Gender differences in myogenic regulation along the vascular tree of the gerbil cochlea

Targeted therapeutic hypothermia protects against noise induced hearing loss

Introduction

Exposure to occupational or recreational loud noise activates multiple biological regulatory circuits and damages the cochlea, causing permanent changes in hearing sensitivity. Currently, no effective clinical therapy is available for the treatment or mitigation of noise-induced hearing loss (NIHL). Here, we describe an application of localized and non-invasive therapeutic hypothermia and targeted temperature management of the inner ear to prevent NIHL.

Methods

We developed a custom-designed cooling neck collar to reduce the temperature of the inner ear by 3-4°C post-injury to deliver mild therapeutic hypothermia.

Results

This localized and non-invasive therapeutic hypothermia successfully mitigated NIHL in rats. Our results show that mild hypothermia can be applied quickly and safely to the inner ear following noise exposure. We show that localized hypothermia after NIHL preserves residual hearing and rescues noise-induced synaptopathy over a period of months.

Discussion

This study establishes a minimally-invasive therapeutic paradigm with a high potential for rapid translation to the clinic for long-term preservation of hearing health.

Sex differences in the auditory functions of rodents

BACKGROUND

In humans, it is well known that females have better hearing than males. The mechanism of this influence of sex on auditory function in humans is not well understood. Testing the hypothesis of underlying mechanisms often relies on preclinical research, a field in which sex bias still exists unconsciously. Rodents are popular research models in hearing, thus it is crucial to understand the sex differences in these rodent models when studying health and disease in humans.

OBJECTIVES

This review aims to summarize the existing sex differences in the auditory functions of rodent species including mouse, rat, Guinea pig, Mongolian gerbil, and chinchilla. In addition, a concise summary of the hearing characteristics and the advantages and the drawbacks of conducting auditory experiments in each rodent species is provided.

DESIGNS

Manuscripts were identified in PubMed and Ovid Medline for the queries "Rodent", "Sex Characteristics", and "Hearing or Auditory Function". Manuscripts were included if they were original research, written in English, and use rodents. The content of each manuscript was screened for the sex of the rodents and the discussion of sex-based results.

CONCLUSIONS

The sex differences in auditory function of rodents are prevalent and influenced by multiple factors including physiological mechanisms, sex-based anatomical variations, and stimuli from the external environment. Such differences may play a role in understanding and explaining sex differences in hearing of humans and need to be taken into consideration for developing clinical therapies aim to improve auditory performances.

[Down-regulation of the Expression of Senescence Proteins P16 and P21 by Activating Connexin 43 in the Smooth Muscle of Spiral Modiolar Artery of Guinea Pigs]

OBJECTIVE

To analyze the correlation between connexin 43 (Cx43) and the expression of P16 and P21, aging-related proteins, and to investigate the possible role of Cx43 in the development of cell senescence with an aging model prepared by D-galactose (D-gal) intervention in the vascular smooth muscle cells (VSMCs) of guinea pig spiral modiolar artery (SMA).

METHODS

The VSMCs of guinea pig SMA were cultured with the adhesion method, and the markers of VSMCs were detected with immunofluorescence technique. The experiment has a control group, a D-gal group, and a group that received D-gal and gap junction agonist AAP10 intervention, hereafter referred to as the AAP10 group. Cell Counting Kit-8 (CCK-8) was used to check VSMC activity and to determine the concentration and duration of D-gal intervention. The mRNA expression of Cx43 in each group was checked with qRT-PCR. The expression of Cx43, P16 and P21 proteins in each group was examined with the Western blot. The expression and distribution of P16 and P21 proteins were examined with immunofluorescence assay.

RESULTS

Immunofluorescence results showed that the positive expression rate of cell actin (α-SM-actin) was over 90%. CCK-8 results showed that the optimal concentration of D-gal intervention was 30 mg/mL and the intervention duration was 48 h. qRT-PCR test showed that the mRNA expression of Cx43 in VSMCs in the D-gal group was significantly lower than that in the control group ( P<0.01), while it is higher in the AAP10 group than that of the D-gal group ( P<0.01); Western blot assay showed that the Cx43 expression level in VSMCs in the D-gal group was significantly lower than that in the control group ( P<0.01) and the expression of P16 and P21 was significantly higher than that in the control group ( P<0.01), the expression of Cx43 protein in AAP10 group was significantly up-regulated compared with that in the D-gal group ( P<0.01), while the expression of P16 and P21 was down-regulated significantly ( P<0.01); The results of immunofluorescence showed that P16 and P21 were mainly expressed in the cell nucleus. Semi-quantitative analysis of fluorescence intensity showed that the level of P16 and P21 protein in the D-gal group was significantly higher than that in the control group, and the fluorescence intensity of AAP10 group was significantly lower than that in the D-gal group ( P<0.01).

