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Spinal nerve ligation decreases γ‐aminobutyric acid B receptors on specific populations of immunohistochemically identified neurons in L5 dorsal root ganglion of the rat
Author(s) -
Engle Mitchell P.,
Merrill Michelle A.,
Marquez De Prado Blanca,
Hammond Donna L.
Publication year - 2012
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.23005
Subject(s) - biology , dorsal root ganglion , ganglion , dorsum , aminobutyric acid , neuroscience , receptor , anatomy , spinal nerve , ligation , microbiology and biotechnology , biochemistry
This study examined the distribution of γ‐aminobutyric acid (GABA) B receptors on immunohistochemically identified neurons, and levels of GABA B(1) and GABA B(2) mRNA, in the L4 and L5 dorsal root ganglia (DRG) of the rat in the absence of injury and 2 weeks after L5 spinal nerve ligation. In uninjured DRG, GABA B(1) immunoreactivity colocalized exclusively with the neuronal marker (NeuN) and did not colocalize with the satellite cell marker S‐100. The GABA B(1) subunit colocalized to >97% of DRG neurons immunoreactive (IR) for neurofilament 200 (N52) or calcitonin gene‐related peptide (CGRP), or labeled by isolectin B4 (IB4). Immunoreactivity for GABA B(2) was not detectable. L5 spinal nerve ligation did not alter the number of GABA B(1) ‐IR neurons or its colocalization pattern in the L4 DRG. However, ligation reduced the number of GABA B(1) ‐IR neurons in the L5 DRG by ≈38% compared with sham‐operated and naïve rats. Specifically, ligation decreased the number of CGRP‐IR neurons in the L5 DRG by 75%, but did not decrease the percent colocalization of GABA B(1) in those that remained. In the few IB4‐positive neurons that remained in the L5 DRG, colocalization of GABA B(1) ‐IR decreased to 75%. Ligation also decreased levels of GABA B(1) and GABA B(2) mRNA in the L5, but not the L4 DRG compared with sham‐operated or naïve rats. These findings indicate that the GABA B receptor is positioned to presynaptically modulate afferent transmission by myelinated, unmyelinated, and peptidergic afferents in the dorsal horn. Loss of GABA B receptors on primary afferent neurons may contribute to the development of mechanical allodynia after L5 spinal nerve ligation. J. Comp. Neurol. 520:1663–1677, 2012. © 2011 Wiley Periodicals, Inc.