Oculomotor Nerve Injury Induces Nuerogenesis in the Oculomotor and Edinger-Westphal Nucleus of Adult Dog

Technical developments have extensively promoted experimental and clinical studies on cranial nerve regeneration, but intracranial nerve recovery is still an unexplored research area compared to peripheral nerve repair. In this study, we researched whether neurogenesis occurs in adult oculomotor (OMN) and Edinger-Westphal nucleus (EWN) or not after oculomotor nerve injury. To assess cell proliferation in response to unilateral oculomotor nerve crush (ONC) in adult beagle dog, repetitive 5-bromo-2'-deoxyuridine (BrdU) intravenous injections were performed during 3 or 7 days before the dogs were euthanized 2 h after the last injection on days 3, 7, 14, and 28 post-ONC. The proliferating cell types were investigated with three cell phenotypic markers and confocal microscopy on serial sections throughout the whole extent of OMN and EWN. BrdU-positive nuclei were detected in bilateral OMNs and EWNs from 3 to 28 days after ONC with the peak value at 3 days. Confocal analysis revealed that partial BrdU-positive cells colocalized with nestin or beta III-tubulin or GFAP, and the number of every kind of double-labeled cell maintained an increased tendency from 3 to 28 days post-ONC. Neither single-labeled BrdU-positive nuclei nor double-labeled cells were detected in the subependymal layer of cerebral aqueduct (SELCA) of all unilateral ONC dogs; also, they were not observed in the OMNs, EWNs, and SELCA of intact and sham-operated dog. These findings demonstrate that ONC can trigger continual mitotic activity, proliferation of NSCs, neurogenesis, and astrogliogenesis in the OMN and EWN of adult dogs.