Prolactin - The Brain Chemical That Can Kill Libido in Long-Term Relationships

This is an interesting article on prolactin, a chemical (hormone) both men and women produce this chemical, which performs a wide variety of roles in the human body. Here is a little from Wikipedia on prolactin:

Prolactin ... stimulates the mammary glands to produce milk (lactation): Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands of the breasts and prepare for the production of milk. Milk production normally starts when the levels of progesterone fall by the end of pregnancy and a suckling stimulus is present. Sometimes, newborn babies (males as well as females) secrete a milky substance from their nipples known as witch's milk. This is in part caused by maternal prolactin and other hormones. 

Prolactin provides the body with sexual gratification after sexual acts: The hormone counteracts the effect of dopamine, which is responsible for sexual arousal. This is thought to cause the sexual refractory period. The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido (see hyperprolactinemia symptoms). 

Highly elevated levels of prolactin decrease the levels of sex hormones — estrogen in women and testosterone in men.[3] The effects of mildly elevated levels of prolactin are much more variable, in women both substantial increase or decrease of estrogen levels may result.

For men in particular, increased levels of prolactin are seriously problematic. As is stated above, prolactin in men decreases testosterone, which decreases libido and sexual function. That is the context of this question/answer article from Alternet (originally from The Guardian [UK]).

"I Love Her But the Sex Has Died": The Brain Chemical That Can Kill Libido in Long-Term Relationships

Trying to sustain a long-term relationship that is also sexual presents humans with a chemical catch-22

July 9, 2013 | By Carole Jahme 

Writer Carole Jahme shines the cold light of evolutionary psychology on readers' problems.

From an anonymous male, aged 40+

I have been in several very loving, amorous, "serious" relationships as an adult, none frivolous and none (at least on a conscious level – who the hell knows what's going on with me subconsiously) with the intention of being short-term.

Inevitably, however, my sexual attraction for my partner wanes to the point where we become virtually non-sexual. This can happen in less that a year after the relationship started. This condition consistently contributes to the relationship falling apart. My emotional feeling of love stays constant, and the breakup is traumatic for both of us. Add to the mix my undeniable enjoyment of and never-failing satisfaction with masturbation, and it seems to be a recipe for disaster. Is there an evolutionary take on any of this?

Carole replies:

Trying to sustain a long-term relationship that is also sexual presents humans with a chemical catch-22.

Studies on the length of relationships have shown that couples in harmonious, stable and trusting long-term relationships have higher blood levels of oxytocin (a chemical that regulates attachment, promotes cooperation and facilitates sensations of joy and love) than people who are not in compatible relationships. These happy couples also reap other benefits in terms of longer lifespan, lower rates of alcoholism, depression and illness, and more rapid recovery after accidental injury.

But there are conflicting chemicals at work in sexual relationships that sometimes prevent them from ever becoming long-term. Dopamine is a neurotransmitter in the limbic system – the brain's primitive reward centre. It mediates both the sex drive and addiction to drugs. Brain scans have shown that the rapid rise in dopamine levels during orgasm is similar to that seen in a heroin high. But dopamine falls rapidly following orgasm in both males and females and is replaced with rising levels of a hormone called prolactin.

Both are part of the brain's "dopaminergic" reward system.

At first, rising prolactin causes sleepy post-orgasm contentment. (Interestingly the amount of prolactin produced is far greater after sex with a partner than after masturbation. Thus there is little prolactin relief for those who masturbate.) But once this sleepy feeling of satiation has passed, prolactin may go on rising and cause problems for couples wanting to sustain a long-term sexual relationship. In both men and women excess levels of prolactin can cause loss of libido, anxiety, headaches, mood swings and depression.

High prolactin is associated with sensations of despair. When the prolactin levels of newly caged wild monkeys were monitored, the hormone was seen to rise once the animals realised they were trapped. Levels of the hormone were much higher in monkeys incarcerated for months compared with wild animals that had only just been caged. Science has yet to determine how long prolactin continues to rise and remain high in humans after orgasm, so this is speculative, but in a relationship with lots of sex it could mean levels are elevated for weeks or even months.

How does all this tie in with your predilection for maturbation? There have been some illuminating studies of this behaviour in non-human primates. It has been found, for example, that male monkeys who masturbate tend to be of low status, whereas high-status male monkeys are likely only to experience ejaculation during sex. It also seems that the frequency of masturbation is higher in captive primates than in wild animals. You can make of this what you will.

The dopaminergic system varies among humans, some people exhibiting more reward-seeking behaviour than others, and this may go some way towards explaining why many relationships are burnt out after a year. In reproductive terms, 12 months is long enough for fertilisation to take place. It is also certainly long enough for prolactin levels to rise. Once your libido flags and anxiety sets in, the short-term reward gained from masturbating may give you a dopamine "high" without risking bringing on that post-orgasmic prolactin "low".

Chemical compatibility is essential to all good relationships. Couples lucky enough to enjoy long-term partnerships may have similar sex drives (perhaps not too much sex, or even none at all?) and dopaminergic systems that don't flood their bodies with too much prolactin. Human behaviour seems to be under the control of two evolutionary programs: one that results in fertilisation, disillusionment and a series of partners, and the other that enables humans to develop the lasting relationships that lead to long, happy and healthy lives.

