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L Beazley, J Springbett, J Rodger, WY Shen, AC E Symonds, PE Rakoczy, SA Dunlop; Partial Denervation of the Superior Colliculus Induces Localised Up-regulation of Ephrin-A2 in the Adult Rat . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4773.
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Purpose: In the vertebrate visual system, the specificity of connections between the retina and superior colliculus (SC) is established by molecular interactions. During development in rat, mapping of naso-temporal retinal ganglion cell axons across the rostro-caudal axis of the SC is directed via graded expression of the tyrosine kinase receptor ligand ephrin-A21. A previous study in adult rat has shown that following optic nerve section, ephrin-A2 is up-regulated as an ascending rostro-caudal gradient across the contralateral and ipsilateral SC2. Here we have used localised retinal lesions to partially denervate the SC and investigate triggers for up-regulation. One series had ventro-temporal lesions to denervate rostral contralateral SC and the minor ipsilateral rostral projection. In another series dorso-nasal lesions denervated only caudal SC contralaterally. Methods: Ventro-temporal (VT; n=3) or dorso-nasal (DN; n=3) retina was ablated using laser surgery (Krypton 647.1nm, Coherent Radiation Systems; Ketamine: 35mg/kg and Xylazine: 5mg/kg, i.p.). One month post surgery, animals were sacrificed (Pentobarbitone 3.5ml, i.p.). Ephrin-A2 expression was investigated using immunohistochemistry and the extent of denervation by anterograde tracing with cholera toxin B. Results: Ephrin-A2 was up-regulated in denervated regions contralaterally, namely in rostral SC for VT lesions and caudal SC for DN lesions (p<0.05). Moreover, for both series, up-regulation was seen in the ipsilateral SC, in regions equivalent to those denervated on the contralateral side (p<0.05). Conclusion: The results indicate that denervation induces localised up-regulation of ephrin-A2. In addition an inter-collicular signal induces up-regulation in the opposite SC. 1. Flanagan, J. & Vanderhaeghen, P. (1998). Ann. Rev. Neurosci. 21:309-345. 2. Rodger, J. et al. (2001). Euro. J. Neurosci. (In Press).
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