Chondroitin sulfates in the developing rat hindbrain confine commissural projections of vestibular nuclear neurons
1 Department of Biochemistry, LKS Faculty of Medicine, The University of Hong Kong, Sassoon Road, Hong Kong, China
2 Cambridge Centre for Brain Repair, Cambridge University, Forvie Site, Robinson Way, Cambridge CB2 0PY, UK
3 Department of Physiology, LKS Faculty of Medicine, The University of Hong Kong, Sassoon Road, Hong Kong, China
4 Department of Anatomy, Histology and Embryology, The Fourth Military Medical University, Xi'an, China
5 Research Centre of Heart, Brain, Hormone and Healthy Aging, LKS Faculty of Medicine, The University of Hong Kong, Sassoon Road, Hong Kong, China
Neural Development 2012, 7:6 doi:10.1186/1749-8104-7-6Published: 3 February 2012
Establishing correct neuronal circuitry is crucial to proper function of the vertebrate nervous system. The abundance of chondroitin sulfate (CS) proteoglycans in embryonic neural environments suggests that matrix proteoglycans regulate axonal projections when fiber tracts have not yet formed. Among the early-born neurons, the vestibular nucleus (VN) neurons initiate commissural projections soon after generation at E12.5 and reach the contralateral target by E15.5 in the rat hindbrain. We therefore exploited 24-hour cultures (1 day in vitro (DIV)) of the rat embryos and chondroitinase ABC treatment of the hindbrain matrix to reveal the role of CS moieties in axonal initiation and projection in the early hindbrain.
DiI tracing from the VN at E12.5(+1 DIV) showed contralaterally projecting fibers assuming fascicles that hardly reached the midline in the controls. In the enzyme-treated embryos, the majority of fibers were unfasciculated as they crossed the midline at 90°. At E13.5(+1 DIV), the commissural projections formed fascicles and crossed the midline in the controls. Enzyme treatment apparently did not affect the pioneer axons that had advanced as thick fascicles normal to the midline and beyond, towards the contralateral VN. Later projections, however, traversed the enzyme-treated matrix as unfasciculated fibers, deviated from the normal course crossing the midline at various angles and extending beyond the contralateral VN. This suggests that CSs also limit the course of the later projections, which otherwise would be attracted to alternative targets.
CS moieties in the early hindbrain therefore control the course and fasciculation of axonal projections and the timing of axonal arrival at the target.