The Influence of Receptors on Awareness

A key aspect of an organism's ability to survive is its ability to be aware of, and respond to the different aspects of its environment. Receptors at the cellular level are responsible for an organism's awareness. Without these cellular receptors the organism is unable to formulate a response and react to stimuli. The use of the protein ChR2, in the retina of the eyeball is proof that receptors are key in an organism's awareness.

Channelrhodopsin-2 (ChR2) is a protein that is endogenously used in chlamydomonas, a species of green alga (Flannery, 2006). The chlamydomonas contains an organelle known as the eye spot. The movement of the chlamydomonas depends on the amount and direction of the light that enters the eyespot. ChR2 acts as a receptor in the eyespot in that it is responsible for the sensitivity of light (Reiss, 2008). After determining the intensity of light, the chlamydomonas responds by either moving to the light rays, or away. Without the presence of ChR2 in the eyespot the chlamydomons does not know where to move because it is unable to detect the intensity of the light rays. Humans have figured out a way to use ChR2 in place of light receptors in other organisms.

The eyeball in mammals contains the retina, which is composed of many photoreceptive cells as well as a pigment known as rhodopsin. Rhodopsin regulates and adapts to the amount of light that enters the eye. If too much light enters the retina of the eye rhodopsin bleaches in order to keep some of the light out (rhodopsin, 2009). Once the light enters the eye the photoreceptors trigger a chemical process which in turn transmits electrical signals to the brain, allowing vision (Reiss, 2008). If these receptors are destroyed the person/animal will be unable to see. Scientists have found a way to restore partial vision by introducing ChR2.

The pigment rhodopsin, found in the retina is very similar to the protein ChR2, in that they both act as light receptors. For this reason scientists are able to introduce the genetic material of ChR2 into the retinas of mammals. They first experimented on rats and mice that had lost their ability to see. Once the ChR2 gene was introduced ChR2 proteins started to form in the ganglion cells of the eyes. These proteins transmitted electrical signals to the mice/rats' brains, allowing them to see (Reiss, 2008).

This experiment is proof that receptors are what allow organisms to be aware. The photoreceptors in the mice/rats were destroyed, making them visually unaware. By introducing the genetic material of ChR2, scientists were able to restore vision in these animals. This is because the ChR2 took the place of the original photoreceptors and functioned as receptor of light. Without receptors and the signals they transmit organisms would be completely unaware of their environment.

Sources

Flannery, JG. And Greenberg, KP. 2006. Looking within for vision, Neuron 50: 1-3.

Reiss, S. 2008. Reviving Vision: Key protein may help researchers restore light sensitivity in damaged retinas. National Eye Institute- NIH. http://www.nei.hih.gov/new/briefs/revivingvision.asp

"rhodopsin." Encyclopedia Britannica. 2009. Encyclopedia Britannica Online. 02 Oct. 2009

http://www.britannica.com/EBchecked/topic/501725/rhodopsin>.