Wednesday, February 14, 2018

The Love Chemical Pageant of 2018

A modified repost of an original article from February 15, 2012.

Hello and welcome to the Love Chemical Pageant of 2018! I’m your host, Miss Behavior, and YOU are the judges.

Since the beginning of…well, social animals, many hormones and neurotransmitters have been quietly working in their own ways to fill our world with love. Lately (over the last few decades), some of them have been brought out of the background and into the limelight, credited with every crush, passionate longing, parental hug, embrace among friends, and cuddle between spouses. But who truly deserves the title of The Love Chemical?

Let’s meet our contestants!

Let’s first meet our reining title-holder, Dopamine! Dopamine is a neurotransmitter produced in the brain. Sex increases dopamine levels in both males and females and blocking its effects during sex can prevent prairie voles (a monogamous species often used to test questions on pair bonding) from forming preferences for their own partner. Dopamine also plays a role in maternal and paternal behaviors.

But dopamine is not just involved in love. It has a wide range of known functions in the brain, involved in everything from voluntary movement, mood, motivation, punishment and reward, cognition, memory, learning, aggression, pain perception and sleep. Abnormally high levels of dopamine have been linked to schizophrenia and psychosis. And dopamine is especially well-known for its role in addiction... in fact, many researchers believe that we may even be addicted to our own romantic partners.

Now let’s meet Dopamine’s partner, Opioids! When natural opioids are released in the brain, they can cause a rewarding feeling that often cause us to seek more of it. When prairie voles are given drugs that prevent opioids from acting on a particular opioid receptor type (mu-opioid receptors) in a particular brain region (the caudate-putamen), they do not form pair bonds with sexual partners. Interestingly, people that see the faces of their loved ones experience lots of activity in the caudate-putamen region of the brain, especially if they rate their relationship with that person as very romantic and passionate. The caudate-putamen region of the brain also uses dopamine, so the two chemicals appear to work together there to promote the feelings of romantic love.

Please welcome Oxytocin! Oxytocin is a peptide hormone, most of which is made in the brain. Some of this oxytocin is released into the blood and affects body organs, such as the uterus and cervix during child birth and the mammary glands during breast feeding. But some of it stays in the brain and spinal cord, acting on neurons with oxytocin receptors to affect a number of behaviors. Released during child birth and nursing, oxytocin is important for helping mammalian mothers behave like moms and in species in which both parents raise young, it helps fathers behave like dads. Also released during sex, oxytocin plays an important role in pair bonding in prairie voles (particularly in the female of the pair). In humans, people given oxytocin nasal sprays have been reported to have less fear, more financial trust in strangers, increased generosity, improved memory for faces, improved recognition of social cues, and increased empathy.

But before you fall head-over-heels for oxytocin, you should know a few more things. For one thing, oxytocin isn’t exclusively linked with feel-good emotions; It has also been associated with territoriality, aggressive defense of offspring, and forming racist associations. Also, oxytocin doesn’t work alone. It has been shown to interact with vasopressin, dopamine, adrenaline and corticosterone and all these interactions affect pair bonding.

Next up is Vasopressin! Vasopressin is closely related to oxytocin. Like oxytocin receptors, vasopressin receptors are expressed in different patterns in the brains of monogamous vole species compared to promiscuous vole species. Released during sex, vasopressin plays an important role in pair bonding in monogamous prairie voles (particularly in the male of the pair). If you block vasopressin in the brain of a paired male prairie vole, he will be more likely to prefer spending time around a new female rather than his mate. On the flip side, if you increase vasopressin activity in specific brain regions of an unpaired male prairie vole or even a promiscuous male meadow vole and introduce him to a female, he will prefer spending time with her than other females. Vasopressin may also make male prairie voles more paternal.

But vasopressin does a lot of things. In the body, its primary function is to regulate water retention. In the brain, it plays a role in memory formation and territorial aggression. And even its role in monogamy is not exclusive: Vasopressin interacts with oxytocin and testosterone when working to regulate pair bonding and parental behavior.

Look out for Cortisol! Cortisol is produced by the adrenal glands (on top of the kidneys) and is involved in stress responses in humans and primates. Both men and women have increased cortisol levels when they report that they have recently fallen in love. Many studies have also found relationships between cortisol and maternal behavior in primates, but sometimes they show that cortisol increases maternal behavior and sometimes it prevents it. In rodents, where corticosterone is similar to cortisol, the story is also not very clear. Corticosterone appears to be necessary for male prairie voles to form pair bonds and it plays a role in maintaining pair bonds and promoting paternal behavior. But in female prairie voles, the opposite seems to be true! Corticosterone in females appears to prevent preference for spending time with their partner and pair bond formation.

Put your hands together for Testosterone! Testosterone is a steroid hormone and is primarily secreted from the gonads (testes in males and ovaries in females). Frequently referred to as “the male hormone”, both males and females have it and use it, although maybe a little differently. Testosterone is associated with sex drive in both men and women. But men who have recently fallen in love have lower testosterone levels than do single males, whereas women who have recently fallen in love have higher testosterone than single gals.

