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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

Confocal and electron microscopy images illustrating appositions between astrocytes and cochlear nucleus neurons in control and deprived rats. Note that astrocytic processes were distributed in the neuropil or closely associated to cochlear nucleus neurons in control and deprived animals (A–C). The utrastructural characteristics of these cells in the cochlear nucleus are shown in D,E. These macroglial cells were contacting with surrounding cellular elements of the neuropil in the control condition and after ossicle removal (asterisks in D,E). A, axon; As, astrocyte; T, terminal; D, dendrite. Scale bar = 20 μm in C (also applies to A,B); 1 μm in D; 2 μm in E.
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Figure 8: Confocal and electron microscopy images illustrating appositions between astrocytes and cochlear nucleus neurons in control and deprived rats. Note that astrocytic processes were distributed in the neuropil or closely associated to cochlear nucleus neurons in control and deprived animals (A–C). The utrastructural characteristics of these cells in the cochlear nucleus are shown in D,E. These macroglial cells were contacting with surrounding cellular elements of the neuropil in the control condition and after ossicle removal (asterisks in D,E). A, axon; As, astrocyte; T, terminal; D, dendrite. Scale bar = 20 μm in C (also applies to A,B); 1 μm in D; 2 μm in E.

Mentions: GFAP immunostaining in unmanipulated animals was observed mostly as branched astroglial processes heterogeneously distributed through the AVCN (Figure 7A). Following UCHL, the morphology and staining features of astrocytes were similar to those observed in control animals (Figures 7A–F). Quantification of the mean gray levels and immunostained areas of GFAP immunostaining in experimental animals indicated that there were no differences at any survival time when compared to either the contralateral side or normal control animals (Figures 7G–J; Table 3). Similar to the control condition, astrocytic processess were found in the neuropil or closely associated with cochlear nucleus cell bodies at all the time points studied (Figures 8A–C). The utrastructural features of astrocytes in the AVCN of control and experimental rats are shown in Figures 8D,E. These macroglial cells contacted surrounding cellular elements in the neuropil (asterisks in Figures 8D,E)


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)

Confocal and electron microscopy images illustrating appositions between astrocytes and cochlear nucleus neurons in control and deprived rats. Note that astrocytic processes were distributed in the neuropil or closely associated to cochlear nucleus neurons in control and deprived animals (A–C). The utrastructural characteristics of these cells in the cochlear nucleus are shown in D,E. These macroglial cells were contacting with surrounding cellular elements of the neuropil in the control condition and after ossicle removal (asterisks in D,E). A, axon; As, astrocyte; T, terminal; D, dendrite. Scale bar = 20 μm in C (also applies to A,B); 1 μm in D; 2 μm in E.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4195288&req=5

Figure 8: Confocal and electron microscopy images illustrating appositions between astrocytes and cochlear nucleus neurons in control and deprived rats. Note that astrocytic processes were distributed in the neuropil or closely associated to cochlear nucleus neurons in control and deprived animals (A–C). The utrastructural characteristics of these cells in the cochlear nucleus are shown in D,E. These macroglial cells were contacting with surrounding cellular elements of the neuropil in the control condition and after ossicle removal (asterisks in D,E). A, axon; As, astrocyte; T, terminal; D, dendrite. Scale bar = 20 μm in C (also applies to A,B); 1 μm in D; 2 μm in E.
Mentions: GFAP immunostaining in unmanipulated animals was observed mostly as branched astroglial processes heterogeneously distributed through the AVCN (Figure 7A). Following UCHL, the morphology and staining features of astrocytes were similar to those observed in control animals (Figures 7A–F). Quantification of the mean gray levels and immunostained areas of GFAP immunostaining in experimental animals indicated that there were no differences at any survival time when compared to either the contralateral side or normal control animals (Figures 7G–J; Table 3). Similar to the control condition, astrocytic processess were found in the neuropil or closely associated with cochlear nucleus cell bodies at all the time points studied (Figures 8A–C). The utrastructural features of astrocytes in the AVCN of control and experimental rats are shown in Figures 8D,E. These macroglial cells contacted surrounding cellular elements in the neuropil (asterisks in Figures 8D,E)

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