Loss Of Melanin Research Articles

Loss of Melanin by Eye Retinal Pigment Epithelium Cells Is Associated with Its Oxidative Destruction in Melanolipofuscin Granules.

The effect of superoxide radicals on melanin destruction and degradation of melanosomes isolated from cells of retinal pigment epithelium (RPE) of the human eye was studied. We found that potassium superoxide causes destruction of melanin in melanosomes of human and bovine RPE, as well as destruction of melanin from the ink bag of squid, with the formation of fluorescent decay products having an emission maximum at 520-525nm. The initial kinetics of the accumulation of the fluorescent decay products is linear. Superoxide radicals lead simultaneously to a decrease in the number of melanosomes and to a decrease in concentration of paramagnetic centers in them. Complete degradation of melanosomes leads to the formation of a transparent solution containing dissolved proteins and melanin degradation products that do not exhibit paramagnetic properties. To completely degrade one melanosome of human RPE, 650 ± 100 fmol of superoxide are sufficient. The concentration of paramagnetic centers in a melanolipofuscin granule of human RPE is on average 32.5 ± 10.4% (p < 0.05, 150 eyes) lower than in a melanosome, which indicates melanin undergoing a destruction process in these granules. RPE cells also contain intermediate granules that have an EPR signal with a lower intensity than that of melanolipofuscin granules, but higher than that of lipofuscin granules. This signal is due to the presence of residual melanin in these granules. Irradiation of a mixture of melanosomes with lipofuscin granules with blue light (450nm), in contrast to irradiation of only melanosomes, results in the appearance of fluorescent melanin degradation products. We suggest that one of the main mechanisms of age-related decrease in melanin concentration in human RPE cells is its destruction in melanolipofuscin granules under the action of superoxide radicals formed during photoinduced oxygen reduction by lipofuscin fluorophores.

Statin Concentrations Below the Minimum Inhibitory Concentration Attenuate the Virulence of Rhizopus oryzae.

Mucormycosis is a destructive invasive mold infection afflicting patients with diabetes and hematologic malignancies. Patients with diabetes are often treated with statins, which have been shown to have antifungal properties. We sought to examine the effects of statins on Rhizopus oryzae, a common cause of mucormycosis. Clinical strains of R. oryzae were exposed to lovastatin, atorvastatin, and simvastatin and the minimum inhibitory concentrations (MICs) were determined. R. oryzae germination, DNA fragmentation, susceptibility to oxidative stress, and ability to damage endothelial cells were assessed. We further investigated the impact of exposure to lovastatin on the virulence of R. oryzae All statins had MICs of >64 µg/mL against R. oryzae Exposure of R. oryzae to statins decreased germling formation, induced DNA fragmentation, and attenuated damage to endothelial cells independently of the expression of GRP78 and CotH. Additionally, R. oryzae exposed to lovastatin showed macroscopic loss of melanin, yielded increased susceptibility to the oxidative agent peroxide, and had attenuated virulence in both fly and mouse models of mucormycosis. Exposure of R. oryzae to statins at concentrations below their MICs decreased virulence both in vitro and in vivo. Further investigation is warranted into the use of statins as adjunctive therapy in mucormycosis.

Skip areas of retained melanin: a clue to the histopathological diagnosis of idiopathic guttate hypomelanosis.

Biopsy findings in 55 cases of idiopathic guttate hypomelanosis (IGH) are reported. Most cases had a flat epidermis with loss of the rete pattern and a thickened orthokeratotic basket weave stratum corneum. The epidermis had markedly decreased to absent melanin in the basal layer and reduced numbers of melanocytes at the dermoepidermal junction. One-third of patients had a sparse perivascular lymphocytic infiltrate, whereas the rest had no significant dermal inflammation. These findings are in concordance with current literature. However, small foci of retained melanin in the basal layer (skip areas) alternating with larger areas of melanin loss were present in almost 80% of cases. This finding has not been reported earlier and appears to be quite specific to IGH and may be used as a clue to differentiate IGH from other similar conditions such as vitiligo and guttate morphea.

