Exposure to Chronic Noise Reduces the Volume of Hippocampal Subregions in Rats

Document Type : Original Article


1 Department of Anatomy, School of Medicine, Yazd University of Medical Sciences, Yazd, Iran

2 Departments of Anatomical Sciences, School of Medicine Isfahan, University of Medical Sciences, Isfahan, Iran


The hippocampal circuit integrity is crucial for learning and memory. Despite the existing reports on hippocampal–dependent memory impairment due to noise stress, there are only a few studies on the effect of noise stress on anatomical structure of hippocampus. The present study is aimed to investigate the likely effects of chronic noise exposure on the volume of rat hippocampus.
Materials and Methods
Two-month male Wistar rats were randomly divided into three groups (n=10 in each group). In the control group rats were maintained under standard laboratory conditions (150 days). In the noise-exposed group: Rats were exposed to 40 dB unmodulated sinosoidal noise with a frequency of 1100 Hz for 20 mins, three times per day for 90 days. The recovery group rats were exposed to noise for 90 days and allowed to survive without further treatment until the day of sacrifice (180th day). The right hemispheres were selected for stereological study. Twenty five μm thick sections were cut along the entire extent of the hippocampus. Using systematic uniformly random sampling, one section from every twenty sections was analyzed. Volume estimation was performed using Cavalieri principle.
Statistical analysis revealed that noise stress induces a significant reduction in volume of all layers of hippocampal subdivisions, except CA1 hippocampal field. In addition, we found that rats which were allowed to recover from noise displayed larger volume ofdentate gyrus and CA3 hippocampal field in comparison to noise-exposed rats.
Reduced volume of hippocampal layers most probably reflects structural alterations in the neurites of related neurons. These results provide a neuroanatomical basis that may be relevant to the reported memory disturbances in human and animals following noise stress.


