Quantitative changes in calretinin immunostaining in the cochlear nuclei after unilateral cochlear removal in young ferrets

Abstract

Neurons of the cochlear nuclei receive axosomatic endings from primary afferent fibers from the cochlea and have projections that diverge to form parallel ascending auditory pathways. These cells are characterized by neurochemical phenotypes such as levels of calretinin. To test whether or not early deafferentation results in changes in calretinin immunostaining in the cochlear nucleus, unilateral cochlear ablations were performed in ferrets soon after hearing onset (postnatal day [P]30-P40). Two months later, changes in calretinin immunostaining as well as cell size, volume, and synaptophysin immunostaining were assessed in the anteroventral (AVCN), posteroventral (PVCN), and dorsal cochlear nucleus (DCN). A decrease in calretinin immunostaining was evident ipsilaterally within the AVCN and PVCN but not in the DCN. Further analysis revealed a decrease both in the calretinin-immunostained neuropil and in the calretinin-immunostained area within AVCN and PVCN neurons. These declines were accompanied by significant ipsilateral decreases in volume as well as neuron area in the AVCN and PVCN compared with the contralateral cochlear nucleus and unoperated animals, but not compared with the DCN. In addition, there was a significant contralateral increase in calretinin-immunostained area within AVCN and PVCN neurons compared with control animals. Finally, a decrease in area of synaptophysin immunostaining in both the ipsilateral AVCN and PVCN without changes in the number of boutons was found. The present data demonstrate that unilateral cochlear ablation leads to 1) decreased immunostaining of the neuropil in the AVCN and PVCN ipsilaterally, 2) decreased calretinin immunostaining within AVCN and PVCN neurons ipsilaterally, 3) synaptogenesis in the AVCN and PVCN ipsilaterally, and 4) increased calretinin immunostaining within AVCN and PVCN neurons contralaterally.

Alterations in calretinin immunostaining in the ferret superior olivary complex after cochlear ablation

“…Under normal conditions, the MSO receives direct excitatory afferents from both the ipsilateral and the contralateral ventral cochlear nucleus neurons (Glendenning et al, 1985;Cant and Casseday, 1986;Cant, 1991;Thompson and Schofield, 2000). Several studies have reported that the majority of these neurons and axons are calretinin-positive, and after unilateral deafferentation a significant decrease within those neurons and fibers is evident in the ipsilateral ventral cochlear nucleus (Winsky and Jacobowitz, 1995;Caicedo et al, 1997;Fuentes-Santamaria et al, 2003b). It is possible that changes in calretinin immunoreactivity in the cochlear nucleus are reflected in their projections to the MSO and therefore to the calretinin-immunoreactive neuropil.…”

Consequences of unilateral hearing loss: Time dependent regulation of protein synthesis in auditory brainstem nuclei

“…Studies on the expression of calcium binding proteins in the central auditory system, calretinin in particular, provide some supportive evidence for this conclusion. Calretinin is found in central auditory system structures related to pathways important for sound localization (e.g., Caicedo et al, 1996), and calretinin immunoreactivity is high in the neuropil and neurons of AVCN, LSO, and MSO (Caicedo et al, 1996;Alvarado et al, 2004;Fuentes-Santamaria et al, 2005). Caicedo et al (1997) demonstrated that within 6 h of temporary deafferentation (by intracochlear AMPA perfusion), there was a significant reduction in calretinin staining only in neurons of the ipsilateral MSO.…”

β‐adrenergic receptors are differentially expressed in distinct interneuron subtypes in the rat hippocampus

“…Anti-calretinin antibody recognized a protein of the expected molecular weight (ϳ31 kDa) by Western blotting in ferret cochlear nucleus lysate (Fuentes-Santamaria et al, 2005). Low-magnification images of ␤1AR and ␤2AR distribution, respectively, in hippocampal sections.…”