Photosensitive ganglion cell

You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.

Photosensitive ganglion cells, or melanopsin-containing ganglion cells, are a recently discovered type of nerve cell in the retina of the eye which, unlike other retinal ganglion cells, are intrinsically photosensitive. This means that they are excited by light even when all influences from classical photoreceptors (rods and cones) are blocked, either by applying pharmacological agents or by dissociating the ganglion cell from the retina. Photosensitive ganglion cells contain the photopigment melanopsin. The giant retinal ganglion cells of the primate retina are examples of photosensitive ganglion cells.

Photosensitive ganglion cells play an important role in synchronizing circadian rhythms to the rising and setting of the sun. They send light information directly to the circadian pacemaker of the brain, the suprachiasmatic nucleus of the hypothalamus. The physiological properties of these ganglion cells match known properties of the synchronization or "light entrainment" mechanism regulating circadian rhythms. This is the mechanism that allows us to overcome jet lag.

Photosensitive ganglion cells also innervate various other brain targets, such as the center of pupillary control, the olivary pretectal nucleus of the midbrain. They contribute to the regulation of pupil size and other behavioral responses to ambient lighting conditions. Photosensitive ganglion cells are responsible for the persistence of circadian and pupillary light responses in mammals with degenerated rod and cone photoreceptors, such as humans suffering from retinitis pigmentosa.

The photopigment of these cells, melanopsin, absorbs light mainly in the blue portion of the visible spectrum (best wavelength = 480 nanometers). The phototransduction mechanism in these cells is not fully understood, but seems likely to resemble that in invertebrate rhabdomeric photoreceptors. Photosensitive ganglion cell respond to light by depolarizing and increasing the rate at which they fire nerve impulses. In addition to responding directly to light, these cells receive excitatory and inhibitory influences from rods and cones by way of synaptic connections in the retina.

References

• Berson, D.M. (2003). Strange vision: ganglion cells as circadian photoreceptors. Trends in Neuroscience 26:314-320.
• Dacey, D.M. et al. (2005). Melanopsin-expressing ganglion cells in primate retina signal colour and

irradiance and project to the LGN. Nature. 433(7027):749-54.

External links

• David Berson's lab at Brown University

v • d • e Sensory system - Visual system - Eye - Retina
cells	Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Ganglion cell Giant retinal ganglion cells - Photosensitive ganglion cell - Muller glia
layers	Inner limiting membrane - Nerve fiber layer - Ganglion cell layer - Inner plexiform layer - Inner nuclear layer - Outer plexiform layer - Outer nuclear layer - External limiting membrane - Layer of rods and cones - Retinal pigment epithelium