Differential regulation of P2X3 mRNA expression by peripheral nerve injury in intact and injured neurons in the rat sensory ganglia

Abstract

The P2X(3) receptor is a ligand-gated cation channel activated by the binding of extracellular adenosine 5'-triphosphate (ATP), an agent that has been suggested to have a role in the nociceptive pathway after tissue and nerve injury. After peripheral nerve injury, both down regulation and up regulation of the P2X(3) receptor in sensory ganglion neurons have been observed. The purpose of this study was to examine the precise regulation of P2X(3) mRNA expression in primary sensory neurons after nerve injury. We used two nerve injury models in the rat, the transection of the tibial and common peroneal nerves and the transection of the infraorbital nerve, and observed dorsal root ganglion (DRG) and trigeminal ganglion neurons, respectively. P2X(3) mRNA in both neuron populations was detected by in situ hybridization with an oligonucleotide probe that was confirmed by Northern blot analysis. To identify axotomized neurons, we examined the expression of activating transcription factor 3 (ATF3), which is regarded as a neuronal-injury marker, using immunohistochemistry. In the DRG, the mean percentage of P2X(3) mRNA-labeled neurons relative to the total number of neurons increased from 32.7% in the naive rats to 42.7% at 3 days after injury. The mean percentage of P2X(3) mRNA-labeled neurons in ATF3 immunoreactive (ir) neurons was 29.5% at 3 postoperative days, which gradually decreased to 11.2% at 28 days after injury. In the trigeminal ganglion, the mean percentage of P2X(3) mRNA-labeled neurons was 36.9% at 3 days after injury, versus 26.0% in the naive rats. In the ATF3-ir neurons, the mean percentage of P2X(3) mRNA-labeled neurons was 25.3% at 1 postoperative day and was reduced to 6.1% at 28 postoperative days. The finding that P2X(3) mRNA in ATF3-ir neurons decreased significantly after injury indicates that axotomized neurons decreased the expression of P2X(3) mRNA, despite the increase in P2X(3) mRNA relative to the total number of sensory ganglion neurons. These data strongly suggest that P2X(3) mRNA expression increases in intact neurons and that P2X(3) mRNA in intact neurons may play a role in the pathomechanism of post-nerve injury in primary sensory neurons.

Role of Mitogen-Activated Protein Kinase Activation in Injured and Intact Primary Afferent Neurons for Mechanical and Heat Hypersensitivity after Spinal Nerve Ligation

“…Virtually all L4 DRG neurons are spared from axotomy in the L5 SNL model To identify the axotomized sensory neurons in the L4 and L5 DRG after the L5 SNL, we examined the immunoreactivity of ATF3, which has been suggested to be a neuronal injury marker (Tsujino et al, 2000;Tsuzuki et al, 2001). ATF3 immunoreactivity was expressed exclusively in the nuclei of virtually all ipsilateral L5 DRG neurons (Fig.…”

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“…Moreover, after lesions in the peripheral nervous system. P2X3 receptor expression in intact neurons, suggesting a role for this receptor in post-traumatic repair [102]. Following trauma, astrocytes increased expression of P2X4 receptors thereby inducing trombospondin-1 secretion, which constitutes an extracellular molecule for synapse formation contributing to CNS remodeling [81,103].…”

An evolving cellular pathology occurs in dorsal root ganglia, peripheral nerve and spinal cord following intravenous administration of paclitaxel in the rat

“…The up-regulation of ATF3 in DRG neurons was first noted at day 1 following the initial intravenous infusion and this increased expression was still present at day 10 post-infusion (the latest time point examined). Previous studies have shown that ATF3 is induced by stress stimuli and cellular damage and may have a survival/ regenerative function in sensory neurons (Seijffers et al, 2006) Following axotomy of sensory nerve fibers within the sciatic nerve (Tsujino et al, 2000), spinal nerves (Wang et al, 2003), or distal branches of the sciatic nerve (Tsuzuki et al, 2001) in the rat, ATF3 is up-regulated in neuronal cell bodies within 24 hours and this de novo expression can be maintained for weeks (Tsujino et al, 2000;Tsuzuki et al, 2001;Shortland et al, 2006). Upregulation of ATF3 in the DRG of axotomized nerves is prevented by the exogenous administration of nerve growth factor (Averill et al, 2004) and glial cell derived nerve growth factor (Wang et al, 2003).…”