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

Abstract

In this study, we used image analysis to assess changes in calretinin immunoreactivity in the lateral (LSO) and medial (MSO) superior olivary nuclei in ferrets 2 months after unilateral cochlear ablations at 30-40 days of age, soon after hearing onset. These two nuclei are the first significant sites of binaural convergence in the ascending auditory system, and both receive direct projections from the deafferented cochlear nucleus. Cochlear ablation results in a decrease in the overall level of calretinin immunostaining within the LSO ipsilaterally compared with the contralateral side and with control animals and within the MSO bilaterally compared with control ferrets. In addition, the level of calretinin immunostaining ipsilaterally within neurons in the LSO was significantly less in cochlear ablated than control animals. In contrast, there was no effect of cochlear ablation on the level of calretinin immunostaining within neurons either in the contralateral LSO or in the MSO. These results are consistent with a downregulation in calretinin within the neuropil of MSO bilaterally and LSO ipsilaterally, as well as a downregulation in calretinin within somata in the ipsilateral LSO as a result of unilateral cochlear ablation soon after hearing onset. Thus, cochlear-driven activity appears to affect calcium binding protein levels in both neuropil and neurons within the superior olivary complex.

Quantitative assessment of developing afferent patterns in the cat inferior colliculus revealed with calbindin immunohistochemistry and tract tracing methods

“…In CNIC, a distinct afferent domain has been described for calretinin-immunopositive fibers. Calretinin immunostaining appears to be a neurochemical marker for the medial superior olivary nucleus (MSO) projections to the IC in birds (Takahashi et al, 1987) and most likely in mammals Alvarado et al, 2004) as well, although other inputs may be included that occupy overlapping domains. The location and pattern of distribution of CB correspond to afferent inputs to the CNIC from LSO.…”

Decreased levels of GABA in the inferior colliculus of the epilepsy-prone hamster (GPG/Vall)

“…The densitometric analysis method used in this study has been described previously (Alvarado et al, 2004;Fuentes-Santamaría et al, 2005). Briefly, analysis of the immunostaining was performed in every fourth section along the rostrocaudal extent of the IC.…”

Morphologic and neurochemical alterations in the superior colliculus of the genetically epilepsy-prone hamster (GPG/Vall)

“…The densitometric analysis method used in this study has been described in detail previously (Fuentes-Santamaria et al, 2003, 2005bAlvarado et al, 2004Alvarado et al, , 2005. The analysis was performed in four equally spaced sections from the middle third of the nucleus in each animal, avoiding the rostral and caudal poles.…”

“…A profile was defined as immunostained if the mean gray value was above that threshold for detection that was set as two standard deviations above the mean optical density of the whole image (Fuentes-Santamaria et al, 2003, 2005aAlvarado et al, 2004Alvarado et al, , 2005Alvarado et al, , 2007. Since it has been reported that immunostaining can be used as a relative measure of antigen levels (Huang et al, 1996;Yao and Godfrey, 1997), the mean gray level within the SC was used as an indirect indicator of the amount of either calbindin or parvalbumin in superficial and deep layers, respectively.…”

“…Calcium-binding proteins contribute to regulation of intracellular calcium concentration in neurons in the nervous system (Baimbridge et al, 1992). Interestingly, it has been suggested that intracellular calcium, and therefore, calcium-binding protein levels, could be regulated by modifications in neuronal electrical activity (Braun et al, 1991;Winsky and Jacobowitz, 1995; Fuentes-Santamaria et al, 2003, 2005bAlvarado et al, 2004Alvarado et al, , 2005. One of these proteins, calbindin, has been used in the present study as a neuronal marker for investigating possible activity-related changes in the superficial layers of the SC of the GPG/Vall hamster.…”