Abstract
BACKGROUND AND OBJECTIVES: Recent experiments have shown that transcranial electrical stimulation significantly increases the potency and duration of the analgesic effects of opioids in humans and rats. In the present study, the influence of transcranial electrical stimulation (TCES) on the analgesic effect of remifentanil hydrochloride (HCl) in rats was determined.METHODS: Experiments were performed on 80 albino male Wistar rats. Rats were randomly assigned to four groups: remifentanil HCl, remifentanil HCl and TCES, TCES, and control (n=20/group). Remifentanil HCl was injected on the 55th minute. Analgesia was assessed using the wet tail-flick latency test.RESULTS: In the remifentanil HCl group, analgesia (10.85±1.04 s) was reached at the fifth minute, and the analgesia was high for the first 10 min. In the remifentanil HCl and TCES group, the latency time peaked (16.60±1.19 s) at the fifth minute. This peak was 150% higher than that for the remifentanil HCl group, and 251% higher than the control or TCES groups. Analgesia in the remifentanil HCl and TCES group was sustained for 20 min at a statistically higher rate than the other treatment groups (P<0.001).CONCLUSIONS: TCES markedly increased the duration and analgesic potency of remifentanil HCl in rats. This effect appeared to be related to the release of enkephalins from brain structures, thus enhancing opioid analgesia.