NMDA-R inhibition affects cellular process formation in Tilapia Melanocytes; a model for pigmented adrenergic neurons in process formation and retraction

Parkinson's disease has long been described to be a product of dopamine and (or) melanin loss in the substanstia nigra (SN). Although most studies have focused on dopaminergic neurons, it is important to consider the role of pigment cells in the etiology of the disease and to create an in vitro live cell model for studies involving pigmented adrenergic cells of the SN in Parkinsonism. The Melanocytes share specific features with the pigmented adrenergic neurons as both cells are pigmented, contain adrenergic receptors and have cellular processes. Although the melanocyte cellular processes are relatively short and observable only when stimulated appropriately by epinephrine and other factors or molecules. This study employs the manipulation of N-Methyl-D-Aspartate Receptor (NMDA-R), a major receptor in neuronal development, in the process formation pattern of the melanocyte in order to create a suitable model to depict cellular process elongation and shortening in pigmented adrenergic cells. NMDA-R is an important glutamate receptor implicated in neurogenesis, neuronal migration, maturation and cell death, thus we investigated the role of NMDA-R potentiation by glutamate/KCN and its inhibition by ketamine in the behavior of fish scale melanocytes in vitro. This is aimed at establishing the regulatory role of NMDA-R in this cell type (melanocytes isolated form Tilapia) in a similar manner to what is observable in the mammalian neurons. In vitro live cell culture was prepared in modified Ringer's solution following which the cells were treated as follows; Control, Glutamate, Ketamine, Glutamate + Ketamine, KCN + Ketamine and KCN. The culture was maintained for 10min and the changes were captured in 3D-Time frame at 0, 5 and 10min for the control and 5, 7 and 10min for each of the treatment category. Glutamate treatment caused formation of short cellular processes localized directly on the cell body while ketamine treatment (inhibition of NMDA-R) facilitated elongation of secondary cellular processes (highly branched) from primary major processes (Less branched); co-incubation of glutamate and ketamine induced short and highly branched process formation. Cyanide toxicity induced degeneration and reduction of cell size while co-treatment of cyanide and ketamine gave changes similar to that observed in glutamate-ketamine co-incubation. NMDA-R is present in the melanocytes. Activation of the receptor reduced elongation process, while inhibition of the receptor facilitated cell process elongation and branching. This confirms that like pigmented adrenergic cells of the nervous system, this cell contains NMDA-R and this receptor also regulates cell process elongation. The study also showed that inhibition of NMDA-R in melanocytes gave opposite outcomes to the role of the receptor in developing neurons; a function that is protective in adult neurons.

Disease duration and the integrity of the nigrostriatal system in Parkinson’s disease

The pace of nigrostriatal degeneration, both with regards to striatal denervation and loss of melanin and tyrosine hydroxylase-positive neurons, is poorly understood especially early in the Parkinson's disease process. This study investigated the extent of nigrostriatal degeneration in patients with Parkinson's disease at different disease durations from time of diagnosis. Brains of patients with Parkinson's disease (n=28) with post-diagnostic intervals of 1-27 years and normal elderly control subjects (n=9) were examined. Sections of the post-commissural putamen and substantia nigra pars compacta were processed for tyrosine hydroxylase and dopamine transporter immunohistochemistry. The post-commissural putamen was selected due to tissue availability and the fact that dopamine loss in this region is associated with motor disability in Parkinson's disease. Quantitative assessments of putaminal dopaminergic fibre density and stereological estimates of the number of melanin-containing and tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta (both in total and in subregions) were performed by blinded investigators in cases where suitable material was available (n=17). Dopaminergic markers in the dorsal putamen showed a modest loss at 1 year after diagnosis in the single case available for study. There was variable (moderate to marked) loss, at 3 years. At 4 years post-diagnosis and thereafter, there was virtually complete loss of staining in the dorsal putamen with only an occasional abnormal dopaminergic fibre detected. In the substantia nigra pars compacta, there was a 50-90% loss of tyrosine hydroxylase-positive neurons from the earliest time points studied with only marginal additional loss thereafter. There was only a ∼10% loss of melanized neurons in the one case evaluated 1 year post-diagnosis, and variable (30 to 60%) loss during the first several years post-diagnosis with more gradual and subtle loss in the second decade. At all time points, there were more melanin-containing than tyrosine hydroxylase-positive cells. Loss of dopaminergic markers in the dorsal putamen occurs rapidly and is virtually complete by 4 years post-diagnosis. Loss of melanized nigral neurons lags behind the loss of dopamine markers. These findings have important implications for understanding the nature of Parkinson's disease neurodegeneration and for studies of putative neuroprotective/restorative therapies.

