Oxytocin is secreted from the pituitary gland and cannot re-enter the brain because of the blood-brain barrier. Instead, the behavioral effects of oxytocin are thought to reflect release from centrally projecting oxytocin neurons, different from those that project to the pituitary gland, or which are collaterals from them. Oxytocin receptors are expressed by neurons in many parts of the brain and spinal cord, including the amygdala, ventromedial hypothalamus, septum, nucleus accumbens and brainstem.
Oxytocin is best known for its roles in female reproduction: 1) it is released in large amounts after distension of the cervix and vagina during labor, and 2) after stimulation of the nipples, facilitating birth and breastfeeding. Recent studies have begun to investigate oxytocin’s role in various behaviors, including orgasm, social recognition, pair bonding, anxiety, and maternal behaviors. For this reason, it is sometimes referred to as the “cuddle hormone.”
The hormone oxytocin has come under intensive study in light of emerging evidence that its release contributes to the social bonding that occurs between lovers, friends, and colleagues. Oxytocin also plays an important role in birth and maternal behavior, but until now, research had never addressed the involvement of oxytocin in the transition to fatherhood.
Three important findings emerged. At both time-points, fathers’ oxytocin levels were not different from levels observed in mothers. Thus, although oxytocin release is stimulated by birth and lactation in mothers, it appears that other aspects of parenthood serve to stimulate oxytocin release in fathers.