Prenatal loud music and noise: differential impact on physiological arousal, hippocampal synaptogenesis and spatial behavior in one day-old chicks.

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.

Effect of prenatal loud music and noise on total number of neurons and glia, neuronal nuclear area and volume of chick brainstem auditory nuclei, field L and hippocampus: a stereological investigation.

The present study explores whether prenatal patterned and unpatterned sound of high sound pressure level (110 dB) has any differential effect on the morphology of brainstem auditory nuclei, field L (auditory cortex analog) and hippocampus in chicks (Gallus domesticus). The total number of neurons and glia, mean neuronal nuclear area and total volume of the brainstem auditory nuclei, field L and hippocampus of post-hatch day 1 chicks were determined in serial, cresyl violet-stained sections, using stereology software. All regions studied showed a significantly increased total volume with increase in total neuron number and mean neuronal nuclear area in the patterned music stimulated group as compared to control. Contrastingly the unpatterned noise stimulated group showed an attenuated volume with reduction in the total neuron number. The mean neuronal nuclear area was significantly reduced in the auditory nuclei and hippocampus but increased in the field L. Glial cell number was significantly increased in both experimental groups, being highest in the noise group. The brainstem auditory nuclei and field L showed an increase in glia to neuron ratio in the experimental groups as compared to control. In the hippocampus the ratio remained unaltered between control and music groups, but was higher in the noise group. It is thus evident that though the sound pressure level in both experimental groups was the same there were differential changes in the morphological parameters of the brain regions studied, indicating that the characteristics of the sound had a role in mediating these effects.

Localization of 4-hydroxy 2-nonenal immunoreactivity in aging human retinal Müller cells.

Müller cells play a pivotal role in maintaining retinal homeostasis of the extracellular fluid environment. Information on whether human retinal Müller cells suffer from oxidative stress with normal aging is lacking. We examined post mortem human retinas for the localization of a biomarker of lipid peroxidation (4-hydroxy 2-nonenal, 4-HNE) by immunohistochemistry. We procured human eyes from donors (N=11; age: 45-91 years; post mortem delay: 1-3h), who had no history of ocular diseases. They were fixed in 4% paraformaldehyde and the retinas cryosectioned and labeled against anti-4-HNE employing the immunoperoxidase method. Compared to the lower age group (45-56 years), in the advanced age group (67-91 years), immunoreactivity (IR) to 4-HNE was prominent in peripheral Müller cell end-feet, select cells in the inner nuclear layer and in outer fibers located in the macular fiber layer of Henle. Colocalization with glutamine synthetase revealed that the 4-HNE positive profiles in the inner nuclear layer were Müller cells. Quantitative analysis revealed that the percentage of immunopositive cells in the inner nuclear layer as well as the grey levels of the immunoreaction products in the parafoveal and peripheral retinal regions significantly increased in the advanced age group. The findings indicate that Müller cells of human retina suffer from lipid peroxidation and are susceptible to damage in the course of normal, advanced aging.