VDR Potentiation and NMDA R Inhibition Facilitates Axo-Dendritic Process Formation in Melanocyte Model for Pigmented Cells in Parkinsonism

Background: A major cellular change in dopaminergic neurons leading to Parkinsonism is the alteration of microtubule proteins that causes accumulation of tau protein, α-syn and β-amyloid plaque in the cells. In this study we investigate the role of Vitamin D3 in relieving the symptoms of Parkinsonism as it is capable of stimulating polymerization of microtubules. The Microtubules (MT) system in the fish scale melanocytes has been modeled for the dopaminergic neurons of the Substantia Nigra (SN). These cells are capable of forming cellular processes similar to what is seen in the dopaminergic neurons; in this study, we investigate the protective effect of Vitamin D3 Receptor Agonist (VDRA) and N-Methyl-D-Aspartate Receptor (NMDA R) inhibition in process formation, synaptic denervation and melanin loss in fish scale melanocytes modeled as pigmented adrenergic cells. Method: The Tilapia scale was isolated and sub cultured in Ringer’s solution following which the cells were prepared for imaging. We incubated the cells with VDRA, Ketamine and a combination of Ketamine and VDRA in separate set ups for 60 minutes. Using brightfield imaging techniques, the cells were viewed during the incubation period and recorded using a Cameroscope connected to a computer interface. Results/Conclusion: The cells incubated with VDRA and NMDA R inhibitor, showed an increase in the number of process and extent of the process formation; the increased number of process is an indication of a rapid rate of polymerization of microtubules. Also, the processes formed are combined long processes peculiar to the NMDA R1 inhibition and short processes characteristic of VDR potentiation as seen in VDRA treatment only. Most of the effects of the VDRA were restricted to process formation around the cell body; this is similar to the microtubule cytoskeletal system found in the dendritic nucleation assembly. This finding confirms the presence of VDR and its likely restriction to d cell body plus its role in facilitating short dendrite-like process formation while NMDA R is located on the processes and facilitates long process formation.

Role of In vivo reflectance confocal microscopy in determining stability in vitiligo: A preliminary study

Background:Vitiligo is an acquired pigmentary disorder. In vivo reflectance confocal microscopy (RCM) reproducible imaging technique has already been reported to be useful in the diagnosis of other skin diseases.Objective:To define RCM features of vitiligo on different clinical stages.Materials and Methods:A total of 125 patients with a clinical diagnosis of vitiligo were included in this study. After informed consent, lesional skins of those vitiligo patients were characterized by using RCM. Five patients with inflammatory cell infiltration observed at the edge of skin lesions and another 5 patients without inflammatory cell infiltration were selected. Biopsies were performed at same sites of the RCM examination areas for histological and immune-histological analysis.Results:In the active stage of vitiligo, the RCM examination revealed that the bright dermal papillary rings presented at the dermoepidermal junction level in normal skin lost their integrity or totally disappeared, border between vitiligo lesion and normal skin became unclear, and highly refractile cells that referred to infiltrated inflammatory cells could be seen within the papillary dermis at the edge of the lesions. In the stable stage of vitiligo, the RCM showed a complete loss of melanin in lesional skin and a clear border between lesional and normal skin.Conclusion:A simple clinical examination with RCM may reliably and efficiently allow evaluation of the stability status of vitiligo lesions.

