Electroacupunture reduces mechanical hyperalgesia produced by repeated intramuscular injections of acidic saline in rats

Abstract

This study aimed to identify the effects of electroacupuncture in the mechanical hyperalgesia produced by repeated intramuscular injections of acidic saline. Twenty four male Wistar rats were divided in four groups (n = 6, in each group): control, acupuncture, electroacupuncture (EA) 15 Hz and electroacupuncture (EA) 100 Hz. Left gastrocnemius muscle from all animals was injected with 100 μL of sterile saline pH 4.0 twice five days apart. Electroacupuncture, acupuncture or control was daily administered (20 min) for 5 consecutive days under isoflurane anesthesia (1%–2%). Needles were placed in the Zuzanli (St36) and Sanyinjiao (SP6). Paw withdrawal threshold to mechanical stimuli was assessed before the two injections, and before and after the each stimulation by using von Frey filaments. The reduced paw withdrawal threshold that occurs 24 hours after the second injection was significantly reversed by the first administration of EA at both 100 Hz and 15 Hz when compared with sham treatment and baseline measures. The analgesic effect lasted for 4 and 3 days when 15 Hz and 100 Hz were applied, respectively. These data suggest that both 15 Hz and 100 Hz electroacupuncture are effective on reducing secondary mechanical hyperalgesia showing a long‐lasting effect. Research support: CAPES, Fapitec.