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The Journal of Neuroscience, March 15, 2001, 21(6):2178-2185
Functional Consequences of 5-HT Transporter Gene Disruption on
5-HT1A Receptor-Mediated Regulation of Dorsal Raphe and
Hippocampal Cell Activity
Clotilde Mannoury la
Cour1,
Claudette
Boni1,
Naïma
Hanoun1,
Klaus-Peter
Lesch2,
Michel
Hamon1, and
Laurence
Lanfumey1
1 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, and 2 Department of Psychiatry, University of
Würzburg, 97080 Würzburg, Germany
The consequences of the absence of 5-HT reuptake on the functional
properties of 5-HT1A 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-HT1A receptor agonists ipsapirone and
5-carboxamidotryptamine inhibited the discharge in both groups. However, the potency of these agonists was markedly decreased (by ~55- and ~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-HT1A receptors, the effects of ipsapirone and 5-carboxamidotryptamine were
competitively inhibited by the selective 5-HT1A antagonist
WAY 100635 in both groups. These data showed that 5-HTT gene knock-out
induced a marked desensitization of 5-HT1A autoreceptors in
the dorsal raphe nucleus without altering postsynaptic
5-HT1A 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-HT1A receptor regulatory mechanisms.
Key words:
5-HT transporter knock-out mice; 5-HT1A
receptors; dorsal raphe nucleus; hippocampus; desensitization; in
vitro electrophysiology
Copyright © 2001 Society for Neuroscience 0270-6474/01/2162178-08$05.00/0
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