Relationships between Hair Melanization, Glutathione Levels, and Senescence in Wild Boars

The synthesis of melanins, which are the most common animal pigments, is influenced by glutathione (GSH), a key intracellular antioxidant. At high GSH levels, pheomelanin (the lightest melanin form) is produced, whereas production of eumelanin (the darkest melanin form) does not require GSH. Oxidative damage typically increases with age, and age-related decreases in GSH have accordingly been found in diverse organisms. Therefore, there should be positive associations between the capacity to produce eumelanic traits, GSH levels, and senescence, whereas there should be negative associations between the capacity to produce pheomelanic traits, GSH levels, and senescence. We explored this hypothesis in a free-ranging population of wild boars Sus scrofa of different ages. As expected from the fact that pheomelanogenesis consumes GSH, levels of this antioxidant in muscle tended to be negatively related to pheomelanization and positively related to eumelanization in pelage, and the degree of pelage pheomelanization was positively related to oxidative damage as reflected by levels of thiobarbituric-acid-reactive substances (TBARS), which is consistent with the hypothesis that pheomelanin synthesis has physiological costs. In our cross-sectional sample, GSH levels did not show senescence effects, and we did not detect senescence effects in pelage melanization. Prime body condition and low TBARS levels were also associated with hair graying, which is attributable to a loss of melanin produced by oxidative stress, thus raising the possibility that hair graying constitutes a signal of resistance to oxidative stress in wild boars. Our results suggest that the degree of melanization is linked to GSH levels in wild boars and that their antioxidant damage shows senescence effects.

Parkinson's disease: Diagnosis

In established PD the Queen Square Brain Bank criteria applied by experts show 90% sensitivity and specificity for the presence of midbrain Lewy bodies. However, in early disease clinical diagnosis is less straightforward. PD diagnosis made in the community by non-experts is associated with a 25% error rate. Nigral abnormalities can now be detected in vivo with 7 tesla MRI and diffusion tensor MRI. Magnetisation transfer can demonstrate melanin loss in the substantia nigra. Transcranial sonography (TCS) detects midbrain hyperechogenicity in both sporadic and genetic PD. PET and SPECT ligands can demonstrate the presence of dopamine terminal dysfunction in early and preclinical disease and an abnormal covariance pattern between levels of resting brain blood flow metabolism in cortical and subcortical regions. In the atypical parkinsonian syndrome multiple system atrophy (MSA) T2-weighted MRI can reveal characteristic changes including reduced putmen signal due to iron deposition and the pontine 'hot cross bun' sign as transverse fibres become visible. Progressive supranuclear palsy (PSP) is associated with midbrain atrophy and 3(rd) ventricular widening. In both these conditions diffusion weighted MRI shows increased striatal water diffusivity but the middle cerebellar peduncle is targeted in MSA and the superior peduncle in PSP. In this review the role of structural and functional imaging for supporting the differential diagnosis of the various degenerative parkinsonian syndromes will be discussed.

