PDF Publication Title:
Text from PDF Page: 006
Rojas and Gonzalez-Lima Dovepress retinal ganglion cells that are important in the regulation of biological clocks). On the other hand, nonspecialized molecules that can absorb light but are not integral to light receptor organs are called photoacceptors. Although photoacceptors can potentially absorb light, they usually are part of meta- bolic pathways not directly related with light processing. Photoacceptors are more ubiquitous and abundant than photo- receptors. In fact, photoacceptors can be artificially introduced into living systems, an early concept that led Niels Finsen to the development of phototherapy for which he was awarded a Nobel prize in Physiology or Medicine in 1903.13 Finsen’s work has been the basis of photodynamic therapy and photo- chemotherapy (eg, photodynamic therapy and psoralen ultra- violet treatment), which are widely used in modern medicine mainly for the treatment of skin conditions. A central concept in the theory of LLLT photobiology is that its mechanism of action is mediated primarily by modulation of photoac- ceptor function. The identification and characterization of the properties of photoacceptors is a work in progress in the field of photobiology, but recent studies in photobiology support that effective stimulation of photoacceptors can induce effects of physiological and clinical relevance. This notion stems from the fact that photoacceptor molecules that are able to absorb light and exert changes in the function or structure of the cell are found in practically all living cells and not only in those of specialized sensory organs such as the eye (Figure 4). Another important concept in the photobiology of LLLT is that of a chromophore. A chromophore is a particular moiety within a photoreceptor or photoacceptor molecule that is responsible for the absorption of light. Chromophores are usually organic cofactors or metal ions within a protein structure and contain electrons that can be excited from ground state to excited state, according to Boltzmann law.14 Excitation induces a molecular conformational change that is linked to changes in molecular function and intracellular metabolism. In cells, chromophores can consist of resonating systems or metal complexes. In resonating systems, electron excitation by light occurs within a structure that alternates single and double bonds, such as retinal, the chromophore linked to rhodopsin. Alternatively, in metal complexes, electron excitation occurs in open or closed pyrrole rings that allow binding of transition metals. The association of chromophores with respiratory enzymes has major implica- tions for functional neural regulation. The unusual redox reactivity of chromophores is structurally coupled to protein distortion. In the case of chromophore-containing enzymes, Pigmented epithelium Photoreceptor outer segment Bipolar cell Retinal ganglion cell Photoreceptor effect: PhotoTRANSDUCTION Photoacceptor effect: PhotoBIOMODULATION 54 submit your manuscript | www.dovepress.com Dovepress Near-infrared light Figure 4 Differential effects of light on photoreceptors and photoacceptors in the retina. Light reaches the retina and travels through the different retinal layers to reach the outermost photoreceptor layer. it then excites the photoreceptor rhodopsin in rods and cones, triggering the process of phototransduction. Phototransduction causes photoreceptor cell hyperpolarization, changes in neurotransmission, and action potentials (yellow arrows) in bipolar cells and ganglion cells. These effects represent the onset of visual information processing. Light can also directly excite photoacceptors in neurons including retinal ganglion cells. The main photoacceptor in the red to near-infrared spectrum is the mitochondrial respiratory enzyme cytochrome oxidase. The effects of light on neuronal cytochrome oxidase induce modulation of cell bioenergetic mechanisms that are independent from visual processing. Yet photobiomodulation has major implications in neuronal physiology and homeostasis. this allows a very efficient coupling of electromagnetic free energy flow to the chemical energy flow of substrate conversion.14,15 As discussed below, it is a remarkable find- ing that in mammalian tissues, the photosensitivity of certain chromophores conserves physiologic significance, in spite of their adaptation to naturally function without external photons.16 A distinctive property of chromophores is that they absorb particular wavelengths and reflect others, thus conferring specific colors to molecules. For example the porphyrin ring in chlorophyll a has peaks of absorption at 430 nm and 662 nm. Similarly, the cones in the human retina contain one of three opsins with different spectral sensitivities and linked to the chromophore 11-cis-retinal or 11-cis-3,4- dihydroretinal, which are derivatives of vitamin A. Thus, there are cones that are maximally sensitive to wavelengths of 430 nm (blue), 530 nm (green), and 560 nm (red). According to the Young–Helmholtz trichromatic theory, the color that we perceive is largely determined by the relative contribu- tions of “blue, green, and red” signals sent from the cones in the retina to the brain. Eye and Brain 2011:3PDF Image | Low-level light therapy of the eye and brain
PDF Search Title:
Low-level light therapy of the eye and brainOriginal File Name Searched:
Low-level_light_therapy_of_the_eye_and_brain.pdfDIY PDF Search: Google It | Yahoo | Bing
Cruise Ship Reviews | Luxury Resort | Jet | Yacht | and Travel Tech More Info
Cruising Review Topics and Articles More Info
Software based on Filemaker for the travel industry More Info
The Burgenstock Resort: Reviews on CruisingReview website... More Info
Resort Reviews: World Class resorts... More Info
The Riffelalp Resort: Reviews on CruisingReview website... More Info
| CONTACT TEL: 608-238-6001 Email: greg@cruisingreview.com | RSS | AMP |