This is Estrogen! Estrogen is another steroid hormone, frequently referred to as “the female hormone”, although again, both males and females have it. Estrogen also seems to play a role in sex drive in both men and women. The combination of high estrogen levels and dropping progesterone levels (another steroid hormone) is critical for the development of maternal behavior in primates, sheep and rodents. But look closer and you will find that the activation of estrogen receptors in particular brain regions is associated with less sexual receptivity, parental behavior, and the preference for spending time with the mate.

So let’s have a round of applause for this year’s contenders in The Love Chemical Pageant! Now it is your turn to voice your opinion in the comments section below. Vote for the neurochemical you believe deserves the title The Love Chemical. Or suggest an alternative pageant result!

Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Fisher, H.E. (1998). Lust, attraction, and attachment in mammalian reproduction. Human Nature, 9(1) 23-52.

Marazziti, D. and Canale, D. (2004). Hormonal changes when falling in love. Psychoneuroendocrinology, 29, 931-936.

Van Anders, S.M. and Watson, N.V. (2006). Social neuroendocrinology: Effects of social contexts and behaviors on sex steroids in humans. Human Nature, 17(2), 212-237.

Young, K.A., Gobrogge, K.L., Liu, Y. and Wang, Z. (2011). The neurobiology of pair bonding: Insights from a socially monogamous rodent. Frontiers in Neuroendocrinology, 32(2011), 53-69.

Tuesday, February 6, 2018

Addicted to Love

Image from imagerymajestic at
Early exposure creates a sense of euphoria, a heightening of senses, a rush of pleasure. In order to recreate and further heighten the experience, more is sought, but the euphoric effect eventually starts to wear off. Craving and palpable longing intensifies in its absence, but the effect of exposure is now a calm relief rather than a euphoric high. And once cut off abruptly and completely, desperation, grief, pain and depression set in. The pull to return to it is (almost) insurmountable.

This describes the phases of substance addiction, listed by the DSM-5, the latest version of the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association. These phases include consumption (taking the substance), reinforcement learning (intense pleasure associated with consuming the substance), seeking more of the substance, developing a tolerance (intense pleasure is replaced with avoidance of discomfort), withdrawal (psychological and physical discomfort associated with not consuming the substance), and relapse (returning to consume the substance, even in the face of large costs of doing so).

Now re-read the first paragraph, but instead of imagining the development of a substance addiction, imagine the process of falling in love.

It sounds the same, doesn’t it? According to one theory, it sounds the same because it is the same. In essence, falling in love is the process of becoming addicted to another individual.

There are undeniable similarities between how the brain responds to substance addiction and how the brain responds to falling in love. Both substances of addiction and individuals we are attracted to cause the brain to release dopamine, a neurotransmitter, into a brain region called the nucleus accumbens. Dopamine acting in this region helps us learn to associate cues with rewarding feelings. However, dopamine acts on two different types of receptors, called D1-receptors and D2-receptors, in complex ways. Activation of D2-receptors promotes bonding with a partner; it also promotes the reward value of a substance. Activation of D1-receptors reduces bonding with a partner; it also reduces the reward value of a substance. During this time early on in a romantic relationship or early exposure to an addictive substance, dopamine is primarily acting on D2 receptors, heightening our senses and focusing our attention on the cues of our next encounter… developing our craving, our longing, our drive for the next meeting.

When we are in the early obsessive stages of love, every encounter (and especially sexual encounters) cause a pleasurable release of not just dopamine, but also natural opioids. These two brain chemicals work together in the brain to continually strengthen the association of the stimulus (the one you are falling in love with) with intense positive feelings. This will cause you to seek more and more of these interactions, craving them intensely in the times in between. These same chemicals act on the same receptors in the same way during the process of forming an addiction to a substance, causing the person to seek more and more of it.

With time, the brain adapts. Repeated encounters no longer cause the same euphoria they once did, but rather, a sense of calm contentment. The dopamine that is released before and during these encounters is now activating more of the D1-receptors, which result in less of a feeling of pleasure, and more agitation and aggression. In terms of relationships, it is thought that this transition actually helps maintain a pair bond with one individual, because in this stage you are less driven to seek a competing pair bond and you are more likely to aggressively defend the pair bond you have already established. In terms of substance abuse, this phase is called tolerance. (I know, this perspective really takes the romance out of long-term marriages, but...)

During this tolerance phase, lack of exposure to the object of your addiction (whether it is a person or a substance) results in a lack of dopamine and opioid release and an increase in stress hormone release. If we are talking about addiction to a substance, we call this withdrawal. If we are talking about a relationship, we call this separation anxiety or even heartbreak. To avoid these horrible feelings, we often relapse… right back into the arms of our addiction.

Love is not listed as a psychological disorder in the DSM-5, nor do we think of it as one. But in a true physiological sense, we may actually be addicted to the ones we love.

Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Potenza, M.N. (2014). Non-substance addictive behaviors in the context of DSM-5. Addictive Behaviors, 39(1): 1-2.