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The Journal of Neuroscience, April 1, 2002, 22(7):2598-2606
Descending 5-Hydroxytryptamine Raphe Inputs Repress the
Expression of Serotonergic Neurons and Slow the Maturation of
Inhibitory Systems in Mouse Embryonic Spinal Cord
Pascal
Branchereau,
Jacqueline
Chapron, and
Pierre
Meyrand
Laboratoire de Neurobiologie des Réseaux, Université
Bordeaux 1 et Centre National de la Recherche Scientifique Unité
Mixte de Recherche 5816, 33405 Talence, France
Spontaneous synchronous rhythmic activities are a common feature of
immature neuronal networks. Although the mechanisms underlying such
activities have been studied extensively, whether they might be
controlled by modulatory information remains questionable. Here, we
investigated the role of descending serotonergic (5-HT) inputs from the
medulla to the spinal cord in the maturation of rhythmic activity. We
found that in spinal cords maintained, as a whole, in organotypic
culture without the medulla, the maturation of spontaneous activity is
similar to that found in spinal cords developed in
utero. Interestingly, in organotypic cultures without the
medulla (i.e., devoid of descending inputs), numerous intraspinal neurons expressed 5-HT, unlike in spinal cords cultivated in the presence of the medulla or matured in utero. We
demonstrated that this 5-HT expression was specifically dependent on
the absence of 5-HT fibers and was repressed by 5-HT itself via
activation of 5-HT1A receptors. Finally, to verify whether
the expression of 5-HT intraspinal neurons could compensate for
the lack of descending 5-HT fibers and play a role in the development
of spontaneous activity, we blocked the 5-HT synthesis using
p-chlorophenylalanine methyl ester in cultures devoid of
the medulla. Surprisingly, we found that this pharmacological treatment
did not prevent the development of spontaneous activity but accelerated
the maturation of intraspinal inhibition at the studied stages.
Together, our data indicate that descending 5-HT raphe inputs (1)
repress the expression of spinal serotonergic neurons and (2) slow the
maturation of inhibitory systems in mouse spinal cord.
Key words:
neuronal phenotype; development; modulatory neurons; serotonin; disinhibition; GABA; glycine; neural networks
Copyright © 2002 Society for Neuroscience 0270-6474/02/2272598-09$05.00/0
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