Narcolepsy Forum Posting

Posted by PHILIP on January 28, 2000 at 13:27:01:

A new pacemaker protein?

SARA ABDULLA

US researchers have discovered a new protein in the human eye that may play a key role in setting our biological clocks. The protein is called 'melanopsin' and it seems to be present in parts of the retina -- the light-sensitive double lining of the back of the eyeball -- that are known to connect to the body's primary, so-called 'circadian' pacemaker.

Melanopsin had been found before in several vertebrates such as frogs and fish, but this research, reported in the Journal of Neuroscience1 , is the first time that it has been detected in mammals. It is one of a class of proteins called 'opsins', which usually form part of the pigments responsible for light-sensitivity in vision. Melanopsin, however, appears to be different.

First, the structure of the gene encoding it is "unique among vertebrate opsins," comment Mark Rollag of the Uniformed Services University of the Health Sciences, Bethesda, Maryland and colleagues, the authors of the study -- and the protein's structure and biochemistry are pretty unusual too. Indeed it seems to have more in common with invertebrate opsins -- in particular one scallop opsin -- than with those of vertebrates.

Second, unlike other opsins, human melanopsin does not seem to be made in the light-sensitive 'photoreceptor' cells of the outer layer of the retina; rather it seems to be made (just as it is in frogs and fish) by cells in the inner layer. This suggests that it is not involved in image formation, but instead that it may have something to do with the production of the hormone melatonin and hence with the regulation of circadian rhythms. In other words, the research hints that it is somehow a part of the way that mammals couple their natural cycles of hunger, wakefulness and so on to the hours of light and dark in a twenty-four hour period.

Rollag's team found that the cells that manufacture this intriguing protein are most probably the very same cells that connect the retina with the body clock's control centre -- the 'superchiasmic nucleus', or SCN. The SCN is located in the 'hypothalamus', the part of the brain, which, broadly speaking, oversees motivated behaviour such as eating, drinking and sex.

This new finding fits in with other research showing that rodents and even some humans that lack the cells necessary to see (technically known as 'rods' and 'cones') still have reasonably regular, light-entrained rhythms of sleeping and waking in a way that those completely without eyes do not.

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