CONCLUSION

Up-regulation of Cx43 expression can reverse the D-gal-induced abnormal expression of P16 and P21, two aging-related proteins, in SMA. It is suggested that Cx43 on SMA may be involved in D-gal-induced cell senescence, which provides a theoretical basis and possible intervention target for the delay of cell senescence.

Novel QUEST MRI In Vivo Measurement of Noise-induced Oxidative Stress in the Cochlea

Effective personalized therapeutic treatment for hearing loss is currently not available. Cochlear oxidative stress is commonly identified in the pathogenesis of hearing loss based upon findings from excised tissue, thus suggesting a promising druggable etiology. However, the timing and site(s) to target for anti-oxidant treatment in vivo are not clear. Here, we address this long-standing problem with QUEnch-assiSTed Magnetic Resonance Imaging (QUEST MRI), which non-invasively measures excessive production of free radicals without an exogenous contrast agent. QUEST MRI is hypothesized to be sensitive to noise-evoked cochlear oxidative stress in vivo. Rats exposed to a loud noise event that resulted in hair cell loss and reduced hearing capability had a supra-normal MRI R1 value in their cochleae that could be corrected with anti-oxidants, thus non-invasively indicating cochlear oxidative stress. A gold-standard oxidative damage biomarker [heme oxidase 1 (HO-1)] supported the QUEST MRI result. The results from this study highlight QUEST MRI as a potentially transformative measurement of cochlear oxidative stress in vivo that can be used as a biomarker for improving individual evaluation of anti-oxidant treatment efficacy in currently incurable oxidative stress-based forms of hearing loss.

The effect of propofol infusion with topical epinephrine on cochlear blood flow and hearing: An experimental study

BACKGROUND AND OBJECTIVE

Propofol is the most commonly used intravenous (IV) anesthetic agent and is associated with hypotension upon induction of anesthesia. Intravenous propofol infusion has several properties that may be beneficial to patients undergoing middle ear surgery. Topical application of concentrated epinephrine is a valuable tool for achieving hemostasis in the middle ear and during mastoid surgery. The purpose of the present study was to determine the effects of propofol infusion with topical epinephrine on cochlear blood flow (CBF) and hearing in rats.

MATERIALS AND METHODS

Twenty one male Sprague-Dawley rats were divided into three groups. The rate of intravenous infusion of propofol was 4-6 ml/kg/hour. The first group (control group, n = 7) was given IV infusion of phosphate buffered saline (PBS) with topical application of PBS in the round window. In study group A (n = 7), the effect of topical phosphate buffered saline with IV infusion of propofol on CBF and hearing was evaluated. In study group B (n = 7), additional effects of topical epinephrine with IV infusion of propofol on CBF and hearing were evaluated. The laser Doppler blood flowmeter, CBF, and the mean arterial blood pressure (MAP) were measured and analyzed. Additionally, hearing test using auditory brainstem response (ABR) was performed in both groups.

RESULTS

In both groups, infusion of propofol induced a time-dependent decrease in MAP. Approximately 30 min after the start of the propofol infusion, the CBF started to decrease slowly. The decrease in CBF was significantly greater in the study group compared to the control group. The threshold was elevated in the study group relative to the control group.

CONCLUSION

During middle ear surgery, use of IV infusion of propofol with topical epinephrine cotton ball or cottonoid application is not recommended.

Ryanodine-induced vasoconstriction of the gerbil spiral modiolar artery depends on the Ca2+ sensitivity but not on Ca2+ sparks or BK channels

Background

In many vascular smooth muscle cells (SMCs), ryanodine receptor-mediated Ca²⁺ sparks activate large-conductance Ca²⁺-activated K⁺ (BK) channels leading to lowered SMC [Ca²⁺]_i and vasodilation. Here we investigated whether Ca²⁺ sparks regulate SMC global [Ca²⁺]_i and diameter in the spiral modiolar artery (SMA) by activating BK channels.

Methods

SMAs were isolated from adult female gerbils, loaded with the Ca²⁺-sensitive flourescent dye fluo-4 and pressurized using a concentric double-pipette system. Ca²⁺ signals and vascular diameter changes were recorded using a laser-scanning confocal imaging system. Effects of various pharmacological agents on Ca²⁺ signals and vascular diameter were analyzed.

