The Effects of Acoustic White Noise on the Rat Central Auditory System During the Fetal and Critical Neonatal Periods: A Stereological Study.
OBJECTIVE
To evaluate the effects of long-term, moderate level noise exposure during crucial periods of rat infants on stereological parameters of medial geniculate body (MGB) and auditory cortex.


METHODS
Twenty-four male offspring of 12 pregnant rats were divided into four groups: fetal-to-critical period group, which were exposed to noise from the last 10 days of fetal life till postnatal day (PND) 29; fetal period group that exposed to noise during the last 10 days of fetal life; critical period group, exposed to noise from PND 15 till PND 29, and control group. White noise at 90 dB for 2 h per day was used.


METHODS
Variance for variables was performed using Proc GLM followed by mean comparison by Duncan's multiple range test.


RESULTS
Numerical density of neurons in MGB of fetal-to-critical period group was lower than control group. Similar results were seen in numerical density of neurons in layers IV and VI of auditory cortex. Furthermore, no significant difference was observed in the volume of auditory cortex among groups, and only MGB volume in fetal-to-critical period group was higher than other groups. Estimated total number of neurons in MGB was not significantly different among groups.


CONCLUSIONS
It seems necessary to prevent long-term moderate level noise exposure during fetal-to-critical neonatal period.
Department of Physiology, Faculty of Biological Sciences and Technology, Shahid Beheshti University, Tehran; Department of Animal Sciences, College of Agriculture, Shiraz University, Shiraz, Iran.
Mohammad Saied
MS
Salehi
Histomorphometry and Stereology Research Center, Shiraz University of Medical Sciences, Shiraz; Clinical Neurology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
Mohammad Reza
MR
Namavar
Transgenic Technology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
Amin
A
Tamadon
Department of Audiology, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran.
Raziyeh
R
Bahmani
Department of Animal Sciences, College of Agriculture, Shiraz University, Shiraz, Iran.
Mohammad Reza
MR
Jafarzadeh Shirazi
Department of Physiology, Faculty of Biological Sciences and Technology, Shahid Beheshti University, Tehran, Iran.
Homayoun
H
Khazali
Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Leila
L
Dargahi
Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Sareh
S
Pandamooz
Department of Animal Sciences, College of Agriculture, Shiraz University, Shiraz, Iran.
Farzad
F
Mohammad-Rezazadeh
Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Fatemeh Sadat
FS
Rashidi
D000818:Animals; D000831:Animals, Newborn; D001303:Auditory Cortex / Q000502:physiology*; D002452:Cell Count; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005829:Geniculate Bodies / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000502:physiology; D009622:Noise; D011247:Pregnancy; D051381:Rats