A novel melano-lysosome in the retinal epithelium of rhesus monkeys

The large phagocytic load that confronts the retinal pigment epithelium (RPE) is thought to play a possible role in the pathogenesis of age related macular degeneration (AMD) that afflicts both humans and monkeys. Our knowledge of how RPE degrades phagosomes and other intra-cellular material by lysosomal action is still rudimentary. In this paper we examine organelles that play a role in this process, melanosome, lysosomes and phagosomes, in the RPE of young and old rhesus monkeys in order to better understand lysosomal autophagy and heterophagy in the RPE and its possible role in AMD.We used electron microscopy to detect and describe the characteristics of melanosomes and lysosome-like organelles in the macular RPE of rhesus monkeys (Macaca mulatta) that were 1, 6, 24, 24, 26 and 35 years of age. The measurements include the number, shape and size of these organelles located in the basal, middle and apical regions of RPE cells. Phaagosomes were also examined but not counted or measured for size or shape because of their rarity.Melanosomes were homogeneously dark with a circular or elliptical shape and decreased in number with age. Smaller melanosomes were more common at the basal side of the RPE. Among the small melanosomes, we found an organelle that was losing melanin in varying degrees; in some cases was nearly devoid of melanin. Because of the melanin loss, we considered this organelle to be a unique type of autophagic melano-lysosome, which we called a Type 1 lysosome. We found another organelle, more canonically lysosomal, which we called a Type 2 lysosome. This organelle was composed of a light matrix containing melanosomes in various stages of degradation. Type 2 lysosomes without melanosomes were rare. Type 2 lysosomes increased while Type 1 decreased in number with age. Phagosomes were rare in both young and old monkeys. They made close contact with Type 2 lysosomes which we considered responsible for their degradation.Melanosomes are being lost from monkey RPE with age. Much of this loss is carried out by two types of lysosomes. One, not defined as unique before, appears to be autophagic in digesting its own melanin; it has been called a Type 1 lysosome. The other, a more canonical lysosome, is both heterophagic in digesting phagosomes and autophagic in digesting local melanosomes; it has been called a Type 2 lysosome. Type 1 lysosomes decrease while type 2 lysosomes increase with age. The loss of melanin is considered to be detrimental to the RPE since it reduces melanin’s protective action against light toxicity and oxidative stress. Phagosomes appear to be degraded by membrane contacts with Type 2 lysosomes. The loss of melanin and the buildup of Type 2 lysosomes occur at an earlier age in monkeys than humans implying that a greater vulnerability to senescence accelerates the rate of AMD in monkeys.

In vivo reflectance confocal microscopy imaging of vitiligo, nevus depigmentosus and nevus anemicus

Hypopigmentary skin disorders such as vitiligo, nevus depigmentosus and nevus anemicus are common diseases in clinic. The lesions of these diseases could be similar to some extent, although each of them has its own characteristic clinical appearance and histological features. Clinically, the atypical lesions are often difficult to be differentiated. In vivo reflectance confocal microscopy (RCM) is a non-invasive, repetitive imaging tool that provides real-time images at a nearly cellular histological resolution. Our aim was to investigate the RCM features of vitiligo, nevus depigmentosus and nevus anemicus. A total of 135 patients with a clinical diagnosis of the aforementioned diseases were included in this study. The RCM images from depigmented skin, border of the white macules, adjacent normal-appearing skin and distant normal skin for all patients at the dermo-epidermal junction (DEJ) level were investigated. In the active phase of vitiligo (AVP), the RCM demonstrated a complete loss of melanin in lesional skin in eight (53; 15.1%) patients. In 45 patients (53; 84.9%) of the AVP, part of the bright dermal papillary rings normally seen at the DEJ level disappeared or part of the rings lost their integrity and the content of melanin decreased obviously. In 20 patients (53; 37.7%) of the AVP, highly refractile inflammatory cells could be seen within the papillary dermis in the lesional and adjacent normal-appearing skin, which may indicate the lesion progresses. In addition, part of the dermal papillary rings showed lack of integrity or their brightness decreased in adjacent normal-appearing skin in all the patients of the AVP. It is important to know that the RCM demonstrated an ill-defined border. In the stable phase of vitiligo (SPV), the RCM demonstrates a complete loss of melanin in lesional skin and a clear border in 31 (41; 75.6%) patients; the content of melanin and dermal papillary rings in adjacent normal-appearing skin show no changes. In 10 (41; 24.4%) patients, the dendritic and highly refractile melanocytes arose in the recovery phase of vitiligo, which may indicate the repigmentation of vitiligo. There are three kinds of repigmentation patterns under RCM: marginal, perifollicular and diffuse. Distant normal skin showed no difference from controls in both the active and the SPV. In all the patients with nevus depigmentosus, the content of melanin decreases obviously but the dermal papillary rings are intact. The dermal papillary rings show no differences between lesional skin and adjacent normal-appearing skin of nevus anemicus. Considering our results, RCM may be useful to non-invasively discriminate vitiligo, nevus depigmentosus and nevus anemicus in vivo.

