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Etude du développement postnatal des interneurones de la couche II interne dans le sous-noyau caudal du trijumeau chez le rat

Abstract : The first postnatal weeks are pivotal for the development of pain sensitivity and are associated with structural and functional reorganization of sensory systems. Interneurons located in the inner part of lamina II(IIi) of the caudal trigeminal subnucleus (Sp5C), the first central node in orofacial tactile and nociceptive pathways, are key elements in circuits underlying the orofacial mechanical allodynia. The aim of this thesis is to study the morphological (by using immunohistochemistry and tridimensional morphological analysis) and functional (by using whole-cell patch-clamp recordings) postnatal development of these interneurons. First, we looked at a very specific population of lamina IIi interneurons expressing the gamma isoform of the protein kinase C (PKCγ). At the earliest stage of our study (3 postnatal days, P3), PKCγ interneurons are present in all superficial layers but PKCγ interneurons can be observed in lamina IIi only at P6. The number of PKCγ interneurons within this lamina then increases gradually up to P11-15. At this age, the number of PKCγ interneurons in lamina IIi is almost the same as that at later ages. Interestingly, we show that neither cell proliferation nor the gradual projection of nociceptive fibers within the Sp5C accounts for such increase. We also studied the development of the whole population of lamina IIi interneurons. These interneurons undergo a large number of morphological changes, in their soma (increased volume) as well as neurites (concomitant increase in length and decrease in number and branching). Furthermore, according to electrophysiological properties, lamina IIi interneurons, at birth, are more depolarized, have a lower rheobase – suggesting that they are more excitable – and exhibit more frequently a single action potential discharge profile compared with mature ones. All these structural and functional changes of lamina IIi interneurons might contribute to the development of orofacial sensitivity.
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Noëmie Mermet-Joret. Etude du développement postnatal des interneurones de la couche II interne dans le sous-noyau caudal du trijumeau chez le rat. Sciences agricoles. Université d'Auvergne - Clermont-Ferrand I, 2016. Français. ⟨NNT : 2016CLF1DD02⟩. ⟨tel-03395053⟩

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