Abstract
Prenatal auditory stimulation in chicks with species-specific sound and music at 65 dB facilitates spatial orientation and learning and is associated with significant morphological and biochemical changes in the hippocampus and brainstem auditory nuclei. Increased noradrenaline level due to physiological arousal is suggested as a possible mediator for the observed beneficial effects following patterned and rhythmic sound exposure. However, studies regarding the effects of prenatal high decibel sound (110 dB; music and noise) exposure on the plasma noradrenaline level, synaptic protein expression in the hippocampus and spatial behavior of neonatal chicks remained unexplored. Here, we report that high decibel music stimulation moderately increases plasma noradrenaline level and positively modulates spatial orientation, learning and memory of one day-old chicks. In contrast, noise at the same sound pressure level results in excessive increase of plasma noradrenaline level and impairs the spatial behavior. Further, to assess the changes at the molecular level, we have quantified the expression of functional synapse markers: synaptophysin and PSD-95 in the hippocampus. Compared to the controls, both proteins show significantly increased expressions in the music stimulated group but decrease in expressions in the noise group. We propose that the differential increase of plasma noradrenaline level and altered expression of synaptic proteins in the hippocampus are responsible for the observed behavioral consequences following prenatal 110 dB music and noise stimulation.
Highlights
Environmental stimuli influence the development of different sensory systems
It was evident from the data that the plasma noradrenaline level was increased following both types of sound stimulation but at the same time it is noteworthy that the increase was moderate in music (Mean difference with control: Male = 20.93, Female = 18.33) and excessive in noise (Mean difference with control: Male = 53.83, Female = 53.82) stimulated group as compared to the control (Fig. 4B)
Further post hoc analysis with Bonferroni test confirmed that the music stimulated chicks showed significantly elevated (p#0.001) plasma noradrenaline level as compared to the control whereas in the noise stimulated chicks, the level was even higher as compared to control (p#0.001) and music (p#0.001) stimulated chicks (Fig. 4B)
Summary
Environmental stimuli influence the development of different sensory systems. The importance of light exposure during development of the visual system has been extensively studied, demonstrating that modifications of visual input or its deprivation result in differential outcomes in brain structure and function [1,2,3,4,5,6]. Auditory stimulation by music or species-specific calls influences the cognitive performance of humans and different animals [7,8,9,10,11,12]. Our previous studies showed improved morphological and biochemical changes in chick hippocampus and facilitation of spatial orientation and learning at 12 hour post hatch consequent to prenatal sound stimulation by species-specific calls and sitar music at 65 dB [18,19,20,21]. The facilitation of learning was observed even at 24 hour post hatch with no further improvement in successive trials following the same sound enrichment protocol suggesting an early maturation of synaptic connectivity following prenatal sound stimulation. The avian hippocampus is involved in spatial learning as well as in memory [23,24,25] and is connected to the auditory pathway directly as well as indirectly [26,27,28,29]
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