Sleep & metabolism: The multitasking ability of lateral hypothalamic inhibitory circuitries

The anatomical and functional mapping of lateral hypothalamic circuits has been limited by the numerous cell types and complex, yet unclear, connectivity. Recent advances in functional dissection of input-output neurons in the lateral hypothalamus have identified subset of inhibitory cells as crucial modulators of both sleep-wake states and metabolism. Here, we summarize these recent studies and discuss the multi-tasking functions of hypothalamic circuitries in integrating sleep and metabolism in the mammalian brain.     

Melanin in the inner ear

Summary Following several studies on the effects of kanamycin toxicity on the inner ears of guinea pigs, we have studied the importance of melanin in this phenomenon. Transmission electron microscopy showed that, under the influence of kanamycin, the intermediate strial cells developed a secretory aspect similar to that seen in skin melanocytes. This aspect as yet has never been described for the inner ear cells. A planimetric, morphometric method was also used to determine the strial cell melanin status in control animals. Additional findings in the study confirmed an increase in the number of melanosomes during kanamycin poisoning. Statistical data are discussed.Presented at the First European Congress of Oto-Rhino-Laryngology and Cervico-Facial Surgery, Paris, 26–29 September 1988     

Melanin in the rat brain

Melanin was measured in various parts of the rat brain by a spectrophotofluorometric assay. This method could detect natural, Sepia melanin as well as melanin synthesized from L-DOPA. Contrary to published expectations of other investigators, measurable amounts of melanin were found in the brain of albino as well as pigmented rats. The highest concentrations of melanin occurred in the pons-medulla and midbrain, but all regions within the blood-brain barrier contained greater concentrations than samples from many other tissues in the body. No significant change in the melanin content was found after various endocrine manipulations such as removal of the pituitary, pineal, adrenals, thyroid, testes, or ovaries, exposure to constant illumination or darkness, and daily injection for 5 weeks of alpha-MSH, Pro-Leu-Gly-NH2 (MIF-I) or melatonin. As expected, retinal tissue from black-hooded rats contained extremely high levels of melanin whereas that from albino rats contained no melanin. It is thought that the presence of melanin in the brain of albino and pigmented rats may have a function which is still unknown.     

Effect of selenium compounds on murine B16 melanoma cells and pigmented cloned pB16 cells

The effects of selenium compounds such as sodium selenite, sodium selenate, seleno-Dl-cystine and seleno-Dl-methionine (100 μM and 10 μM) on B16 and pigmented cloned pB16 murine melanoma cells were investigated in vitro. At the tested concentrations, B16 cells showed a greater sensitivity to the toxic effects of sodium selenite and seleno-Dl-cystine than pB16 cells, whereas no decrease of B16 and pB16 cell number was observed after incubation with sodium selenate or seleno-Dl-methionine. Glutathione (GSH) percentages were strongly decreased only by selenite and seleno-Dl-cystine; it was marked more in B16 than in pB16 cells. The pretreatment of B16 cells with a GSH depleting agent (10 μM buthionine-[S,R]-sulfoximine) did not significantly influence the cytotoxic effects of selenite and seleno-Dl-cystine. On both cell populations, GSH preincubation (50 μM) enhanced the cytotoxicity of selenite whereas the survival of seleno-Dl-cystine treated cells was increased. Glutathione peroxidase (GSH-Px) activity in B16 cells was more sensitive than in pB16 cells to the activating effect of selenite, and particularly of seleno-Dl-cystine; however, cell-free controls indicated that activation was mainly due to glutathione reductase. The rate of⁷⁵Se (as sodium selenite) uptake in both cell populations was maximal within the first hour of incubation, with a preferential accumulation in the cytosol; after 24 h of incubation, the amount of⁷⁵Se in cytosol and pellet was approximately the same. Gel filtration chromatography of lysed cells after incubation for 6 h with 10 μM⁷⁵Se-selenite showed that the radioactivity was eluted as two peaks corresponding to low (4–9 kDa) and high (280–320 kDa) molecular weights. Possible toxicological mechanisms are discussed at molecular level. For selenite, a major involvement of GSH is proposed, with production of selenodiglutathione and selenopersulfide, which should be directly responsible of the decrease in cell number, thiol oxidation and protein synthesis inhibition. For selenocystine, an active selenol species (Cy-Se⁻) is also hypothesized as being responsible for thiol oxidation and mutagenic effects. For both compounds oxygen active species could also be formed; however, a relevant role of GSH-Px was not apparent. The minor sensitivity of pB16 cells to the toxic effects of selenite and seleno-Dl-cystine could be explained by the smaller depletion of GSH induced by those compounds in pB16 cells, a minor formation of selenium active species, the larger amount present of the oxyradical scavenger melanin, the secretion of some mitogenic factor by pB16 cells and/or a greater resistance to autocrine cytotoxic factors.     

