Loud noise exposure affects rat hippocampal areas but not auditory structures

URAN, SL; AÓN BERTOLINO, L; PELLEGRINO, F; CACERES, LG; CAPANI, F; GUELMAN, LR

Congreso; 41stAnnual Meeting of the SocietyforNeuroscience (SFN),; 2011

It has been reported that loud noise exposure can affect extra-auditory areas of the Central Nervous System such as the hippocampus (Hip), a structure known to be involved in memory processes, resulting in memory impairment. However, hippocampal histological damage would not be discarded. On the other hand, acoustic contamination is the major factor causing hearing loss on living organisms, being responsible of cochlear mechanical and metabolic damage. Single or continuous exposure to high levels of noise (more than 100 dB) for long periods can cause transient or permanent noise-induced hearing loss. However, the vulnerability of the auditory system of different animal models to loud noise is very variable, mainly depending on noise intensity. Therefore, the aim of the present work was to elucidate if loud noise exposure during the rat developmental period induces histological and/or functional changes in the auditory pathway and if the Hip-related behavioral alterations depended on hippocampal histological impairment. Male Wistar rats of 15 days were exposed to white noise (95-97 dB, 2h/day) and separated into two groups, acute (AE, 2h/day) and chronic exposure (CE, 2h/day for 15 d). The integrity of the auditory pathway was evaluated by obtaining auditory brainstem response (ABR) thresholds in 30-days-old rats. Moreover, histological assessment of the cochlea and the Hip was also performed to evaluate possible damage in control and exposed animals. Results showed that there were no differences in ABR in rats exposed to loud noise, both in AE and in CE groups, when compared with control animals. These data were consistent with histological results, where no loss or damage of outer and inner hair cells was found. In contrast, histological changes were found in Hip of noise-exposed rats, since nuclear hyperchromasia and cytoplasmatic shrinkage were found in CA1 and CA3 regions. In adittion, the number of piknotic nuclei was increased in these regions when compared to control (CA1, AE p< 0.001; CA3, AE p< 0.001; CE p< 0.05) and the thickness of the layers was decreased only in CA3 layer (CA1, NS; CA3, AE p< 0.01; CE p< 0.01).These results suggest that AE and CE to loud noise in developing rats are capable of inducing hippocampal abnormalities, without producing auditory dysfunction when evaluated at 30 days.