Located very deep within your brain is the pineal gland, which produces your body’s melatonin. Melatonin is the hormone that regulates your circadian rhythm, thus regulating your sleep and awake cycles. Disruptions to the circadian rhythm can have broad effects on your overall health.
Let’s take a deeper look at the pineal gland, its anatomy, location, and function. Let’s also take a deeper dive into how it impacts sleep, affects seasonal reproduction in animals, and how it may be impacted by brain tumors.
Anatomy and structure of the pineal gland
The pineal gland is a small organ located in the third ventricle of the brain. It is approximately the size of a grain of rice. Ventricles are filled with fluid, and the third ventricle extends from the large lateral ventricles to the narrow cerebral aqueduct, passing between the two halves of the part of the brain called the diencephalon.
The cells that make up the tissue of the pineal gland include hormone-producing pinealocytes and supportive interstitial cells. Nerve cells may influence the pinealocytes by secreting specific chemicals called neurotransmitters. Nerve fibers reach the gland via the pineal stalk and contain many substances, including:
- Serotonin
- Histamine
- Oxytocin
- GABA
- Orexin
- Vasopressin
The pinealocyte cells have receptors for all these neurotransmitters, suggesting that they all can influence the brain at various times. This influence extends to a collection of neurons located in the sympathetic superior cervical ganglia and the parasympathetic sphenopalatine and otic ganglia. This connection is a relay from the pineal gland to the suprachiasmatic nucleus (SCN), located in the hypothalamus.
The SCN is critical because it plays the role of the primary pacemaker to your circadian rhythm, which is impacted by the perception of light detected by the retina and sent along the retinohypothalamic tract.
Ok, those are a lot of big words, so let’s break this down to learn about what the pineal gland does.
What the pineal gland does
The pineal gland produces melatonin, which is synthesized from molecules of the neurotransmitter serotonin. It has important effects on your circadian rhythm and sleep.
Serotonin is derived from the amino acid called tryptophan, and it goes through a change when an acetyl group and then a methyl group are added to produce melatonin. The production of melatonin is impaired by light exposure.
How does light affect melatonin production within the pineal gland? In order to answer this question, it is important to understand how light generally affects the circadian rhythms of the body. Your circadian rhythm impacts sleep, wakefulness, and may also impact the release of hormones, coordination of the body’s interconnected systems, and the use of energy to optimize metabolism.
Light passes through the retina and activates receptors called intrinsically photosensitive retinal ganglion cells (ipRGC). These cells contain the photopigment called melanopsin. From here, the signal is relayed from the eyes to the pineal gland.
First, the message is passed along the retinohypothalamic tract that extends from the retinal cells to the SCN in the anterior hypothalamus in the brain. The paraventricular nucleus of the hypothalamus then sends the signal along to the preganglionic sympathetic neurons in the spinal cord, to the superior cervical ganglion, and finally on to the pineal gland.
Now the pineal gland can act. It changes its production of melatonin based on the amount of light passing through the retina. The release of melatonin must remain balanced for homeostasis. Without homeostasis, you may experience health issues.
We don’t understand all of the actions that melatonin has on the body. We do know that in animals, melatonin can decrease gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. This may have an inhibitory effect on reproductive functions. We don’t know if this same action occurs in humans. This is why pregnant women and children should be cautious when taking a melatonin supplement. Always check with your doctor first.
In addition, melatonin is a very effective antioxidant. It may protect neurons within the central nervous system from free radicals, such as nitric oxide or hydrogen peroxide. These chemicals are generated in active neural tissues. Free radicals may increase the risk of tissue damage and dysfunction, including the risk of medical problems like cancer and neurodegenerative disease.
It is also known that melatonin production decreases with natural aging, and scientists are investigating how this impacts disease.
Health issues due to a dysfunctional pineal gland
The pineal gland and its production of melatonin are central to circadian rhythm disorders that affect sleep. It may exacerbate insomnia. It also may have a role in seasonal affective disorder. In addition, when the pineal gland is affected by tumors, the effects require brain surgery to correct the situation.
Circadian rhythm disorders
These conditions occur when the synchrony between the patterns of wakefulness and sleep do not align with your routine or the natural rhythm of light and darkness. You may experience insomnia and improperly timed sleepiness. The circadian sleep disorders include:
Irregular sleep-wake rhythm: Shorter intervals of sleep over the 24-hour day, rather than a prolonged sleep period overnight
Delayed sleep phase syndrome: Night owls who have difficulty getting to sleep and trouble waking at an early time
Advanced sleep phase syndrome: Characterized by early sleep onset and early morning awakening
Free-running, or non-24: Most often found in blind people without light perception, the timing of sleep may shift gradually over weeks or months
How can the timing of sleep be disordered? Ultimately, this may depend on personal perspective, largely influenced by social context. One must be careful to avoid labeling normal variations of physiologic patterns as a disease. When there is significant social and occupational dysfunction (including absenteeism from school or work), treatment may be appropriate. Fortunately, for those whose irregular sleep patterns are without consequence, medical help is not typically sought.
Seasonal affective disorder (SAD)
With the prolonged darkness of night that occurs in the winter months, seasonal affective disorder may develop. The condition may be associated with other symptoms, including reduced physical activity and weight gain.
Phototherapy may be helpful with the artificial application of light from a light box or light therapy glasses. The timing of the light is typically in the morning, but it is important to follow the guidance of a medical professional.
Pineal gland tumors
Cancer may rarely affect the pineal gland. In fact, less than 1% of brain tumors occur in the pineal gland, but 3%–8% of brain tumors in children are found here. Generally, pineal gland tumors occur more among young adults, those individuals between 20 and 40 years of age.
These tumors may grow large enough to obstruct the normal flow of the cerebrospinal fluid within the ventricles. It is estimated that 10%–20% of the pineal gland tumors may also spread via this medium, especially the more aggressive pineoblastoma variant. Fortunately, these cancers rarely metastasize elsewhere in the body.
Other conditions
It is notable that certain medications may affect the relay from the eye’s perception of light to the production of melatonin within the pineal gland. In particular, beta-blocking medications that are used to treat hypertension, tachycardia, and heart disease may interfere with the normal release of melatonin.3 Beta-blockers include Lopressor (metoprolol), Tenormin (atenolol), and Inderal (propranolol). If this significantly impacts sleep or health, a different medication may need to be used.
The pineal gland may become calcified in older individuals, lighting up on computed tomography (CT) scans due to their increased density, and leading to the presence of “brain sand” on a pathological assessment of the tissue.
Tests
In most cases, testing to assess the pineal gland is not indicated. Melatonin levels can be measured in the saliva, blood, and urine without direct assessment of the pineal gland; however, this is mostly done in the context of research studies and not in clinical care. Given its size, some imaging techniques may provide only limited data about the structure. In the context of pineal gland tumors, the following tests may be appropriate:
- CT scan
- Magnetic resonance imaging (MRI) scan
- Brain biopsy (removing a sample of tissue for further testing in a lab)
Further assessment of circadian disorders may require evaluation by a board-certified sleep specialist who will ask targeted questions to further understand the patterns and impacts of the problem.
Tracking of the circadian rhythm may be done longitudinally with sleep logs or actigraphy. Wearable technology, including common fitness trackers, may provide some of this biometric data. The doctor may suggest appropriate interventions, including the potential use of melatonin supplementation or phototherapy to optimize sleep and well-being.