Electroacupuncture may alleviate inflammatory pain by downregulating the expression of P2Y14 receptor in the primary somatosensory cortex

Abstract

Increasing evidence indicated that purinergic signalling involved in electroacupuncture (EA)-induced analgesia. Whether purinergic P2Y₁₄ receptor contributes to EA-mediated analgesia remains unclear. Here, we report that the expression of P2Y₁₄ receptor in the hindlimb region of the primary somatosensory cortex (S1HL) was significantly upregulated on Complete Freund's Adjuvant (CFA)-induced pain model mice, while was downregulated after EA treatment (2 Hz frequency, 1 mA intensity, and 30 min duration) at "Zusanli" (also named ST36 acupoint). EA-mediated analgesia could be reversed by injection of P2RY₁₄ agonist uridine diphosphate glucose (UDPG) into the bilateral S1HL, while prolonged by injection of P2RY₁₄ antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPTN). It suggested that EA may alleviate inflammatory pain by downregulating the expression of P2RY₁₄ in the S1HL.

Keywords: Electroacupuncture analgesia; Inflammatory pain; P2RY14; Primary somatosensory cortex of hindlimb.

Fig. 1

EA relieved CFA-induced nociceptive hypersensitivity and downregulated the P2RY₁₄expression in S1HL of CFA mice. (A) The study schedule. One week after CFA injection, the Hargreaves test was conducted to establish baseline paw withdrawal latency (PWL). The CFA + EA and CFA + sham EA groups then underwent 30 min of EA and sham EA treatments at ST36, respectively. PWL was measured at 0, 30, 60, 120, and 180 min post-treatment. (B-G) Time-dependent changes in PWL values following different interventions. (H and I) Quantitative protein analysis and comparison of P2RY₁₄ expression in S1HL across groups. (J and K) Immunofluorescence co-localization of P2RY₁₄ (red) with the neuronal marker NeuN (green) and comparison of mean fluorescence intensity of P2RY₁₄ among groups. The short scale bars = 50 μm, and the long scale bars = 20 μm. The sample size is represented by the numbers in the bar graph. ns: not significant; *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ****p ≤ 0.0001

Fig. 2

P2RY₁₄in S1HL were downregulated by EA in CFA mice.(A) The study schedule. After a one-week adaptation, catheters were surgically implanted into the bilateral S1HL of each mouse (as shown in the immunofluorescence image) for subsequent drug administration. One week after catheterization, an inflammatory pain model was established by injecting CFA into the right hind paw. A week later, drugs were bilaterally administered through the implanted catheters, and paw withdrawal latency (PWL) was measured 30 min before EA treatment. EA treatment was then performed for 30 min, with PWL measured at the following time points: 0, 30, 60, 120, 180, 240, and 300 min post-treatment. (B-I) Time-dependent changes in PWL following microinjection of DMSO, PPTN, or UDPG into bilateral S1HL, combined with EA treatment at ST36. (J and K) Quantitative protein analysis and comparison of P2RY₁₄ expression in S1HL across group. (L and M) Immunofluorescence co-localization of P2RY₁₄ (red) with the neuronal marker NeuN (green) and comparison of mean fluorescence intensity of P2RY₁₄ among groups. The short scale bars = 50 μm, and the long scale bars = 20 μm. The sample size is represented by the numbers in the bar graph. ns: not significant; *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ****p ≤ 0.0001