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Jae Hyek Choi, Joseph Novak, Teresa A Burke, Brian J Lund, Anthony James Johnson, Jeffery Cleland, Heuy-Ching Hetty Wang, ; Assessment of apoptosis along the optic nerve after low-level repeated blast exposure. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6228.
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Visual dysfunction is a common symptom observed in victims of blast-induced TBI. While effects on the brain of primary blast exposure have been extensively studied, there is little research on primary blast effects on the eye or visual system. In particular, little is known about the cumulative effects of repeated low-level blast exposure. The purpose of the present study is to characterize the effects of repeated low-level blast exposure on the optic nerve using a rat model.
A compressed-air driven shock tube was used to expose Long-Evans rats to blast waves of peak overpressure 68.0 ± 2.7 kPa and positive peak duration 2.8 ± 0.1 msec. For repeated blast exposure (RBE), rats were exposed once daily for five consecutive days then euthanized on day 5, one hour after the last blast exposure. Rats subjected to a single blast exposure (SBE) were euthanized 5 days following the one blast exposure, and rats not exposed to blast were included as controls. Optic nerve tissues were collected and processed for immunohistochemistry to detect activated caspase 3 and glial fibrillary acidic protein (GFAP). Quantification of caspase 3 positive cells was achieved using a morphometric grid on each 1 mm of the optic nerve.
Activated caspase 3 was detectable in the optic nerves from rats exposed to both SBE and RBE. For both SBE and RBE rats, a significantly higher number of caspase 3 positive cells were found in the 1 mm of optic nerve closest to the eye and optic chiasm. However, the presence of caspase 3 positive cells was significantly higher for the RBE rats than the SBE rats. In addition, increased GFAP was detected in the optic nerve from all animals subjected to blast exposure. Tissues from control animals not exposed to blast exposure were negative for activated caspase 3 and GFAP.
Low-level repeated blast exposure lead to an increase in apoptosis in the optic nerve, as indicated by an increase in caspase 3 positive cells. The section of the optic nerve closest to the eye was especially sensitive. This suggests that there is a cumulative effect to low-level blast exposure that may eventually lead to visual dysfunction.
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