In Renee Descartes referred to the pineal gland as the “Seat of the Soul,” and it is located in the centre of the brain, where she defined it as “the seat of the soul.” The pineal gland’s primary purpose is to receive information about the condition of the light-dark cycle from the environment and transmit that information to the brain, which then uses that information to synthesise and emit the hormone melatonin. In many cultures, the production of melatonin, which is produced solely during the darkest hours of the day, is utilised to determine the phase of the internal circadian clock. Melatonin is used as a treatment for some sleep disorders associated with anomalies in the body’s circadian cycle, as well as for the reduction of jet lag.
Melatonin has been linked to a variety of physiological functions, suggesting that it may have a broader range of therapeutic applications in the future. It has immediate physiological effects throughout the night or in complete darkness, and it has prospective effects during the day when melatonin levels are undetectable. Melatonin is engaged in a variety of processes, including the regulation of the circadian clock and sleep patterns, cell protection, neuroprotection, and the regulation of the reproductive system, to name a few examples. Injury to the pineal gland, such as pineal tumours, craniopharyngiomas, or other injuries that affect the sympathetic innervation of the gland, as well as uncommon genetic diseases that influence melatonin secretion can cause reduced pineal gland function and melatonin secretion.
Pineal gland: An overview
Pineal gland’s primary purpose is to receive and transmit information about the current light-dark cycle from the environment. Melatonin is produced and secreted by the pineal gland cyclically during the night as a result of this information transmission (dark period). Even though the pineal gland is photosensitive in cold-blooded vertebrates (lower-vertebrate species), this trait is not retained in higher vertebrates such as humans. Light is perceived by the inner retina (retinal ganglion cells) in higher vertebrates, which sends neural impulses to the vision parts of the brain.
However, a small number of retinal ganglion cells carry melanopsin and have inherent photoreceptor capability, which allows them to send neural signals to non-image-forming parts of the brain, such as the pineal gland, via intricate neuronal connections. The retina sends photic information to the suprachiasmatic nucleus (SCN), which is the principal rhythm-generating mechanism or “clock” in mammals, which then sends the information to the hypothalamus for processing.
It is believed that when the light signal is positive, the SCN secretes the neurotransmitter gamma-amino butyric acid, which is responsible for the inhibition of neurons that synapse in the paraventricular nucleus (PVN) of the hypothalamus. As a result, the signal from the SCN to the pineal gland is interrupted, and thus no melatonin is produced. When there is no light (darkness), on the other hand, the SCN secretes glutamate, which is responsible for the transfer of the signal from the PVN to the pineal gland through the pathway of the SCN.
This nucleus communicates with the higher thoracic segments of the spinal column, transmitting information to the superior cervical ganglion, which then transmits the final signal to the pineal gland through sympathetic postsynaptic fibres, resulting in the release of norepinephrine from the pineal gland (NE). N-acetyltransferase (AA-NAT) is the enzyme that initiates melatonin production in the pinealocytes by activating transcription of the mRNA encoding the enzyme arylalkylamine N-acetyltransferase (AA-NAT), which is the first molecular step in melatonin synthesis.
Factors stimulating the pineal gland
Melatonin and its precursor, serotonin, both of which are produced chemically from the alkaloid substance tryptamine, are both synthesised in the pineal gland. Melatonin and serotonin are both neurotransmitters that regulate sleep. The pineal gland, along with other brain regions, may be responsible for the production of neurosteroids. When consumed in large quantities, ayahuasca (made from Banisteriopsis caapi, a South American jungle vine) produces dimethyltryptamine (DMT), a hallucinogenic compound chemically similar to melatonin and serotonin.
It is considered to be a trace substance in human blood and urine and is present in the Amazonian botanical drink ayahuasca (made from Banisteriopsis caapi, a South American jungle vine). Despite the fact that DMT is thought to be synthesised by the pineal gland, it has not been consistently found in human pineal microdialysis (purified pineal extracts), and there is no evidence that it is subjected to a controlled biosynthesis in the mammalian pineal gland. As a result, despite the fact that the 17th-century French philosopher René Descartes came to the conclusion that the pineal gland is the seat of the soul, there is little evidence to support the assumption that secretions from the pineal gland play a significant role in cognition.
Other tissues that synthesise melatonin include the vertebrate retina, which uses local receptors designated MT1 and MT2 to transmit information about environmental light, and the gastrointestinal tract and the skin. Melatonin is also synthesised in the pineal gland and in the gastrointestinal tract and the skin. The conversion of serotonin to N-acetylserotonin is catalysed by an enzyme known as serotonin N-acetyltransferase (AANAT), which is usually considered to be the rate-limiting step in melatonin production.
The enzyme acetylserotonin O-methyltransferase then catalyses the conversion of that molecule into melatonin (ASMT). Increased circulating melatonin levels that arise and are maintained after dusk and with darkness corresponds with the activation of the AANAT transcription factor during these periods of darkness.
Melatonin concentrations are likewise higher in the cerebrospinal fluid (CSF) of the third ventricle of the brain than in the cerebrospinal fluid (CSF) of the fourth ventricle of the brain or in the blood. According to this hypothesis, melatonin is also produced directly into the cerebrospinal fluid (CSF), where it may exert direct and possibly more-durable effects on specific parts of the central nervous system.
Pineal cells are photosensitive in certain species, but not all. In humans and higher mammals, a “photo endocrine system” composed of the retina, the suprachiasmatic nucleus of the hypothalamus, and noradrenergic sympathetic fibres (neurons responsive to the neurotransmitter norepinephrine) terminating in the pineal gland provides information about light and the time of day, which regulates pineal melatonin secretion in the pineal gland.
For example, melatonin concentrations in humans are very variable compared to those found in many other endocrine hormones. Furthermore, serum melatonin levels fall significantly during childhood due to the fact that the pineal gland does not expand after the age of roughly one year.
Conclusion
Among the most well-known functions of the pineal gland is the production of the hormone melatonin, which is released into the bloodstream and probably also into the cerebrospinal fluid, which is the fluid that surrounds the brain. melatonin, produced by the pineal gland, is a hormone that governs the body’s daily (circadian) clock; therefore, melatonin is frequently employed in human study to better understand the body’s biological time. A rhythmic pattern may be observed in the biology of the pineal gland, and the amount of melatonin secreted is proportional to the amount of daylight a person is exposed to. It changes in response to changes in day duration, which is why the pineal gland is regarded as both an endocrine clock and an endocrine calendar at different periods.