Resumo

OBJECTIVE: The glial cell line-derived neurotrophic factor (GDNF) has an important role in the development and function of the nervous system. Intraocular injections of GDNF stimulate the survival of photoreceptors and retinal ganglion cells. Indeed, GDNF and its receptors have been described both in retina and superior colliculus. The development of retinotectal topography takes place during the first two post-natal week. Therefore, herein we evaluated the effect of in vivo administration of GDNF upon the retino-collicular topographic map formation. METHODS: Lister Hooded rats received a single intravitreal injections of GDNF (7.5 ng/ ml) or PBS (vehicle) in the right eye at post-natal day 10 (PND 10). At PND 13, animals were injected in the left eye with horseradish peroxidase (HRP, Sigma type VI), used as an anterograde tracer to evaluate the distribution of retinal axons in the superior colliculus. 24 hours after HRP injection, animals were perfused through the heart and the brains removed. Sections obtained in a cryostate were processed for HRP histochemistry. RESULTS: Our data shown that PBS-injected rats display at PND 14, a normal distribution of ipsilateral retinotectal axons, characterized by a dense and well-defined terminal zone located at the ventral border of the SGS in the anterior third of the colliculus. Conversely, a single intravitreal injection of GDNF leads to an expansion of uncrossed projection throughout the superior colliculus. In this group, we observed an increase in HRP terminal/fiber labeling both in rostro-caudal and medio-lateral axis of superior colliculus. CONCLUSIONS: Our data shown that exogenous GDNF leads to a sprouting of uncrossed retinotectal axons in the opposite eye. This response suggests that GDNF has a neuromodulatory role on active reorganization of the axons leaving the retina towards the superior colliculus. Keywords: GDNF, Retinotectal, Development Financial support: FAPERJ, CNPq, PRONEX-MCT, PROPPi-UFF, PROAP-UFF