The integrity of the anterior pretectal nucleus and dorsolateral funiculus is necessary for electroacupuncture-induced analgesia in the rat tail-flick test

Previous studies have indicated that the anterior pretectal nucleus (APtN) is implicated in pathways that descend through the dorsolateral funiculus (DLF) to modulate nociceptive inputs in the spinal dorsal horn. The activation of descending inhibitory mechanisms also seems to be involved in electroacupuncture (EA)-induced analgesia. This study utilized the tail-flick test to examine the changes produced by DLF lesion or injection of 2% lidocaine into the APtN in the analgesia induced by 2 or 100 Hz EA applied to the Zusanli (ST36) and Sanyinjiao (SP6) acupoints in lightly anesthetized rats. Tail-flick latency was significantly increased by EA, the effect of 2 Hz EA lasting longer than that produced by 100 Hz EA. The effect of either 2 or 100 Hz EA did not occur in DLF lesion rats. The effect of 2 Hz EA did not occur in rats with neural block of the whole or dorsal APtN. In contrast, the effect of 100 Hz EA was reduced in rats with neural block of the whole APtN, but remained unchanged in rats with neural block of the dorsal APtN. We thus conclude that the integrity of the APtN and DLF is necessary for EA-induced analgesia in the rat tail-flick test. In addition, the integrity of the dorsal APtN is necessary for the analgesic effect of 2 but not 100 Hz EA.