Publications using TDT

Signal transducer and activator of transcription 1 (STAT1) is known to be an important player in inflammatory responses. STAT1 as a transcription factor regulates the expression of multiple proinflammatory genes. Inflammatory response is one of the common effects of ototoxicity. Our group reported that hair cells of STAT1 knockout (STAT1-KO) mice are less sensitive to ototoxic agents in-vitro. The effect of inflammatory responses in STAT1-KO mice has primarily been studied challenging them with several pathogens and analyzing different organs of those mice. However, the effect of STAT1 ablation in the mouse inner ear has not been reported. Therefore, we evaluated the cochlear function of wild type and STAT1-KO mice via auditory brain stem response (ABR) and performed histopathologic analysis of their temporal bones. We found ABR responses were affected in STAT1-KO mice with cases of bilateral and unilateral hearing impairment. Histopathologic examination of the middle and inner ears showed bilateral and unilateral otitis media. Otitis media was characterized by effusion of middle and inner ear that varied between the mice in volume and inflammatory cell content. In addition, the thickness of the middle ear mucosae in STAT1-KO mice were more pronounced than those in wild type mice. The degree of middle and inner ear inflammation correlated with ABR threshold elevation in STAT1-KO mice. It appears that a number of mice with inflammation underwent spontaneous resolution. The ABR thresholds were variable and showed a tendency to increase in homozygous and heterozygous STAT1-KO mice. These findings suggest that STAT1 ablation confers an increased susceptibility to otitis media leading to hearing impairment. Thus, the study supports the new role of STAT1 as otitis media predisposition gene.

Background In addition to the direct effects of irradiation, the induced inflammatory response may play an important role in the damage to the inner ear caused by radiotherapy for the treatment of head and neck cancers. Resolvin E1 (RvE1) has anti-inflammatory activity, acting by reducing neutrophil infiltration and proinflammatory cytokine expression. Therefore, in this study we sought to confirm whether the inflammation induced by irradiation was involved in damage to the inner ear after radiotherapy and to investigate the protective effect and underlying mechanism of RvE1 using mouse models. Methods A dose of RvE1 was delivered by intraperitoneal injection to mice before irradiation. Changes in the auditory brainstem response (ABR), relative balance ability, inner ear morphology and the expression levels of inflammatory factors in the inner ear were analyzed on days 7 and 14 after irradiation and compared among different experimental groups. Results Changes of ABR and relative balance ability showed the inner functions of experimental mice presented severe damage after irradiation, but the damage was significantly alleviated after RvE1 pretreatment compared to irradiation alone. Morphological analysis of the inner ear showed severe damage to the cochlea and vestibule after irradiation. In contrast, damage to the cochlea and vestibule was significantly reduced in the RvE1-pretreated group compared to that in the irradiation alone group. Along with these functional and morphological changes, the mRNA expression level of anti-inflammatory factors interleukin-2 was significantly increased, while those of proinflammatory factors interleukin-6 and tumor necrosis factor-α were significantly decreased in the inner ear of mice after RvE1 pretreatment compared to irradiation alone. Conclusions We believe that inflammation induced by irradiation is involved in the damage to the inner ear caused by radiotherapy, and that RvE1 reduces the damage caused by irradiation to the inner ear by regulating the induced inflammatory response.

Age-related hearing loss (ARHL) is the most common sensory disorder among the elderly, associated with aging and auditory hair cell death due to oxidative-stress-induced mitochondrial dysfunction. Although transgenic mice and long-term aging induction cultures have been used to study ARHL, there are currently no ARHL animal models that can be stimulated by intermittent environmental changes. In this study, an ARHL animal model was established by inducing continuous oxidative stress to promote short-term aging of cells, determined on the basis of expression of hearing-loss-induced phenotypes and aging-related factors. The incidence of hearing loss was significantly higher in dual- and triple-exposure conditions than in intermittent hypoxic conditions, high-fat diet (HFD), or d-galactose injection alone. Continuous oxidative stress and HFD accelerated cellular aging. An increase in Ucp2, usually expressed during mitochondrial dysfunction, was observed. Expression of Cdh23, Slc26a4, Kcnq4, Myo7a, and Myo6, which are ARHL-related factors, were modified by oxidative stress in the cells of the hearing organ. We found that intermittent hypoxia, HFD, and galactose injection accelerated cellular aging in the short term. Thus, we anticipate that the development of this hearing loss animal model, which reflects the effects of intermittent environmental changes, will benefit future research on ARHL.

