q000378:metabolism; D044302:Receptor, Serotonin, 5-HT1B / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D058829:Serotonin 5-HT1 Receptor Antagonists
D017660:Autoreceptors; D010879:Piperazines; D011725:Pyridines; D044302:Receptor, Serotonin, 5-HT1B; D058829:Serotonin 5-HT1 Receptor Antagonists; D005473:Fluoxetine; D044282:Receptor, Serotonin, 5-HT1A; D012701:Serotonin; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide