Differences in animal holder configuration used in primary blast injury studies affect functional outcomes

Abstract

Purpose : Blast injury is the signature injury of current military conflicts, and can be influenced by primary, secondary or tertiary forces. Here, we assessed how different animal holder configurations used in an acoustic blast overpressure (ABO) model can affect the type and magnitude of eye and brain injury.

Methods : Anesthetized adult male Long-Evans rats were placed into two different holders: “open” (whole head and neck exposed, body enclosed; n = 7), or “enclosed” (body enclosed, with window for ABO exposure; n = 15). ABO exposure (single blast; 63 kPa, 195 dB-SPL, to right side of head) was performed as previously described (Allen RS et al., J. Neurotrauma, 2018). At 2, 4, and 6 months post-ABO, visual function (optomotor response, OMR) was assessed in ABO- vs. non-ABO-exposed (control) rats (n = 22/group). Cognitive function (Y-maze) was assessed at 3 months post-ABO. Data was analyzed using one-way ANOVA (Y-maze) and two-way repeated measures ANOVA (OMR).

Results : Ipsilateral ABO-exposed eyes showed similar OMR deficits with both holders, e.g., significant deficits in spatial frequency (p < 0.001) and contrast sensitivity (p < 0.05). Contralateral eyes showed greater OMR deficits with the enclosed vs. the open holder for both spatial frequency (p < 0.01) and contrast sensitivity. ABO-exposed rats exhibited cognitive deficits with the open, but not the enclosed, holder (p < 0.05).

Conclusions : Animal holder configuration used in ABO model experiments can significantly affect outcomes. Using an enclosed holder may cause concussive injury to the contralateral eye due to contact with the holder wall or reflection of blast waves. With the open configuration, coup-contrecoup motion may damage the brain, whereas the enclosed configuration minimizes such motion and provides some protection. These results highlight the secondary and tertiary forces of blast exposure that should be considered when evaluating visual deficits in patients with blast injuries.

This is a 2020 ARVO Annual Meeting abstract.