Deletion of Shank1 has minimal effects on the molecular composition and function of glutamatergic afferent postsynapses in the mouse inner ear

Abstract

Shank proteins (1–3) are considered the master organizers of glutamatergic postsynaptic densities in the central nervous system, and the genetic deletion of either Shank1, 2, or 3 results in altered composition, form, and strength of glutamatergic postsynapses. To investigate the contribution of Shank proteins to glutamatergic afferent synapses of the inner ear and especially cochlea, we used immunofluorescence and quantitative real time PCR to determine the expression of Shank1, 2, and 3 in the cochlea. Because we found evidence for expression of Shank1 but not 2 and 3, we investigated the morphology, composition, and function of afferent postsynaptic densities from defined tonotopic regions in the cochlea of Shank1−/− mice. Using immunofluorescence, we identified subtle changes in the morphology and composition (but not number and localization) of cochlear afferent postsynaptic densities at the lower frequency region (8 kHz) in Shank1−/− mice compared to Shank1+/+ littermates. However, we detected no differences in auditory brainstem responses at matching or higher frequencies. We also identified Shank1 in the vestibular afferent postsynaptic densities, but detected no differences in vestibular sensory evoked potentials in Shank1−/− mice compared to Shank1+/+ littermates. This work suggests that Shank proteins play a different role in the development and maintenance of glutamatergic afferent synapses in the inner ear compared to the central nervous system.

Early communication deficits in the Shank1 knockout mouse model for autism spectrum disorder: Developmental aspects and effects of social context

“…One could argue that via deletion of Shank1 an auditory deficit might be causing the Shank1 −/− pups uttering fewer USV, since Braude et al [] found evidence for expression of Shank1 , but not Shank2 and Shank3 , in the cochlea. However, they did not detect any differences in auditory brainstem responses.…”

Sodium-activated potassium channels shape peripheral auditory function and activity of the primary auditory neurons in mice

“…All quantitative image analysis was performed on the raw image stacks, without deconvolution, filtering, or gamma correction. The number of synaptic elements per IHC were determined from 3D reconstructions generated using Imaris 6.4 software (Bitplane) as described previously 72 . Final figures were assembled using Adobe PhotoShop and Illustrator software (Adobe Systems).…”

Altered cochlear innervation in developing and mature naked and Damaraland mole rats

“…To obtain cochleae, animals were deeply anesthetized by either isoflurane inhalation (University of Groningen and University of Illinois at Chicago) or injection of a lethal dose of pentobarbital (University of Oldenburg) and then rapidly decapitated. Procedures published previously were used to isolate intact organs of Corti from cochleae for immunofluorescence (Braude et al, ; McLean, Smith, Glowatzki, & Pyott, ). To prevent differences in antigen detection due to differences in processing, identical fixation and immunostaining conditions were used for all specimens.…”