Purinergic receptor P2Y1 regulates polymodal C-fiber thermal thresholds and sensory neuron phenotypic switching during peripheral inflammation

Abstract

We have recently found that following complete Freund’s adjuvant (CFA) induced inflammation that cutaneous polymodal nociceptors (CPM) lacking the transient receptor potential vanilloid 1 (TRPV1) are sensitized to heat stimuli. In order to determine possible mechanisms playing a role in this change, we examined gene expression in the L2/L3 sensory ganglia following CFA injection into the hairy hindpaw skin and found that G-protein coupled purinoreceptor P2Y1 expression was increased. This receptor is of particular interest as most CPMs innervating mouse hairy skin bind isolectin B4 (IB4), which co-localizes with P2Y1. Additionally, our recent findings have shown that cutaneous CPMs in P2Y1−/− mice, displayed significantly reduced thermal sensitivity. Together these findings suggested a possible role for P2Y1 in inflammation-induced heat sensitization in these fibers. To test this hypothesis, we utilized our in vivo siRNA technique to knockdown the inflammation-induced increase in P2Y1 expression and then examined the functional effects using ex vivo recording. We found that the normal reduction of heat thresholds in CPM fibers induced by CFA was completely blocked by inhibition of P2Y1. Surprisingly, inhibition of P2Y1 during inflammation also significantly increased the number of CPM neurons expressing TRPV1 without a change in the total number of TRPV1 positive cells in the L2 and L3 DRGs. These results show that the inflammation-induced enhanced expression of P2Y1 is required for normal heat sensitization of cutaneous CPM fibers. They also suggest that P2Y1 plays a role in the maintenance of phenotype in cutaneous afferent fibers containing TRPV1.

Growth hormone regulates the sensitization of developing peripheral nociceptors during cutaneous inflammation: Erratum.

“…It has been hypothesized that this phenomenon is due to altered peripheral Afiber sensitization along with improper development of glycinergic inhibition [25,27]; a notion that was recently supported by our laboratory [24]. In our previous report, we also found that developing cutaneous nociceptors were sensitized to heat and mechanical stimuli in a pattern that differed from adults [23].…”

“…For P7 mice, siRNAs were injected one day before inflammation, and for P14 mice, siRNAs were injected two days before inflammation. This strategy follows a modified version of our previous reports [21][22][23].…”

P2Y purinergic receptors: New targets for analgesic and antimigraine drugs

“…Conversely, both P2Y 1 and P2Y 2 mRNAs are upregulated in mouse L2/L3 DRG cells at 14 and 21 days after nerve transection [53]. The upregulation of P2Y 1 mRNA in mouse DRGs appears to be necessary for heat sensitization of cutaneous polymodal nociceptors in response to CFA injection in the skin [54]. Although the evaluation of the mRNA expression levels has been performed on total ganglia, and a contribution of glial P2Y…”

Physiological temperatures drive glutamate release onto trigeminal superficial dorsal horn neurons

“…Primary afferent neurons discharge little in the absence of peripheral stimulation or injury (Jankowski et al 2012;Pitcher and Cervero 2010), and, therefore, their central terminals might be expected to have similarly low rates of neurotransmitter release in basal conditions. However, at central synapses measured in slices, neurotransmitter release occurs spontaneously, and such events are commonly viewed as arising from infrequent and stochastic release from the same pools of vesicles as action potential-evoked release (Ermolyuk et al 2013;Katz 1971).…”