Prenatal auditory enrichment with species-specific calls and sitar music modulates expression of Bcl-2 and Bax to alter programmed cell death in developing chick auditory nuclei

Postnatal auditory stimulation influences early perceptual learning. Previously we reported morphological effects of prenatal auditory stimulation by species-specific and sitar musical sounds on the chick brainstem auditory nuclei-nucleus magnocellularis and nucleus laminaris. At hatching, these two nuclei of auditory enriched embryos showed higher neuronal numbers, amongst other morphological changes. There were also increases in synaptophysin and syntaxin1 expressions in the sound enriched groups and modulation of the developmental expression of transcription factors c-Fos and c-Jun. We hypothesized that prenatal auditory enrichment may have reduced embryonic apoptosis in these nuclei with possible alteration of molecular mechanisms enhancing the postsynaptic neuron's ability to survive. In the present study, therefore, we examined apoptotic cell death by TUNEL technique and Bcl-2 expression using immunohistochemistry and immunoblotting. In the controls, a peak percentage in the TUNEL-positive cells was noted in the auditory nuclei at embryonic day 12, which was reduced at embryonic day 16. Bcl-2 immunoreactivity decreased from embryonic day 8 to embryonic day 12 overlapping the period of embryonic cell death in these nuclei. The stimulated groups, however, showed fewer apoptotic neurons and higher Bcl-2 level than that in the controls. On the other hand, Bax immunohistochemistry showed correlated reverse changes compared to Bcl-2 expression. Thus prenatal extra-acoustic stimulation appears to alter Bcl-2 and Bax expression to support cell survival and differentiation, thereby augmenting the development of auditory nuclei.