Oxytocin: Starting with the basics

Nov 09 2009 Published by under Neuroscience

So sometimes, Sci gets questions, and sometimes those questions...are close enough to requests. And so, today Sci will begin what is probably going to be an extensive basic series on oxytocin. We ALL love oxytocin, right? Right! And we all missed Sci's big honkin' basic science posts right? Of course right!
So the question basically came down to this: What are the effects of oxytocin in female vs males, in particular the effects on sexual and bonding behavior, and how does this influence the autonomy of people (eg, are we really the tools of our hormones). The short answer: yes and no. The long answer: is very long. So today Sci is going to begin with a background post on oxytocin, what it is, where it acts, and some basic functions. The next post will be on effects of ocytocin in females specifically, and then a post on ocytocin in males specifically. And then, the synthesis. And interspersed in there, a few Friday Weird Sciences. I mean, oxytocin makes for some GREAT weird science. 🙂 Keep in mind, though, that although Sci has done a boatload of research getting ready to blog this topic, she by no means going to hit ALL of EVERYTHING. She might have to blog some specific papers in the future, and she definitely welcomes anyone willing to chime in the comments with more info!
So here we go.

Oxytocin is one of the two major hormones which are secreted from an area of the brain called the posterior pituitary (the other one is called vasopressin, and is involved in water regulation, though it also has been known to curl the toes of male voles).
Before we get into oxytocin specifically, it occurs to Sci that that last sentence was really complicated. So we're going to need a quick lesson in beginning endocrinology.
Let's start with what a hormone is. We hear a lot about hormones in our daily lives. Ah, that guy's voice is breaking, heh, hormones. Those two teenagers are fondling each other in public. Heh, hormones.

But hormones are much more than just things that influence your sex life. Hormones can have three major types of action: autocrine, paracrine, and endocrine. Autocrine refers to chemicals released from a cell that have an action on that same cell (like negative feedback, where a cell releases a chemical that hits receptors on the same cell, and stops further release of the chemical). Paracrine refers to chemicals released from a cell that have actions on other cells nearby (like neurotransmitters). And endocrine (which you've probably heard of) refers to chemicals released from one type of cell and have effects on other types of cells or tissues (like insulin, which is released from the pancreas, and has effects everywhere else, or like the hormones you typically associate with horny teenagers). And the really wild thing about hormones is that a single chemical can be acting as ALL THREE of these things at once, autocrine, paracrine, AND endocrine.
Oxytocin, along with vasopressin, is secreted from an area of the brain known as the posterior pituitary. Located here:

(See how it dangles there? Calling the pituitary the nutsack of the brain would not be entirely inappropriate.)
The posterior pituitary is the one further toward the back of the head. But oxytocin is not made there, it's actually made ABOVE the pituitary, in the area of the brain called the hypothalamus (The supraoptic and paraventricular nuclei, if you want to be all particular about it), and the cells within the hypothalamus extend all the way to the posterior pituitary, allowing oxytocin to be made in one place and released in another.
So oxytocin is made, and when stimulated correctly, the brain releases it. Oxytocin has endocrine actions throughout the body. It plays a very big role in sexual arousal and orgasm in both sexes. In women, oxytocin is VERY important in stimulating uterine contractions prior to birth, so much so that oxytocin is given to induce labor, and drugs that antagonize oxytocin are used to suppress it if labor is premature. Oxytocin also plays a huge role in milk letdown in women, allowing them to nurse.
But oxytocin doesn't just act on the body, it also has some rather big impacts on the brain. Some studies have shown that oxytocin has strong effects on trust and generosity, making it an important chemical in human social interaction. In addition to these big effects, there may be roles for oxytocin in autism, in depression (particularly in females), and of course in things like social bonding.
So that's a brief introduction to oxytocin. Next time we're going to discuss the specific, known roles for oxytocin in women, especially in labor and during milk letdown, and some of the social bonding aspects. Stay tuned!

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