POTENTIATION OF FENTANYL SUPPRESSION OF THE JAW-OPENING REFLEX BY TRANSCRANIAL ELECTRICAL-STIMULATION

Stinus et al. [L. Stinus, M. Auriacombe, J. Tignol, A. Limoge, M. Le M eal, Transcranial electrical stimulation with high frequency intermitt ent current (Limoge's) potentiates opiate-induced analgesia: blind stu dies, Pain, 42 (1990) 351-363.] observed that transcranial electrical stimulation (TCES) with high-frequency intermittent current potentiate d opiate-induced analgesia using the tail-flick test. In unanesthetize d, chronic preparations, electrical stimulation (0.5 Hz) of the lower incisor pulp of rats elicits a short-(6 ms) and a long-latency (12-18 ms) jaw-opening reflex (JOR) without any evidence of aversive behavior [J. Azerad, F. Fuentes, I. Lendais, A. Limoge, B. Pollin, Methods for selective tooth pulp stimulation in acute and chronic preparations in rats, J. Physiol., 405 (1988) 3P.]. Fentanyl increases thresholds of both reflexes and transiently suppresses the long-latency JOR. We then decided to look at the influence of TCES on both drug-induced mean of maximal threshold variation (MMTV) and duration of JOR suppression pe riod. These parameters have been investigated in 43 Wistar rats with o r without TCES administered for 3 h before the drug injection and thro ughout the testing period. TCES alone has no effect. In contrast, it s ignificantly increases the duration of the reflex suppression period ( 149 +/- 5% vs. control, P < 0.001) while fentanyl-increased reflex thr esholds remain unchanged. The fentanyl-induced JOR suppression period returns to the control values 2 days later. When a second 3-h TCES ses sion is delivered 2 or 4 days after the first TCES session, a similar increase of this suppression period is observed. Moreover, 2 days afte r a second TCES session, an increase of the duration of the fentanyl-i nduced JOR suppression period is systematically observed. In contrast, a 6-h TCES session never induces such effects, These results confirm a potentiating effect of TCES on opioid action and demonstrate the val ue of repeated TCES sessions. (C) 1997 Elsevier Science B.V.