Raphe 5-HT1A autoreceptors, but not postsynaptic 5-HT1A receptors or beta-adrenoceptors, restrain the citalopram-induced increase in extracellular 5-hydroxytryptamine in vivo.
In vivo microdialysis in rat ventral hippocampus was used (i) to verify the importance of 5-HT1A autoreceptors in the raphe as targets for drugs that enhance the citalopram-induced elevation of forebrain 5-hydroxytryptamine (5-HT), and (ii) to further examine the specificity of (-)-penbutolol in this regard. The selective 5-HT1A receptor antagonist WAY100635 (s.c., or intra-raphe) or the mixed 5-HT1A/1B/beta-adrenoceptor antagonist (-)-penbutolol (s.c.), potentiated the citalopram-induced 5-HT rise, whereas local "reverse' dialysis of WAY100635 into the ventral hippocampus did not. Furthermore, the (-)-penbutolol-induced augmentation proved stereoselective and not mediated by beta-adrenoceptors (no effect of s.c. (+)-penbutolol, or beta 1- and beta 2-adrenoceptor blockers (betaxolol, ICI118.551)). These data provide direct evidence that increased stimulation of 5-HT1A autoreceptors in the midbrain raphe impedes the effect of citalopram on forebrain extracellular 5-HT, whereas neither postsynaptic 5-HT1A receptors nor beta-adrenoceptors appear to be involved.
Hjorth
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Department of Pharmacology, University of Göteborg, Sweden. Stephan.Hjorth@pharm.gu.se
Bengtsson
H J
HJ
Milano
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S
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D015784:Betaxolol / Q000494:pharmacology; D015283:Citalopram / Q000494:pharmacology*; D005110:Extracellular Space / Q000378:metabolism; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D017551:Microdialysis; D010394:Penbutolol / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D011985:Receptors, Serotonin / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*
D000319:Adrenergic beta-Antagonists; D015784:Betaxolol; D015283:Citalopram; D010394:Penbutolol; D010879:Piperazines; D011412:Propanolamines; D011725:Pyridines; D011943:Receptors, Adrenergic, beta; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin; D012702:Serotonin Antagonists; D017367:Selective Serotonin Reuptake Inhibitors; C026777:ICI 118551; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide