There is a fundamental gap in our understanding of the mitochondrial functions that are activated in afferent neurons during mechanotransduction and prolonged glutamate receptor activation. Our current objectives are 1.) to determine the extent to which the zebrafish lateral line afferent neurons phenocopy one the hallmarks of glutamate excitotoxicity observed in mammalian cochlea;and 2.) to identify the mitochondrial processes that may change their signaling during moderate levels of mechanotransduction vs. prolonged glutamate receptor activation. Our central hypotheses are that: 1.) prolonged glutamate receptor application will lead to swelling of afferent terminals and a disruption in afferent neuron firing in zebrafish;and 2.) moderate levels of mechanotransduction increase mitochondrial activity while prolonged glutamate receptor activation leads to mitochondrial stress and damage. The rationale for the proposed research is that protection of afferent neurons following noise overexposure requires an understanding of how normal levels of mechanotransduction and potentially excitotoxic insults trigger homeostatic and cytotoxic mechanisms in afferent neurons. Guided by preliminary data, this hypothesis will be tested by pursuing two specific aims: 1.) determine the extent to which prolonged glutamate receptor activation disrupts afferent neuron firing and compromises afferent terminal morphology;and 2.) identify mitochondrial processes that are activated in response to varying degrees of afferent neuron stimulation. To address these aims, we are using a combination of electrophysiology, immunohistochemistry, transmission electron microscopy and in vivo time-lapse imaging of zebrafish lateral line afferent neurons, which receive inputs from mechanosensory hair cells. The approach is innovative because it utilizes fluorescence reporters of cytoplasmic and mitochondrial function to visualize how afferent terminals vs. cell bodies respond to mechanotransduction and AMPA exposure in real time in an intact vertebrate. The proposed research is significant, because it will expand our understanding of how afferent neurons respond to the metabolic demands of mechanotransduction and will likely identify mitochondrial markers that are activated in response to AMPA exposure.
The proposed research is relevant to public health because it will expand our understanding of how auditory neurons respond to the metabolic demands of varying levels of sensory input, including both normal and excessive levels of activity. Thus, the proposed research is relevant to the part of NIH's mission that pertains to developing fundamental knowledge of how auditory neurons function and how they are affected by noise overexposure.