ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00415.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00416.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00417.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00418.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

There are two ways in which white light is transformed into colored light by interaction with matter: absorption and scattering. Absorption transforms light into other forms of energy, whereas scattering redirects it. Reflection, refraction, and diffraction are not distinct from scattering but rather are manifestations of it. There is a hierarchy of theories for describing any color phenomenon. For example, many features of rainbows—but not all—can be described satisfactorily by geometrical optics. More accurate descriptions require more exact theories. What one observes when matter is illuminated depends on its disposition. A microscope slide scatters light mostly in two directions. When smashed to bits, it scatters in all directions. Yet its chemical composition has not changed. Glass particles, unlike those in smoke, are usually too large to give colors upon scattering. The colors one sees when smoke is illuminated depend on whether one observes light that has or has not been scattered. Moreover, particle size is crucial in determining what colors are observed. As with scattering, there is a hierarchy of theories of absorption. One can content oneself with an empirical description of absorption or seek a fuller understanding by appealing to microscopic theories. Yet it is sometimes difficult to associate a definite microscopic mechanism with a given absorption feature. Ice is intrinsically blue, yet this cannot be attributed readily to a specific mechanism. Beer has no yellow absorption feature; absorption by it is least in the red and rises steadily toward the blue. Over short paths, beer is yellow; over long paths, it is reddish. Selective scattering by molecules causes the blue of the sky. Yet it is not uniformly blue. To understand why requires invoking multiple scattering. Snow is another multiple scattering medium. Although we usually think of snow as white, deep within it there is blue light more vivid than the bluest sky. This is the result of multiple scattering by particles that are not selective scatterers but selective absorb

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00419.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The human skin is submitted to solar, essentially ultraviolet radiation (UVR), aggressions, and develops, for sufficient doses, erythema and pigmentation. The individual sun‐sensitivity depends on the nature and the quantity of melanins present in the epidermis. These parameters are inherited as genetic traits which account for the large variations of the constitutive and adaptive pigmentation encountered in the caucasian populations. From red‐haired skin‐sensitive individuals, to dark‐haired sun‐resistant individuals, phaeomelanins (red) and eumelanins (black) are mixed in variable proportions. Pure melanins extracted from red hairs and black hairs behave differently when submitted to ultraviolet radiations: phaeomelanins develop aggressive species of molecules responsible for DNA damages, mutations, and cell death. On the contrary, eumelanins are less toxic for the major cellular metabolisms. The sun‐sensitive populations suffer from more skin cancer of all types than the dark ones. In particular, they are exposed significantly to higher risk of melanoma and to the risk of bearing more nevi following large solar exposures early

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00420.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Extra‐cutaneous melanocytes derive from either the neural crest, the outer wall of the optic cup, or the cranial neural tube. Those of neural crest origin reach most bodily regions, and may give rise to primary melanoma in various tissues. The Kupffer cell produces a form of melanin, but is hardly a melanocyte. Melanocytes of the internal ear may be concerned with secretion of endolymph, trans‐epithelial ion transport, and with protection against ototoxic drugs and high‐intensity noise damage. There is evidence from albino animals that retinal pigment epithelium determines co‐ordinates of the neural retina, and its decussation pattern during development.Neuromelanin derives from Dopamine, and is found in dopaminergic neurons widely distributed throughout the brain‐stem and hypothalamus, and which project to the striatum and limbic system. Parkinsonism is due to degeneration of melanin‐containing dopaminergic neurons of locus coeruleus and substantia nigra, and MPTP provides an investigative probe for studying the causes of Parkinsonism. Neuromelanin should not be regarded as a waste‐product, but as something which can affect the firing properties of neurons with specific func

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00421.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The presence of melanin in the inner ear was established more than a century ago, but the exact biological function of the pigment in the labyrinth has yet to be deter‐mined. In this brief review, the correlation of pigmentation and inner ear function, as well as the presumed role of melanocytes in hereditary diseases are discussed. Special attention was drawn to the composition of melanin and its presumed function as a biological reservoir for divalent ions and as an ion exchanger, as well as an intracellular buffering system for calcium. It is pointed out that melanin is capable of binding ototoxic drugs. Finally, morphological responses of melanocytes to local disturbance of Ca++homeostasis in the inner ear are described as 1) intracellular movement and intraepithelial deposition of melanosomes; 2) cell motility; 3) neomelanogenesis; and 4) enhanced exocytotoxic/endocytotic activity. The possible consequences of this malfunction of the melanocytes on the inner ear function are discusse

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00422.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In this report we show the most important results obtained from our study of the pigment liver cells of Amphibia and Reptilia.Contrary to the cutaneous pigment cells that derive from the neural crest, the liver pigment cells, instead, derive from the Kupffer cells: this can be seen from the results obtained from labelled precursor incorporation experiments, not only in vivo but also in vitro, using surviving liver slices or isolated melanosomes.Chemical analysis of both liver and cutaneous melanosomes reveal a great difference in their chemical composition, and this is in agreement with the different origins of these cells.We therefore propose that: liver pigment cells of Amphibia and Reptilia should be classified as “Extra Cutaneous Pigment Cells from Histocytic Origin”.As regards the function of melanins, we show that O2is trapped by these substances.Moreover, in my laboratory we have shown in several animal species, that the super‐oxide dismutase activity is inversely proportional to the quantity of melanin present; thus, we think that melanin could mime SOD act

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00423.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1988.tb00424.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY