Calbindin D-28K and parvalbumin expression in embryonic chick hippocampus is enhanced by prenatal auditory stimulation

Abstract

Calcium-binding proteins (CaBPs) buffer excess of cytosolic Ca²⁺, which accompanies neuronal activity following external stimuli. Prenatal auditory stimulation by species-specific sound and music influences early maturation of the auditory pathway and the behavioral responses in chicks. In this study, we determined the volume, total number of neurons, proportion of calbindin D-28K and parvalbumin-positive neurons along with their levels of expression in the developing chick hippocampus following prenatal auditory stimulation. Fertilized eggs of domestic chicks were exposed to sounds of either species-specific calls or sitar music at 65 dB for 15 min/h round the clock from embryonic day (E) 10 until hatching. Hippocampi of developmental stages (E12, E16 and E20) were examined. With an increase in embryonic age during normal development, the hippocampus showed an increase in its volume, total number of neurons as well as in the neuron proportions and levels of expression of calbindin D-28K and parvalbumin. A significant increase of volume at E20 was noted only in the music-stimulated group compared to that of their age-matched control (p < 0.05). On the other hand, both auditory-stimulated groups showed a significant increase in the proportion of immunopositive neurons and the levels of expression of calbindin D-28K and parvalbumin as compared to the control at all developmental stages studied (p < 0.003). The increase in proportions of CaBP neurons during development and in the sound-enriched groups suggests an activity-dependent increase in Ca²⁺ influx. The enhanced expression of CaBPs may help in cell survival by preventing excitotoxic death of neurons during development and may also be involved in long-term potentiation.