Behavioral Evidence of Blast-induced Tinnitus in Chinchilla using Preyer Reflex.

Prepulse inhibition (PPI) of acoustic startle reflex (ASR) measures sensory-motor gating. Further, it provides a platform to assess tinnitus using a gap as a prepulse in the middle of background noise (GPIAS). Despite its validity and debate on neural circuits, GPIAS is being tested on various species, such as rats, mice, guinea pigs, and gerbils. However, there is a considerable lack of evidence of PPI on chinchillas which is an ideal animal model in auditory studies. When optimizing parameters, we used the set parameters to assess blast-induced tinnitus using GPIAS. In this study, before subjecting animals to GPIAS, inhibition of startle using an NBPIAS paradigm was measured using a noise-burst as a prepulse stimulus and was presented 200 ms before the startle stimuli (broadband noise bursts at 120 dB SPL, 20 ms with rise/fall time of 1 ms). The prepulse: no prepulse ratio was calculated based on the Preyer response from the trials with and without prepulse. However, whole-body movement responses were also collected. The animals that robustly exhibited PPI were subjected to the GPIAS paradigm to measure inhibition of startle response using gap detection as a cue. In GPIAS, the background noise is either a narrow-band noise (one-third of octave bandwidth) centered at 1, 2, 4, 8 & 10 kHz or broadband noise presented at 75 dB SPL for 30 s before the presentation of startle stimuli. A gap duration of 100 ms was introduced into background noise in 50% of the trials at 200 ms before the startle stimuli. Both startle response magnitude and pinna displacement were measured. The gap startle ratio was calculated for a given frequency. Before blast exposure, tinnitus was measured by gap detection using prepulse inhibition. The flexion of the pinna was tracked using four IR cameras with reflective markers on the pinna and the center of the body. X, Y & Z coordinates over time were exported to MATLAB, and the magnitude of Preyer’s reflex was calculated for all error-free trials using pinna displacement. Importantly, in addition to the Preyer reflex, for analysis, we used logarithmized ASR ratios with a normal distribution instead of raw PPI values of non-normal distribution to infer GPIAS deficits. The parametric study of GPIAS using logarithmized ASR ratios provides a better interpretation of GPIAS deficits. Using the Preyer reflex instead of whole-body movement provides a better interpretation of GPIAS deficits in chinchillas. These results set the platform for using Chinchilla as a model to study tinnitus using the GPIAS paradigm.