The Journal of Neuroscience, February 15, 2001, 21(4):1313-1326
Ontogeny of Modulatory Inputs to Motor Networks: Early
Established Projection and Progressive Neurotransmitter
Acquisition
Yves
Le Feuvre,
Valérie S.
Fénelon, and
Pierre
Meyrand
Laboratoire de Neurobiologie des Réseaux, Centre National de
la Recherche Scientifique Unité Mixte de Recherche 5816, Université Bordeaux I, 33405 Talence cedex, France
Modulatory information plays a key role in the expression and the
ontogeny of motor networks. Many developmental studies suggest that the
acquisition of adult properties by immature networks involves their
progressive innervation by modulatory input neurons. Using the
stomatogastric nervous system of the European lobster Homarus gammarus, we show that contrary to this
assumption, the known population of projection neurons to motor
networks, as revealed by retrograde dye migration, is established early
in embryonic development. Moreover, these neurons display a large
heterogeneity in the chronology of acquisition of their full adult
neurotransmitter phenotype.
We performed retrograde dye migration to compare the neuronal
population projecting to motor networks located in the stomatogastric ganglion in the embryo and adult. We show that this neuronal population is quantitatively established at developmental stage 65%, and each
identified projection neuron displays the same axon projection pattern
in the adult and the embryo. We then combined retrograde dye migration
with FLRFamide-like, histamine, and GABA immunocytochemistry to
characterize the chronology of neurotransmitter expression in
individual identified projection neurons. We show that this early
established population of projection neurons gradually acquires its
neurotransmitter phenotype complement. This study indicates that (1)
the basic architecture of the known population of projection inputs to
a target network is established early in development and (2)
ontogenetic plasticity may depend on changes in neurotransmitter phenotype expression within preexisting neurons rather than in the
addition of new projection neurons or fibers.
Key words:
central pattern generator; development; modulatory
neurons; FLRFamide; GABA; histamine
Copyright © 2001 Society for Neuroscience 0270-6474/01/2141313-14$05.00/0