1.   Spreng M. Possible health effect of noise induced cortisol increase. Noise Health 2000; 2:59-64.
2.   Spreng M. Central nervous system activation by noise. Noise Health 2000; 2:49-58.
3.   Eichenbaum H, Oto T. The hippocampus – what does it do?  Behav Neuroal Biol 1992; 57:2-36.
4.  Rusakov DA, Davies HA, Harrison E, Diana G, Richter LG, Bliss TVP. Ultrastructural synaptic correlates of spatial learning in rat hippocampus. Neuroscience 1997; 80:69-77.
5.  Sousa RJ, Tannary NH, Lafer EM. In situ hybridisation mapping of glucocorticoid receptor messenger ribonucleic acid in rat brain. Mol Endocrinol 1989; 3:481- 494.
6.  Prior H. Effects of predictable and unpredictable intermittent noise on spatial learning in rats. Behav Brain Res 2002; 133: 117-124.
7.  Manikandan S, Padma MK, Srikumar R, Jeya Parthasarathy N, Muthuvel A, Sheela Devi R. Effects of chronic noise stress on spatial memory of rats in relation to neuronal dendritic alteration and free radical-imbalance in hippocampus and medial prefrontal cortex. Neurosci Lett 2006; 399:17-22.
8.  Haines MM, Brentnall SL, Stansfeld SA, Klineberg E. Qualitative responses of children to environmental noise. Noise Health  2003; 19:19-30.
9.  Sabahi AR. Hosseini-sharifabad M. Effect of noise pollution on passive avoidance learning and the size of hippocampus in rat. J Isfahan Med Sch 2006; 24:44-48.
10. Gundersen HJG, Jensen EB. Stereological estimation of the volume-weighted mean volume of arbitrary particles observed on random sections. J Microsc 1985; 138:127-142.
11.  West MJ, Slomianka L, Gundersen, HJG. Unbiased stereological estimation of the total number of neurons in the subdivisions of the rat hippocampus using the optical fractionator. Anat Rec 1991; 231:482-497.
12.  Gundersun HJG, Jensen EB. The efficiency of systematic sampling in stereology and its prediction. J Microsc 1987; 147:229-263.
13.  West MJ, Gundersen HJG. Unbiased stereological estimations of the number of neurons in the human hippocampus. J Comp Neurol 1990; 296:1-22
14.  Monsefi M, Bahoddini A, Nazemi S, Dehghani GA. Effects of noise exposure on the volume of adrenal gland and serum levels of cortisol in rat. Iran J Med Sci 2006; 31:5-8.
15.  Spreng M. Cortical excitations, cortisol excretion and estimation of tolerable nightly over-flights. Noise Health 2002; 4:39-46.
16.  Sabahi AR, Moradi I. Study of serum cortisol in relation to noise pollution in rats. J Isfahan Med Sch 2003; 68: 17-19.
17.  McEwen BS, Magarinos AM. Stress and hippocampal plasticity: implications for the pathophysiology of affective disorders. Hum Psychopharmacol 2001; 16: 7-19.
18.    Gould E, Tanapat P. Stress and Hippocampal Neurogenesis. Biol Psychiatry 1999; 46:1472-1479.
19.  Sapolsky RM. Stress, glucocorticoids, and damage to the nervous system: The current state of confusion. Stress 1996; 1:1-19.
20.  Sapolsky RM, Krey LC, McEwen BS. Prolonged glucocorticoid exposure reduces hippocampal neuron number: implications for aging. J Neurosci 1985; 5:1221-1227.
21.  Uno H, Eisele S, Sakai A, Shelton S, Baker E, DeJesus O. Neurotoxicity of glucocorticoids in the primate brain. Horm Behav 1994;28:336-348.
22.  Smith MA, Makino S, Kvetnansky R, Post R M. Stress and glucocorticoids affect the expression of brain-derived neurotrophic factor and neurotrophin-3 mRNAs in the hippocampus. J Neurosci 1995; 15:1768–1777.
23.  Sofroniew MV, Cooper JD, Svendsen CN, Crossman P, Ip NY, Lindsay RM, et al. Atrophy but not death of adult septal cholinergic neurons after ablation of target capacity to produce mRNAs for NGF, BDNF, and NT3. J Neurosci 1993; 13:5263-5276.
24.  De Kloet ER, Vreugdenhil E, Oitzl MS, Joels M. Brain corticosteroid receptor balance in health and disease. Endocr Rev 1998; 19:269-301.
25.   Reul JM, De Kloet ER. Two receptor systems for corticosterone in rat brain: microdistribution and differential occupation. Endocrinology1985; 117:2505-2511.
26.  Amaral DG, Witter MP. The three-dimensional organization of the hippocampal formation: a review of anatomical data. Neuroscience 1989; 31:571-591.
27.  Amaral DG, Dent JA. Development of the mossy fibers of the dentate gyrus: A light and electron microscopic study of the mossy fibers and their expansions. J Comp Neurol 1981; 195:51-86.
28.  Gould E, Woolley CS, McEwen BS. Short-term glucocorticoid manipulations affects neuronal morphology and survival in the adult dentate gyrus. Neuroscience 1990; 37:367-375.
29.  Cunningham TJ. Naturally occuring neuron death and its regulation by developing neural pathways. Int Rev Cytol 1982; 74: 163-186.
30.  Gaarskjaer FB. The organization and development of the hippocampal mossy fiber syetem, Brain Res Rev 1986; 11:335-57.
31.  Madeira MD, Paula-Barbosa M M. Reorganization of the mossy fiber synapses in male and female hypothyroid rats: a stereological study. J Comp Neurol 1993; 337: 334-352.
32.  Sousa N, Lukoyanov NV, Madeira MD, Almeida, OF, Paula-Barbosa, MM. Reorganization of the morphology of hippocampal neurites and synapses after stress-induced damage correlates with behavioral improvement. Neuroscience 2000; 97:253-266.
33.  Bayer SA, Yackel P S, Puri P S. Neurons in the rat dentate gyrus granular layer substantially increase during juvenile and adult life. Science 1982; 216:890-892.
34.  Gould E, Cameron HA. Regulation of neuronal birth, migration and death in the dentate gyrus. Devl Neurosci 1996; 18:22-35.
35.  Saljo A, Bao F, Jingshan S, Hamberger A, Hansson HA, Haglid KG. Exposure to short-lasting impulse noise causes neuronal c-Jun expression and induction of apoptosis in the adult rat brain. J Neurotrauma 2002; 19: 985-991.
36.  Kim H, Lee MH, Chang HK, Lee TH, Lee HH, Shin MC, et al.  Influence of prenatal noise and music on the spatial memory and neurogenesis in the hippocampus of developing rats. Brain Dev 2006; 28: 109-114.