Expression of Synaptic Proteins in the Hippocampus and Spatial Learning in Chicks following Prenatal Auditory Stimulation

Abstract

Prenatal auditory stimulation by species-specific sound influences the expression and levels of calcium-binding proteins in the chick hippocampus, which is important to learning and memory. Stimulation by sitar music additionally produces structural changes in the hippocampus. Synapse density, which influences the synaptic plasticity, is also increased following both types of sound stimulation. Here we report the expression of mRNA as well as levels of synaptic proteins (synaptophysin, synapsin I and PSD-95) in the hippocampus of developing chicks subjected to prenatal auditory stimulation. Further, to evaluate the behavioral outcome following acoustic stimulation, posthatch day 1 (PH1) chicks were analyzed by T-maze test for spatial learning. Fertilized zero day eggs were incubated under normal conditions and subjected to patterned sounds of species-specific or sitar music at 65 dB levels for 15 min/h over 24 h at a frequency range of 100–6,300 Hz for a period of 11 days from embryonic day (E) 10 until hatching. Following both types of prenatal acoustic stimulation, a significant increase in the levels of synaptophysin mRNA and protein was found from E12, whereas that of synapsin I and PSD-95 was observed from E16, suggesting early maturation of the excitatory synapse. A significant decrease in the time taken to reach the target over the 3 trials in both sound-stimulated groups indicates improved spatial learning. In the music-stimulated group, however, the time taken to reach the target was reduced from the very first trial, which may point to an involvement of other behavioral attributes in facilitating spatial navigation.