Decreasing dorsal cochlear nucleus activity ameliorates noise-induced tinnitus perception in mice

Abstract

Background The dorsal cochlear nucleus (DCN) is a region known to integrate somatosensory and auditory inputs and is identified as a potential key structure in the generation of phantom sound perception, especially noise-induced tinnitus. Yet, how altered homeostatic plasticity of the DCN induces and maintains the sensation of tinnitus is not clear. Here, we chemogenetically decrease activity of a subgroup of DCN neurons, Ca2+/Calmodulin kinase 2 α (CaMKII α)-positive DCN neurons, using Gi-coupled human M4 Designer Receptors Exclusively Activated by Designer Drugs (hM4Di DREADDs), to investigate their role in noise-induced tinnitus. Results Mice were exposed to loud noise (9–11kHz, 90dBSPL, 1h, followed by 2h of silence), and auditory brainstem responses (ABRs) and gap prepulse inhibition of acoustic startle (GPIAS) were recorded 2 days before and 2 weeks after noise exposure to identify animals with a significantly decreased inhibition of startle, indicating tinnitus but without permanent hearing loss. Neuronal activity of CaMKII α+ neurons expressing hM4Di in the DCN was lowered by administration of clozapine-N-oxide (CNO). We found that acutely decreasing firing rate of CaMKII α+ DCN units decrease tinnitus-like responses (p = 3e −3, n = 11 mice), compared to the control group that showed no improvement in GPIAS (control virus; CaMKII α-YFP + CNO, p = 0.696, n = 7 mice). Extracellular recordings confirmed CNO to decrease unit firing frequency of CaMKII α-hM4Di+ mice and alter best frequency and tuning width of response to sound. However, these effects were not seen if CNO had been previously administered during the noise exposure (n = 6 experimental and 6 control mice). Conclusion We found that lowering DCN activity in mice displaying tinnitus-related behavior reduces tinnitus, but lowering DCN activity during noise exposure does not prevent noise-induced tinnitus. Our results suggest that CaMKII α-positive cells in the DCN are not crucial for tinnitus induction but play a significant role in maintaining tinnitus perception in mice.

Alterations of auditory sensory gating in mice with noise-induced tinnitus treated with nicotine and cannabis extract

“…Analysis of auditory brainstem responses was done as pre-413 viously described (Malfatti et al, 2022) and consisted of 414 averaging the 529 trials, filter the signal using a 3rd order 415 butterworth bandpass filter from 600-1500 Hz, and slice 416 the data 12 ms after the sound pulse onset. Thresholds 417 were defined by automatically detecting the lowest inten-418 sity that can elicit a wave peak one standard deviation 419 above the mean, and preceded by a peak in the previous 420 intensity ( Malfatti et al, 2022). Effect of noise exposure 421 5/18 on ABR thresholds was evaluated using the Friedman Test, and pairwise comparisons were performed using the Wilcoxon test.…”

“…The frequency bands tested were: 8-10 kHz, 9-11 kHz, 10-12 kHz, 12-14 kHz and 14-16 kHz. Pulses were presented at 80 dBSPL in decreasing steps of 5 dBSPL to the final intensity 45 dB-SPL as previously described (Malfatti et al, 2022). The experimenter was blinded to the animal group during the ABR recordings.…”

“…Mice were initially screened 3 days before the noise exposure for their ability to detect the gap. Animals were then tested again 3 days after noise exposure or sham procedures (no noise), as previously described (Malfatti et al, 2022). In detail, animals were placed in custom-made acrylic cylinders perforated at regular intervals.…”

Alterations of auditory sensory gating in mice with noise-induced tinnitus treated with nicotine and cannabis extract

“…Mice were then screened 3 days before the noise exposure for their ability to detect the gap. Animals were then tested again 3 days after noise exposure or sham procedures (no noise), as previously described (Malfatti et al, 2022). Animals were placed in custom-made acrylic cylinders perforated at regular intervals.…”

Neurobiological Signatures of Auditory False Perception and Phantom Perception as a Consequence of Sensory Prediction Errors

“…We focused on neuroscientific evidence that there may be a cerebellum-like circuit that cancels responses to self-generated sounds at the earliest level (brainstem) for auditory processing [ 15 ]. The dorsal cochlear nucleus (DCN) operates as the key structure at the earliest level [ 16 ], and hearing deafferentation leads to a decrease in auditory input with a subsequent increase in somatosensory input to the DCN, which may play a role in the pathogenesis of tinnitus [ 17 ]. Moreover, the auditory predictions at higher stages in the hierarchy of auditory processing are made in the paraflocculus in the cerebellum, which is thought to integrate ECs [ 18 ].…”