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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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Electron microscopic images that illustrate immunoreactivity for the β3 subunit of the GABAA receptor and for GABA in the superficial dorsal horn 28 days after SNI. (a, b) Reference sections showing synapses on the ipsilateral (ipsi) and contralateral (contra) sides, respectively. In each case, an axonal bouton (a) is presynaptic to a small dendritic profile (d) and there is a precipitate of DAB (which represents the GABAA receptor β3 subunit) on the post-synaptic aspect (arrows). (c, d) Serial sections to those illustrated in a and b, which have been reacted by a post-embedding immunogold method. In both cases the axonal bouton is heavily labeled with 15 nm gold particles, which represent GABA-immunoreactivity. Scale bar=0.5 μm.
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fig2: Electron microscopic images that illustrate immunoreactivity for the β3 subunit of the GABAA receptor and for GABA in the superficial dorsal horn 28 days after SNI. (a, b) Reference sections showing synapses on the ipsilateral (ipsi) and contralateral (contra) sides, respectively. In each case, an axonal bouton (a) is presynaptic to a small dendritic profile (d) and there is a precipitate of DAB (which represents the GABAA receptor β3 subunit) on the post-synaptic aspect (arrows). (c, d) Serial sections to those illustrated in a and b, which have been reacted by a post-embedding immunogold method. In both cases the axonal bouton is heavily labeled with 15 nm gold particles, which represent GABA-immunoreactivity. Scale bar=0.5 μm.

Mentions: In ultrathin sections from this material that had not undergone post-embedding immunocytochemistry for GABA, electron microscopy revealed DAB labeling that was invariably associated with synapses, where it was always located at the post-synaptic aspect (Fig. 2a, b). In agreement with the findings of Castro-Lopes et al. (1990) we observed that type I glomeruli were not present in the denervated region on the ipsilateral side in the SNI rats.


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)

Electron microscopic images that illustrate immunoreactivity for the β3 subunit of the GABAA receptor and for GABA in the superficial dorsal horn 28 days after SNI. (a, b) Reference sections showing synapses on the ipsilateral (ipsi) and contralateral (contra) sides, respectively. In each case, an axonal bouton (a) is presynaptic to a small dendritic profile (d) and there is a precipitate of DAB (which represents the GABAA receptor β3 subunit) on the post-synaptic aspect (arrows). (c, d) Serial sections to those illustrated in a and b, which have been reacted by a post-embedding immunogold method. In both cases the axonal bouton is heavily labeled with 15 nm gold particles, which represent GABA-immunoreactivity. Scale bar=0.5 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig2: Electron microscopic images that illustrate immunoreactivity for the β3 subunit of the GABAA receptor and for GABA in the superficial dorsal horn 28 days after SNI. (a, b) Reference sections showing synapses on the ipsilateral (ipsi) and contralateral (contra) sides, respectively. In each case, an axonal bouton (a) is presynaptic to a small dendritic profile (d) and there is a precipitate of DAB (which represents the GABAA receptor β3 subunit) on the post-synaptic aspect (arrows). (c, d) Serial sections to those illustrated in a and b, which have been reacted by a post-embedding immunogold method. In both cases the axonal bouton is heavily labeled with 15 nm gold particles, which represent GABA-immunoreactivity. Scale bar=0.5 μm.
Mentions: In ultrathin sections from this material that had not undergone post-embedding immunocytochemistry for GABA, electron microscopy revealed DAB labeling that was invariably associated with synapses, where it was always located at the post-synaptic aspect (Fig. 2a, b). In agreement with the findings of Castro-Lopes et al. (1990) we observed that type I glomeruli were not present in the denervated region on the ipsilateral side in the SNI rats.

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