Electrical stimulation reduces secondary mechanical hyperalgesia in a non-inflammatory pain model in rats

Abstract

Fibromyalgia is a musculoskeletal disease characterized by widespread pain. Its physiological mechanisms are not clear yet, which directly interferes on the quality of pain management. Electrical therapeutic approaches such as interferential current (IFC) and transcutaneous electrical nerve stimulation (TENS) have been used in several pain conditions. To our knowledge this is the first study investigating the effects of both IFC and TENS on reduction of secondary mechanical hyperalgesia in a non-inflammatory muscle pain models in rats. Double intramuscular injection of acid saline (Ph 4.0) was performed five days apart on the left gastrocnemius muscle. Twenty male Wistar rats were divided in four groups: high frequency TENS (100Hz), low frequency TENS (5Hz), interferential current-IFC (modulated frequency of 100Hz) and sham stimulation. Control animals received the same treatment but with no delivery of electrical stimulation. A pair of round electrodes were placed at the lateral and medial aspects of the left gastrocnemius muscle. Animals were lightly anesthetized (5%-2%) with isoflurane and received a single stimulation for 20 minutes. Sensorial intensity was set for starting stimulation. Mechanical hyperalgesia was assessed through von Frey filaments with increasing bending forces before both first and second acid saline injections, 24 h after second injection and following the treatment. All animals showed significant reduction of the mechanical hyperalgesia 24 h after the second injection (p< 0.05). There was a significant reduction of the mechanical hyperalgesia in IFC-treated (p< 0.01) and both high and low frequency TENS-treated animals (p<0,03) compared to sham animals. Thus we suggest that both IFC and TENS at both high and low frequencies promote antinociceptive effect on muscle pain model. Fibromyalgia is a musculoskeletal disease characterized by widespread pain. Its physiological mechanisms are not clear yet, which directly interferes on the quality of pain management. Electrical therapeutic approaches such as interferential current (IFC) and transcutaneous electrical nerve stimulation (TENS) have been used in several pain conditions. To our knowledge this is the first study investigating the effects of both IFC and TENS on reduction of secondary mechanical hyperalgesia in a non-inflammatory muscle pain models in rats. Double intramuscular injection of acid saline (Ph 4.0) was performed five days apart on the left gastrocnemius muscle. Twenty male Wistar rats were divided in four groups: high frequency TENS (100Hz), low frequency TENS (5Hz), interferential current-IFC (modulated frequency of 100Hz) and sham stimulation. Control animals received the same treatment but with no delivery of electrical stimulation. A pair of round electrodes were placed at the lateral and medial aspects of the left gastrocnemius muscle. Animals were lightly anesthetized (5%-2%) with isoflurane and received a single stimulation for 20 minutes. Sensorial intensity was set for starting stimulation. Mechanical hyperalgesia was assessed through von Frey filaments with increasing bending forces before both first and second acid saline injections, 24 h after second injection and following the treatment. All animals showed significant reduction of the mechanical hyperalgesia 24 h after the second injection (p< 0.05). There was a significant reduction of the mechanical hyperalgesia in IFC-treated (p< 0.01) and both high and low frequency TENS-treated animals (p<0,03) compared to sham animals. Thus we suggest that both IFC and TENS at both high and low frequencies promote antinociceptive effect on muscle pain model.