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Issue 125, 15 January 2003
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Shining a new light on the eye
by Tony Stephenson MELANOPSIN, a recently identified protein, plays a key role in a
completely new light detection system in the eye, according to
researchers from Imperial College London, and American
universities, Johns Hopkins University and Brown University. Professor Russell Foster of Imperial College London at Charing
Cross Hospital explained: "It has long been assumed that the rod
and cone cells of the retina are responsible for all light
detection. "However, during the last few years, our research has revealed a
third light detection system that has lain undiscovered for more
than 100 years." A deeper understanding of these latest photoreceptors may
provide new ways to overcome jet-lag and treatments for disorders
such as SAD (Seasonally Affective Disorder) that can be caused by a
lack of light, particularly during the winter months. Dr Rob Lucas of Imperial College London at Charing Cross
Hospital added: "Melanopsin is particularly important in the
detection of bright light as we believe this new photoreceptor is
responsible for telling our bodies that it is daytime - daylight is
always bright light. "Apart from regulating pupil size, the melanopsin photoreceptors
may be responsible for a broad range of responses to light,
including its ability to keep us awake and alert. It is also likely
that these photoreceptors are responsible for resetting our
internal body clocks to local time following a flight across
time-zones." Melanopsin , expressed in a small number of ganglion cells in
the retina of the eye, was tested by measuring light-induced
papillary constriction in genetically modified mice that lacked
melanopsin. When mice that lacked melanopsin were exposed to low light,
their pupillary response was the same as normal mice, but when they
were exposed to bright light, their pupil constriction was
incomplete. The research, entitled: "Diminshed Pupillary Light Reflex at
High Irradiances in Melanopsin - Knockout Mice", was published this
month in Science. |
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©2003 Imperial College London |