Phototransduction in a Rabbit Model with Retinitis Pigmentosa

                                     http://austinpublishinggroup.com/clinical-ophthalmology/

Retinitispigmentosa (RP) is a progressive disease that exhibits abnormalities in the photoreceptor cells of the rods and cones that detect light, and is characterized by symptoms such as night blindness, visual field constriction especially in the peripheral field, and reduced visual acuity. In Japan, this disorder is estimated to affect approximately 20 in 100,000 people and is the third leading cause of blindness following glaucoma and diabetic retinopathy. RP appears through a variety of genetic inheritance modes, including autosomal dominant, autosomal recessive, and X-linked recessive patterns, and 40 or more causative genes have been identified. In many patients, however, genetic abnormalities cause this disorder to be under diagnosed.

Toovercome these difficulties, transgenic (Tg) rabbits with a P347L rhodopsin mutation were created by Kondo et al. They displayed symptoms extremely similar to findings in patients with RP and are considered to offer a useful animal model for elucidating the pathology of RP. However, when and where the degeneration begins are unclear, as are its underlying mechanisms and pathologies. There are many other unknown issues as well, such as how light is received and converted to electric signals in the steps leading to blindness, and why organisms with undeveloped vision such as rabbits receive light, and where photoreceptors are located in these animals. In humans, light is received by photoreceptor cells and is converted to electric signals to visualize an object.

Inclinical settings, we encounter patients with RP who maintain circadian rhythms in which the body wakes in the morning and becomes sleepy at night, and those who present a residual light response in which the pupil becomes smaller on exposure to light. This is unlike patients who have lost their vision due to other eye diseases. In other words, RP patients show partial response to light even when blind and unable to sense light. Based on these facts, we hypothesized the existence of photoreceptors other than the rods and cones of the photoreceptor cells. In this review based on our previous studies we report the mechanism of retinal degeneration and describe the process of phototransduction in Tg rabbits with a P347L rhodopsin mutation.