Calretinin expression in the chick cochlear nucleus after deafferentation

The expression of the calcium-binding protein calretinin (CR) in the chick cochlear nucleus, nucleus magnocellularis (NM), was examined after unilateral cochlea removal in hatchlings and 3-week-old birds. Following survival times of 3, 6 or 12 h or 1, 3 or 7 days, CR mRNA was localized by in situ hybridization using a radiolabeled chick CR probe. Levels of CR protein were assessed by CR-immunoreactivity (CR-I) using a calcium-independent CR antiserum and immunohistochemistry. At survival times of 1 day or less, cochlea removal did not change relative levels of CR mRNA or CR-I in NM between the deafferented and the unoperated sides of the brain. Decreases in CR expression on the cochlea removal side were observed, however, at times that coincide with deafferentation-induced cell loss (3 and 7 days). Additionally, bilateral cochlea removal had no apparent effect on CR-I in NM neurons when compared to those in normal animals. Thus, CR mRNA and protein appear to be constitutively expressed in NM neurons and are not affected by sensory deprivation.