Acoustic and optoacoustic stimulations in auditory brainstem response test in salicylate induced tinnitus

Transcriptional profile changes caused by noise-induced tinnitus in the cochlear nucleus and inferior colliculus of the rat

INTRODUCTION

Tinnitus is a prevalent and disabling condition characterized by the perception of sound in the absence of external acoustic stimuli. The hyperactivity of the auditory pathway is a crucial factor in the development of tinnitus. This study aims to examine genetic expression variations in the dorsal cochlear nucleus (DCN) and inferior colliculus (IC) following the onset of tinnitus using transcriptomic analysis. The goal is to investigate the relationship between hyperactivity in the DCN and IC.

METHODS

To confirm the presence of tinnitus behavior, we utilized the gap pre-pulse inhibition of the acoustic startle (GPIAS) response paradigm. In addition, we conducted auditory brainstem response (ABR) tests to determine the baseline hearing thresholds, and repeated the test one week after subjecting the rats to noise exposure (8-16 kHz, 126 dBHL, 2 h). Samples of tissue were collected from the DCN and IC in both the tinnitus and non-tinnitus groups of rats. We employed RNA sequencing and quantitative PCR techniques to analyze the changes in gene expression between these two groups. This allowed us to identify any specific genes or gene pathways that may be associated with the development or maintenance of tinnitus in the DCN and IC.

RESULTS

Our results demonstrated tinnitus-like behavior in rats exposed to noise, as evidenced by GPIAS measurements. We identified 61 upregulated genes and 189 downregulated genes in the DCN, along with 396 upregulated genes and 195 downregulated genes in the IC. Enrichment analysis of the DCN revealed the involvement of ion transmembrane transport regulation, synaptic transmission, and negative regulation of neuron apoptotic processes in the development of tinnitus. In the IC, the enrichment analysis indicated that glutamatergic synapses and neuroactive ligand-receptor interaction pathways may significantly contribute to the process of tinnitus development. Additionally, protein-protein interaction (PPI) networks were constructed, and 9 hub genes were selected based on their betweenness centrality rank in the DCN and IC, respectively.

CONCLUSIONS

Our findings reveal enrichment of differential expressed genes (DEGs) associated with pathways linked to alterations in neuronal excitability within the DCN and IC when comparing the tinnitus group to the non-tinnitus group. This indicates an increased trend in neuronal excitability within both the DCN and IC in the tinnitus model rats. Additionally, the enriched signaling pathways within the DCN related to changes in synaptic plasticity suggest that the excitability changes may propagate to IC.

NEW AND NOTEWORTHY

Our findings reveal gene expression alterations in neuronal excitability within the DCN and IC when comparing the tinnitus group to the non-tinnitus group at the transcriptome level. Additionally, the enriched signaling pathways related to changes in synaptic plasticity in the differentially expressed genes within the DCN suggest that the excitability changes may propagate to IC.

Earable Multimodal Sensing and Stimulation: A Prospective Towards Unobtrusive Closed-Loop Biofeedback

The human ear has emerged as a bidirectional gateway to the brain's and body's signals. Recent advances in around-the-ear and in-ear sensors have enabled the assessment of biomarkers and physiomarkers derived from brain and cardiac activity using ear-electroencephalography (ear-EEG), photoplethysmography (ear-PPG), and chemical sensing of analytes from the ear, with ear-EEG having been taken beyond-the-lab to outer space. Parallel advances in non-invasive and minimally invasive brain stimulation techniques have leveraged the ear's access to two cranial nerves to modulate brain and body activity. The vestibulocochlear nerve stimulates the auditory cortex and limbic system with sound, while the auricular branch of the vagus nerve indirectly but significantly couples to the autonomic nervous system and cardiac output. Acoustic and current mode stimuli delivered using discreet and unobtrusive earables are an active area of research, aiming to make biofeedback and bioelectronic medicine deliverable outside of the clinic, with remote and continuous monitoring of therapeutic responsivity and long-term adaptation. Leveraging recent advances in ear-EEG, transcutaneous auricular vagus nerve stimulation (taVNS), and unobtrusive acoustic stimulation, we review accumulating evidence that combines their potential into an integrated earable platform for closed-loop multimodal sensing and neuromodulation, towards personalized and holistic therapies that are near, in- and around-the-ear.

Photobiomodulation therapy in improvement of harmful neural plasticity in sodium salicylate-induced tinnitus

Tinnitus is a common annoying symptom without effective and accepted treatment. In this controlled experimental study, photobiomodulation therapy (PBMT), which uses light to modulate and repair target tissue, was used to treat sodium salicylate (SS)-induced tinnitus in a rat animal model. Here, PBMT was performed simultaneously on the peripheral and central regions involved in tinnitus. The results were evaluated using objective tests including gap pre-pulse inhibition of acoustic startle (GPIAS), auditory brainstem response (ABR) and immunohistochemistry (IHC). Harmful neural plasticity induced by tinnitus was detected by doublecortin (DCX) protein expression, a known marker of neural plasticity. PBMT parameters were 808 nm wavelength, 165 mW/cm2 power density, and 99 J/cm2 energy density. In the tinnitus group, the mean gap in noise (GIN) value of GPIAS test was significantly decreased indicated the occurrence of an additional perceived sound like tinnitus and also the mean ABR threshold and brainstem transmission time (BTT) were significantly increased. In addition, a significant increase in DCX expression in the dorsal cochlear nucleus (DCN), dentate gyrus (DG) and the parafloccular lobe (PFL) of cerebellum was observed in the tinnitus group. In PBMT group, a significant increase in the GIN value, a significant decrease in the ABR threshold and BTT, and also significant reduction of DCX expression in the DG were observed. Based on our findings, PBMT has the potential to be used in the management of SS-induced tinnitus.