In vivo confocal laser scanning microscopy of hypopigmented macules: a preliminary comparison of confocal images in vitiligo, nevus depigmentosus and postinflammatory hypopigmentation

The use of confocal laser scanning microscopy (CLSM) may be an eligible alternative for confirmation of the diagnosis of hypopigmented macules. Our purpose was to evaluate CLSM features for non-invasive imaging of vitiligo, nevus depigmentosus and postinflammatory hypopigmentation in vivo. A total of 68 patients with a clinical diagnosis of the aforementioned diseases were included in this study. CLSM was performed on lesional and adjacent normal appearing skin for all patients. In the active and stable phases of vitiligo, CLSM demonstrated a complete loss of melanin in lesional skin in 14 of 25 patients (56.0%) and 16 of 20 patients (80.0%), respectively. In 11 of 25 (44.0%) patients, the amount of melanin in lesional skin decreased in the active phase of vitiligo, but it is noteworthy to know that the melanin was distributed homogeneously in the dermal papillary rings. In four of 20 patients (20.0%), the dermal papillary rings disappeared completely, but some refractile granules and dendrites could be seen in the stable phase of vitiligo, which may indicate the start of vitiligo repigmentation. Although, in 20 of 20 patients (100%) with nevus depigmentosus, the dermal papillary rings lost their integrity and the content of melanin decreased obviously, there must have been melanin in the dermal papillary rings during its development in all patients. Simultaneously, the melanin was distributed heterogeneously in the dermal papillary rings. The content of melanin and dermal papillary rings in postinflammatory hypopigmentation probably depend on the depth and site of the inflammation; moreover, melanophages were observed in postinflammatory hypopigmentation but did not exist in vitiligo and nevus depigmentosus. In addition, the content of melanin and dermal papillary rings in adjacent normal appearing skin showed changes in the active phase of vitiligo but showed no changes in any of the patients in the stable phases of vitiligo, nevus depigmentosus and postinflammatory hypopigmentation. Differences based on CLSM in the aforementioned diseases were the content of melanin and its distribution pattern. CLSM may be useful to discriminate vitiligo, postinflammatory hypopigmentation and nevus depigmentosus in a non-invasive fashion.

Spectrophotometric Intracutaneous Analysis

The noncontact spectrophotometric intracutaneous analysis scope (SIAscope) is a novel portable imaging device that rapidly produces images of the blood and melanin content of large areas of skin. The estimation of burn depth is often difficult in the clinical setting, and this pilot study was conducted to assess the potential for the SIAscope in aiding burn assessment. Nine patients with a variety of burn injuries had images taken of their acute burns within 48 hours of injury, both with a noncontact SIAscope and a laser Doppler perfusion imaging system (LDPI). Results showed that superficial partial thickness burns had increased hemoglobin and loss of melanin on SIAgraphs, whereas deep partial thickness burns had more pronounced hemoglobin concentrations and apparent melanin increases, helping to differentiate these 2 burn types. The SIAscope, a relatively inexpensive, portable device, has the potential to be a highly useful clinical adjunct in the bedside estimation of acute burn depth.

Straylight after cataract operation

Abstract Purpose: To measure intraocular straylight in patients with pseudophakia and to compare the results with those of patients in a large population sample without eye diseases and with different signs of cataract. Methods: In a large prospective European study with five participating eye clinics a total of 2211 active drivers, 45 years of age and older, were included. The examination included a complete ophthalmological evaluation with multiple visual function tests and the measurement of intraocular straylight with a newly developed system. Lens opacities were classified with the LOCS III lens classification system. Results: Increasing density of lens opacification was significantly related to increased straylight values. This resulted in a modified behavior regarding the patients driving habits.Unexpectedly, patients with bilateral pseudophakia showed similar straylight values as those that were classified as having bilateral moderate cataract. Mean age of the pseudophakic patient group was similar to subjects with more severe forms of cataract. Conclusions: Following cataract surgery and implantation of a clear artificial lens, one would expect intraocular straylight to be significantly lower that in the control population with moderate cataract. This was not the case in this large series of patients, however.Several causes may be considered relevant for this observation:First pseudophakia‐related changes, such as untreated posterior capsular fibrosis and, possibly IOL decentration, have to be considered.Secondly increasing straylight values with age that are not only lenticular of origin, but also a consequence of age‐related pigmentary changes such as migration and thinning of uveal pigment from the iris, increasing vitreal opacities and loss of melanin within the retinal pigment epithelium itself.

