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Tactile allodynia can occur in the spared nerve injury model in the rat without selective loss of GABA or GABA(A) receptors from synapses in laminae I-II of the ipsilateral spinal dorsal horn.

Polgár E, Todd AJ - Neuroscience (2008)

Bottom Line: We found no difference in the intensity of immunolabeling for any of these markers on the two sides of the superficial dorsal horn.These results suggest that there is no significant loss of GABAergic boutons from the denervated area after SNI (which is consistent with the finding that neuronal death does not occur in this model) and that there is no depletion of GABA or GABA(A) receptors at GABAergic synapses within this region.An alternative explanation for disinhibition after nerve injury is that it results from reduced excitatory drive to GABAergic dorsal horn neurons following loss of primary afferent input to these cells.

View Article: PubMed Central - PubMed

Affiliation: Spinal Cord Group, Faculty of Biomedical and Life Sciences, West Medical Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK. e.polgar@bio.gla.ac.uk

ABSTRACT
Although there is evidence that reduced inhibition in the spinal dorsal horn contributes to neuropathic pain, the mechanisms that underlie this are poorly understood. We have previously demonstrated that there is no loss of neurons from laminae I-III in the spared nerve injury (SNI) model [Polgár E, Hughes DI, Arham AZ, Todd AJ (2005) Loss of neurons from laminas I-III of the spinal dorsal horn is not required for development of tactile allodynia in the SNI model of neuropathic pain. J Neurosci 25:6658-6666]. In this study we investigated whether there was a difference between ipsilateral and contralateral sides in the levels of GABA, the vesicular GABA transporter (VGAT), or the beta3 subunit of the GABA(A) receptor at synapses in the medial part of the superficial dorsal horn in this model. Tissue from rats that had undergone SNI 4 weeks previously was examined with an electron microscopic immunogold method to reveal GABA, following pre-embedding detection of GABA(A) beta3 to allow identification of GABAergic terminals. Assessment of labeling for the GABA(A) beta3 subunit and VGAT was performed by using immunofluorescence and confocal microscopy. We found no difference in the intensity of immunolabeling for any of these markers on the two sides of the superficial dorsal horn. These results suggest that there is no significant loss of GABAergic boutons from the denervated area after SNI (which is consistent with the finding that neuronal death does not occur in this model) and that there is no depletion of GABA or GABA(A) receptors at GABAergic synapses within this region. An alternative explanation for disinhibition after nerve injury is that it results from reduced excitatory drive to GABAergic dorsal horn neurons following loss of primary afferent input to these cells.

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Immunostaining for the GABAA receptor and VGAT in the medial part of the dorsal horn on each side of the spinal cord 28 days after SNI. (a, b) The GABAA receptor β3 subunit (GABAA) was revealed by antigen retrieval with pepsin. (c, d) VGAT-immunoreactivity in a section that was not treated with pepsin. a and c are from the side ipsilateral (ipsi) to the nerve injury; b and d are from the contralateral (contra) side. In each case, parts of laminae I–III within the territory of the common peroneal and tibial nerves are illustrated. Note that with each antibody there is no detectable difference in immunostaining intensity between the two sides. Confocal images were obtained from single optical sections scanned through a 20× objective lens. Scale bar=50 μm.
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fig4: Immunostaining for the GABAA receptor and VGAT in the medial part of the dorsal horn on each side of the spinal cord 28 days after SNI. (a, b) The GABAA receptor β3 subunit (GABAA) was revealed by antigen retrieval with pepsin. (c, d) VGAT-immunoreactivity in a section that was not treated with pepsin. a and c are from the side ipsilateral (ipsi) to the nerve injury; b and d are from the contralateral (contra) side. In each case, parts of laminae I–III within the territory of the common peroneal and tibial nerves are illustrated. Note that with each antibody there is no detectable difference in immunostaining intensity between the two sides. Confocal images were obtained from single optical sections scanned through a 20× objective lens. Scale bar=50 μm.

Mentions: We then compared immunostaining intensity on the sides ipsilateral and contralateral to the nerve injury for the GABAA receptor β3 subunit and for VGAT on sections reacted for the corresponding marker. No consistent differences in the immunostaining for either GABAA β3 (Fig. 4a, b) or VGAT (Fig. 4c, d) were seen between the two sides in any of the rats. The ratios of mean pixel intensities (ipsilateral/contralateral) ranged between 0.97–1.04 (mean 1.00±0.01, S.E.M., n=5) for GABAA receptor β3 subunit, and from 0.92–1.07 (mean 1.01±0.03, S.E.M., n=5) for VGAT. Neither of these was significantly different from one (one-sample t-test, P=0.8 for GABAA β3 and 0.85 for VGAT).


