Effect of prenatal auditory stimulation on numerical synaptic density and mean synaptic height in the posthatch Day 1 chick hippocampus

Abstract Previous studies on prenatal auditory stimulation by species‐specific sound or sitar music showed enhanced morphological and biochemical changes in chick hippocampus, which plays an important role in learning and memory. Changes in the efficiency of synapses, synaptic morphology and de novo synapse formation affects learning and memory. Therefore, in the present study, we set out to investigate the mean synaptic density and mean synaptic height at posthatch Day 1 in dorsal and ventral part of chick hippocampus following prenatal auditory stimulation. Fertilized 0 day eggs of domestic chick incubated under normal conditions were exposed to patterned sounds of species‐specific and sitar music at 65 dB levels for 15 min/h round the clock (frequency range: 100–6300 Hz) from embryonic Day 10 till hatching. The synapses identified under transmission electron microscope were estimated for their numerical density by physical disector method and also the mean synaptic height calculated. Our results demonstrate a significant increase in mean synaptic density with no alterations in the mean synaptic height following both types of auditory stimulation in the dorsal as well as ventral part of the hippocampus. The observed increase in mean synaptic density suggests enhanced synaptic substrate to strengthen hippocampal function. Synapse 63:152–159, 2009. © 2008 Wiley‐Liss, Inc.