New finding for neuronal basis of the learned helplessness syndrome secondary to loudness: nonresistant rats have more damaged neurons in the amygdala than resistant rats

Abstract

Objective: Learned helplessness syndrome is a psychological condition where individuals learn that their actions have no effect on outcomes. This phenomenon can be influenced by various environmental factors, including noise. The relationship between the harmful neurological effects of noise and learned helplessness syndrome has not been studied yet. This subject was investigated. Methods: Thirty-two healthy Sprague-Dawley rats were divided into three groups: The control group (G-I, n = 6), the low-level noise exposure group (80 dB, G-II, n = 10), and the high-level noise exposure group (100 dB, G-III, n = 16). Animals were exposed to impulse noise. Resistance score (RS) was designed as no reaction (0P), alertness (1P), staying away from the source of the sound (2P), fussiness (3P), crowding up (4P), trying to escape from cages (5P), biting the bars (6P), and hair loss and self injury (7P). Results: After decapitation, the degenerated neuron densities of the amygdala were compared with RS values. The RS scores of rats were changed from 0–6 in G-I, 6–15 in G-II, and 10–28 in G-III. The apoptotic neuron density of the amygdala was estimated as 12 ± 4/mm3 in G-I (p > 0.5), 231 ± 56/mm3 in G-II (p < 0.005), and 1143 ± 102/mm3 in G-III (p < 0.0005). Conclusion: The animals with a higher RS score (>21) showed less neuronal apoptosis than animals with a lower RS score. In conclusion, this study indicates that the noise exposure-related neurodegeneration of the amygdala in rats may cause ‘learned helplessness’ syndrome.