Cryosurgical depigmentation of the gingiva

Gingival melanin pigmentation (GMP) occurs in all races of man. Although clinical melanin pigmentation does not present a medical problem, demand for cosmetic therapy is commonly made by fair-skinned people with moderate GMP. The present study was undertaken to test the effectiveness of cryosurgical destruction of the gingival epithelium in the removal of gingival melanin pigmentation. The patient was a fair-skinned Ashkenazi Jew with moderate GMP who demanded any possible "cosmetic therapy" which would convert her "black gums" to "normal". Gingival cryosurgery was carried out by segments. A gas expansion cryoprobe cooled to -81 degrees C was applied to the gingiva for 10 s. Frozen sites thawed spontaneously within 1 min. Superficial necrosis became apparent within a week. Treated sites were covered by epithelium within 2 weeks following freezing and keratinization was completed after 3-4 weeks. The treated gingiva appeared normal and remained depigmented until the present time, 20 months following freezing. It is concluded that cryosurgery may prove to be the treatment of choice when gingival depigmentation is indicated.     

Melanin in the trabecular meshwork is associated with age, POAG but not Latanoprost treatment. A masked morphometric study

We wished to conduct a light and electron microscopic investigation of pigmentation within the trabecular meshwork of normals and primary open angle glaucoma (POAG) patients. In particular we wished to get a precise determination of whether there was a relationship between pigmentation and age. In addition we wanted to know if there was a difference between normals and POAGs and whether trabecular meshwork hyperpigmentation was associated with topical latanoprost medication. A total of 25 sham trabeculectomies conducted on post mortem donor eyes provided the age-matched normals and there were 62 trabeculectomy specimens from POAG patients. These were masked and the meshwork subjected to qualitative and quantitative morphological investigation. Light and electron microscopy confirmed that most of the trabecular meshwork melanin was phagocytosed and within meshwork cells. The granules were measured and found to be of the large iris epithelial type. Light microscopic morphometric analysis showed that the number of meshwork cell profiles that contained melanin increased both in normals and POAGs with age. However there was nearly three times more pigmented meshwork cells in the POAGs than the normals. The POAGs were divided into three groups of (1) minimal or no medication prior to surgery, (2) maximal medical therapy and (3) maximum medical therapy including latanoprost (12 specimens). All groups were significantly greater that the normals but of the three it was the maximal medical therapy group (without latanoprost) that had the highest pigmentation. We concluded that pigmentation of the meshwork is age-related and it is elevated in POAG by mechanisms unknown. The melanin accumulation seems to be partly due to the disease process, partly as a consequence of chronic antiglaucoma medication but interestingly not due to latanoprost even in patients where there is iris darkening (four specimens).     

A study of skin color by melanin index according to site, gestational age, birth weight and season of birth in Korean neonates

Human skin color shows variations throughout life and influenced by various factors such as race, sex, age and hormones. Since the development of spectrophotometer, many studies on human skin color have been done. However, few studies have been carried out to measure the skin color of neonatal infants. The aim of our study was to assess the variations in skin color according to site, gestational age, birth weight and season of birth in Korean neonates. A total of 447 healthy neonates (3 days after birth, 213 males and 234 females) were enrolled in the present study. Skin pigmentation was measured by reflectance spectrophotometer (Derma-Spectrophotometer, Cortex technology, Hadsund, Denmark) at four different sites (forehead, upper arm, abdomen, and inguinal area). The forehead showed highest melanin index in all sites measured (p<0.05). There was no significant difference according to gestational age, birth weight, and season of birth. This result imply that the skin color in neonates is mainly determined genetically.     

