Vestibular Evoked Potential Thresholds Research Articles

Linear Acceleration Response Variation in Inbred Strains of Mice: The Requisite for Gene Discovery

Objectives: (1) Evaluate gravity receptor function using vestibular evoked potentials (VsEPs) recordings in different strains of mice. (2) Indicate functional variation in VsEPs response parameters across strains for the Genome-Wide Association Study (GWAS) mapping of the vestibular system. Methods: Mice (6 weeks old) were anesthetized with ketamine 100 mg/kg and xylazine 10 mg/kg and were positioned supine with the head mount coupled and the cranium securely fastened to a mechanical shaker. Stimuli consisted of linear acceleration (17 pulses/s) applied to the cranium in the naso-occipital axis. The first (P1) and second (P2) positive and negative response peaks were measured as phenotypes. Mice were selected based on a combined set of classic inbred (CI) and recombinant inbred (RI) strains from the Hybrid Mouse Diversity Panel (HMDP). A total of 13 CI (C57BL/6J, FVB/NJ, Balb/cJ, C3H/HeJ, Balb/cByJ, AKR/J, 129x1/SvJ, A/J, DBA/2J, SJL/J, CBA/J, SEA/GnJ, and NOD/ShiLtJ) and 10 RI (BXA14/PgnJ, BXD84/RwwJ, BXH19/TyJ, BXH22/KccJ, BXH9/TyJ, BXH10/TyJ, BXA14/PgnJ, BXA4/PgnJ, BXA16/PgnJ, and CXB9/HiAJ) were evaluated with an average of 2.7 mice/strain. Results: A wide range of phenotypic responses was observed. The mean threshold (–8.73 ± 5.1 dB re: 1 g/ms) and P2-N2 amplitude at +6 dB re: 1 g/ms (0.682 ± 0.51 mV) both demonstrated statistical significant variation (analysis of variance) in VsEP thresholds ( P = .008) and P2-N2 amplitude ( P = .001). Conclusions: These data demonstrate significant variation in VsEP response parameters across strains, strongly suggesting the hypothesis that there exists functional variation of vestibular function among strains of mice and the genetic determinants of such variation can be mapped using GWAS.

A null mutation of mouse Kcna10 causes significant vestibular and mild hearing dysfunction

KCNA10 is a voltage gated potassium channel that is expressed in the inner ear. The localization and function of KCNA10 was studied in a mutant mouse, B6-Kcna10TM45, in which the single protein coding exon of Kcna10 was replaced with a beta-galactosidase reporter cassette. Under the regulatory control of the endogenous Kcna10 promoter and enhancers, beta-galactosidase was expressed in hair cells of the vestibular organs and the organ of Corti. KCNA10 expression develops in opposite tonotopic gradients in the inner and outer hair cells. Kcna10TM45 homozygotes display only a mild elevation in pure tone hearing thresholds as measured by auditory brainstem response (ABR), while heterozygotes are normal. However, Kcna10TM45 homozygotes have absent vestibular evoked potentials (VsEPs) or elevated VsEP thresholds with prolonged peak latencies, indicating significant vestibular dysfunction despite the lack of any overt imbalance behaviors. Our results suggest that Kcna10 is expressed primarily in hair cells of the inner ear, with little evidence of expression in other organs. The Kcna10TM45 targeted allele may be a model of human nonsyndromic vestibulopathy.

Hearing and vestibular deficits in the Coch −/− null mouse model: Comparison to the Coch G88E/G88E mouse and to DFNA9 hearing and balance disorder