Results

Ca²⁺ sparks and waves were observed in pressurized SMAs. Inhibition of Ca²⁺ sparks with ryanodine increased global Ca²⁺ and constricted SMA at 40 cmH₂O but inhibition of Ca²⁺ sparks with tetracaine or inhibition of BK channels with iberiotoxin at 40 cmH₂O did not produce a similar effect. The ryanodine-induced vasoconstriction observed at 40 cmH₂O was abolished at 60 cmH₂O, consistent with a greater Ca²⁺-sensitivity of constriction at 40 cmH₂O than at 60 cmH₂O. When the Ca²⁺-sensitivity of the SMA was increased by prior application of 1 nM endothelin-1, ryanodine induced a robust vasoconstriction at 60 cmH₂O.

Conclusions

The results suggest that Ca²⁺ sparks, while present, do not regulate vascular diameter in the SMA by activating BK channels and that the regulation of vascular diameter in the SMA is determined by the Ca²⁺-sensitivity of constriction.

High vascular tone of mouse femoral arteries in vivo is determined by sympathetic nerve activity via α1A- and α1D-adrenoceptor subtypes

Background and purpose

Determining the role of vascular receptors in vivo is difficult and not readily accomplished by systemic application of antagonists or genetic manipulations. Here we used intravital microscopy to measure the contributions of sympathetic receptors, particularly α₁-adrenoceptor subtypes, to contractile activation of femoral artery in vivo.

Experimental approach

Diameter and intracellular calcium ([Ca²⁺]_i) in femoral arteries were determined by intravital fluorescence microscopy in mice expressing a Myosin Light Chain Kinase (MLCK) based calcium-calmodulin biosensor. Pharmacological agents were applied locally to the femoral artery to determine the contributions of vascular receptors to tonic contraction and [Ca²⁺]_i,.

Key results

In the anesthetized animal, femoral arteries were constricted to a diameter equal to 54% of their passive diameter (i.e. tone = 46%). Of this total basal tone, 16% was blocked by RS79948 (0.1 µM) and thus attributable to α₂-adrenoceptors. A further 46% was blocked by prazosin (0.1 µM) and thus attributable to α₁-adrenoceptors. Blockade of P_2X and NPY₁ receptors with suramin (0.5 mM) and BIBP3226 (1.0 µM) respectively, reduced tone by a further 22%, leaving 16% of basal tone unaffected at these concentrations of antagonists. Application of RS100329 (α_1A-selective antagonist) and BMY7378 (α_1D-selective) decreased tone by 29% and 26%, respectively, and reduced [Ca²⁺]_i. Chloroethylclonidine (1 µM preferential for α_1B-) had no effect. Abolition of sympathetic nerve activity (hexamethonium, i.p.) reduced basal tone by 90%.

Conclusion and Implications

Tone of mouse femoral arteries in vivo is almost entirely sympathetic in origin. Activation of α_1A- and α_1D-adrenoceptors elevates [Ca²⁺]_i and accounts for at least 55% of the tone.

White matter hyperintensities predict low frequency hearing in older adults

Vascular disease has been proposed as a contributing factor for presbyacusis (age-related hearing loss). While this hypothesis is supported by pathological evidence of vascular decline in post-mortem human and animal studies, evidence in human subjects has been mixed with associations typically reported between a measure of vascular health and low frequency hearing in older women. Given the difficulty of characterizing the in vivo health of the cochlear artery in humans, an estimate of cerebral small vessel disease was used to test the prediction that age-related change in low frequency hearing and not high frequency hearing is related to a global decline in vascular health. We examined the extent to which these associations were specific to women and influenced by a history of high blood pressure in 72 older adults (mean age 67.12 years, SD = 8.79). Probability estimates of periventricular white matter hyperintensities (WMH) from T1- and fluid attenuated T2-weighted magnetic resonance images were significantly associated with a low frequency hearing metric across the sample, which were independent of age, but driven by women and people with a history of high blood pressure. These results support the premise that vascular declines are one mechanism underlying age-related changes in low frequency hearing.