Tactile allodynia can occur in the spared nerve injury model in the rat without selective loss of GABA or GABA(A) receptors from synapses in laminae I-II of the ipsilateral spinal dorsal horn.

Polgár E, Todd AJ - Neuroscience (2008)

Immunostaining for the GABAA receptor and VGAT in the medial part of the dorsal horn on each side of the spinal cord 28 days after SNI. (a, b) The GABAA receptor β3 subunit (GABAA) was revealed by antigen retrieval with pepsin. (c, d) VGAT-immunoreactivity in a section that was not treated with pepsin. a and c are from the side ipsilateral (ipsi) to the nerve injury; b and d are from the contralateral (contra) side. In each case, parts of laminae I–III within the territory of the common peroneal and tibial nerves are illustrated. Note that with each antibody there is no detectable difference in immunostaining intensity between the two sides. Confocal images were obtained from single optical sections scanned through a 20× objective lens. Scale bar=50 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2553186&req=5

fig4: Immunostaining for the GABAA receptor and VGAT in the medial part of the dorsal horn on each side of the spinal cord 28 days after SNI. (a, b) The GABAA receptor β3 subunit (GABAA) was revealed by antigen retrieval with pepsin. (c, d) VGAT-immunoreactivity in a section that was not treated with pepsin. a and c are from the side ipsilateral (ipsi) to the nerve injury; b and d are from the contralateral (contra) side. In each case, parts of laminae I–III within the territory of the common peroneal and tibial nerves are illustrated. Note that with each antibody there is no detectable difference in immunostaining intensity between the two sides. Confocal images were obtained from single optical sections scanned through a 20× objective lens. Scale bar=50 μm.
Mentions: We then compared immunostaining intensity on the sides ipsilateral and contralateral to the nerve injury for the GABAA receptor β3 subunit and for VGAT on sections reacted for the corresponding marker. No consistent differences in the immunostaining for either GABAA β3 (Fig. 4a, b) or VGAT (Fig. 4c, d) were seen between the two sides in any of the rats. The ratios of mean pixel intensities (ipsilateral/contralateral) ranged between 0.97–1.04 (mean 1.00±0.01, S.E.M., n=5) for GABAA receptor β3 subunit, and from 0.92–1.07 (mean 1.01±0.03, S.E.M., n=5) for VGAT. Neither of these was significantly different from one (one-sample t-test, P=0.8 for GABAA β3 and 0.85 for VGAT).

Bottom Line: We found no difference in the intensity of immunolabeling for any of these markers on the two sides of the superficial dorsal horn.These results suggest that there is no significant loss of GABAergic boutons from the denervated area after SNI (which is consistent with the finding that neuronal death does not occur in this model) and that there is no depletion of GABA or GABA(A) receptors at GABAergic synapses within this region.An alternative explanation for disinhibition after nerve injury is that it results from reduced excitatory drive to GABAergic dorsal horn neurons following loss of primary afferent input to these cells.

View Article: PubMed Central - PubMed

Affiliation: Spinal Cord Group, Faculty of Biomedical and Life Sciences, West Medical Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK. e.polgar@bio.gla.ac.uk

ABSTRACT
Although there is evidence that reduced inhibition in the spinal dorsal horn contributes to neuropathic pain, the mechanisms that underlie this are poorly understood. We have previously demonstrated that there is no loss of neurons from laminae I-III in the spared nerve injury (SNI) model [Polgár E, Hughes DI, Arham AZ, Todd AJ (2005) Loss of neurons from laminas I-III of the spinal dorsal horn is not required for development of tactile allodynia in the SNI model of neuropathic pain. J Neurosci 25:6658-6666]. In this study we investigated whether there was a difference between ipsilateral and contralateral sides in the levels of GABA, the vesicular GABA transporter (VGAT), or the beta3 subunit of the GABA(A) receptor at synapses in the medial part of the superficial dorsal horn in this model. Tissue from rats that had undergone SNI 4 weeks previously was examined with an electron microscopic immunogold method to reveal GABA, following pre-embedding detection of GABA(A) beta3 to allow identification of GABAergic terminals. Assessment of labeling for the GABA(A) beta3 subunit and VGAT was performed by using immunofluorescence and confocal microscopy. We found no difference in the intensity of immunolabeling for any of these markers on the two sides of the superficial dorsal horn. These results suggest that there is no significant loss of GABAergic boutons from the denervated area after SNI (which is consistent with the finding that neuronal death does not occur in this model) and that there is no depletion of GABA or GABA(A) receptors at GABAergic synapses within this region. An alternative explanation for disinhibition after nerve injury is that it results from reduced excitatory drive to GABAergic dorsal horn neurons following loss of primary afferent input to these cells.

Show MeSH
Related in: MedlinePlus