References
1. Carter, SC (1998) Neuroendocrine perspectives on social attachment and love. Psychoneuroendocrinology; 23(8): 779-818.

2. DeVries, C, Glasper, ER (2005) Social structure influences effects of pair-housing on wound healing. Brain, Behavior, and Immunity; 19(1): 61-68.

3. Coan, JA et al (2006) Lending a hand: social regulation of the neural response to threat. Psychological Science, A Journal of the Association for Psychological Science; 17(12): 1032-1039.

4. Holden, AEC et al (2008) The influence of depression on sexual risk reduction and STD infection in a controlled, randomized intervention trial. Journal of Sexually Transmitted Diseases; 35(10): 898-904.

5. Holstege, G et al (2003) Brain activation during human male ejaculation. The Journal of Neuroscience; 23(27): 9185-9193.

6. Heaton, JPW (2003) Prolactin: An integral player in hormonal politics.Contemporary Urology; 15: 17-25.

7. Suleman, BVM, Mbaruk, A et al. (2004) Physiologic manifestations of stress from capture and restraint of free-ranging male African green monkeys (Cercopithecus aethiops). Journal of Zoo and Wildlife Medicine; 35(1): 20-24.

8. Thomsen, R, Soltis, J (2004) Male masturbation in free-ranging Japanese macaques. International Journal of Primatology; 25(5): 0164-0291.

9. Guo, G, Tong, Y et al (2007) Dopamine transporter, gender, and number of sexual partners among young adults. European Journal of Human Genetics; 15: 279–287.

Neuroecology - How little we know about the neuroscience of fatherhood

Neuroecology offered this brief research review on Father's Day weekend - it's a little late, but it's still good information on the neuroscience of being a dad. The study looked at the two primary hormones/neuropeptides associated with paternal behavior - prolactin and oxytocin. The results revealed different behaviors associated with each chemical:

Each were associated with a specific paternal behavior: prolactin with facilitation of a child’s exploratory behavior and oxytocin with how much the fathers matched their facial emotions with that of their children.  Since this is only a correlational study, we cannot say for sure whether or not these neuropeptides are directly causing these behaviors.

Interesting - and we know that each of these chemicals is associated with lower testosterone levels, which can lead to post-natal depression and other health issues. On the other hand, we want men to engage in these paternal behaviors, especially mirroring, which was correlated with oxytocin.

The trick, then, is to balance paternal hormones with enough T to prevent depression and other health issues.

How little we know about the neuroscience of fatherhood

June 19, 2012

 

Fathers caring for their children is the general rule across most vertebrates; almost all nonmammalian vertebrates use fathers as a prime caregiver.  And yet, the world of neuroscience knows little about paternal care. This is partly because the males of our common laboratory species, the lab mouse and rat, are more likely to eat their young than show any special care for them.  The resulting deficit in knowledge is obvious with any cursory look through a textbook on the neurobiology of parental behavior: after ten chapters detailing maternal behavior, there might be one perfunctory chapter detailing how little we know about paternal behavior.  But here’s a cool fact I learned from one of those chapters: did you know that male Djungarian hamsters assist in delivering pups by tearing away the membranes just after birth.  They play midwife!

It seems like the precise neural circuitry for maternal and paternal care are different; lesioning the amygdala decreases paternal care and increases maternal care.  Likewise, many neurohormones that cause maternal behavior have little effect on males.  But some of these pathways are likely to be the same.  I’ll quickly discuss a paper which describes the influence of the neuropeptides prolactin and oxytocin on paternal care.  Oxytocin is the ‘love hormone’ and strongly stimulates pair-bonding, influences social recognition, and has strong effects on general sociality.  Although it is typically thought of as having a pro-social influence, the reality is a bit more complicated (of course!).  Prolactin is a bit of a sex hormone, providing the body with sexual gratification after intercourse and counteracting the effects of testosterone, estrogen, and dopamine.  It clearly has a stronger social effect as well or I wouldn’t be talking about it in relation to child-rearing!

In order to assess the relationship between these two neuropeptides and fatherhood, Gordon et al. first measured  their concentration in fathers across time and found them to be fairly stable.  When they compared the of these neuropeptides to the propensity of the fathers to play with their children, they found them to be strongly related.  Each were associated with a specific paternal behavior: prolactin with facilitation of a child’s exploratory behavior and oxytocin with how much the fathers matched their facial emotions with that of their children.  Since this is only a correlational study, we cannot say for sure whether or not these neuropeptides are directly causing these behaviors.  However, these are similar to what are seen with maternal behaviors, allowing the researchers to compare their results to the richer maternal literature in the future.  It will be interesting to see if future work can relate receptor variants for these neuropeptides to differences in paternal behavior.  Perhaps we can get a genetics of daddyhood?

Reference
Gordon I, Zagoory-Sharon O, Leckman JF, & Feldman R (2010). Prolactin, Oxytocin, and the development of paternal behavior across the first six months of fatherhood. Hormones and behavior, 58 (3), 513-8 PMID: 20399783