Elsevier

Neuroscience

Volume 147, Issue 2, 29 June 2007, Pages 469-490
Neuroscience

Expression of the vesicular glutamate transporters-1 and -2 in adult mouse dorsal root ganglia and spinal cord and their regulation by nerve injury

https://doi.org/10.1016/j.neuroscience.2007.02.068Get rights and content

Abstract

The expression of two vesicular glutamate transporters (VGLUTs), VGLUT1 and VGLUT2, was studied with immunohistochemistry in lumbar dorsal root ganglia (DRGs), the lumbar spinal cord and the skin of the adult mouse. About 12% and 65% of the total number of DRG neuron profiles (NPs) expressed VGLUT1 and VGLUT2, respectively. VGLUT1-immunoreactive (IR) NPs were usually medium- to large-sized, in contrast to a majority of small- or medium-sized VGLUT2-IR NPs. Most VGLUT1-IR NPs did not coexpress calcitonin gene-related peptide (CGRP) or bound isolectin B4 (IB4). In contrast, ∼31% and ∼42% of the VGLUT2-IR DRG NPs were also CGRP-IR or bound IB4, respectively. Conversely, virtually all CGRP-IR and IB4-binding NPs coexpressed VGLUT2. Moderate colocalization between VGLUT1 and VGLUT2 was also observed. Sciatic nerve transection induced a decrease in the overall number of VGLUT1- and VGLUT2-IR NPs (both ipsi- and contralaterally) and, in addition, a parallel, unilateral increase of VGLUT2-like immunoreactivity (LI) in a subpopulation of mostly small NPs. In the spinal cord, strong VGLUT1-LI was detected, particularly in deep dorsal horn layers and in the ventral horns. VGLUT2-LI was abundant throughout the gray spinal matter, ‘radiating’ into/from the white matter. A unilateral dorsal rhizotomy reduced VGLUT1-LI, while apparently leaving unaffected the VGLUT2-LI. Transport through axons for both VGLUTs was confirmed by their accumulation after compression of the sciatic nerve or dorsal roots. In the hind paw skin, abundant VGLUT2-IR nerve fibers were observed, sometimes associated with Merkel cells. Lower numbers of VGLUT1-IR fibers were also detected in the skin. Some VGLUT1-IR and VGLUT2-IR fibers were associated with hair follicles. Based on these data and those by Morris et al. [Morris JL, Konig P, Shimizu T, Jobling P, Gibbins IL (2005) Most peptide-containing sensory neurons lack proteins for exocytotic release and vesicular transport of glutamate. J Comp Neurol 483:1–16], we speculate that virtually all DRG neurons in adult mouse express VGLUTs and use glutamate as transmitter.

Section snippets

Animals

Male NMRI mice were used (body weight 25–30 g; n=19; B&K, Stockholm, Sweden). The animals were maintained under standard conditions on a 12-h light/dark cycle (light on, 7:00 a.m.), with water and food ad libitum.

The experiments were conducted in accordance with the Society for Neuroscience policy for the use of research animals, and were approved by the local ethical committee (Stockholms Norra Djurförsöksetiska Nämnd; #219/03, #385/04, #397/04). All experiments conformed to international

Dorsal root ganglia

In L4-5 DRGs of the naïve adult mouse around 11.9%±1% were VGLUT1-IR (Fig. 1A, C;Table 1; control, n=4) and 65.4%±4.5% VGLUT2-IR (Fig. 1B, D; Table 1; control, n=4). VGLUT1-IR NPs of different sizes were observed, with areas ranging from 323 μm2 to 2534 μm2, and with a peak between 600 and 1400 μm2, characteristic of medium- and large-sized DRG neurons (Figs. 1A, C; 2A). VGLUT2 showed NP areas ranging from 83 μm2 to 2169 μm2, and a peak between 200 and 600 μm2, thus favoring small- and

Discussion

In the present study we have analyzed the protein expression of two of the three known vesicular glutamate transporters in adult mouse DRGs and spinal cord. In DRGs, VGLUT1 was present in some medium- to large-sized and VGLUT2 in many small- to medium-sized neurons. Virtually all CGRP-IR and IB4-binding neurons were VGLUT2-IR, supporting an important functional role of glutamate in sensory transmission, including nociception. The expression of the VGLUTs in DRGs was affected by peripheral nerve

Acknowledgments

The present study was supported by the Swedish Research Council (04X-2887), the Marianne and Marcus Wallenberg Foundation, the Knut and Alice Wallenberg Foundation. P.B. has been supported by Karolinska Institutet and the Austral University. We are grateful to Prof. Lars Terenius, Center for Molecular Medicine, Karolinska Institutet, Stockholm and to Professor Elvar Theodorsson, Department of Biomedicine and Surgery, Division of Clinical Chemistry, University Hospital, Linköping, Sweden, for

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