Pineal Gland

Cross references:   Melatonin   Serotonin  Parapineal   Parietal Eye   
Lamellar Body = Pineal Gland     Lamellar Body = Pineal Eye  
Lamprey Serotonin System    Dictionary     Figure Labels      

The book briefly discusses the pineal on [K&W: 194-195 & 458]. 

Pineal gland (Wiki) 
    "The pineal gland (also called the pineal body, epiphysis cerebri, epiphysis, conarium or the "third eye") is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions.[1][2] Its shape resembles a tiny pine cone (hence its name), and it is located near the centre of the brain, between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join."  
Pineal gland
Illu pituitary pineal glands.jpg
Diagram of pituitary and pineal glands in the human brain

The pineal gland is reddish-gray and about the size of a grain of rice (5–8 mm) in humans, located just rostro-dorsal to the superior colliculus and behind and beneath the stria medullaris, between the laterally positioned thalamic bodies. It is part of the epithalamus.
The pineal gland receives a sympathetic innervation from the superior cervical ganglion. However, a parasympathetic innervation from the sphenopalatine and otic ganglia is also present. Further, some nerve fibers penetrate into the pineal gland via the pineal stalk (central innervation). Finally, neurons in the trigeminal ganglion innervate the gland with nerve fibers containing the neuropeptide, PACAP.
Pinealocytes in many non-mammalian vertebrates have a strong resemblance to the photoreceptor cells of the eye. Some evolutionary biologists believe that the vertebrate pineal cells share a common evolutionary ancestor with retinal cells.[9]
    In some vertebrates, exposure to light can set off a chain reaction of enzymatic events within the pineal gland that regulate circadian rhythms.[10]  
    Some early vertebrate fossil skulls have a pineal foramen (opening). This correlates with the physiology of the modern "living fossils," the lamprey and the tuatara, and some other vertebrates that have a parietal organ or "third eye," which, in some of them, is photosensitive.  
    The third eye represents evolution's earlier approach to photoreception.[11] The structures of the third eye in the tuatara are homologous to the cornea, lens and retina, though the latter resembles that of an octopus rather than a vertebrate retina.  
    The asymmetrical whole consists of the "eye" to the left and the pineal sac to the right. "In animals that have lost the parietal eye, including mammals, the pineal sac is retained and condensed into the form of the pineal gland."[11]
Unlike much of the rest of the mammalian brain, the pineal gland is not isolated from the body by the blood-brain barrier system;[12] it has profuse blood flow, second only to the kidney.[8]
    Fossils seldom preserve soft anatomy. The brain of the Russian Melovatka bird, about 90 million years old, is an exception, and it shows a larger-than-expected parietal eye and pineal gland.[13]
    In humans and other mammals, the light signals necessary to set circadian rhythms are sent from the eye through the retinohypothalamic system to the suprachiasmatic nuclei (SCN) and the pineal.
Photosensitive cells in the retina detect light and directly signal the SCN, entraining its rhythm to the 24-hour cycle in nature. Fibers project from the SCN to the paraventricular nuclei (PVN), which relay the circadian signals to the spinal cord and out via the sympathetic system to superior cervical ganglia (SCG), and from there into the pineal gland.
Pineal cytostructure seems to have evolutionary similarities to the retinal cells of chordates.[9] Modern birds and reptiles have been found to express the phototransducing pigment melanopsin in the pineal gland. Avian pineal glands are believed to act like the SCN in mammals.[23]

Pineal Gland and Melatonin  (Goog) 
Long, informative article in plain English available online. 
The pineal gland or epiphysis synthesizes and secretes melatonin, a structurally simple hormone that communicates information about environmental lighting to various parts of the body."
    "The light-transducing ability of the pineal gland has led some to call the pineal the "third eye".
The pineal gland is a small organ shaped like a pine cone (hence its name). It is located on the midline, attached to the posterior end of the roof of the third ventricle in the brain.

See also:  

Melatonin and the Pineal Gland  (Kimball)   

The pineal gland is a tiny structure located at the base of the brain.
Link to graphic showing the location of the pineal and other endocrine glands (92K).

