Percutaneous Application of Galvanic Current in Rodents Reverses Signs of Myofascial Trigger Points

Abstract

An increase in the spontaneous release of acetylcholine (ACh) at the motor endplate is directly related to the generation of myofascial trigger points (MTrPs). In this study, percutaneous electric fields were applied to an animal model of MTrPs with high levels of spontaneous ACh release. All experiments were performed on Swiss mice and Sprague Dawley rats. For evaluating the spontaneous neurotransmission, intracellular recordings were performed, and the frequency of miniature endplate potentials was evaluated. Electromyographic recordings were also conducted to evaluate the endplate noise. Finally, the number and strength of local twitch responses (LTR) were evaluated using ultrasound recordings. The protocols used for the electric currents were 0.4 mA for five seconds and four repetitions (protocol 1), 1.5 mA for five seconds and three repetitions (protocol 2), and 3 mA for three seconds and three repetitions (protocol 3). After a subcutaneous injection of neostigmine (NTG), a great increase was observed in the frequency of mEPPs, together with an elevated endplate noise. Protocols 2 and 3 were the most effective. Protocol 3 could completely reverse the action of NTG at both three hours and 24 hours, respectively. The application of percutaneous currents produced both an increase in the number (144%) and in the speed (230% faster) of LTR compared with dry needling. In conclusion, higher doses of electrical current are more effective for decreasing MTrPs findings in an animal model.

Conflict of interest statement

The authors declare no conflicts of interest.

Copyright © 2020 R. Margalef et al.

Figures

Figure 1

Timeline of the experimental procedure. CTR, control; NTG, neostigmine; EC + NTG, electric currents applied to animals treated with neostigmine. In the lower part of the line there are experimental methodologies: intracellular recordings in mice; EMG, electromyography in mice; Ultrasonography is performed in rats.

Figure 2

Determination of speed of the local twitch response. The local twitch response (LTR) can be seen by ultrasound technique as a very discreet area (gray ellipse; see supplementary videos). This area is called the “LTR area.” After determining the LTR area, the distance from the point at the beginning of the LTR and the tibia (X1) and the distance from the point at the end of the LTR and the tibia (X2) were measured. In all cases, three measurements were made. X1-X2 = distance traveled by the LTR during the spasm. The total LTR duration was extracted from the video analyzers. These parameters were used to calculate the speed (v) of LTR: v= (X1−X2)/LTR duration.

Figure 3

Intracellular recordings. After the subcutaneous injection of neostigmine, several electric current protocols have been applied: (a) protocol 1 (4 repetitions of 0.4 mA for 5 seconds), (b) protocol 2 (3 repetitions of 1.5 mA for 5 seconds), and (c) protocol 3 (3 repetitions of 3 mA for 3 seconds). The recordings were made 3 hours and 24 hours after applying the protocols. The values are expressed in events per minute (mean ± SEM). Control = 7 muscles; 66 fibers were recorded in total. Neostigmine = 5 muscles; 45 fibers recorded in total. (neostigmine + protocol 1) = 3 muscle; 39 fibers were recorded in total. (neostigmine + protocol 2) = 4 muscles; 36 fibers were recorded in total. (neostigmine + protocol 3) = 4 muscles; 71 fibers were recorded in total. (neostigmine + protocol 1) = 3 muscles; 40 fibers recorded in total. (neostigmine + protocol 2) = 3 muscles; 36 fibers were recorded in total. (neostigmine + protocol 3) = 3 muscles; 56 fibers were recorded in total. ∗P < 0.05with respect to control values.

Figure 4

Electromyography. (a) Number of areas with endplate noise. (b) Endplate noise frequency. On the left, 3h after injection of neostigmine (NTG). On the right, 24 h after injection of neostigmine. Values are expressed in % of variation between experimental values registered in the right leg and control values registered in the left leg (mean ± SEM). For each experimental series, n = 5 animals (5 control gastrocnemius and 5 gastrocnemius treated). ∗P < 0.05 with respect to control values.

Figure 5

Ultrasonography. (a) Average number of local twitch responses obtained with dry needling and galvanic current. (b) Speed obtained for each local twitch response during the dry needling technique and after applying galvanic current. The values are expressed in machine units (mean ± SEM). N = 6 rats. ∗P < 0.05 for values obtained with galvanic current compared to values obtained using the dry needling technique.