The maturation state of the auditory nerve and brainstem in rats exposed to lead acetate and supplemented with ferrous sulfate

Zucki, Fernanda; Morata, Thais C.; Duarte, Josilene L.; Ferreira, Maria Cecília F.; Salgado, Manoel H.; Alvarenga, Kátia F.

doi:10.1016/j.bjorl.2016.12.004

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Brazilian Journal of Otorhinolaryngology

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Original articles • Braz. j. otorhinolaryngol. 84 (2) • Mar-Apr 2018 • https://doi.org/10.1016/j.bjorl.2016.12.004 copy

The maturation state of the auditory nerve and brainstem in rats exposed to lead acetate and supplemented with ferrous sulfate^☆ ☆ Please cite this article as: Zucki F, Morata TC, Duarte JL, Ferreira MC, Salgado MH, Alvarenga KF. The maturation state of the auditory nerve and brainstem in rats exposed to lead acetate and supplemented with ferrous sulfate. Braz J Otorhinolaryngol. 2018;84:150-8.

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Introduction

The literature has reported the association between lead and auditory effects, based on clinical and experimental studies. However, there is no consensus regarding the effects of lead in the auditory system, or its correlation with the concentration of the metal in the blood.

Objective

To investigate the maturation state of the auditory system, specifically the auditory nerve and brainstem, in rats exposed to lead acetate and supplemented with ferrous sulfate.

Methods

30 weanling male rats (Rattus norvegicus, Wistar) were distributed into six groups of five animals each and exposed to one of two concentrations of lead acetate (100 or 400 mg/L) and supplemented with ferrous sulfate (20 mg/kg). The maturation state of the auditory nerve and brainstem was analyzed using Brainstem Auditory Evoked Potential before and after lead exposure. The concentration of lead in blood and brainstem was analyzed using Inductively Coupled Plasma-Mass Spectrometry.

Results

We verified that the concentration of Pb in blood and in brainstem presented a high correlation (r = 0.951; p < 0.0001). Both concentrations of lead acetate affected the maturation state of the auditory system, being the maturation slower in the regions corresponding to portion of the auditory nerve (wave I) and cochlear nuclei (wave II). The ferrous sulfate supplementation reduced significantly the concentration of lead in blood and brainstem for the group exposed to the lowest concentration of lead (100 mg/L), but not for the group exposed to the higher concentration (400 mg/L).

Conclusion

This study indicate that the lead acetate can have deleterious effects on the maturation of the auditory nerve and brainstem (cochlear nucleus region), as detected by the Brainstem Auditory Evoked Potentials, and the ferrous sulphate can partially amend this effect.

KEYWORDS
Hearing; Auditory evoked potentials; Lead acetate; Blood lead levels; Ferrous sulfate

Groups	[Lead] blood (µg/dL)	[Lead] brainstem (ng/g)
Control	0.19 ± 0.10	11.18 ± 4.42
100 mg/L Pb	10.56 ± 5.29^a a Mean with significant difference when compared control with experimental groups. ,^b b Mean with significant difference between the groups 100 mg/L Pb and 100 mg/L Pb + FeSO4.	27.21 ± 7.03
100 mg/L Pb + FeSO₄	3.89 ± 2.04^a a Mean with significant difference when compared control with experimental groups.	19.53 ± 9.41
400 mg/L Pb	48.39 ± 8.66^a a Mean with significant difference when compared control with experimental groups.	259.88 ± 76.53^a a Mean with significant difference when compared control with experimental groups.
400 mg/L Pb + FeSO₄	25.85 ± 3.61^a a Mean with significant difference when compared control with experimental groups.	208.87 ± 91.10
FeSO₄	0.13 ± 0.02	8.54 ± 1.34^c c Mean with significant difference between the groups FeSO4, 400 mg/L Pb and 400 mg/L Pb + FeSO4.

Group Effect (n = 30)	Waves (ms)
	I		II		III		IV
	Exposure		Exposure		Exposure		Exposure
	Pre	Post	Pre	Post	Pre	Post	Pre	Post
Control	1.388	1.236	2.566	2.109	3.418	2.882	4.895	4.128
100 mg/L Pb	1.292	1.167	2.278	2.079	3.101	2.888	4.594	4.091
100 mg/L Pb + FeSO₄	1.231	1.230	2.328	2.038	3.067	2.753	4.490	3.850
400 mg/L Pb	1.324	1.197	2.345	2.106	3.181	2.827	4.582	3.987
400 mg/L Pb + FeSO₄	1.378	1.110	2.539	2.007	3.340	2.692	4.753	3.854
FeSO₄	1.270	1.195	2.451	2.118	3.152	2.844	4.822	4.017
p	0.237	0.397	0.066	0.468	0.030^a a p obtained from the comparison of the groups at each time (pre and post-exposure to Pb).	0.189	0.175	0.125

Group Effect (n = 30)	Interpeak intervals (ms)
	I-II		II-III		III-IV		I-IV
	Exposure		Exposure		Exposure		Exposure
	Pre	Post	Pre	Post	Pre	Post	Pre	Post
Control	1.178	0.873	0.852	0.773	1.477	1.246	3.507	2.892
100 mg/L Pb	0.986	0.912	0.823	0.809	1.493	1.203	3.302	2.924
100 mg/L Pb + FeSO₄	1.097	0.808	0.739	0.715	1.423	1.097	3.259	2.620
400 mg/L Pb	1.021	0.909	0.836	0.721	1.401	1.160	3.258	2.790
400 mg/L Pb + FeSO₄	1.161	0.897	0.801	0.685	1.413	1.162	3.375	2.744
FeSO₄	1.181	0.923	0.701	0.726	1.670	1.173	3.552	2.822
p	0.011^a a p obtained from the comparison of the groups at each time (pre and post-exposure to Pb).	0.131	0.384	0.200	0.192	0.270	0.143	0.033^a a p obtained from the comparison of the groups at each time (pre and post-exposure to Pb).

Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Sede da Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico Facial, Av. Indianópolia, 1287, 04063-002 São Paulo/SP Brasil, Tel.: (0xx11) 5053-7500, Fax: (0xx11) 5053-7512 - São Paulo - SP - Brazil
E-mail: revista@aborlccf.org.br

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[1] * Corresponding author. E-mail:fernandazucki@hotmail.com (F. Zucki).