Ein bisher kaum bekanntes gliogenes Melanin des Gehirns („Cerebellares Gliamelanin“)

Summary Melanosis of the dentate nucleus is an extremely rare condition in which pigment is formed within the cytoplasm and cytoplasmic processes of astrocytes in the dentate nucleus and the cerebellar granular cell layer. The pigment occurs as irregular polygonal structures of rather homogeneous appearance unlike granular neuromelanin located within neurons of the substantia nigra. The diameter of these pigment masses may reach 30 m or more. Their absorption of visible light increases steadily towards the shorter wavelengths, and the material is virtually opaque in the violet and ultraviolet region, resembling melanin in this respect. Since the absorption spectrum described by Rabl exhibited a small peak at 525 nm, he regarded the pigment as the hemoglobin derivative pentdyopent. We were unable, however, to confirm this observation. On X-ray diffraction the pigment produced a sharp reflex at 4.93 å as did synthetic melanin prepared from dopamine (but not melanin prepared from serotonin). These observations supported the assumption made by others based on histochemical evidence, that the pigment in the dentate nucleus may belong to the group of melanins. Presumably the glial melanin somehow arises from the metabolic pathway leading to DOPA. An astrocytic site of melanin formation other than in the cerebellum has not been previously described, and this melanin differs in appearance from the granular neuromelanin found in neurons in the substantia nigra. Thus cerebellar glial melanin contrasts with neuromelanin of the substantia nigra both in its site of formation and in its morphology.The underlying cause of the glial melanin formation in the cerebellum is not known. There are six cases in the world literature, 5 females and 1 male, ranging in age from 58 to 103 years.Involutional alterations in metabolism related to endocrine factors may possibly play an important part. To the best of our knowledge cerebellar melanosis is of no clinical relevance.

     

Ultrastructural characterization of the distribution of melanin and epidermal macrophages in photodamaged skin

We examined the characteristics of melanin distribution, the possible mechanisms underlying the histological incontinence of pigment, and the significance of epidermal macrophages in photodamaged skin. We used electron microscopy to compare and quantitate melanin distribution in various types of cells and structures, to qualitatively observe associations of melanin granules with melanophages, and to examine morphological differences of epidermal macrophages in sun-exposed versus sun-protected facial skin. Melanin-containing cells (such as Langerhans cells) and melanin-containing structures (such as colloid bodies) in photodamaged skin were more numerous than in sun-protected skin, in proportion to differences in melanocyte density and in epidermal melanin content. Although the precise mechanism(s) of histological incontinence of pigment in photoaging skin appear to be very complicated, it is certainly one of the morphological hallmarks of photodamaged facial skin, and the degeneration of keratinocytes (noted by their electron-lucent properties), a feature characteristic of photoaging, contributes to that process. Furthermore, the increased numbers of epidermal macrophages in sun-exposed skin may be associated with photoaging processes (probably through their phagocytic function) as well as alterations of the cutaneous immune system.     

Melanocytic Schwa n no ma in the Spinal Canal

A case of melanocytic schwannoma, a rare form of schwannian neoplasm, in the thoracolumbar spinal canal of a 52-year-old man is presented. Histopathologically, the tumor was composed of irregularly interlacing spindle-shaped cells showing cystic degeneration, with occasional pigmented tumor cells. The tumor cells showed a low degree of nuclear pleomorphism without any mitotic figures. These histological features were considered to be consistent with a benign schwannian tumor showing pigmentation. Most of the pigments were considered to be melanin histochemically and immunohistochemically. According to the pathological features of the present tumor and those described previously in the literature, the neoplastic Schwann cells were assumed to have melanogenetic capacity, and the concept of the common neural crest origin of Schwann cells and melanocytes appeared to be demonstrated in the present tumor. Acta Pathol Jpn 41: 685–688, 1991.