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, Atp2b2^dfw-2J, Spnb4^qv-lnd2J, Spnb4^qv-3J, Myo7a^sh1, Tmie^sr, Myo6^sv, jc, Pcdh15^av-J, Pcdh15^av-2J, Pcdh15^av-3J, Cdh23^v-2J, Sans^js, hr, Kcne1^pkr, and Pou3f4^del. 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 Catna2^cdf, Grid2^ho4J, Wnt1^sw, qk, and Mbp^shi strains and heterozygotes of Grid2^lc 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 Mbp^shi 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, Otx1^jv, had all VsEP response parameters within normal limits - an expected finding because the abnormality in Otx1^jv 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.