Background: In continuing our work on effects of noise stress, this study aimed to determine the effect of noise stress on the anxiety and the volume of the amygdale nuclei as a key brain component plays role in the anxiety. Methods: In this experimental study, two-months old Wistar male rats were randomly divided into noise stress and control groups (n=10 in each group). Control rats were maintained under standard laboratory conditions and noise-stressed rats were exposed to 75 dB noise (1100Hz), 20 min/3 times/day for 90 days. The anxiety behaviors were assessed applying elevated plus maze and Territory discrimination test. Coronal serial sections of 25 µm thickness through rat amygdale were made. Every 2th section was selected and the volume of amygdale nuclei was determined by using Cavalieri's principle. Results: Results indicated that the noise-exposed rats had fewer entrances to open arm of elevated plus maze and spend less time in this arm. In territory discrimination test, noise stressed group had more latency to enter in unknown compartment. The volume of lateral nucleus of amygdale was significantly higher in noise stressed group compared to control animal. Conclusion: Result of this study indicated that the chronic exposure to noise induces anxiety behavior and caused increase in central nucleus of amygdale volume. In this view, our experimental research may present a useful approach in understanding some aspects of the pathophysioloy of anxiety disorders due to noise stress.

Keywords: Amygdale, Anxiety, noise stress, stereology

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