NOS inhibition enhances myogenic tone by increasing rho-kinase mediated Ca2+ sensitivity in the male but not the female gerbil spiral modiolar artery

Cochlear blood flow regulation is important to prevent hearing loss caused by ischemia and oxidative stress. Cochlear blood supply is provided by the spiral modiolar artery (SMA). The myogenic tone of the SMA is enhanced by the nitric oxide synthase (NOS) blocker L-N^G-Nitro-Arginine (LNNA) in males, but not in females. Here, we investigated whether this gender difference is based on differences in the cytosolic Ca²⁺ concentration and/or the Ca²⁺ sensitivity of the myofilaments. Vascular diameter, myogenic tone, cytosolic Ca²⁺, and Ca²⁺ sensitivity were evaluated in pressurized SMA segments isolated from male and female gerbils using laser-scanning microscopy and microfluorometry. The gender difference of the LNNA-induced tone was compared, in the same vessel segments, to tone induced by 150 mM K⁺ and endothelin-1, neither of which showed an apparent gender-difference. Interestingly, LNNA-induced tone in male SMAs was observed in protocols that included changes in intramural pressure, but not when the intramural pressure was held constant. LNNA in male SMAs did not increase the global Ca²⁺ concentration in smooth muscle cells but increased the Ca²⁺ sensitivity. This increase in the Ca²⁺ sensitivity was abolished in the presence of the guanylyl cyclase inhibitor ODQ or by extrinsic application of either the nitric oxide (NO)-donor DEA-NONOate or the cGMP analog 8-pCPT-cGMP. The rho-kinase blocker Y27632 decreased the basal Ca²⁺ sensitivity and abolished the LNNA-induced increase in Ca²⁺ sensitivity in male SMAs. Neither LNNA nor Y27632 changed the Ca²⁺ sensitivity in female SMAs. The data suggest that the gender difference in LNNA-induced tone is based on a gender difference in the regulation of rho-kinase mediated Ca²⁺ sensitivity. Rho-kinase and NO thus emerge as critical factors in the regulation of cochlear blood flow. The larger role of NO-dependent mechanisms in male SMAs predicts greater restrictions on cochlear blood flow under conditions of impaired endothelial cell function.

Capitalizing on diversity: an integrative approach towards the multiplicity of cellular mechanisms underlying myogenic responsiveness

The intrinsic ability of resistance arteries to respond to transmural pressure is the single most important determinant of their function. Despite an ever-growing catalogue of signalling pathways that underlie the myogenic response, it remains an enigmatic mechanism. The myogenic response's mechanistic diversity has largely been attributed to 'hard-wired' differences across species and vascular beds; however, emerging evidence suggests that the mechanistic basis for the myogenic mechanism is, in fact, 'plastic'. This means that the myogenic response can change quantitatively (i.e. change in magnitude) and qualitatively (i.e. change in mechanistic basis) in response to environmental challenges (e.g. disease conditions). Consequently, understanding the dynamics of how the myogenic response capitalizes on its mechanistic diversity is key to unlocking clinically viable interventions. Using myogenic sphingosine-1-phosphate (S1P) signalling as an example, this review illustrates the remarkable plasticity of the myogenic response. We propose that currently unidentified 'organizational programmes' dictate the contribution of individual signalling pathways to the myogenic response and introduce the concept that certain signalling elements act as 'divergence points' (i.e. as the potential higher level regulatory sites). In the context of pressure-induced S1P signalling, the S1P-generating enzyme sphingosine kinase 1 serves as a divergence point, by orchestrating the calcium-dependent and -independent signalling pathways underlying microvascular myogenic responsiveness. By acting on divergence points, the proposed 'organizational programmes' could form the basis for the flexible recruitment and fine-tuning of separate signalling streams that underlie adaptive changes to the myogenic response and its distinctiveness across species and vascular beds.

Arteriolar vascular smooth muscle cells: mechanotransducers in a complex environment

Contraction of small artery (diameters typically less than 250 μm) vascular smooth muscle cells (VSMCs) plays a critical role in local control of blood flow and arterial pressure through its affect on vascular caliber. Specifically, contraction of small arteries in response to increased intraluminal pressure is referred to as the myogenic response and represents an important role for mechanotransduction. Critical questions remain as to how changes in pressure are sensed by VSMCs and transduced across the cell membrane to tune the contractile state of the cell. Recent studies suggest a pivotal role for interactions between VSMCs and extracellular matrix (ECM) proteins. Thus, pressure-induced deformation of ECM proteins and their cell surface receptors (for example, integrins) may initiate contraction and cytoskeletal remodeling through modulation of ion channels, membrane depolarization, increased intracellular Ca(2+) and actomyosin crossbridge cycling. Importantly, it is argued that the contractile properties of small artery VSMCs reflect an intimate and integrated interaction with their extracellular environment and the three-dimensional structure of the vessel wall.