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The Journal of Neuroscience, November 1, 2001, 21(21):8378-8386
Agonist-Induced Internalization of Serotonin-1A Receptors in the
Dorsal Raphe Nucleus (Autoreceptors) But Not Hippocampus
(Heteroreceptors)
Mustapha
Riad1,
Kenneth
C.
Watkins1,
Edith
Doucet2,
Michel
Hamon2, and
Laurent
Descarries1
1 Départements de Pathologie et Biologie
Cellulaire et de Physiologie, and Centre de Recherche en Sciences
Neurologiques, Faculté de Médecine, Université de
Montréal, Montreal, Quebec, Canada H3C 3J7, and
2 Institut National de la Santé et de la Recherche
Médicale U288, Neuropsychopharmacologie, Faculté de
Médecine Pitié-Salpêtrière, 75634 Paris Cedex
13, France
Serotonin-1A (5-HT1A) receptors in the CNS are a
major target for psychotropic drugs. In nucleus raphe dorsalis (NRD)
and hippocampus (CA3), the selective 5-HT1A agonist
(+)-8-hydroxy-2-(di-N-propylamino) tetralin
(8-OH-DPAT) reduces the firing activity of serotoninergic (5-HT)
and pyramidal neurons, respectively. When located on 5-HT (autoreceptors), but not on non-5-HT (heteroreceptors) neurons, 5-HT1A receptors are known to be subject to
desensitization. Using quantitative electron microscopy after
pre-embedding immunogold labeling with specific antibodies, we examined
the subcellular distribution of these receptors after acute
administration of 8-OH-DPAT (0.5 mg/kg, i.v.). Silver-intensified
immunogold particles associated with the plasma membrane or the
cytoplasm were counted in somata and dendrites within the NRD, 15 min,
1 hr and 24 hr after 8-OH-DPAT injection, and in hippocampal dendrites
1 hr after the same treatment. Significant decrease in the density of
membrane labeling and concomitant increase of cytoplasmic labeling were demonstrated in the NRD, 15 min and 1 hr after 8-OH-DPAT
administration, with a return to baseline level at 24 hr.
Internalization was blocked by previous administration of the
5-HT1A antagonist
N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane-carboxamide (WAY 100635), which, by itself, was
without apparent effect. In hippocampus (CA3), there were no apparent changes in the distribution of the receptor after 8-OH-DPAT
administration. These findings are in line with earlier results showing
a desensitization of 5-HT1A autoreceptors but not
heteroreceptors after treatment with 5-HT1A receptor
agonist. They suggest that this desensitization is the result of
autoreceptor internalization.
Key words:
agonist; 5-HT1A receptors; desensitization; internalization; serotonin; 8-OH-DPAT; nucleus raphe dorsalis; hippocampus; immunocytochemistry
Copyright © 2001 Society for Neuroscience 0270-6474/01/21218378-09$05.00/0
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