Recovery of chronic noise exposure induced spatial learning and memory deficits in young male Sprague-Dawley rats.

OBJECTIVE Noise has always been an important environmental public health issue for mankind. Although reports exist on hippocampal-dependent spatial learning and memory (LM) impairment due to noise, there are only a few studies that have examined the effects of recovery from noise stress on LM impairments. Therefore, the present study investigated the effects of recovery from chronic noise exposure on LM deficits. MATERIALS AND METHODS In this study, the detrimental effects of noise stress on young male rats in the Morris water maze (MWM) were investigated at 1, 10, 20, 30, and 40 days after the discontinuation of chronic noise exposure of 80 dB or 100 dB for 4 h per day, for 30 days. The levels of monoamine neurotransmitters in the hippocampus were also evaluated by HPLC-EC at the end of each behavioral test. RESULTS Statistical analysis revealed that rats in the noise-treated groups failed to reach the same level of performance as the controls in the MWM. Further, the levels of dopamine (DA), norepinephrine (NE) and 5-hydroxytryptamine (5-HT) were significantly decreased in the hippocampus after noise exposure. However, the reduction in monoamine levels and impaired water maze performance recovered over time, so that by 30th day after cessation of noise exposure the 80 dB group showed no performance difference from the controls, and by 40th day, the 100 dB group also showed no performance difference from the control. CONCLUSION Our findings suggest that noise impaired LM in young male rats and reduced monoamine neurotransmitters in the hippocampus. However, the noise-induced water maze deficits recovered over time, and the concurrent restoration of hippocampal monoamine neurotransmitter levels suggest that they are involved in LM impairments.