Circadian (8): The Third Eye

Serotonin is not done with us yet. So far, we have covered serotonin in the Raphe nuclei (contentment), the dorsal column (pain control), and the ventral column (posture and motor) of the spinal cord. I am not going to talk about serotonin’s wonderful role in the gut and the skin in this series, but there is one major topic we have not yet covered with regards to this hormone’s role in maintaining our body clock. This is where things get quite mystical. Buckle up, folks.

Serotonin is the fuel for our "third eye." Although we have two external eyes to look at light, shapes, and colours, our third eye is hidden deep in the brain structure. Although it cannot see light, it receives light signals from the eyes to do its job. Its cells are identical to the cells in the retina of our two eyes. This third eye is called the pineal gland. When the two eyes can see the three-dimensional world, the third eye can see the fourth dimension: time.

Understandably, this special eye has been the subject of much speculation over the past two thousand years. The Egyptians linked it to royal power, while the Greeks believed it was a gate that kept thought or spirit flowing. In Hindu traditions, it is considered the center of intuition, long before Descartes famously wrote about it as the link between the non-physical soul and the physical body. Modern science is still grappling with this mystical gland’s role in the human experience beyond serotonin; we have evidence that it also produces trace amounts of DMT, pinoline, and vasotocin. We know that, in normal concentrations, they affect our psychedelic experience, contentment, and dream intensity. What we do not yet know is if the pineal gland’s secretion of these hormones is enough to affect us in any substantive manner.

Until the next discovery is published, let’s focus on what we think we know. When I spoke about serotonin in Circadian 6, did you ever wonder why the enzyme responsible for converting tryptophan to serotonin in the brainstem is called TPH2 and not simply TPH? Well, as with everything we have named, if there are multiple products of the same family, we tend to order them with numbers. For example, if you have heard of Vitamin B12, there probably were 11 other Bs prior to the twelfth. In the case of TPH, the isoforms are TPH1 (found in non-neuronal tissues) and TPH2 (neuronal tissues). You might think that the pineal gland should have TPH2 due to its proximity to the brain. But the reality is, the gland only has TPH1, which, although it carries the same function as TPH2, is anatomically distinct from it. Both turn tryptophan into serotonin, but the machines are not built the same. In this way, the pineal gland actually aligns itself with the rest of the body and not the brain. Curious, isn’t it?

The truth is, it has a foot in both camps. When it comes to tryptophan, the pineal gland has immediate access to it without the obstacle of the blood-brain barrier. The gland sits neatly between the brain and the main circulation, such that part of the gland has contact with the ventricles and the other part with the systemic circulation. In this way, as long as you supply the body with tryptophan, the pineal gland will always have access to it without having to worry about any competition from the other amino acids to go through the LAT1 gate. But, as you read on, you will appreciate that the advantage is twofold.

So, in the gland, tryptophan is turned into serotonin via the enzyme TPH1. Unlike the Raphe nuclei, in the pineal gland, serotonin stays put. It doesn’t leave the pineal gland to act on other parts of the brain to make you feel better, or on parts of the spinal cord to help with pain or posture. The only time it can leave the gland is when it is changed into another hormone: melatonin.

The story is that TPH1 is an enzyme that is active all of the time; it is less affected by the circadian rhythm than its cousin TPH2. So, the pineal gland will always use what available tryptophan it has to turn into serotonin—24/7. After some time, the gland will be rich with serotonin, as you can imagine, but it has no physiological function to the body so long as it stays within the boundaries of the gland. Serotonin’s exit pathway is basically the enzyme called AANAT, which turns it into melatonin. AANAT, however, is never present when the pineal gland detects light signals; the reaction is almost instantaneous and is considered one of the fastest in human biology.

When night falls, AANAT is free to roam again in the pineal gland. AANAT efficiently changes the serotonin you have stored throughout the whole day into melatonin at a rate faster than the serotonin production itself, such that by the end of the night you have a lot less serotonin left in the pineal gland, ready for its next recharge. This way, the pineal gland makes so much melatonin that there is enough of it to supply both the brain and the body with this hormone. Remember, the pineal gland has direct communication with the brain where melatonin can now go to and perform its magic. It also has the other foot in our main circulation for the rest of the body to benefit from this melatonin surge. It has always been the perfect master plan: sleep heals both the mind and the body.

That is, until we think we are too clever for our own good. We often identify our material goals and plunge into them without paying attention to our body's demands for balance and equilibrium. We brighten our nights, darken our days, and even feast on screen light in the deepest hours of the night. AANAT goes away, melatonin production is stopped, the sleep cycle becomes clunky, the body accumulates "dirt" and inflammation, diseases build up, and illnesses ensue. In this example, we make little serotonin in the day in the Raphe nuclei as our indoor environment rarely gives us more than 1,000 lux, and we stop AANAT—and therefore melatonin production—as our screens and light environment will always provide us with at least 30 lux. We are permanently trapped in the "twilight zone," an artificial light cage we have built around ourselves to our own detriment.

We have a third eye which has been speculated by many to be the gateway to the metaphysical exploration of our reality, but we can barely even maintain its basic, known, proven, and undisputed physical function. Perhaps it is time we focus on sleep to awaken what has been long dormant in our beautifully designed biology.