5-HT1A receptor-mediated autoinhibition does not function at physiological firing rates: evidence from in vitro electrophysiological studies in the rat dorsal raphe nucleus.
5-HT(1A)-mediated autoinhibition of neurones in the dorsal raphe nucleus (DRN) is considered to be the principal inhibitory regulator of 5-HT neuronal activity. The activation of this receptor by endogenous 5-HT was investigated using electrophysiological recordings from the rat DRN in vitro. At a concentration which blocked the inhibitory effect of exogenous 5-HT, the 5-HT(1A) antagonist WAY 100635 did not alter basal firing rate or modulate the excitatory response to the alpha(1)-agonist phenylephrine. Blockade of 5-HT reuptake by a concentration of fluoxetine, which enhanced the inhibitory effect of exogenous 5-HT, lowered phenylephrine-induced basal firing presumably due to potentiation of the effect of endogenous 5-HT. However, this effect was not firing rate dependent and neither the proportional increase nor the time-course of the response to a higher concentration of phenylephrine were altered in the presence of fluoxetine. These data suggest that the inhibitory 5-HT(1A) receptor on raphe neurones is neither tonically activated nor plays any role in modulating the response to excitatory transmitters. Thus, at physiological firing rates this receptor does not appear to function as an autoreceptor of serotonergic neurones of the DRN.
Johnson
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DA
Psychobiology Research Group, University of Newcastle upon Tyne, School of Neurosciences and Psychiatry, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK. d.a.johnson@ncl.ac.uk
Gartside
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SE
Ingram
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D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005473:Fluoxetine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D013997:Time Factors
D000316:Adrenergic alpha-Agonists; D003346:Corticotropin-Releasing Hormone; D005473:Fluoxetine; D010656:Phenylephrine; D010879:Piperazines; D011725:Pyridines; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists; D017367:Selective Serotonin Reuptake Inhibitors; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide