Rotational Responses of Vestibular–Nerve Afferents Innervating the Semicircular Canals in the C57BL/6 Mouse

Abstract

Extracellular recordings were made from vestibularnerve afferents innervating the semicircular canals in anesthetized C57BL/6 mice ranging in age from 4-24 weeks. A normalized coefficient of variation was used to divide afferents into regular (CV*G0.1) and irregular (CV*90.1) groups. There were three overall conclusions from this study. First, mouse afferents resemble those of other mammals in properties such as resting discharge rate and dependence of response dynamics on discharge regularity. Second, there are differences in mouse afferents relative to other mammals that are likely related to the smaller size of the semicircular canals. The rotational sensitivity of mouse afferents is approximately threefold lower than that reported for afferents in other mammals. One consequence of the lower sensitivity is that mouse afferents have a larger linear range for encoding head velocity. The long time constant of afferent discharge, which is a measure of low-frequency response dynamics, is shorter in mouse afferents than in other species. Third, juvenile mice (age 4-7 weeks) appear to lack a class of low-sensitivity, highly irregular afferents that are present in adult animals (age 10-24 weeks). By analogy to studies in the chinchilla, these irregular afferents with low sensitivities for lower rotational frequencies correspond to calyx-only afferents. These findings suggest that, although the calyx ending on to type I hair cells is morphologically complete in mice by the age of about 1 month, the physiological response properties in these juvenile animals are not equivalent to those in adults.

Resting Discharge Patterns of Macular Primary Afferents in Otoconia-Deficient Mice

“…The range of normalized CV* values obtained from mice of the present study is comparable to that reported for mouse canal afferents (Lasker et al 2008;Yang and Hullar 2007). The range of CVs as well as the mean CV for the OTO+ data closely approximate those reported in Figure 1 of Yang and Hullar (2007) for "wild-type" C57 mice (no significant difference, p90.2).…”

“…These authors have argued that because CV for a given neuron can take on wide ranging values and because the curves of individual neurons tend not to intersect those of other neurons, cells may be uniquely ranked based on CV provided the comparison across neurons is made at the same discharge rate. For these reasons, procedures for normalizing CV for particular rates (generally designated CV*) have been developed and widely used e.g., Baird and Lewis 1986;Goldberg et al 1982Goldberg et al , 1990bLasker et al 2008;Yang and Hullar 2007). Here, we normalized CV to a 15-ms interval based on the coefficients of Baird et al (1988) for the chinchilla and on those of Lasker et al (2008)for the mouse.…”

Statistics of the Vestibular Input Experienced during Natural Self-Motion: Implications for Neural Processing

“…In addition, the arguments outlined above assume that either of the response dynamics of vestibular neurons or the statistics of natural vestibular stimuli are similar between humans and monkeys. Although comparison of vestibular neuron response properties across amniotes has revealed striking similarities (Fernández and Goldberg, 1971;Hullar et al, 2005;Sadeghi et al, 2007;Yang and Hullar, 2007;Lasker et al, 2008), further studies conducted in monkeys will be needed to test whether the statistics of natural vestibular stimuli are similar to those reported here.…”

Functional Development of the Vestibular System

“…Part of this early maturation depends on the initial growth of the animal. Hence the size of the vestibular organs, in particular of the semicircular canals, is a biomechanical constraint for the detection of the head movements (Muller, 1999;Yang and Hullar, 2007;Lambert et al, 2008;Lasker et al, 2008). In rats, the semicircular canals have reached ∼75% of their size at birth (Curthoys, 1979b).…”