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Elife 2018 May 30;7. doi: 10.7554/eLife.30693.
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Functional limb muscle innervation prior to cholinergic transmitter specification during early metamorphosis in Xenopus.

Lambert FM , Cardoit L , Courty E , Bougerol M , Thoby-Brisson M , Simmers J , Tostivint H , Le Ray D .

In vertebrates, functional motoneurons are defined as differentiated neurons that are connected to a central premotor network and activate peripheral muscle using acetylcholine. Generally, motoneurons and muscles develop simultaneously during embryogenesis. However, during Xenopus metamorphosis, developing limb motoneurons must reach their target muscles through the already established larval cholinergic axial neuromuscular system. Here, we demonstrate that at metamorphosis onset, spinal neurons retrogradely labeled from the emerging hindlimbs initially express neither choline acetyltransferase nor vesicular acetylcholine transporter. Nevertheless, they are positive for the motoneuronal transcription factor Islet1/2 and exhibit intrinsic and axial locomotor-driven electrophysiological activity. Moreover, the early appendicular motoneurons activate developing limb muscles via nicotinic antagonist-resistant, glutamate antagonist-sensitive, neuromuscular synapses. Coincidently, the hindlimb muscles transiently express glutamate, but not nicotinic receptors. Subsequently, both pre- and postsynaptic neuromuscular partners switch definitively to typical cholinergic transmitter signaling. Thus, our results demonstrate a novel context-dependent re-specification of neurotransmitter phenotype during neuromuscular system development.

PubMed ID: 29845935
PMC ID: PMC5997451
Article link: Elife
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: chat grin1 grin2b isl1 slc17a7 slc18a3 syn1 syp
Antibodies: Chat Ab1 Fluoro-BT Ab Grin1 Ab1 Grin2b Ab1 Isl1/2 Ab1 Neuronal Ab4 slc17a7 Ab1 slc18a3 Ab1

Article Images: [+] show captions
References [+] :
Akerman, Depolarizing GABAergic conductances regulate the balance of excitation to inhibition in the developing retinotectal circuit in vivo. 2006, Pubmed, Xenbase