Expression of calcium-binding proteins in the chick auditory nuclei following prenatal auditory stimulation

Abstract

Aim: Auditory stimulation during development influences the morphological and neurochemical substrate of chick brainstem auditory nuclei, nucleus magnocellularis (NM) and nucleus laminaris (NL). Calcium-binding proteins (CaBPs) - calretinin (CR), calbindin (CALB), and parvalbumin (PV) - are known to buffer cytosolic calcium transients that occur with activation of neurons. In the present study, we examined the expression of three CaBPs - CR, CALB, and PV - in the NM and NL at embryonic days E12, E16, E20, and posthatch dayl (PH1), following prenatal sound enrichment protocol. Materials and methods: The incubating eggs were exposed to species-specific sound or music (sitar) at 65 dB for 15 min/h over a day/night cycle from E10 to E14 (low frequency) and E15 till hatching (high frequency). Results: Calretinin and parvalbumin were present in the developing normal and stimulated auditory nuclei, while CALB was absent. Calretinin-immunoreactivity (CR-IR) was present from E12 onward in NM and NL neurons of all the groups. The auditory stimulated groups showed no change in the expression of CR-IR in NM and NL. During normal development, PV was restricted to the cochlear nerve fibers at E16, and appeared in their terminals on the NM somata at PH1. In both stimulated groups, however, PV appeared earlier at E12 in the cochlear fibers and was prominently visualized from E16 in the NM and E20 in the NL neurons. Conclusions: Thus, CR and PV but not CALB are present in chick brainstem auditory nuclei for mediating calcium signaling and homeostasis. Prenatal sound caused an early activity-dependent maturation of PV but not CR which is a constitutive protein.