"Modern medical dissection has already discovered that the front section of the pineal gland is equipped with the complete structure of a human eye. Because it grows inside one's skull, it is thus said to be a vestigial eye. Whether it is a vestigial eye or not, our community of cultivators has reservations. Yet modern medicine has, after all, already recognized that there is an eye in the middle of the human brain. The passageway that we open targets exactly that location, and this happens to agree completely with the understanding of modern medicine." --Zhuan Falun (English, Page 51, the 3rd translation edition, The Universe Publishing Co., NY)

In recent years, scientists gradually discovered that the mammalian pineal gland is photo sensitive. However, the mammalian pineal, unlike that of other vertebrates, is not thought to be directly light sensitive. Melatonin, the principal product of the mammalian pineal gland, acts as an internal representative of nighttime. The secretion of melatonin is increased under light-dark cycles, with an increase in the dark period and a decrease in the light period (1). Photic information reaches it via a multi synaptic pathway originating in retina and passing through suprachiasmatic regions of the hypothalamus (1). In the conventional theory, it is considered that the rod and cone photoreceptors in the retina account for all photoreceptive input (2). In the past, it is considered that photic suppression of pineal melatonin is also carried out through this conventional routine (3,4). Since the pineal gland is concealed in the skull, it is hard to imagine that it is able to respond to light directly. Even if the pineal gland is photo sensitive, it is very hard to test this hypothesis in vivo because of the existence of photoreceptors in the retina.

Five years after the publication of Zhuan Falun, Lucas et al. (5) published a paper in Science, one of the most well known scientific journals. They described several experiments they did with mice that genetically lacked retinal photoreceptors. The experiments revealed that photic suppression of pineal melatonin remained unaffected in mice genetically lacking cones or both rods and cones. That is to say, mice genetically lacking retinal photoreceptors responded normally to light. What is especially noticeable is that one group of mice genetically lacking retinal photoreceptors also had defection in their optic signal transduction pathways and yet their photic suppression of pineal melatonin remained unaffected.

It is well known, with neither retinal photoreceptors nor optic signal transduction pathways, that the conventional visual pathway cannot be established. The authors were unable to explain how the pineal concealed in the skull could respond to light. They proposed the assumption of the existence of "unconventional photoreceptors". They proposed that there are non-rod and non-cone, ocular photoreceptors ("unconventional photoreceptors"), which are able to carry "non-image, non-visual" optical signal transduction. However, little evidence could support this assumption currently. The authors Lucas and Foster also doubted the function and existence of "unconventional photoreceptors". They believed that this was still subject to further discussion (6,7).

On the contrary, much evidence suggests that the pineal gland may be able to directly sense the light. Immunocytochemically, it is reasonable to believe that the pineal gland can be photo-receptive. Scientists have already realized the structural similarity between the pineal and the retina. The pineal was simply called "folded retina", a variety of genes that are only expressed in eyes are expressed in the pineal gland as well (9,10). The pineal gland not only has photoreceptors, but also has a complete system for optical signal transduction (11,13). That is to say, if there is a light-transducing passageway, a pineal gland is capable of detecting light. This can explain why photic suppression of pineal melatonin remained unaffected in mice genetically lacking retinal photoreceptors. There may exist a secret unknown light transducing passageway that allows the mammalian pineal gland to detect light directly.

References:

1. Rodieck, R.W., The First Steps in Seeing (Sinauer, Sunderland, MA,1998)

2. Borjigin, J., X. Li, S.H. Snyder, Annu. Rev. Pharmacol. Toxicol. 39:53,1999.

3. Klein,D.C., and J.L. Weller, Science, 177:532,1972

4. Deguchi, T., and J. Axelrod, Proc. Natl. Acad Sci. U.S.A., 69:2547,1972

5. Lucas, R.J., et. al., Science, 284:505,1999

6. Lucas, R.J., and R.G. Foster, J. BiolRhythms 14(1):4,1999

7. Lucas, R.J., and R.G. Foster, Curr. Biol, (6):R214,1999

8. Vigh, B., et. al., Biol Cell 90(9):653,1998

9. Faure, J.P., and M. Mirshahi, Curr. eye Res., 9(Suppl):163-7,1990

10. Yokoyama, S., Genes Cells, 1(9):787,1996

11. Lolley, R.N., C.M. Craft, and R.H. Lee, Neurochem Res, 17(1):81,1992

12. Schomerus, C., P. Ruth, and H.W. Korf., Acta Neurobiol Exp (Warsz), :54(Suppl):9, 1994

13.Max, M. et. al., J. Biol Chem., 273(41):26820, 1998

Category: Perspective