Human pathogenic variants of TBC1D24 are associated with clinically heterogeneous phenotypes, including recessive nonsyndromic deafness DFNB86, dominant nonsyndromic deafness DFNA65, seizure accompanied by deafness, a variety of isolated seizure phenotypes and DOORS syndrome, characterized by deafness, onychodystrophy, osteodystrophy, intellectual disability and seizures. Thirty-five pathogenic variants of human TBC1D24 associated with deafness have been reported. However, functions of TBC1D24 in the inner ear and the pathophysiology of TBC1D24-related deafness are unknown. In this study, a novel splice-site variant of TBC1D24 c.965 + 1G > A in compound heterozygosity with c.641G > A p.(Arg214His) was found to be segregating in a Pakistani family. Affected individuals exhibited, either a deafness-seizure syndrome or nonsyndromic deafness. In human temporal bones, TBC1D24 immunolocalized in hair cells and spiral ganglion neurons, whereas in mouse cochlea, Tbc1d24 expression was detected only in spiral ganglion neurons. We engineered mouse models of DFNB86 p.(Asp70Tyr) and DFNA65 p.(Ser178Leu) nonsyndromic deafness and syndromic forms of deafness p.(His336Glnfs*12) that have the same pathogenic variants that were reported for human TBC1D24. Unexpectedly, no auditory dysfunction was detected in Tbc1d24 mutant mice, although homozygosity for some of the variants caused seizures or lethality. We provide some insightful supporting data to explain the phenotypic differences resulting from equivalent pathogenic variants of mouse Tbc1d24 and human TBC1D24.

Genetic hearing loss is a common health problem with no effective therapy currently available. DFNA15, caused by mutations of the transcription factor POU4F3, is one of the most common forms of autosomal dominant non-syndromic deafness. In this study, we established a novel mouse model of the human DFNA15 deafness, with a Pou4f3 gene mutation (Pou4f3Δ) identical to that found in a familial case of DFNA15. The Pou4f3(Δ/+) mice suffered progressive deafness in a similar manner to the DFNA15 patients. Hair cells in the Pou4f3(Δ/+) cochlea displayed significant stereociliary and mitochondrial pathologies, with apparent loss of outer hair cells. Progression of hearing and outer hair cell loss of the Pou4f3(Δ/+) mice was significantly modified by other genetic and environmental factors. Using Pou4f3(-/+) heterozygous knockout mice, we also showed that DFNA15 is likely caused by haploinsufficiency of the Pou4f3 gene. Importantly, inhibition of retinoic acid signaling by the aldehyde dehydrogenase (Aldh) and retinoic acid receptor inhibitors promoted Pou4f3 expression in the cochlear tissue and suppressed the progression of hearing loss in the mutant mice. These data demonstrate Pou4f3 haploinsufficiency as the main underlying cause of human DFNA15 deafness and highlight the therapeutic potential of Aldh inhibitors for treatment of progressive hearing loss.

The stria vascularis (SV) generates the endocochlear potential (EP) in the inner ear and is necessary for proper hair cell (HC) mechanotransduction and hearing. Cell junctions are indispensable for the establishment of compositionally distinct fluid compartments in the inner ear. Ototoxic drug cisplatin can damage SV and cause sensorineural hearing loss; however, the underlying mechanisms behind such injury are unclear. In this study, after the intraperitoneal injection of cisplatin (3 mg/kg/day for 7 days) in mice, we determined the auditory function by EP recording and auditory brainstem response (ABR) analysis, observed the ultrastructure of SV by transmission electron microscopy (TEM), and examined the expression and distribution of cell junction proteins by western blot, PCR, and immunofluorescence staining. We discovered that the EP was significantly reduced while ABR thresholds were significantly elevated in cisplatin-treated mice; cisplatin induced ultrastructural changes in marginal cells (MCs), endothelial cells (ECs), pericytes, etc. We found that cisplatin insulted auditory function not only by reducing the expression of zonula occludens protein-1 (ZO-1) in MCs of the SV but also by decreasing the expression of connexin 26 (Cx26) and connexin 43 (Cx43) in MCs and basal cells (BCs). More importantly, cisplatin induced activations of perivascular-resident macrophage-like melanocytes (PVM/Ms) and interleukin-1beta (IL-1 β ) as well as increased expressions of profibrotic proteins such as laminin and collagen IV in SV. Thus, our results firstly showed that cisplatin induced fibrosis, inflammation, and the complex expression change of cell junctions in SV.

