Functional consequences of 5-HT transporter gene disruption on 5-HT(1a) receptor-mediated regulation of dorsal raphe and hippocampal cell activity.
The consequences of the absence of 5-HT reuptake on the functional properties of 5-HT(1A) receptors were examined in the dorsal raphe nucleus and the hippocampus of knock-out mice lacking the serotonin transporter (5-HTT). Extracellular recordings showed that application of selective 5-HT reuptake inhibitors such as paroxetine and citalopram onto brainstem slices resulted in a concentration-dependent inhibition of 5-HT neuron firing in the dorsal raphe nucleus of wild-type 5-HTT+/+ mice, but not 5-HTT-/- mutants. By contrast, the 5-HT(1A) receptor agonists ipsapirone and 5-carboxamidotryptamine inhibited the discharge in both groups. However, the potency of these agonists was markedly decreased (by approximately 55- and approximately 6-fold, respectively) in 5-HTT-/- compared with 5-HTT+/+ animals. Similarly, intracellular recordings showed that the potency of 5-carboxamidotryptamine to hyperpolarize 5-HT neurons in the dorsal raphe nucleus was significantly lower in 5-HTT-/- than in 5-HTT+/+ animals. These data contrasted with those obtained with hippocampal slices in which 5-carboxamidotryptamine was equipotent to hyperpolarize CA1 pyramidal neurons in both mutant and wild-type mice. As expected from their mediation through 5-HT(1A) receptors, the effects of ipsapirone and 5-carboxamidotryptamine were competitively inhibited by the selective 5-HT(1A) antagonist WAY 100635 in both groups. These data showed that 5-HTT gene knock-out induced a marked desensitization of 5-HT(1A) autoreceptors in the dorsal raphe nucleus without altering postsynaptic 5-HT(1A) receptor functioning in the hippocampus. Similarities between these changes and those evoked by chronic treatment with 5-HT reuptake inhibitors emphasize the existence of regional differences in 5-HT(1A) receptor regulatory mechanisms.
Mannoury la Cour
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Institut National de la Santé et de la Recherche Médicale U288, Neuropsychopharmacologie Moléculaire, Cellulaire et Fonctionnelle, Faculté de Médecine Pitié-Salpêtrière, 75634 Paris Cedex 13, France. mannoury@idf.ext.jussieu.fr
Boni
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Hanoun
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Lesch
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Hamon
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Lanfumey
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D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D017660:Autoreceptors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000235:genetics*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D026901:Membrane Transport Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017966:Pyramidal Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011903:Raphe Nuclei / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists / Q000494:pharmacology; D050486:Serotonin Plasma Membrane Transport Proteins; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology
D017660:Autoreceptors; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists; D050486:Serotonin Plasma Membrane Transport Proteins; D017366:Serotonin Receptor Agonists; D017367:Selective Serotonin Reuptake Inhibitors; C493231:Slc6a4 protein, mouse