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Open Access Research

Spatial and temporal pattern of changes in the number of GAD65-immunoreactive inhibitory terminals in the rat superficial dorsal horn following peripheral nerve injury

Louis-Etienne Lorenzo123, Claire Magnussen12, Andrea L Bailey12, Manon St Louis1, Yves De Koninck123 and Alfredo Ribeiro-da-Silva124*

Author Affiliations

1 Department of Pharmacology and Therapeutics, McGill University, 3655 Promenade Sir-William-Osler, Montreal, Quebec H3G 1Y6, Canada

2 Alan Edwards Centre for Research on Pain, McGill University, Montreal, Quebec H3A 2B2, Canada

3 Institut Universitaire en Santé Mentale de Québec, Québec, QC G1J 2G3, Canada

4 Departments of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 2B2, Canada

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Molecular Pain 2014, 10:57  doi:10.1186/1744-8069-10-57

Published: 4 September 2014

Abstract

Inhibitory interneurons are an important component of dorsal horn circuitry where they serve to modulate spinal nociception. There is now considerable evidence indicating that reduced inhibition in the spinal dorsal horn contributes to neuropathic pain. A loss of these inhibitory neurons after nerve injury is one of the mechanisms being proposed to account for reduced inhibition; however, this remains controversial. This is in part because previous studies have focused on global measurements of inhibitory neurons without assessing the number of inhibitory synapses. To address this, we conducted a quantitative analysis of the spatial and temporal changes in the number of inhibitory terminals, as detected by glutamic acid decarboxylase 65 (GAD65) immunoreactivity, in the superficial dorsal horn of the spinal cord following a chronic constriction injury (CCI) to the sciatic nerve in rats. Isolectin B4 (IB4) labelling was used to define the location within the dorsal horn directly affected by the injury to the peripheral nerve. The density of GAD65 inhibitory terminals was reduced in lamina I (LI) and lamina II (LII) of the spinal cord after injury. The loss of GAD65 terminals was greatest in LII with the highest drop occurring around 3–4 weeks and a partial recovery by 56 days. The time course of changes in the number of GAD65 terminals correlated well with both the loss of IB4 labeling and with the altered thresholds to mechanical and thermal stimuli. Our detailed analysis of GAD65+ inhibitory terminals clearly revealed that nerve injury induced a transient loss of GAD65 immunoreactive terminals and suggests a potential involvement for these alterations in the development and amelioration of pain behaviour.

Keywords:
Pain; Inhibition; Chronic constriction injury; Neuropathic; IB4; GAD65; Non-peptidergic C fibre; Inhibitory interneurons; Synaptic boutons