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The Journal of Neuroscience, August 15, 2000, 20(16):5932-5939
Somatostatin-Induced Regulation of SST2A Receptor
Expression and Cell Surface Availability in Central Neurons: Role
of Receptor Internalization
Hélène
Boudin1,
Philippe
Sarret2,
Jean
Mazella2,
Agnes
Schonbrunn3, and
Alain
Beaudet1
1 Montreal Neurological Institute, McGill University,
Montréal, Québec H3A 2B4, Canada, 2 Institut de
Pharmacologie Moléculaire et Cellulaire, Centre National de la
Recherche Scientifique, Université de Nice-Sophia Antipolis,
Valbonne, France, and 3 University of Texas, Houston
Medical School, Houston, Texas 77225
To investigate the effects of somatostatin (somatotropin
release-inhibiting factor, SRIF) on the regulation of
SST2A receptors in mammalian brain, we examined how
blockade of SRIF release or stimulation by the SRIF analog
[D-Trp8]-SRIF would affect the
expression and cell surface availability of SST2A receptors
in rat brain slices. First, we measured the intensity of
SST2A immunoreactivity, using quantitative light microscopic immunocytochemistry, and levels of SST2A mRNA,
using semiquantitative RT-PCR, under conditions of acute SRIF release blockade. Incubation of slices from the claustrum or basolateral amygdala, two regions previously shown to contain high concentrations of SST2A receptors, in Ca2+-free
Ringer's for 40 min induced a decrease in the intensity of
SST2A receptor immunoreactivity and concentration of
SST2A mRNA as compared with control values obtained in
Ca2+-supplemented Ringer's. These effects were
counteracted in a dose-dependent manner by the addition of 10-100
nM [D-Trp8]-SRIF to the
Ca2+-free medium. Furthermore, both of these effects
were abolished in the presence of the endocytosis inhibitors
phenylarsine oxide or hyperosmolar sucrose, suggesting that they were
dependent on receptor internalization. Electron microscopic immunogold
labeling confirmed the existence of an agonist-induced internalization of SST2A receptors in central neurons. At a high (10 µM), but not at a low (10 nM), concentration
of agonist this internalization resulted in a significant decrease in
cell surface receptor density, irrespective of the presence of
Ca2+ in the medium. Taken together, these results
suggest that ligand-induced endocytosis is responsible for rapid
transcriptional (increase in SST2A expression) and
trafficking (loss of cell surface receptors) events involved in the
control of the somatostatinergic signal.
Key words:
somatostatin; endocytosis; receptor; immunocytochemistry; electron microscopy; signaling
Copyright © 2000 Society for Neuroscience 0270-6474/00/20165932-08$05.00/0
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