Two mouse models, the Coch G88E/G88E or “knock-in” and the Coch −/− or “knock-out” ( Coch null), have been developed to study the human late-onset, progressive, sensorineural hearing loss and vestibular dysfunction known as DFNA9. This disorder results from missense and in-frame deletion mutations in COCH ( coagulation factor C homology), encoding cochlin, the most abundantly detected protein in the inner ear. We have performed hearing and vestibular analyses by auditory brainstem response (ABR) and vestibular evoked potential (VsEP) testing of the Coch −/− and Coch G88E/G88E mouse models. Both Coch −/− and Coch G88E/G88E mice show substantially elevated ABRs at 21 months of age, but only at the highest frequency tested for the former and all frequencies for the latter. At 21 months, 9 of 11 Coch −/− mice and 4 of 8 Coch G88E/G88E mice have absent ABRs. Interestingly Coch −/+ mice do not show hearing deficits, in contrast to Coch G88E/+ , which demonstrate elevated ABR thresholds similar to homozyotes. These results corroborate the DFNA9 autosomal dominant mode of inheritance, in addition to the observation that haploinsufficiency of Coch does not result in impaired hearing. Vestibular evoked potential (VsEP) thresholds were analyzed using a two factor ANOVA (Age X Genotype). Elevated VsEP thresholds are detected in Coch −/− mice at 13 and 21 months, the two ages tested, and as early as seven months in the Coch G88E/G88E mice. These results indicate that in both mouse models, vestibular function is compromised before cochlear function. Analysis and comparison of hearing and vestibular function in these two DFNA9 mouse models, where deficits occur at such an advanced age, provide insight into the pathology of DFNA9 and age-related hearing loss and vestibular dysfunction as well as an opportunity to investigate potential interventional therapies.

Gravity Receptor Aging in the CBA/CaJ Strain: A Comparison to Auditory Aging

The CBA/CaJ mouse strain is commonly used as a control as it has no known genetic mutations affecting the inner ear, maintains hearing sensitivity throughout life, and serves as a background for creating new genetic strains. The purpose of the present study was to characterize the effects of age and gender on gravity receptor function and compare functional changes between auditory and vestibular modalities. Vestibular-evoked potentials (VsEPs), auditory brainstem responses (ABRs), and distortion product otoacoustic emissions were measured in 131 mice. VsEP thresholds deteriorated an average of 0.39dB re: 1.0g/ms per month and at the oldest ages (18-23months old) showed an average loss of 49% of VsEP dynamic range. No significant gender differences were found for VsEPs. ABR thresholds increased by an average of 1.35, 1.38, and 1.15dB pe SPL per month for ABR stimulus frequencies of 8, 16, and 32kHz, respectively, demonstrating an average decrease in auditory dynamic range of 25-35% at advanced ages. Both modalities declined with age. Age-related decreases in gravity receptor sensitivity should be considered when using the CBA/CaJ strain for vestibular studies.

A comparison of vestibular and auditory phenotypes in inbred mouse strains

The purposes of this research were to quantify gravity receptor function in inbred mouse strains and compare vestibular and auditory function for strain- and age-matched animals. Vestibular evoked potentials (VsEPs) were collected for 19 inbred strains at ages from 35 to 389 days old. On average, C57BL/6J (35 to 190 days), BALB/cByJ, C3H/HeSnJ, CBA/J, and young LP/J mice had VsEP thresholds comparable to normal. Elevated VsEP thresholds were found for elderly C57BL/6J, NOD.NONH2 kb, BUB/BnJ, A/J, DBA/2J, NOD/LtJ, A/WySnJ, MRL/MpJ, A/HeJ, CAST/Ei, SJL/J, elderly LP/J, and CE/J. These results suggest that otolithic function varies among inbred strains and several strains displayed gravity receptor deficits by 90 days old. Auditory brainstem response (ABR) thresholds were compared to VsEP thresholds for 14 age-matched strains. C57BL/6J mice (up to 190 days) showed normal VsEPs with normal to mildly elevated ABR thresholds. Four strains (BUB/BnJ, NOD/LtJ, A/J, elderly LP/J) had significant hearing loss and elevated VsEP thresholds. Four strains (DBA/2J, A/WySnJ, NOD.NONH2 kb, A/HeJ) had elevated VsEP thresholds (including absent VsEPs) with mild to moderate elevations in ABR thresholds. Three strains (MRL/MpJ, Ce/J, SJL/J) had significant vestibular loss with no concomitant hearing loss. These results suggest that functional change in one sensory system does not obligate change in the other. We hypothesize that genes responsible for early onset hearing loss may affect otolithic function, yet the time course of functional change may vary. In addition, some genetic mutations may produce primarily gravity receptor deficits. Potential genes responsible for selective gravity receptor impairment demonstrated herein remain to be identified.

