Neuro-hormonal Theory and acupuncture

The transmission of pain between the various points of our body and brain can be modulated at different levels in the brain.

Different structures in the brain will process different aspects of pain, such as the experience of emotional pain, the perception of what pain feels like, the recognition of how harmful the pain will be and where the pain is coming from.
The blocking of pain is mediated by what we call neuro-hormones that are attached to the receptors which are responsible for blocking pain. Pain relief using the drug morphine acts on the same receptors that are responsible for blocking pain as those addressed by endorphins, which is a natural substance produced by the body for blocking pain.

Studies have shown that the pain killing properties of acupuncture come about by stimulating the flow of natural endorphins in the brain.

This can be scientifically or medically proven by blocking the action of endorphins using a drug called naloxone. When naloxone is administered, the pain killing effect of the endorphin is nullified and the patient feels pain again. Furthermore, when naloxone was given to a patient being actively treated by acupuncture, the pain relieving effects of acupuncture were also reversed. This means that the site where acupuncture is applied is subject to the natural release of endorphins by the brain.
Recent studies have also show that acupuncture releases the levels of nitric oxide in the region of treatment, and that this, it turn, increases blood circulation in the region.