Tissue-specific alternative splicing (AS) is emerging as one of the most exciting types of mechanisms associated with organ development and disease. In the auditory system, many hearing-related genes undergo AS, and errors in this process result in syndromic or non-syndromic hearing loss. However, little is known about the factors and mechanisms directing AS in the inner ear. In the present study, we identified a novel RNA-binding protein, Rbm24, which was critically involved in regulating inner-ear-specific AS. Rbm24 deletion resulted in hearing loss and defects in motor coordination. Global splicing analysis showed Rbm24 was required for correct splicing of a subset of pre-mRNA transcripts with essential roles in stereocilia integrity and survival of hair cells. Furthermore, we identified that Rbm24 directly regulated the splicing of Cdh23, a known disease gene responsible for human Usher syndrome 1D and non-syndromic autosomal recessive deafness DFNB12. In conclusion, our findings demonstrated that Rbm24 was a critical factor in regulating inner-ear-specific splicing and maintaining the hearing and motor coordination function of the inner ear. Our data not only offer mechanistic insights but also provide functional annotation of Rbm24 splicing targets that contribute to hearing loss.

Cells of the immune system are present in the adult cochlea and respond to damage caused by noise exposure. However, the types of immune cells involved and their locations within the cochlea are unclear. We used flow cytometry and immunostaining to reveal the heterogeneity of the immune cells in the cochlea and validated the presence of immune cell gene expression by analyzing existing single-cell RNA-sequencing (scRNAseq) data. We demonstrate that cell types of both the innate and adaptive immune system are present in the cochlea. In response to noise damage, immune cells increase in number. B, T, NK, and myeloid cells (macrophages and neutrophils) are the predominant immune cells present. Interestingly, immune cells appear to respond to noise damage by infiltrating the organ of Corti. Our studies highlight the need to further understand the role of these immune cells within the cochlea after noise exposure.

The administration of immune checkpoint inhibitors (ICIs) often leads to immune-related adverse events. However, their effect on auditory function is largely unexplored. Thorough preclinical studies have not been published yet, only sporadic cases and pharmacovigilance reports suggest their significance. Here we investigated the effect of anti-PD-1 antibody treatment (4 weeks, intraperitoneally, 200 μg/mouse, 3 times/week) on hearing function and cochlear morphology in C57BL/6J mice. ICI treatment did not influence the hearing thresholds in click or tone burst stimuli at 4–32 kHz frequencies measured by auditory brainstem response. The number and morphology of spiral ganglion neurons were unaltered in all cochlear turns. The apical-middle turns (<32 kHz) showed preservation of the inner and outer hair cells (OHCs), whilst ICI treatment mitigated the age-related loss of OHCs in the basal turn (>32 kHz). The number of Iba1-positive macrophages has also increased moderately in this high frequency region. We conclude that a 4-week long ICI treatment does not affect functional and morphological integrity of the inner ear in the most relevant hearing range (4–32 kHz; apical-middle turns), but a noticeable preservation of OHCs and an increase in macrophage activity appeared in the >32 kHz basal part of the cochlea.

Introduction Music is ubiquitous and powerful in the world's cultures. Music listening involves abundant information processing (e.g., pitch, rhythm) in the central nervous system and can also induce changes in the physiology, such as heart rate and perspiration. Yet, previous studies tended to examine music information processing in the brain separately from physiological changes. In the current study, we focused on the temporal structure of music (i.e., beat and meter) and examined the physiology, neural processing, and, most importantly, the relation between the two areas. Methods Simultaneous MEG and ECG data were collected from a group of adults ( N = 15) while they passively listened to duple and triple rhythmic patterns. To characterize physiology, we measured heart rate variability (HRV), indexing the parasympathetic nervous system function (PSNS). To characterize neural processing of beat and meter, we examined the neural entertainment and calculated the beat‐to‐meter ratio to index the relation between beat‐level and meter‐level entrainment. Specifically, the current study investigated three related questions: (a) whether listening to musical rhythms affects HRV; (b) whether the neural beat‐to‐meter ratio differed between metrical conditions, and (c) whether neural beat‐to‐meter ratio is related to HRV. Results Results suggest that while at the group level, both HRV and neural processing are highly similar across metrical conditions, at the individual level, neural beat‐to‐meter ratio significantly predicts HRV, establishing a neural–physiological link. Conclusion This observed link is discussed under the theoretical “neurovisceral integration model,” and it provides important new perspectives in music cognition and auditory neuroscience research.

