Natcher Conference Center
National Institutes of Health
June 9–10, 2005
Kerstin Uvnas Moberg, M.D., Ph.D., Professor, Department of Environment and Health, Swedish University of Agriculture, Sweden
Somatosensory stimulation is normally associated with pain and stress reactions. It is however also possible to induce an anti-stress pattern including stimulation of social behavior, mental calm and physical relaxation by non-noxious somatosensory stimulation. Thick myelinated fibers as well as thin C fiber afferents may be involved in these effects.
The peptide oxytocin is produced in the SON and PVN of the hypothalamus and released from neurons projecting not only to the neurohypophysis but also to the amygdala, PAG, hippocampus, striatum, raphe nuclei, NTS, DMX etc. OT stimulates milk ejection, maternal behavior, induces calm, increases pain threshold and induces physical relaxation including lowering of blood pressure and cortisol levels when released by breastfeeding. In addition the activity of the vagal nerve is increased to promote digestive processes and storing of nutrients.
The same effect pattern is induced if oxytocin is administered to male or female rats suggesting that the effects are not restricted to lactating females. In addition if oxytocin is given repeatedly, long-term effects are induced by secondary effects on other transmitter systems. The function of alfa 2 receptors is increased and opioidergic, serotonergic, and cholinergic function may be influenced. The function of the HPA axis is influenced in an anti-stress direction at the level of the hippocampus (MR, GR) hypothalamus (CRF), pituitary (ACTH) and adrenal (corticosterone production). If oxytocin is administered repeatedly during the neonatal period, lifelong effects may be induced.
Interestingly oxytocin can be released and an oxytocin like effect spectrum induced by non-noxious stimulation from several parts of the body in both sexes to e.g. by stroking, warmth, light pressure, low intensity nerve stimulation in anaesthetized animals. If a conscious rat (male or female) is stroked on the ventral side at a frequency of 40 strokes/ minute for 5 minutes, an anxiolytic like and or calming effect is induced, pain threshold is elevated, blood pressure, pulse rate and cortisol levels fall and the levels some gastrointestinal hormones rise. The effects are particularly strong when induced on the front side. This may be due the presence of a subpopulation of vagal nerve afferents originating in this area. Most of the effects are blocked by an oxytocinantagonist suggesting that oxytocin may be an important mediator of the anti-stress effects induced by non-noxious sensory stimulation. A similar response pattern is induced in humans of both sexes and all ages in response to close physical contact.