Enhanced MRI and Acoustic Startle Reflex Testing

Avril Genene Holt, David Bissig, Najab Mirza, Gary Rajah, Bruce Berkowitz Introduction Between the military weapons and loud rock concerts emerging over the past couple decades a major growing health care concern is tinnitus, which is the perception of being able to hear a stimulus such as ringing, buzzing, or hissing that is not actually present. In the late, it has been found that tinnitus can be linked to an increase in spontaneous neuronal activity, but little is known about exact brain regions that tinnitus effects making drug targeting only partially successful. This was the first in vivo study examining specific auditory pathways and the correlated neuronal activity in subjects experiencing tinnitus. Methods • Auditory Brainstem response Testing • Salicylate and Noise Exposer induced tinnitus • Acoustic Startle Reflex Testing • MeMRI Results Implementing tinnitus inducing protocols using salicylate and noise exposer, tinnitus was induced in both groups of rats. However, it was seen that tinnitus in salicylate treated rats only experienced acute tinnitus that dissipated with the removal of salicylate. On the other hand, the noise induced group was seen to have permanent tinnitus perception showing limited ability to inhibit ASR 2 days post exposer. In MeMRI studies, the targeted brain regions were normalized to anterior pituitary uptake of manganese as well as local muscle uptake. It was seen that the DCN showed greater spontaneous activity compared to VCN in both normal hearing animals and tinnitus induced animals (no VCN activity was seen in tinnitus induced animals). Salicylate induced tinnitus animals displayed bilateral increases in manganese uptake following a systemic injection that was predicted. However, the noise induced animals also showed a bilateral increase in manganese uptake that was not predicted due to the fact that tinnitus was only induced in one ear with an ear plug protecting the opposing ear. This result was thought to be seen as a result of enough hearing preservation to successfully perform ASR testing, but enough damage to alter neural tissue activity in the IC. Finally, the DCN showed increased spontaneous neuronal activity via manganese uptake in only the salicylate group. With no significant changes in the DCN in the noise induced group, the authors’ hypothesize that the imaging time point may not have been correct at 2 days post exposer, because other studies have shown spontaneous neuronal activity 5 days post noise exposer. However in the IC both salicylate and noise-induced tinnitus groups a significant increase in manganese uptake was observed. The next study the authors’ would like to undertake is studying the auditory brain regions involved in tinnitus over a longer time frame, ie. A longitudinal study. ~JI