The relationship between type 1 diabetes and hearing loss is not well known, although based on many pathological studies, type 2 diabetes induced hearing loss is associated with microcirculation problems in the inner ear. The purpose of this study was to investigate the correlation between type 1 diabetes and hearing loss through hearing function and immunohistochemical analyses using type 1 diabetic Akita or wild-type (WT) mice. The Akita mice had a significant increase in hearing thresholds, blood glucose, and insulin tolerance compared to WT mice. Histological analysis showed that the loss of cells and damage to mitochondria in the spiral ganglion neurons of Akita mice were significantly increased compared to WT. Also, the stria vascularis showed decreased thickness, loss of intermediate cells, and disturbance in blood capillary shape in the Akita mice. Moreover, a reduction in type I, II, and IV fibrocytes and Na+/K+-ATPase α1 expression in spiral ligament was also observed. Cleaved caspase-3 expression was highly expressed in spiral ganglion neurons. In conclusion, hearing loss in type 1 diabetes is caused not only by ion imbalance and blood flow disorders of cochlear endolymph, but through the degenerative nervous system via apoptosis-mediated cell death.

The auditory efferent system comprises descending projections from the cerebral cortex to subcortical nuclei, reaching the cochlear receptor through olivocochlear fibres. One of the functions attributed to this corticofugal system is to suppress irrelevant sounds during selective attention to visual stimuli. Medial olivocochlear neurons can also be activated by sounds through a brainstem reflex circuit. Whether the individual variability of this reflex is related to the cognitive capacity to suppress auditory stimuli is still controversial. Here we propose that the individual strength per animal of the olivocochlear reflex is correlated with the ability to suppress auditory distractors during visual attention in awake chinchillas. The olivocochlear reflex was elicited with a contralateral broad-band noise at ~ 60 dB and ipsilateral distortion product otoacoustic emissions were obtained at different frequencies (1–8 kHz). Fourteen chinchillas were evaluated in a behavioural protocol of visual attention with broad-band noise and chinchilla vocalizations as auditory distractors. Results show that the behavioural performance was affected by both distractors and that the magnitudes of the olivocochlear reflex evaluated at multiple frequencies were relevant for behavioural performance during visual discrimination with auditory distractors. These results stress the ecological relevance of the olivocochlear system for suppressing natural distractors.

Stress has pleiotropic physiologic effects, but the neural circuits linking stress to these responses are not well understood. Here, we describe a novel population of lateral septum neurons expressing neurotensin (LS Nts ) in mice that are selectively tuned to specific types of stress. LS Nts neurons increase their activity during active escape, responding to stress when flight is a viable option, but not when associated with freezing or immobility. Chemogenetic activation of LS Nts neurons decreases food intake and body weight, without altering locomotion and anxiety. LS Nts neurons co-express several molecules including Glp1r (glucagon-like peptide one receptor) and manipulations of Glp1r signaling in the LS recapitulates the behavioral effects of LS Nts activation. Activation of LS Nts terminals in the lateral hypothalamus (LH) also decreases food intake. These results show that LS Nts neurons are selectively tuned to active escape stress and can reduce food consumption via effects on hypothalamic pathways.

Transcranial alternating current stimulation increases neural spike entrainment and burstiness in the awake primate brain.

Long-term reliability of intracortical microelectrodes remains a challenge for increased acceptance and deployment. There are conflicting reports comparing measurements associated with recording quality with postmortem histology, in attempts to better understand failure of intracortical microelectrodes (IMEs). Our group has recently introduced the assessment of motor behavior tasks as another metric to evaluate the effects of IME implantation. We hypothesized that adding the third dimension to our analysis, functional behavior testing, could provide substantial insight on the health of the tissue, success of surgery/implantation, and the long-term performance of the implanted device. Here we present our novel analysis scheme including: (1) the use of numerical formal concept analysis (nFCA) and (2) a regression analysis utilizing modern model/variable selection. The analyses found complimentary relationships between the variables. The histological variables for glial cell activation had associations between each other, as well as the neuronal density around the electrode interface. The neuronal density had associations to the electrophysiological recordings and some of the motor behavior metrics analyzed. The novel analyses presented herein describe a valuable tool that can be utilized to assess and understand relationships between diverse variables being investigated. These models can be applied to a wide range of ongoing investigations utilizing various devices and therapeutics.