Significance of a basal melanin layer to production of non-iridescent structural plumage color: evidence from an amelanotic Steller's jay(Cyanocitta stelleri)

Non-iridescent structural plumage color is typically produced by coherent scattering of light within a matrix of keratin and air (a ;spongy layer') in feather barbs. It remains unclear what role, if any, the basal melanin layer underlying this spongy layer plays in the production of coloration. Amelanism in birds with structural color is a ;natural experiment' in which melanin pigmentation is lost, allowing us to identify the effects of the loss of melanin on structural color production. Here we use full-spectrum spectrometry, transmission electron microscopy and Fourier analysis to compare the color and nanostructure of an amelanotic Steller's jay (Cyanocitta stelleri Gmelin) feather with a normal blue Steller's jay feather. As a control, we also examined a white domestic chicken (Gallus gallus Linnaeus) feather. The pale amelanotic jay feather had a broad reflectance curve with a blue/green peak, while the typical blue feather had a typical distinct bell-shaped blue curve with a UV/violet peak. The white chicken feather had a typical white reflectance curve with no discrete peaks. Electron microscopy revealed that both the amelanotic and blue feather barbs contained well-formed spongy layers that were of the correct size and arrangement to produce their measured peak reflectance values, whereas the chicken feather had no spongy layer. The washed-out color of the amelanotic jay feather was thus most probably caused by the loss of the basal melanin layer, suggesting that melanin functions to absorb incoherently scattered white light from the feather barb thereby increasing the purity of the color produced by the spongy layer.

Late-Onset Leanness in Mice with Targeted Ablation of Melanin Concentrating Hormone Neurons

The observation that loss of orexin (hypocretin) neurons causes human narcolepsy raises the possibility that other acquired disorders might also result from loss of hypothalamic neurons. To test this possibility for body weight, mice with selective loss of melanin concentrating hormone (MCH) neurons were generated. MCH was chosen to test because induced mutations of the MCH gene in mice cause hypophagia and leanness. Mice with ablation of MCH neurons were generated using toxin (ataxin-3)-mediated ablation strategy. The mice appeared normal but, after 7 weeks, developed reduced body weight, body length, fat mass, lean mass, and leptin levels. Leanness was characterized by hypophagia and increased energy expenditure. To study the role of MCH neurons on obesity secondary to leptin deficiency, we generated mice deficient in both ob gene product (leptin) and MCH neurons. Absence of MCH neurons in ob/ob mice improved obesity, diabetes, and hepatic steatosis, suggesting that MCH neurons are important mediators of the response to leptin deficiency. These data show that loss of MCH neurons can lead to an acquired leanness. This has implications for the pathogenesis of acquired changes of body weight and might be considered in clinical settings characterized by substantial weight changes later in life.

Loss of melanin from human RPE with aging: possible role of melanin photooxidation

The pigment melanin, which is believed to play a photoprotective role, was quantified here in human RPE cells from donors of different age. Electron spin resonance (ESR) spectroscopy was shown to provide a quantitative measure of melanin and was used as a non-destructive measure of melanin content. Results indicated an age-related melanin loss in RPE cells, with melanin content diminishing 2·5-fold between the first and the ninth decade of life. To determine whether photo-oxidation may contribute to age-related changes in RPE melanin, RPE in human eyecups, isolated human and bovine RPE cells, purified melanin granules, or synthetic dopa melanin were irradiated with various wavelengths and intensities of visible light. Samples were analysed for changes in melanin content by ESR spectroscopy, and by absorption and emission spectrophotometry. The concentration of hydrogen peroxide was measured in some samples, and some human eyecups were examined by transmission electron microscopy. Irradiation of RPE in eyecups with intense visible light was found to produce a time-dependent photobleaching of melanosomes that was accompanied by the formation of hydrogen peroxide. Photobleaching of isolated RPE melanosomes and synthetic dopa melanin resulted in enhanced melanin fluorescence, as previously shown for melanin from aged donors by others, and significantly reduced ESR signal intensity, resembling the changes in melanin with aging observed here. We conclude that the content of melanin in RPE cells undergoes an age-related change to which photo-oxidation may contribute. This observation raises the question of whether age-related changes in melanin reduce the photoprotective role of the pigment in aging RPE cells.