A Quantitative Survey of Gravity Receptor Function in Mutant Mouse Strains

The purpose of this research was to identify vestibular deficits in mice using linear vestibular evoked potentials (VsEPs). VsEP thresholds, peak latencies, and peak amplitudes from 24 strains with known genetic mutations and 6 inbred background strains were analyzed and descriptive statistics generated for each strain. Response parameters from mutant homozygotes were compared with heterozygote and/or background controls and all strain averages were contrasted to normative ranges. Homozygotes of the following recessive mutations had absent VsEPs at the ages tested: Espn(je), Atp2b2dfw-2J, Spnb4qv-lnd2J, Spnb4qv-3J, Myo7ash1, Tmie(sr), Myo6sv, jc, Pcdh15av-J, Pcdh15av-2J, Pcdh15av-3J, Cdh23v-2J, Sans(js), hr, Kcne1pkr and Pou3f4del. These results suggest profound gravity receptor deficits for these homozygotes, which is consistent with the structural deficits that have been documented for many of these strains. Homozygotes of Catna2cdf, Grid2ho4J, Wnt1sw, qk, and Mbpshi strains and heterozygotes of Grid2lc had measurable VsEPs but one or more response parameters differed from the respective control group (heterozygote or background strain) or were outside normal ranges. For example, qk and Mbpshi homozygotes showed significantly prolonged latencies consistent with the abnormal myelin that has been described for these strains. Prolonged latencies may suggest deficits in neural conduction; elevated thresholds suggest reduced sensitivity, and reduced amplitudes may be suggestive for reduced neural synchrony. One mutation, Otx1jv, had all VsEP response parameters within normal limits--an expected finding because the abnormality in Otxljv is presumably restricted to the lateral semicircular canal. Interestingly, some heterozygote groups also showed abnormalities in one or more VsEP response parameters, suggesting that vestibular dysfunction, although less severe, may be present in some heterozygous animals.

Gravity receptor function in mice with graded otoconial deficiencies

The purpose of the present study was to examine gravity receptor function in mutant mouse strains with variable deficits in otoconia: lethal milk ( lm), pallid ( pa), tilted ( tlt), mocha ( mh), and muted ( mu). Control animals were either age-matched heterozygotes or C57BL/6J (abbr. B6) mice. Gravity receptor function was measured using linear vestibular evoked potentials (VsEPs). Cage and swimming behaviors were also documented. Temporal bones were cleared to assess the overall otoconial deficit and to correlate structure and function for lm mice. Results confirmed the absence of VsEPs for mice that lacked otoconia completely. VsEP thresholds and amplitudes varied in mouse strains with variable loss of otoconia. Some heterozygotes also showed elevated VsEP thresholds in comparison to B6 mice. In lm mice, which have absent otoconia in the utricle and a variable loss of otoconia in the saccule, VsEPs were present and average P1/N1 amplitudes were highly correlated with the average loss of saccular otoconia ( R=0.77, p<0.001). Cage and swimming behavior were not adversely affected in those animals with recordable VsEPs. Most, but not all, mice with absent VsEPs were unable to swim. Some animals were able to swim despite having no measurable gravity receptor response. The latter finding underscores the remarkable adaptive potential exhibited by neurobehavioral systems following profound sensory loss. It also shows that behavior alone may be an unreliable indicator of the extent of gravity receptor deficits.

Stimulus and recording variables and their effects on mammalian vestibular evoked potentials

Linear vestibular evoked potentials (VsEPs) measure the collective neural activity of the gravity receptor organs in the inner ear that respond to linear acceleration transients. The present study examined the effects of electrode placement, analog filtering, stimulus polarity and stimulus rate on linear VsEP thresholds, latencies and amplitudes recorded from mice. Two electrode-recording montages were evaluated, rostral (forebrain) to ‘mastoid’ and caudal (cerebellum) to ‘mastoid’. VsEP thresholds and peak latencies were identical between the two recording sites; however, peak amplitudes were larger for the caudal recording montage. VsEPs were also affected by filtering. Results suggest optimum high pass filter cutoff at 100–300 Hz, and low pass filter cutoff at 10000 Hz. To evaluate stimulus rate, linear jerk pulses were presented at 9.2, 16, 25, 40 and 80 Hz. At 80 Hz, mean latencies were longer (0.350–0.450 ms) and mean amplitudes reduced (0.8–1.8 μV) for all response peaks. In 50% of animals, late peaks (P3, N3) disappeared at 80 Hz. The results offer options for VsEP recording protocols.