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Glia-related mechanisms in the anteroventral cochlear nucleus of the adult rat in response to unilateral conductive hearing loss.

Fuentes-Santamaría V, Alvarado JC, López-Muñoz DF, Melgar-Rojas P, Gabaldón-Ull MC, Juiz JM - Front Neurosci (2014)

Bottom Line: Diminished cochlear activity after middle ear ossicle removal leads to a significant ipsilateral increase in the mean gray levels and stained area of microglial cells but not astrocytes in the AVCN at 1 and 4 d post-lesion as compared to the contralateral side and control animals.These results suggest that microglial cells but not astrocytes may act as dynamic modulators of synaptic transmission in the cochlear nucleus immediately following unilateral hearing loss.On the other hand, NT-3 immunostaining was localized mainly in neuronal cell bodies and axons and was upregulated at 1, 4 and 7 d post-lesion.

View Article: PubMed Central - PubMed

Affiliation: Facultad de Medicina, Instituto de Investigación en Discapacidades, Neurológicas (IDINE), Universidad de Castilla-La Mancha Albacete, Spain.

ABSTRACT
Conductive hearing loss causes a progressive decline in cochlear activity that may result in functional and structural modifications in auditory neurons. However, whether these activity-dependent changes are accompanied by a glial response involving microglia, astrocytes, or both has not yet been fully elucidated. Accordingly, the present study was designed to determine the involvement of glial related mechanisms in the anteroventral cochlear nucleus (AVCN) of adult rats at 1, 4, 7, and 15 d after removing middle ear ossicles. Quantitative immunohistochemistry analyses at light microscopy with specific markers of microglia or astroglia along with immunocytochemistry at the electron microscopy level were used. Also, in order to test whether trophic support by neurotrophins is modulated in glial cells by auditory activity, the expression and distribution of neurotrophin-3 (NT-3) and its colocalization with microglial or astroglial markers was investigated. Diminished cochlear activity after middle ear ossicle removal leads to a significant ipsilateral increase in the mean gray levels and stained area of microglial cells but not astrocytes in the AVCN at 1 and 4 d post-lesion as compared to the contralateral side and control animals. These results suggest that microglial cells but not astrocytes may act as dynamic modulators of synaptic transmission in the cochlear nucleus immediately following unilateral hearing loss. On the other hand, NT-3 immunostaining was localized mainly in neuronal cell bodies and axons and was upregulated at 1, 4 and 7 d post-lesion. Very few glial cells expressed this neurotrophin in both control and experimental rats, suggesting that NT-3 is primarily activated in neurons and not as much in glia after limiting auditory activity in the AVCN by conductive hearing loss.

No MeSH data available.


Related in: MedlinePlus

Line graphs illustrating the effects of UCHL over the auditory thresholds at all frequencies tested. (A) There was a significant threshold elevation in the ipsilateral side at all timepoints after the UCHL in comparison with control animals and the contralateral side of deprived rats. (B) The threshold shift was of 30–40 dB SPL in comparison to the contralateral side and unoperated rats. The error bars indicate the standard errors of the mean.
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Figure 2: Line graphs illustrating the effects of UCHL over the auditory thresholds at all frequencies tested. (A) There was a significant threshold elevation in the ipsilateral side at all timepoints after the UCHL in comparison with control animals and the contralateral side of deprived rats. (B) The threshold shift was of 30–40 dB SPL in comparison to the contralateral side and unoperated rats. The error bars indicate the standard errors of the mean.

Mentions: To evaluate alterations in auditory function following UCHL, ABR recordings were performed in rats before (pre-lesion ABR) and after (post-lesion ABR) unilateral ossicle removal for each of the time points described in the Materials and Methods Section. Similar to the control condition, the pre-lesion recordings showed a distinctive wave pattern characterized by four to five positive peaks generated after a stimulus (Figure 1A). Meanwhile, the post-lesion ABR in the ear ipsilateral to the lesion (Figures 1C–F) showed differences in the wave amplitudes at all the frequencies tested when compared to the contralateral side (Figure 1B) and control animals (Figure 1A). Experimental rats had significant thresholds elevations at all frequencies and time points studied after UCHL which were indicative of decreased activity in the ipsilateral auditory nuclei (Figure 2).