Influence of Tyrosinase Levels on Pigment Accumulation in the Retinal Pigment Epithelium and on the Uncrossed Retinal Projection

To study the relationship among tyrosinase activity, melanin production, and the routing of retinal ganglion cell (RGC) axons at the optic chiasm, we analysed mice with varying doses of the tyrosinase gene. These include the dark-eyed albino (Tyrc44H), a radiation-induced hypomorphic allele of tyrosinase; and transgenic mice carrying 1 or 2 alleles of a tyrosinase minigene on both wild-type (Tyr+) and albino (Tyrc) backgrounds. Melanization of the retinal pigment epithelium (RPE) occurred gradually even at <2% wild-type tyrosinase activity and was sensitive to tyrosinase activity up to <35% of wild-type levels, beyond which melanin synthesis appeared to be saturated. Overexpression of tyrosinase led to tyrosinase activity above wild type level, but did not increase melanin production. Although a loss of melanin because of a mutation in tyrosinase is associated with a decrease in the number of uncrossed fibers, elevating tyrosinase levels does not appear to cause an increase in the size of the uncrossed retinal projection. Our results suggest that replacing less than 35% of wild-type tyrosinase activity is sufficient to restore normal pigmentation of the RPE, and potentially, to allay visual defects.

Parasite-Associated Phenotype Modifications in Threespine Stickleback

The threespine stickleback fish, Gasterosteus aculeatus, is parasitized by the tapeworm Schistocephalus solidus in freshwater habitats. The competency of the parasite to infect a definitive host, one of many piscivorous birds, is associated with behavioral changes in parasitized stickleback that are likely to increase the chance of transmission to a definitive host. Over a limited geographical range, large tapeworm size is also associated with demelanization, a phenotypic change in the stickleback host that involves a dramatic loss of melanin in the skin and, simultaneously, a darkening of the eye. We demonstrate that stickleback harboring a worm large enough to be infective to a definitive host exhibit behavioral shifts likely to enhance transmission, but that these changes are substantially magnified in demelanized individuals, all of which were infected by large tapeworms. The results were similar whether we used a model of a bird flown over an aquarium, or a preserved trout moved to simulate attack under field conditions. Because changes in the levels of response to both kinds of predators were similar, we infer that behavioral modifications that enhance susceptibility to visually hunting predators that are definitive hosts also enhance susceptibility to visually hunting predators (e.g. trout) that are not. In lakes where predatory fishes are common, the impact on S. solidus transmission could be substantial. Although other studies have suggested that positive buoyancy, forcing infected fish to remain near the surface, is one cause of these behavioral shifts, we detected no differences in water column position among unparasitized and parasitized classes of stickleback. Instead, infected stickleback appeared to move sluggishly and were less likely to respond to simulated attacks than were uninfected fish, and the behavioral shift was most dramatic in demelanized stickleback.

Vitiligo in Two Water Buffaloes: Histological, Histochemical, and Ultrastructural Investigations

Vitiligo, a skin disease, characterized by the spontaneous loss of melanin, has been described in several animals as well as in humans. Most of the reports of large domestic animals have dealt with clinical investigations without morphological data. In this report, the histological and ultrastructural characteristics of two cases of vitiligo in water buffaloes (Bubalus bubalis) are presented. Interestingly, many of the ultrastructural observations for vitiliginous buffaloes resemble those previously described for other species, e.g., humans, mouse, and chicken. These data suggest that one or more forms of human vitiligo may have a similar etiopathogenesis to that of the buffalo. Therefore, it is proposed that vitiliginous buffalo may prove to be a useful animal model for the human disease.