We normally regard sleep and wake as two distinct opposing brain states, where sleep requires silence of wake-promoting structures such as the locus coeruleus (LC)-norepinephrine (NE) system. We set out to investigate how cortical NE dynamics and NE-related astrocytic activity relates to LC population activity during sleep states. We show that LC displays regular phasic activity bouts during NREM sleep leading to a slow oscillatory pattern of prefrontal NE levels of which the majority of NE increases does not lead to awakening. NE troughs link to sleep spindles and continued NE decline transitions into REM sleep. Last, we show that prefrontal astrocytes have reduced sensitivity towards NE during sleep. Our results suggest that dynamic changes in the activity of wake-promoting systems during sleep create alternation between crucial sleep processes and broadening of sensitivity towards incoming sensory input. Highlights Extracellular levels of norepinephrine display dynamic changes during NREM and REM sleep Phasic activity of locus coeruleus neurons during NREM underlies slow norepinephrine oscillations Spindles occur at norepinephrine troughs and are abolished by norepinephrine increases Increased spindles prior to REM reflect the beginning of a long-lasting norepinephrine decline REM episodes are characterized by a sub-threshold continuous norepinephrine decline The responsiveness of astrocytic Ca 2+ to norepinephrine is reduced during sleep

Ventral tegmental area (VTA) neurons play roles in reward and aversion. We recently discovered that the VTA has neurons that co-transmit glutamate and GABA (glutamate-GABA co-transmitting neurons), transmit glutamate without GABA (glutamate-transmitting neurons), or transmit GABA without glutamate (GABA-transmitting neurons). However, the functions of these VTA cell types in motivated behavior are unclear. To identify the functions of these VTA cell types, we combine recombinase mouse lines with INTRSECT2.0 vectors to selectively target these neurons. We find that VTA cell types have unique signaling patterns for reward, aversion, and learned cues. Whereas VTA glutamate-transmitting neurons signal cues predicting reward, VTA GABA-transmitting neurons signal cues predicting the absence of reward, and glutamate-GABA co-transmitting neurons signal rewarding and aversive outcomes without signaling learned cues related to those outcomes. Thus, we demonstrate that genetically defined subclasses of VTA glutamate and GABA neurons signal different aspects of motivated behavior.

Acoustic information transduced by cochlear hair cells is continuously relayed from the auditory pathway to other sensory, motor, emotional and cognitive centers in the central nervous system. Human epidemiological studies have suggested that hearing loss is a risk factor for dementia and cognitive decline, but the mechanisms contributing to these memory and cognitive impairments are poorly understood. To explore these issues in a controlled experimental setting, we exposed adult rats to a series of intense blast wave exposures that significantly reduced the neural output of the cochlea. Several weeks later, we used the Morris Water Maze test, a hippocampal-dependent memory task, to assess the ability of Blast Wave and Control rats to learn a spatial navigation task (memory acquisition) and to remember what they had learned (spatial memory retention) several weeks earlier. The elevated plus maze and open field arena were used to test for anxiety-like behaviors. Afterwards, hippocampal cell proliferation and neurogenesis were evaluated using bromodeoxyuridine (BrdU), doublecortin (DCX), and Neuronal Nuclei (NeuN) immunolabeling. The Blast Wave and Control rats learned the spatial navigation task equally well and showed no differences on tests of anxiety. However, the Blast Wave rats performed significantly worse on the spatial memory retention task, i.e., remembering where they had been two weeks earlier. Deficits on the spatial memory retention task were associated with significant decreases in hippocampal cell proliferation and neurogenesis. Our blast wave results are consistent with other experimental manipulations that link spatial memory retention deficits (long term memory) with decreased cell proliferation and neurogenesis in the hippocampus. These results add to the growing body of knowledge linking blast-induced cochlear hearing loss with the cognitive deficits often seen in combat personnel and provide mechanistic insights into these extra auditory disorders that could lead to therapeutic interventions.

Sensory-driven decisions are formed by accumulating information over time. Although parietal cortex activity is thought to represent accumulated evidence for sensory-based decisions, recent perturbation studies in rodents and non-human primates have challenged the hypothesis that these representations actually influence behavior. Here, we asked whether the parietal cortex integrates acoustic features from auditory cortical inputs during a perceptual decision-making task. If so, we predicted that selective inactivation of this projection should impair subjects' ability to accumulate sensory evidence. We trained gerbils to perform an auditory discrimination task and obtained measures of integration time as a readout of evidence accumulation capability. Minimum integration time was calculated behaviorally as the shortest stimulus duration for which subjects could discriminate the acoustic signals. Direct pharmacological inactivation of parietal cortex increased minimum integration times, suggesting its role in the behavior. To determine the specific impact of sensory evidence, we chemogenetically inactivated the excitatory projections from auditory cortex to parietal cortex and found this was sufficient to increase minimum behavioral integration times. Our signal-detection-theory-based model accurately replicated behavioral outcomes and indicated that the deficits in task performance were plausibly explained by elevated sensory noise. Together, our findings provide causal evidence that parietal cortex plays a role in the network that integrates auditory features for perceptual judgments.