Glia-related mechanisms in the anteroventral cochlear nucleus of the adult rat in response to unilateral conductive hearing loss.

Fuentes-Santamaría V, Alvarado JC, López-Muñoz DF, Melgar-Rojas P, Gabaldón-Ull MC, Juiz JM - Front Neurosci (2014)

Line graphs illustrating the effects of UCHL over the auditory thresholds at all frequencies tested. (A) There was a significant threshold elevation in the ipsilateral side at all timepoints after the UCHL in comparison with control animals and the contralateral side of deprived rats. (B) The threshold shift was of 30–40 dB SPL in comparison to the contralateral side and unoperated rats. The error bars indicate the standard errors of the mean.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4195288&req=5

Figure 2: Line graphs illustrating the effects of UCHL over the auditory thresholds at all frequencies tested. (A) There was a significant threshold elevation in the ipsilateral side at all timepoints after the UCHL in comparison with control animals and the contralateral side of deprived rats. (B) The threshold shift was of 30–40 dB SPL in comparison to the contralateral side and unoperated rats. The error bars indicate the standard errors of the mean.
Mentions: To evaluate alterations in auditory function following UCHL, ABR recordings were performed in rats before (pre-lesion ABR) and after (post-lesion ABR) unilateral ossicle removal for each of the time points described in the Materials and Methods Section. Similar to the control condition, the pre-lesion recordings showed a distinctive wave pattern characterized by four to five positive peaks generated after a stimulus (Figure 1A). Meanwhile, the post-lesion ABR in the ear ipsilateral to the lesion (Figures 1C–F) showed differences in the wave amplitudes at all the frequencies tested when compared to the contralateral side (Figure 1B) and control animals (Figure 1A). Experimental rats had significant thresholds elevations at all frequencies and time points studied after UCHL which were indicative of decreased activity in the ipsilateral auditory nuclei (Figure 2).

Bottom Line: Diminished cochlear activity after middle ear ossicle removal leads to a significant ipsilateral increase in the mean gray levels and stained area of microglial cells but not astrocytes in the AVCN at 1 and 4 d post-lesion as compared to the contralateral side and control animals.These results suggest that microglial cells but not astrocytes may act as dynamic modulators of synaptic transmission in the cochlear nucleus immediately following unilateral hearing loss.On the other hand, NT-3 immunostaining was localized mainly in neuronal cell bodies and axons and was upregulated at 1, 4 and 7 d post-lesion.

View Article: PubMed Central - PubMed

Affiliation: Facultad de Medicina, Instituto de Investigación en Discapacidades, Neurológicas (IDINE), Universidad de Castilla-La Mancha Albacete, Spain.

ABSTRACT
Conductive hearing loss causes a progressive decline in cochlear activity that may result in functional and structural modifications in auditory neurons. However, whether these activity-dependent changes are accompanied by a glial response involving microglia, astrocytes, or both has not yet been fully elucidated. Accordingly, the present study was designed to determine the involvement of glial related mechanisms in the anteroventral cochlear nucleus (AVCN) of adult rats at 1, 4, 7, and 15 d after removing middle ear ossicles. Quantitative immunohistochemistry analyses at light microscopy with specific markers of microglia or astroglia along with immunocytochemistry at the electron microscopy level were used. Also, in order to test whether trophic support by neurotrophins is modulated in glial cells by auditory activity, the expression and distribution of neurotrophin-3 (NT-3) and its colocalization with microglial or astroglial markers was investigated. Diminished cochlear activity after middle ear ossicle removal leads to a significant ipsilateral increase in the mean gray levels and stained area of microglial cells but not astrocytes in the AVCN at 1 and 4 d post-lesion as compared to the contralateral side and control animals. These results suggest that microglial cells but not astrocytes may act as dynamic modulators of synaptic transmission in the cochlear nucleus immediately following unilateral hearing loss. On the other hand, NT-3 immunostaining was localized mainly in neuronal cell bodies and axons and was upregulated at 1, 4 and 7 d post-lesion. Very few glial cells expressed this neurotrophin in both control and experimental rats, suggesting that NT-3 is primarily activated in neurons and not as much in glia after limiting auditory activity in the AVCN by conductive hearing loss.

No MeSH data available.


Related in: MedlinePlus