Introduction
In the developing brain, axons use different mechanisms in order to find their correct path and target. A critical element helping to guide axons through long distance is the presence of intermediate targets or guidepost cells which provide information all along the path. During development, cortico-cortical (callosal) projections traverse a complex environment and need to make several critical decisions before reaching their target. Glial cells localized around the corpus callosum are believed to be the principal actors involved in the guidance of callosal axons during the early developmental stages.

Current research
While the guidepost function of glial cells has been well documented, the contribution of neurons is also suggested. In a series of experiments, we have discorvered that, during developement, the corpus callosum, considered as a neuron-poor structure, is in fact populated by numerous glutamatergic and GABAergic neurons. With the use of various transgenic mice and transplant experiments, we demonstrated that the neurons of the corpus callosum are essential for the correct midline crossing of callosal axons. Thus neurons and glia provide complementary guiding cues to build up the corpus callosum. Based on these data, the aim of our project is to better characterize the respective contribution of neurons and glial in the formation of the midline cerebral structures. Cécile Lebrand, external collaborator at the DNF, is associated with the team of Jean-Pierre Hornung

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