A Role for Brain Neurotransmitters in the Action of Acupuncture
All studies measuring neurochemical responses to acupuncture provided evidence for the biological effects of acupuncture that ultimately may help to understand how acupuncture can be used to treat disease. Moreover, in a more general sense, these results suggest that acupuncture can correct reversible malfunctions of the body by direct activation of brain pathways and thus contribute to the biochemical balance in the central nervous system by regulating neurotransmitters that control health and disease. The discovery of the central endorphin system was a prominent step toward understanding the analgesic effect of acupuncture.[51,52] It is now well established that endorphinergic neurons in the hypothalamus projecting to the dosal raphe nucleus and periaqueductal gray matter of the mesencephalon are primarily responsible for acupuncture analgesia. Additionally, other brain areas such as the nucleus accumbens, with interconnections to the descending pathway from the hypothalamus to the dorsal raphe nucleus and periaqueductal gray matter, might also mediate opioid- and acupuncture-induced analgesia.[54,55] In the nucleus accumbens, drugs of abuse act to produce a large increase in dopamine that has long been associated with addictive behavior. The descending antinoceptive pathway from the hypothalamus appears to depend on the activation of the anterolateral tract by acupuncture. Also, several brain neurotransmitter systems such as serotonin, catecholamines and amino acids including GABA have been implicated in the analgesic effects of acupuncture.
Although few experiments have investigated the effect of acupuncture on GABAergic neuron, GABA-related studies provided evidence that acupuncture stimulation may produce the inhibitory effect via GABAergic neuron. For example, it has been shown that electroacupuncture exerted depressor effect by inhibition of the sympathetic nervous system and this effect was mediated through GABA in the rostral ventrolateral medulla. This inhibitory effect via GABAergic neuron was reversed with injection of GABA antagonist.[59,60] GABA has also been implicated in the therapeutic effect of cerebral ischemia by electroacupuncture using middle cerebral artery occlusion (MCAO) rats. Electroacupuncture effectively reduced infarct area in the cerebral cortex and hippocampus and increased GABA immunoreactivity. Inhibition of infarction by electroacupuncture was completely prevented by a GABA receptor's antagonist.
With regard to serotonin, microdialysis study showed that acupuncture at bilateral Shenshu acupoints significantly increased serotonin release in the rat nucleus accumbens. The authors suggested the possibility that acupuncture affect the reward system pathway of the brain by activation of serotonergic neurons. Further support for a role of acupuncture in regulating brain serotonin is the observation that electroacupuncture prevented restraint-induced decreases in serotonin levels in the nucleus accumbens. Serotonin has long been hypothesized to have a role in mediating the efficacy of acupuncture in the treatment of drug withdrawal. Considerable evidence showed marked differences between the alcohol-preferring rats and normal rats in that the alcohol-preferring rats have fewer serotonin neurons and higher levels of enkephalin in the hypothalamus, fewer GABA neurons, lower dopamine release and dopamine D2 receptors in the nucleus accumbens.[65–68] Based on these observations, it was postulated that chronic exposure to drugs might cause 'reward deficiency syndrome' resulting from a basal dysfunction of brain reward dopamine function. These authors proposed that activation of serotonin neurons in the hypothalamus induces met-enkephalin release in the VTA, and as a consequence, GABA neurons in the VTA are inhibited, thereby increasing dopamine release in the nucleus accumbens. This proposal, combined with the finding that acupuncture activates the descending serotonergic pathways via the anterolateral tract, have suggested that acupuncture may have a role in normalizing the release of dopamine via serotonin neurons in the hypothalamus.
Evid Based Complement Alternat Med. 2008;5(3):257-266. © 2008 Oxford University Press
Cite this: A Possible Mechanism Underlying the Effectiveness of Acupuncture in the Treatment of Drug Addiction - Medscape - Sep 01, 2008.