P2Y1 Purinergic Receptor Contributes to Remifentanil-Induced Cold Hyperalgesia via Transient Receptor Potential Melastatin 8-Dependent Regulation of N-methyl-d-aspartate Receptor Phosphorylation in Dorsal Root Ganglion

Astrocytic purinergic signalling contributes to the development and maintenance of neuropathic pain via modulation of glutamate release

Although activation of astrocytes is critical in developing neuropathic pain (NP) following nerve injury, the underlying mechanisms of NP and therapeutic management for NP are still vague. Importantly, the decreases in the levels of astrocytic glutamate transporter-1 (GLT-1) in the spinal dorsal horn result in enhanced excitatory transmission and cause persistent pain. P2Y1 purinergic receptor (P2Y1R) has been shown to enhance many inflammatory processes. The up-regulated expression of astrocytic P2Y1R is crucial to participate in pain transduction under conditions of nerve injury and peripheral inflammation considering that P2Y1R is potentially involved in glutamate release and synaptic transmission. This study indicates that the expression of P2Y1R in the spinal cord was increased accompanied by the activation of A1 phenotype astrocytes in the rat model of spinal nerve ligation (SNL). Astrocyte-specific knockdown of P2Y1R alleviated SNL-induced nociceptive responses and mitigated A1 reactive astrocytes, which subsequently increased GLT-1 expression. Conversely, in naïve rats, P2Y1R over-expression induced a canonical NP-like phenotype and spontaneous hypernociceptive responses and increased the concentration of glutamate in the spinal dorsal horn. Besides, our in vitro data showed that the proinflammatory cytokine tumour necrosis factor-alpha contributes to A1/A2 astrocyte reactivity and Ca²⁺ -dependent release of glutamate. Conclusively, our results provide novel insights that as a significant regulator of astrocytic A1/A2 polarization and neuroinflammation, P2Y1R may represent a potential target for the treatment of SNL-induced NP.

Single-cell RNA sequencing reveals distinct transcriptional features of the purinergic signaling in mouse trigeminal ganglion

Trigeminal ganglion (TG) is the first station of sensory pathways in the orofacial region. The TG neurons communicate with satellite glial cells (SGCs), macrophages and other cells forming a functional unit that is responsible for processing of orofacial sensory information. Purinergic signaling, one of the most widespread autocrine and paracrine pathways, plays a crucial role in intercellular communication. The multidirectional action of purinergic signaling in different cell types contributes to the neuromodulation and orofacial sensation. To fully understand the purinergic signaling in these processes, it is essential to determine the shared and unique expression patterns of genes associated with purinergic signaling in different cell types. Here, we performed single-cell RNA sequencing of 22,969 cells isolated from normal mouse TGs. We identified 18 distinct cell populations, including 6 neuron subpopulations, 3 glial subpopulations, 7 immune cell subpopulations, fibroblasts, and endothelial cells. We also revealed the transcriptional features of genes associated with purinergic signaling, including purinergic receptors, extracellular adenosine triphosphate (eATP) release channels, eATP metabolism-associated enzymes, and eATP transporters in each cell type. Our results have important implications for understanding and predicting the cell type-specific roles of the purinergic signaling in orofacial signal processing in the trigeminal primary sensory system.