Its principal hormone is melatonin, a derivative of the amino acid tryptophan.

Synthesis and release of melatonin is
  • stimulated by darkness and
  • inhibited by light.

But even without visual cues, the level of melatonin in the blood rises and falls on a daily (circadian) cycle with peak levels occurring in the wee hours of the morning.

However, this cycle tends to drift in people who are totally blind — often making them sleepy during the day and wide awake at night. Giving melatonin at bedtime has proved helpful in a number of cases. [More]

Melatonin is readily available in drug stores and health food stores, and it has become quite popular. Ingesting even modest doses of melatonin raises the melatonin level in the blood to as much as 100 times greater than normal. These levels appear:

  • to promote going to sleep and thus help insomnia
  • to hasten recovery from jet lag
  • not to have dangerous side effects.
Welcome&Next Search

1989    PubMed search for "Lamprey Brain"   693<984 
Central projections of the pineal complex in the silver lamprey Ichthyomyzon unicuspis.    
    "The central projections of the pineal complex of the silver lamprey Ichthyomyzon unicuspis were studied by injection of horseradish peroxidase. The pineal tract courses caudally along the left side of the habenular commissure, and a few fibers penetrate the brain through the caudalmost portion of this commissure. Most of the fibers, however, continue caudally and enter the brain through the posterior commissure. The pineal tract projects bilaterally to the subcommissural organ, the superficial and periventricular pretectum, the posterior tubercular nucleus, the dorsal and ventral thalamus, the dorsal hypothalamus, the optic tectum, the torus semicircularis, the midbrain tegmentum, and the oculomotor nucleus. A few fibers decussate in the tubercular commissure, but the course of these decusate fibers could not be followed owing to the bilateral nature of the projections. No retrogradely labeled cells were found in the brain. With the exception of the projections to the optic tectum and torus semicircularis, the pineal projections in the silver lamprey are similar to those reported in other anamniote vertebrates."  
    136 Related citations     
    and 2 Cited by's.   

Cholinergic and GABAergic neuronal elements in the pineal organ of lampreys, and tract-tracing observations of differential connections of pinealofugal neurons.   
The putative cholinergic and GABAergic elements of the pineal organ of lampreys were investigated with immunocytochemistry to choline acetyltransferase (ChAT) and gamma-aminobutyric acid (GABA), and by acetylcholinesterase (AChE) histochemistry. For comparison we also carried out immunocytochemistry to serotonin (5-HT) and a tract-tracing investigation of the two types of projecting cells, i. e., ganglion cells and long-axon photoreceptors. Most photoreceptors were ChAT-immunoreactive (ChAT-ir) and AChE-positive, while ganglion cells and the pineal tract were ChAT-negative and AChE-negative or only faintly positive. These results strongly suggest the presence of a cholinergic system of photoreceptors in the lamprey pineal organ. GABA-ir fibers that appear to originate from faintly to moderately stained ganglion cells were observed in the pineal stalk. Immunocytochemistry to 5-HT indicated the presence of two types of 5-HT-ir cells, bipolar cells and ganglion-like cells. The connections of the ganglion cells and long-axon photoreceptors were also studied by application of DiI to the pineal stalk in fixed brains or of biotinylated dextran amine (BDA) to one of the main targets of pinealofugal fibers (optic tectum or mesencephalic tegmentum) in isolated brains in vitro. Some long-axon photoreceptors and ganglion cells were labeled from the optic tectum. However, BDA application to the tegmentum exclusively labeled ganglion cells in the pineal organ. These results indicate that the two morphological types of afferent pineal neuron have different projections. No labeled cells were observed in the parapineal organ in BDA experiments, indicating that this organ and the pineal organ are involved in different neural circuits."  
    270 Related citations:       
    and 1 Cited by. 

A possible pathway connecting the photosensitive pineal eye to the swimming central pattern generator in young Xenopus laevis tadpoles.

Jamieson D, Roberts A.

Brain Behav Evol. 1999 Dec;54(6):323-37.

[PubMed - indexed for MEDLINE]