Antipruritic effect of cold stimulation at the Quchi acupoint (LI11) in mice

Abstract

Background: Acupuncture and moxibustion are used to treat pruritus and atopic dermatitis. However, whether cold stimulation (defined as that the temperature conducted under skin temperature) of acupoints affects itching in experimental murine models remains unclear.

Methods: The present study was designed to determine the therapeutic effects of different thermal stimulations at the Quchi acupoint (LI11) in a murine model in which scratching behaviour was elicited by subcutaneous injection with a pruritogenic agent (compound 48/80). Male ICR mice were divided into several groups as follows: control (saline), those receiving compound 48/80 and compound 48/80 with various thermal stimulations (5°C-45°C) at LI11 (n = 6 per group). The scratch response of each animal to these stimulations was recorded for 30 min. The antipruritic effect of the acupoint was further evaluated in LI11 and sham (non-acupoint) groups (n = 6 per group).

Results: Treatment with lower temperature (20°C) at the LI11 acupoint significantly attenuated compound 48/80-induced scratching; however, this antipruritic effect was not observed with stimulation at the sham point. The expression of c-fos in the neuron of the cervical spine induced by compound 48/80 was suppressed by cold stimulation at LI11. The antipruritic effect of cold stimulation was blocked by ruthium red (RR), a non-selective transient receptor potential (TRP) channel blocker, suggesting that TRP channels may play an important role in the antipruritic effect of cold stimulation at LI11 in mice.

Conclusions: This study demonstrated that cold stimulation at LI11 attenuated compound 48/80-induced scratching behaviour in mice, possibly by a TRP-related pathway.

Figure 1

Evaluating the antipruritic effect of different thermal stimulations over Quchi (LI11) acupoint on compound 48/80-induced scratching behavior. (A) Flow chart depicting steps involved in the study. (B) The probes (arrows) of constant temperature tissue cooling apparatus. (C) Localization and (D) operation of LI11 acupoint stimulated in the mice. It is located at the depression medial to the extensor carpi radialis, at the lateral end of the cubital crease. The sham point was located at the midpoint of the acromial part of the deltoid muscle, which is distant from classical acupoints.

Figure 2

Effects of different thermal stimulations at LI11 for compound 40/80-evoked scratching. Both parameters, within-bout scratching frequency (A) for 5°C and 15°C, (B) 20°C and 25°C, and (C) 35°C and 45°C and (D) number of scratch bouts, were shown. **P < 0.01 compared to control group. ^# P < 0.05 compared to compound 40/80 group).

Figure 3

Evaluating the antiprurtic efficacy of acupoint with a sham (non-acupoint) control. **P < 0.01 compared to control group. ^# P < 0.05 compared to compound 40/80 group).

Figure 4

c-fos expression in the cervical spinal cord. (A) Representative photomicrographs and (B) quantitative results of c-fos expression in the spinal cord. The c-fos-positive neurons were observed under a light microscope at high-power field (HPF) magnification, and the average number of c-fos-positive neurons was counted single-blind using the imaging software. **P < 0.01 compared to control group. ^# P < 0.05 compared to compound 40/80 group).

Figure 5

Evaluating the effect of TRP ion channels blocker (Ruthium red; RR). (A) Injection with RR at LI11 decreased the antipruritic effect of cold stimulation at LI11. (B) Local RR administration with compound 48/80 on mouse back significantly reduced scratching bouts. **P < 0.01 compared to control group. ^# P < 0.05 compared to compound 40/80 group. ^† P < 0.05 compared to saline group).