Air pollution is associated with brainstem auditory nuclei pathology and delayed brainstem auditory evoked potentials

Abstract

We assessed brainstem inflammation in children exposed to air pollutants by comparing brainstem auditory evoked potentials (BAEPs) and blood inflammatory markers in children age 96.3±8.5 months from highly polluted (n=34) versus a low polluted city (n=17). The brainstems of nine children with accidental deaths were also examined. Children from the highly polluted environment had significant delays in wave III (t(50)=17.038; p<0.0001) and wave V (t(50)=19.730; p<0.0001) but no delay in wave I (p=0.548). They also had significantly longer latencies than controls for interwave intervals I-III, III-V, and I-V (all t(50)>7.501; p<0.0001), consisting with delayed central conduction time of brainstem neural transmission. Highly exposed children showed significant evidence of inflammatory markers and their auditory and vestibular nuclei accumulated α synuclein and/or β amyloid(1-42). Medial superior olive neurons, critically involved in BAEPs, displayed significant pathology. Children's exposure to urban air pollution increases their risk for auditory and vestibular impairment.

Figure 1

Morphology of neurons in the superior olivary complex Figure 1A and B Shown in this figure are neurons from the medial superior olivary nucleus (MSO) from two specimens stained for Nissl substance (14 year old females, control in A and exposed in B). In A, MSO neurons display the typical fusiform cell bodies (arrows) and issue medial and lateral dendrites. Medial and lateral to the MSO cell column is a region with a high density of dendritic processes (asterisks). In B, MSO neurons have cell bodies that are generally smaller and more round (arrows) and do not appear to issue large caliber primary dendrites as in control child. The scale corresponds to 20 μm. C. MSO neurons from a 14y old MC girl showing the round abnormal morphology (arrow heads) surrounded by astrocyte-like cells with abundant cytoplasm (long arrow) and oligodendrocyte-like cells (short arrows). Hematoxylin and eosin stain × 100 D. MSO neurons from an 11 y old Mexico City girl showing strong immunoreactivity (IR) for 8 hydroxydeoxyguanosin (brown product) indicative of oxidative stress. Immunohistochemistry for 8OHdG 1: 100 × 20 E. MSO neurons from a 13y old Mexico City girl showing strong IR for β amyloid with the 6E10 antibody (brown product) reactive to amino acid residue 1-16 of beta amyloid (the epitope lies within amino acids 3–8 of beta amyloid). Immunohistochemistry for βA 6E10 1: 2000 counterstained with hematoxilin × 10

Figure 2

Medulla oblongata at the level of the dorsal cochlear nucleus. A. Medulla oblongata in an 11 year old MC female: the dorsal cochlear nucleus exhibits positive α synuclein IR in neurons, threads and dots. Immunohistochemistry for α synuclein 1: 500 red product × 20 B. Same child as A, dorsal cochlear nucleus neurons surrounded by microglia positive for Iba-1. Immunohistochemistry for Iba-1 1:1000 brown product, counterstained with hematoxilin × 20 C. Thirteen year old MC female dorsal cochlear nucleus neurons (arrow heads) showing strong IR for β amyloid with the 4G8 antibody reactive to amino acid residues 17-24 of the human beta amyloid peptide (epitope lies within amino acids 18–22 of the beta amyloid). Glial-like cells (arrows) with abundant IR are proximal to the neurons. Immunohistochemistry for βA 1: 2500, brown product × 40 D. An isolated neuron IR for α synuclein in the tectospinal tract region. Eleven year old Mexico City girl. Immunohistochemistry for α synuclein 1: 500 red product × 40 E. A cluster of positive α synuclein neurons, threads and dots located in the spinal lemniscus region. Same child as D. Immunohistochemistry for α synuclein 1: 500 red product × 40 F. Positive Iba-1 perivascular mononuclear cells and microglia (brown product) in the region of the nucleus ambiguus. There is a significant variation in the number of mononuclear perivascular cells with IR to Iba-1 in medullary blood vessels as observed in the upper left blood vessel compared to the right lower larger vessel. Eleven year old from MC. Immunohistochemistry for Iba-1 1:1000 counterstained with hematoxilin × 20 G. Medial vestibular nucleus with abundant positive Iba-1 activated microglia (brown product). Immunohistochemistry for Iba-1 1:1000 counterstained with hematoxilin × 20 H. 15 year old Mexico City girl: cluster of perivascular cells positive for HLA-DR (brown product) in a blood vessel located in the region of the medial longitudinal fasciculus. Immunohistochemistry for HLA-DR 1:1000 × 40

Figure 3

Medulla oblongata at mid-olivary level. A. Area postrema in a 15 year old Mexico City girl showing a significant number of CD163 immunoreactive perivascular and microglia-like cells scattered in the region. Immunohistochemistry for CD163 1:100 brown product × 10 B. Cuneate fasciculus in a 19 year old Mexico City male showing immunoreactive CD163 perivascular and microglia-like scattered cells. Immunohistochemistry for CD163 1:100 brown product × 10 C. Same subject as B, gracilis fasciculus with significant numbers of immunoreactive CD163 perivascular and microglia-like cells. Immunohistochemistry for CD163 1:100 brown product × 10 D. The dorsal motor nucleus of the vagus in an 11y MC girl exhibits positive α synuclein IR in neurons, threads and dots. Immunohistochemistry for α synuclein 1: 500 red product × 20 E. Same block as D stained with Iba-1 shows the dorsal motor nucleus of the vagus neurons surrounded by IR microglia. Immunohistochemistry for Iba-1 1:1000 brown product × 20 F. Same dorsal motor nucleus of the vagus block as D and E stained with glial fibrillary acidic protein Ab GFAP to define reactive astrocytes (brown product) around neurons. Reactive astrocytes with abundant IR cytoplasm are identified with head arrows. Immunohistochemistry for GFAP 1:100 counterstained with hematoxilin × 40 G. Solitary nucleus in an 11y old MC girl stained with GFAP. Scattered IR astrocytes are seen. Immunohistochemistry for GFAP 1:100 brown product counterstained with hematoxilin × 20 H. Arcuate nucleus cluster of IR α synuclein neurons. Same child as D. Immunohistochemistry for α synuclein 1: 500 red product × 40

Figure 4

Mesencephalon at the level of the inferior colliculus A. Pigmented neurons from the pars compacta substantia nigrae showing an astrocyte-like cell with abundant eosinophilic cytoplasm (arrow) and macrophage-like cells (head arrows). Hematoxilin-eosin × 100 B. Same section as A to show two white blood cells attached to the endothelium of a capillary in the pars compacta. A polymorphonuclear cell (long arrow) and the mononuclear cell (head arrow) both are attached to the endothelial cells. An adjacent glial cell (short arrow) exhibits abundant cytoplasm. The pigmented neuron in the center of the picture is surrounded by glial-like cells. Hematoxilin-eosin × 100 C. A blood vessel in the midst of the substantia nigrae pars compacta exhibit numerous Iba-1 IR cells and positive cells are seen surrounding the pigmented neurons. Immunohistochemistry for Iba-1 1:1000 red product, counterstained with hematoxylin × 40 D. The substantia nigrae from a control 17 year old male shows numerous well pigmented neurons and few Iba-1 IR cells surrounding the pigmented neurons. Notice a few perivascular Iba-1 IR cells. Immunohistochemistry for Iba-1 1:1000 red product, counterstained with hematoxylin × 20 E. Close up of a substantia nigrae pigmented neuron with IR for α synuclein in a 13y female contrast with the insert showing a pigmented negative neuron. Immunohistochemistry for α synuclein 1: 500 red product × 60