Oxytocin - a possible mediator of anti stress effects induced by Acupuncture?
Kerstin Uvnäs Moberg
Oxytocin a polypeptide, containing 9 aminoacids, is produced in the paraventricular and the suproptical nuclei of the hypothalamus. Oxytocin is secreted inte the circulation to produce hormonal effects such as stimulation of milkejection and uterine contractions. In addition oxytocin is released from oxytocin containing nerve fibres that reach various areas in the brain such as other parts of the hypothalamus, the amygdala, the raphe nuclei, PAG., striatum and brainstem centres for control of autonomic nervous function. Thus oxytocin may influence endocrine functions, but also exert anxiolytic and sedative effects, elevate painthreshold decrease sympathetic nerve activity and increase vagal parasympathetic nerve activity. Taken together oxytocin induces a psycho-physiological pattern consistent with increased social behaviour, antistress and promotion of growth. These effects become particularly prominent if oxytocin is given repeatedly. 5 dayly injections of oxytocin elevate painthreshold for 10 days after the last injection and bloodpressure may be reduced for up to 3 weeks in female rats. When the antistress is established it can be maintained by treatment given at longer intervals.
The longterm effects of oxytocin and some of the acute effects, are mediated by secondary changes in the activity in other transmittor systems. The pain relieving effects involve an increased activity in central opioid systems e.g in PAG, whereas the antistress effects are mediated by an enhanced activity in the alfa 2 adrenoceptors in various brain areas reached by oxytocin containing nerves. Since these receptors exert an inhibitory effect on NA release, the activity in the central NA bundles emanating from the locus ceruleous and which are linked to arousal and agression, is decreased. At the same time activation of EPI neurons in the brainstem lead to an inhibition the of the peripheral sympathetic system and increase the activity in the parasympathetic system and as a consequence anti stress and growth promotion is induced.
Originally it was assumed that oxytocin was only released during labour and breastfeeding in response to activation of sensory nerves in the mammary gland and uterus. However it has recently been established that oxytocin can be released in response to touch, warmth and light pressure from all parts of the body. Obviously stimulation of non noxious somatosensory afferents does not only result in "a localized sensation of touch", it also results in physical relaxation and a sense of wellbeing. In a rat model in which the abdomen is being stroked with a frequncy of 40 strokes perminut for 5 minutes, all the effects that can be induced by oxytocin (increased friendly social interaction and the antistress -like effects) are induced. Administration of an oxytocin antagonists inhibits the effects of the massage like stroking acutely but also the longterm effects seen after repeated treatments. Interestingly the massage like stroking induces more powerful effects if applied on the ventral side. This can be an effect which is secondary to the more dense innervation of the front side. However immunohistological studies have revealed the presence of an extra type of sensory nerves originating in the skin on the ventral side, which do not project to the spinal cord, but directly to the vagal nerve to reach the NTS. Thus some of the cutaneous afferents travel to the brain via the afferents from the viscera e.g. the gastrointestinal tract. The NTS is in turn directly connected to the PVN where oxytocin is produced. It is possible that activation of these special cutaneous afferents lie behind the more powerful effects of touch, warmth and light pressure, when triggered from the front side.
The mechanisms by which acupuncture induces its effects are only partly known and are under debate. However in particular the long term antistress like effects of this treatment may well include activation of oxytocinergic pathways and mechanisms. Some animal experimental data indicate that painrelief induced by acupuncture is abolished not only by opioid antagonists but also by oxytocinantagonists. Oxytocin has also been shown to alleviate back and cancer induced pain in humans. Further studies are needed to explore the relationship between oxytocin and the effects of acupuncture.