Disinhibitory Involvement of the Anterior Cingulate Cortex in the Descending Antinociceptive Effect Induced by Electroacupuncture Stimulation in Rats

Abstract

The present study was conducted to clarify the role of the anterior cingulate cortex (ACCX) in acupuncture analgesia. Experiments were performed on 35 female Wistar albino rats weighing about 300 g. Single unit recordings were made from ACCX neurons with a tungsten microelectrode. Descending ACCX neurons were identified by antidromic activation from electrical shocks applied to the ventral part of the ipsilateral PAG through a concentric needle electrode. Cathodal electroacupuncture stimulation of Ho-Ku (0.1 ms in duration, 45 Hz) for 15 min was done by inserting stainless steel needles bilaterally. An anodal silver-plate electrode (30 mm x 30 mm) was placed on the center of the abdomen. Naloxone (1.0 mg/kg, i.v.) was used to test whether changes of ACCX activities were induced by the endogenous opioid system. Data were collected from a total of 73 ACCX neurons. Forty-seven neurons had descending projection to the PAG, and the other 26 had no projections to the PAG. A majority of descending ACCX neurons were inhibited by electroacupuncture stimulation. By contrast, non-projection ACCX neurons were mainly unaffected by electroacupuncture. Naloxone did not reverse acupuncture effects on the changes of ACCX neuronal activities. Acupuncture stimulation had predominantly inhibitory effects on the activities of descending ACCX neurons. Since the functional connection between ACCX and PAG is inhibitory, electroacupuncture caused disinhibition of PAG neurons, whose activity is closely related to descending antinociception to the spinal cord. This disinhibitory effect elicited by acupuncture stimulation is thought to play a significant role in acupuncture analgesia.

The Involvement of Descending Pain Inhibitory System in Electroacupuncture-Induced Analgesia

“…On a short-term level, the activation of ACC may regulate the descending pain inhibitory system, whereas on a long-term level, it may trigger the affection-related regions and thereby pain-related aversiveness may be inhibited. These findings are consistent with previous reports that the connection between ACC and PAG could be inhibited by EA and thus cause disinhibition of PAG neurons that contribute to anti-nociception, which in turn activates the descending inhibitory pathways (Hirano et al, 2008). However, the relevance of ACC to acupuncture analgesia seems to be controversial with the demonstration that ACC contributes to the descending facilitatory rather than inhibitory modulation of pain (Calejesan et al, 2000; Lei et al, 2004; Zhang et al, 2005).…”

From Peripheral to Central: The Role of ERK Signaling Pathway in Acupuncture Analgesia

“…Acupuncture also has been reported to activate some brain structures such as the periaqueductal gray, nucleus raphe magnus, locus coeruleus, and arcuate nucleus that contribute to descending inhibitory modulation, as well as deactivate multiple limbic areas modulating pain emotion, such as insula and the anterior cingulate cortex. 8,9,20-22,30,42,55,68 …”

Stress-induced modulation of nociceptive responses in the rat anterior cingulate cortex

“…Excitatory and inhibitory responses are also observed in ACCX neurons with descending projection to the PAG after electroacupuncture, a potentially stressful form of somatic stimulation (Hirano, et al, 2008). Therefore, it is apparent that somatosensory stimulation evokes responses in the ACCX in a bimodal fashion (Calejesan, et al, 2000;Vaccarino& Chorney, 1994).…”