Hormone Effects on the Brain: A Series

A cartoon of four types of hormones partying, suggesting hormone effects on the brain

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When we hear the words “hormone effects on the brain”, we usually think of sex hormones, estrogen and testosterone. And involuntarily, we tend to picture some sort of erratic behaviour: either increased aggressivity or “excessive” emotions. But did you know that there are many more hormones out there which act on your brain? Did you know that many of your behaviours, not just emotions, are controlled by hormones? And that, simply put, you wouldn’t be who you are without the wonderful work they do in your brain?

What is a hormone?

Before we dive deep into how hormones influence our minds, we should make clear what a hormone actually is. A hormone is any signaling molecule which affects the activity of another body part. As you can see, this is a very lax definition. In other words, a lot of substances in our bodies can be classified as hormones.

Hormones are produced and secreted by glands. Unlike neurotransmitters, which produce fast effects in small spaces (i.e. synapses), hormones can act over much longer periods of time and are capable of reaching a lot more areas in the body. Additionally, the effects they produce usually depend on hormone concentration, while in the case of neurotransmitters the response occurs in an all-or-nothing manner.

Types of hormones

There are several ways in which we can classify hormones, but two stand out as the most important: the type of signaling and the chemical class.

Based on type of signaling, we distinguish between four classes of hormones:

  1. endocrine hormones are released into the bloodstream and usually travel larger distances before reaching their target cells, on which they subsequently act;
  2. paracrine hormones diffuse over short distances, basically acting only on nearby cells;
  3. autocrine hormones act on the same cell which secreted them;
  4. intracrine hormones also act on the same cell which produced them. But, unlike the autocrine ones, they never reach the outside of the cell.

We should note here that the four classes mentioned above sometimes overlap. That means that, for example, a hormone normally involved in endocrine signaling can, under certain circumstances, also have paracrine, autocrine, or intracrine effects.

Based on chemical class, we again find another four classes of hormones (this time with no overlap):

  1. peptides are chains of amino acids (you can think of these as the basic Lego block of proteins). Some examples of peptide hormones are oxytocin and insulin;
  2. amino acid hormones are basically, as the name suggests, amino acids, but which have suffered some small chemical alterations. Some examples here are thyroxine (the thyroid hormone) and melatonin (the one with the sleep regulation);
  3. steroids come from cholesterol and include perhaps the most popular hormones: the sex hormones and cortisol;
  4. eicosanoids are also derived from lipids and they’re probably the least known class of hormones, so we’ll reserve any mention of them for a later post.

What do hormones control?

The answer to this one is fairly easy: almost everything. From your appetite (controlled by leptin and ghrelin), to your sleep cycle (melatonin), or even how much you can tan (thanks to melanocyte-stimulating hormones and their receptors), hormones are present in virtually every aspect of your life. In terms of brain function specifically, they control cognition (e.g., thyroxine), social bonding, anxiety and empathy (e.g., oxytocin), learning and memory (e.g., estradiol) and much more.

Why it matters

Now you might think: “ok, this is all fine and dandy, but why should I care about all these hormone effects on the brain? Leptin will control my appetite regardless of whether I know about it or not!” And that is perfectly true, leptin has done a great job without your awareness until now. But wouldn’t it be nice to learn about the wonderful work your hormones are doing for you? Additionally, this kind of knowledge could come in handy if something were to ever go wrong (not to diagnose yourself, mind you, but to point you in the direction of the right specialist). And finally, if you didn’t know that already, it might make you realize that we’re all hormonal beings pretty much all of the time 😉

So if you’d like to learn more about your hormones, stay tuned for the next posts, where we will discuss various hormones in a lot more detail.

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