Changes in expression of NMDA receptor subunits in the rat lumbar spinal cord following neonatal nerve injury

Abstract

The vulnerability of motoneurones to glutamate has been implicated in neurological disorders such as amyotrophic lateral sclerosis but it is not known whether specific receptor subtypes mediate this effect. In order to investigate this further, the expression of N-methyl-D-aspartate (NMDA) receptor subunits was studied during the first three post-natal weeks when motoneurones are differentially vulnerable to injury following neonatal nerve crush compared to the adult. Unilateral nerve crush was carried out at day 2 after birth (P2) which causes a decrease of 66% in motoneurone number by 14 days (P14). To study receptor expression in identified motoneurones, serial section analysis was carried out on retrogradely labelled common peroneal (CP) motoneurones by combined immunocytochemistry and in situ hybridization (ISH). mRNA levels were also quantified in homogenates from lumbar spinal cords in which the side ipsilateral to the crush was separated from the contralateral side. The NR1 subunit of the NMDA receptor was widely distributed in the spinal cord being expressed most strongly in motoneurone somata particularly during the neonatal period (P3-P7). The NR2 subunits were also expressed at higher levels in the somata and dendrites of neonatal motoneurones compared to older animals. NR2B mRNA was expressed at low to moderate levels throughout the studied period whereas NR2A mRNA levels were low until P21. Following unilateral nerve crush, an initial decrease in NR1 mRNA occurred at one day after nerve crush (P3) in labelled CP motoneurones ipsilateral to the crush which was followed by a significant increase in NR1 subunit expression at 5 days post-injury. This increase was bilateral although reaching greater significance ipsilateral to the crush compared with sham-operated animals. A significant increase in NR1 and NR2B mRNA post injury was also detected in spinal cord homogenates. In addition, the changes in levels of NR1 and NR2B mRNA were reflected by comparable bilateral changes at P7 in receptor protein determined by quantitative immunocytochemical analysis of NR1 and NR2 subunit expression in identified CP motoneurones indicating a co-ordinated regulation of receptor subunits in response to injury.

Spinal IL-33/ST2 Signaling Contributes to Neuropathic Pain via Neuronal CaMKII–CREB and Astroglial JAK2–STAT3 Cascades in Mice

“…20 However, there is inconsistency regarding the expression of the spinal NR1 subunit of NMDARs after peripheral nerve injury. 47 In addition, it has been reported that the expression of NR1 mRNA in the lumbar spinal cord was increased slightly on the 14th day in an SNI-induced rat neuropathic pain model. For example, spinal NR1 expression was significantly increased on the 7th day in chronic constriction sciatic nerve-injured mice and in rat neuropathic pain models.…”

Altered Glutamate Receptor Function during Recovery of Bladder Detrusor-External Urethral Sphincter Coordination in a Rat Model of Spinal Cord Injury

“…CPP has different affinities to NMDA receptors, depending upon the NR2 subunit present as part of the receptor complex. NMDA receptors in the rat spinal cord consist of NR2A, NR2B, and NR2D subunits (Luque et al, 1994;Virgo et al, 2000) and are characterized by different CPP affinity to a receptor containing these sub- Fig. 4.…”

NMDA receptor mediates chronic visceral pain induced by neonatal noxious somatic stimulation

“…In a recent publication, we demonstrated the development of chronic colonic hyperalgesia following neonatal cystitis that was associated with an increase in the spinal NR1 subunit expression (Miranda et al, 2011). The expression of NR1 and NR2B subunits, both at the mRNA and protein level, is also increased in the rat lumbar spinal cord following neonatal nerve crush injury (Virgo et al, 2000). The models of early life pain and the role of NMDA in maintaining hypersensitivity states is particularly interesting, especially since, the NMDAR subunit (NR1, NR2A and NR2B) expression in the rat spinal cord is known to be high during the first three weeks after birth and then decreases to normal levels as the animal approaches adulthood (Brown et al, 2002).…”

“…Animal models have demonstrated a critical time during development in which the spinal cord is vulnerable to permanent structural and functional alterations in pain pathways (Lidow et al, 2001; Ren et al, 2004; Traub et al, 2004; Virgo et al, 2000). We have previously shown the development of chronic visceral hyperalgesia in a model of early life somatic pain.…”