Figure 1.

Species differences in the expression of P2X2 mRNA. A, In situ hybridization of P2X3 and P2X2 mRNA expression in rat, monkey, and human DRGs. P2X3 mRNA was predominantly detected in small-diameter neurons, and this pattern was consistent across species. B, P2X2 was found in small- and medium-diameter neurons in rat DRGs but was virtually absent in monkey and human DRGs. Neurons were considered positive when there was an accumulation of grains above the level of background (see Materials and Methods). Some human samples contained lipofuscin, which was clearly identified as such in microscopy. C, RT-PCR amplification of mRNA from monkey DRG homogenates reveals P2X1, P2X3, and P2X4 expression and confirms the absence of P2X2 mRNA.