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The Brain Chemistry of Sexual Bonding

The Chemistry of Orgasm

The Magical High

It turns out that the biochemical oxytocin creates the magical high of orgasm. Oxytocin is produced in the hypothalamus and released into the blood from the posterior lobe of the pituitary gland in both sexes during orgasm. (Oxytocin injected into the cerebrospinal fluid causes spontaneous erections in rats, reflecting actions in the hypothalamus and spinal cord.) Oxytocin has a half-life of typically about three minutes in the blood.

Other Benefits of Oxytocin

As an anti-stress function, oxytocin reduces blood pressure and cortisol levels, increasing tolerance to pain, and reducing anxiety. PET scans of human volunteers showed that both the female and male orgasm shut down areas in the brain associated with anxiety and fear (the amygdala).

Cuddling Hormone

In other functions, oxytocin receptors in the brain are instrumental in social recognition and bonding (hence the term “cuddling hormone”) and are believed to be involved in the forming of trust between people. Oxytocin released into the brain of the Prairie Vole female during sexual activity is important for forming a monogamous pair bond with her sexual partner.

Vasopressin

Vasopressin appears to have a similar bonding effect in males. Vasopressin, released by the hypothalamus into the brain during sexual activity, initiates and sustains patterns of activity that support the pair bond between the sexual partners. Evidence for this comes from experimental studies in several species where there are consistent differences between monogamous species and promiscuous species in the distribution of vasopressin receptors.

Is Passion a Chemical?

What causes people to fall passionately in love? We all know the symptoms, your heartbeat accelerates, butterflies flutter in the stomach, you feel euphoric. Now researchers at the University of Pavia, in Italy, publishing their report in the Psychoneuroendocrinology journal, may have discovered why: a protein called nerve growth factor (NGF). Scientists examined the blood of 58 new lovers compared to others involved in long-term relationships.

After a year later, they re-examined the two groups again and found, alas, those who had been together for a year or more had much the same levels as the long-term couples. What gives?

NGF Blood Levels

It seems that the “so-crazy-hot-for-each-other” phase lasts about a year (at most two), after which NGF blood levels return to a normal level. The scientists found that the lusty NGF molecule was replaced by oxytocin (the so-called "cuddle hormone") in couples that had been together for several years.

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Sources: Oxytocin / Vasopressin Wikipedia (http://en.wikipedia.org) Raised Plasma Nerve Growth Factor Levels Associated with Early-Stage Romantic Love Psychoneuroendocrinology 2006 Apr;31(3):288-94

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