RETINAL PHOTORECEPTOR CELLS: PHOTOTRANSDUCTION MECHANISMS IN HEALTH AND DISEASE

CONTIN MARIA ANA; ARIETTI, MILAGROS; GUIDO MARIO EDUARDO

''Photoreceptors: Physiology, Types and Abnormalities'.

Nova Science Publishers, Inc.

Lugar: New York; Año: 2011; p. 1 - 23

The retina is the part of the central nervous system adapted to the initial capture and processing of visual signals. However, its organization makes it vulnerable to dysfunction. Retinitis pigmentosa (RP) is a group of dystrophies that leads to retinal degeneration and eventually blindness. In most typical cases the rods are the predominantly affected cells in the retina, generating symptoms including night blindness, bilateral symmetric loss of the mind-peripheral visual field, or/and electroretinographic (EGR) abnormalities. Some forms of RP kill the photoreceptor cells, causing visual damages ranging from mild (in night blindness) to severe visual impairment owing to the high rate and constitutive activation of the phototransduction process. The question therefore arises as to why phototransduction causes cell death. A powerful approach to the understanding of etiologies of visual impairment at the cellular and molecular levels has been the use of experimental animal models that mimic the damage caused in human pathologies for a number of inherited retinal diseases, by exposing animals carrying specific retinal gene mutations or wild-type animals to continuous light treatment. The death of photoreceptor cells induced by low light intensity requires the activation of photopigments and a consequent downstream signal transduction cascade. Light exposure has therefore served as a model for human retinal degeneration arising from environmental insult and genetic disease. In this chapter we will discuss the different retinal degenerations related to retinitis pigmentosa (RP) disease, with special emphasis on those caused by genetic defects, vitamin A deficiency or prolonged light exposure producing the constitutive activation of the phototransduction pathway. We will also examine the mechanisms of apoptotic death occurring after retinal light damage and provide insight into the positive and negative aspects of retinal degeneration models. We consider that the molecular mechanism taking place in damage caused by low light intensity can provide valuable experimental models for studying the effects of clinical genetic disorders related to defects in the phototransduction mechanism.