TNF-α Signaling in Noise Trauma-Induced PV Neuron Loss and Dysfunction

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PROJECT SUMMARY/ABSTRACT Noise trauma can lead to loss of parvalbumin-positive inhibitory interneurons in the auditory cortex, which is associated with audiotory processing deficit and tinnitus in rodent models. The mechanisms underlying noise- induced PV neuron loss are unknown. We propose to examine the hypothesis that differential activation of TNFR1 and TNFR2 in cortical PV neurons determines the fate of the PV neurons following noise trauma, with TNFR1 biasing for, and TNFR2 biasing against, neuronal loss and dysfunction. Specific Aim 1. Determine the effects of TNFR1 or TNFR2 knockdown on noise-induced PV neuron loss. PV-Cre-tdTomato mice will be injected with one of three viral vectors (with TNFR1 shRNA, TNFR2 shRNA or scrambled sequences as a control) in the auditory cortex, and exposed or sham-exposed to noise trauma. PV neurons will be visualized by the Cre reporter tdTomato in auditory cortical sections. Transfected neurons will be visualized with the viral reporter GFP. Our hypothesis predicts that noise-induced PV neuron loss will be reduced by TNFR1 knockdown, but enhanced by TNFR2 knockdown for the transfected PV neurons. Cell loss should not be altered for the populations of un-transfected PV neurons, and PV neurons transfected with the scrambled sequences. Specific Aim 2. Examine the effects of TNFR1 or TNFR2 knockdown on noise-induced dysfunction of PV neuron synapses. Our pilot data indicate that noise trauma leads to a reduced transmitter release probability at the output synapses of the PV neurons, and accelerated neurotransmitter depletion. We hypothesize that this synaptic dysfunction depends on the activation of TNFR1 in the surviving PV neurons, and knockdown of TNFR1 will prevent the synaptic deficits. In addition, knockdown of TNFR2 should exacerbate PV neuron dysfunction. PV-Cre-ChR2-tdTomato mice will be injected with one of the three viral vectors in the auditory cortex, and be exposed or sham-exposed to noise trauma. We will record optically activated inhibitory synaptic current in Layer2/3 pyramidal neurons in acute auditory cortical slices. Synaptic input-output curve, paired-pulse modulation and depletion will be examined. Afterward, the slices will be fixed and imaged to quantify PV neuron loss and viral transfection rate in the surviving PV neurons, which will then be correlated with PV neuron synaptic dysfunction.We hypothesize that noise exposure disrupts cortical PV neuron function, and PV neuron dysfunction is a cause of gap detection deficit. We propose to use a mouse model to test this central hypothesis in the follwing specific aims.