Studies have demonstrated that optic nerve transection results in apoptotic cell death of retinal ganglion cells (RGCs) and neurons within lateral geniculate nucleus (LGN). Heat shock protein (Hsp) 70 was reported to be involved in protecting cells from injury under various pathological conditions in vivo and in vitro. To determine the involvement of Hsp70 in protecting neurons within LGN against damage or loss induced by optic nerve injuries, we observed the changes in protein expression and distribution of Hsp70 in LGN at days 1, 3, 7, 14 and 28 after unilateral optic nerve transection in the left eye of Sprague-Dawley rats by using Western blot analysis and immunohistochemical staining. We found that the levels of Hsp70 protein expression increased significantly (p < 0.05, n = 6 for each group) in both right and left LGN of rats following left optic nerve transection 1-7 days. The maximum of Hsp70 expression reached at day 3. However, Hsp70 protein expression levels in both right and left LGN returned to control levels at 14 and 28 days after left optic nerve lesion. In addition, the increased Hsp70 expression, which mainly localized in the intergeniculate leaflet of LGN, was also observed by immunostaining in right LGN at the end of day 3 after the lesion. These results suggest that increased expression of Hsp70 may be involved in protecting neurons within LGN against damage or loss induced by left optic nerve transection at early stage. (c) 2006 Published by Elsevier Ireland Ltd.