Changes in the gene expression of six subtypes of P2X receptors in rat dorsal root ganglion after spinal nerve ligation

Abstract

Increased purinergic sensitivity of injured sensory neurons suggests the possible involvement of purinoceptors for the generation of pain after nerve injury. To identify the purinoceptors that are involved, the changes in mRNA levels of 6 subtype purinoceptors were examined in the dorsal root ganglia (DRG) of the normal rat and after spinal nerve ligation, using RNase protection assay (RPA). In addition, the P2X 2 containing neurons were examined in the L5 DRG, using an immunohistochemical method. The relative amounts of mRNAs for the six purinoceptor subtypes were in the order of P2X 3⪢P2X 4>P2X 6>P2X 5≈P2X 2>P2X 1 in the normal lumbar DRG. After nerve injury, the mRNA of P2X 5 was increased, those of P2X 3 and P2X 6 were decreased, and those of P2X 2 and P2X 4 were unchanged. Immunohistochemical studies, however, showed 23% of the total DRG neurons are P2X 2 positive in the normal L5 DRG, but that increased to 73% after nerve ligation. These data suggest that not only transcriptional but also posttranscriptional changes of multiple purinoceptors might be involved in the enhancement of purinergic sensitivity in injured sensory neurons.