Correlation of histomorphometric changes with diffusion tensor imaging for evaluation of blast-induced auditory neurodegeneration in chinchilla.

In present study, we have evaluated the blast-induced auditory neurodegeneration in chinchilla by correlating the histomorphometric changes with diffusion tensor imaging. The chinchillas were exposed to single unilateral blast-overpressure (BOP) at ~17 dB peak SPL and the pathological changes were compared at the post-1 week and post-1 month of BOP. The functional integrity of the auditory system was assessed by auditory brainstem response and distortion product otoacoustic emissions (DPOAE). The axonal integrity was assessed using diffusion tensor imaging at regions of interests (ROIs) of the central auditory neuraxis (CAN) including the cochlear nucleus (CN), inferior colliculus (IC) and auditory cortex (AC). Post-BOP, cyto-architecture metrics such as viable cells, degenerating neurons and apoptotic cells were quantified at CAN ROIs using light microscopic studies using cresyl-fast violet, hematoxylin and eosin and modified crossmon's trichrome stains. We observed mean ABR threshold shifts of 30- and 10-dB SPL at post-BOP 1-week and 1-month respectively. A similar pattern was observed in DPAOE amplitudes shift. In the CAN ROIs, diffusion tensor imaging studies showed a decreased axial diffusivity in CN at post-BOP 1-month and a decreased mean diffusivity and radial diffusivity at post-BOP 1-week. However, morphometric measures such as decreased viable cells and increased degenerating neurons and apoptotic cells were observed at CN, IC and AC. Specifically, increased degenerating neurons and reduced viable cells were high on the ipsilateral side when compared to contralateral side. These results indicate that a single blast significantly damages structural and functional integrity at all levels of CAN ROIs.