Mechanisms responsible of sensory afferent projections into the hindbrain

Animals perceive the external world through their sensory systems, which consists in: i) sensory receptors that detect external stimuli; ii) neuronal pathways that convey the sensory information to the brain; and iii) central neurons organized in relay nuclei that process this information. To study the selective innervation of hindbrain regions by sensory afferents, we mapped the fine-grained topographical representation of sensory projections at the central level: sensory ganglia located more anteriorly project more medially than do ganglia located more posteriorly, and this relates to the time of sensory ganglia differentiation. This somatotopic arrangement is laid out very early, prompting the question of the origin of the signals involved in the induction and maintenance of this patterning. Up to date, several studies have tried to unveil how peripheral ganglia “send” afferent projections to “reach” their entry points in the hindbrain exploring whether these neurons search for axon guidance cues coming from the vicinity tissues or whether they intrinsically know where to go. This view seems to consider differentiated neurons as a population of cells arising in the middle of nowhere that should cross through axonal navigation, a mesenchyme sort of dark forest. By SPIM in vivo imaging we demonstrate that once placodal-derived neurons of dorsal posterior cranial ganglia differentiate, they never lose contact with neural ectoderm. First, delaminated neuroblasts differentiate in close contact with the neural tube, and afferents entrance points are established by plasma membrane interactions between primary differentiated peripheral sensory neurons and neural tube border cells, with the cooperation of neural crest cells. Then, neural crest cells and repulsive slit1/robo2 guidance cues guide later-differentiated axons and mediate sensory ganglion coalescence, axonal branching and fasciculation. ; Los animales perciben el mundo externo a través de los sistemas sensoriales. Estos consisten en: i) los receptores ...