1. Analgesic (anti-nociceptive) effects of acupuncture: Opioid neurons play an important role to reduce painful sensation (analgesic effects or anti-nociceptive effects). Nociceptive messages from the spinal cord to the brain is suppressed by the descending inhibition system. Opioid neurons at the periaqueductal gray (PAG) play an important role of descending inhibition (Descending inhibition; 2002).
It has been well demonstrated that the analgesic effects of acupuncture are mediated by an endogenous opioid pathway. Opioid-induced anti-nociception is mediated by a pathway from the PAG to the various brain nuclei. Opioids are likely to exert direct effects on PAG projection neurons through both delta- and mu-opioid receptors. Acupuncture can induce the expression of opioid peptides and opioid receptors in the CNS.
2. Anti-emetic effects of acupuncture: Acupoint of pericardium-6 (PC-6; hand) has been used for nausea and vomiting. PC-6 is located in the groove caudal to the flexor carpi radialis and cranial to the superficial digital flexor muscles. There is clear evidence that acupuncture treatment is effective on postoperative and chemotherapy-induced nausea and vomiting (Dundee et al., 1990).
Opioids have dual effects: an anti-emetic effect as well an emetic effect. It has been shown that central opioid plays a major role in mediating anti-emetic effect (Costello et al., 1977). The anti-emetic effect of acupuncture is mediated via the central opioid pathway (Tatewaki et al. 2005).
3. Anti-stress effects of acupuncture: Animal studies demonstrate that acupuncture attenuates various stress-induced physiological responses. Central oxytocin (OXT) has an anti-stress effects via inhibiting CRF neurons at the hypothalamus (PVN) . The anti-stress effects of acupuncture are also mediated via the stimulation of hypothalamic OXT expression. A recent study showed that acupuncture increased the OXT neurons and decreased CRF neurons at the hypothalamus (PVN) following chronic stress . These suggest that acupuncture may act on OXT neurons at the PVN, resulting in reduced CRF expression and stress responses (Yoshimoto et al. 2012).
In humans, post-traumatic stress disorders (PTSD) are marked by deficits in anxiety, stress regulation and in social functioning. A recent clinical trial demonstrated that acupuncture is effective for treating the patients with PTSD. Compared with the cognitive-behavioral therapy, acupuncture provided significant effects on PTSD. Symptom reductions observed at the time that acupuncture treatments ended, were maintained at 3-month follow-up (Hollifield et al. 2007).