SynopsisSince ancient times, human beings have been trying to protect their skin against the adverse effects of the sun. From the first mineral sunscreens used by Egyptians, to the current more sophisticated ultraviolet (UVA/UVB) organic sunscreens, progress has been made in terms of sun protection and deeper knowledge of skin physiology has been acquired in the process. The solar spectrum is composed of radiations of various wavelengths having specific, as well as overlapping effects on skin. UVB is mainly responsible for sunburn and DNA dimer formation that can lead to mutation. UVA generates oxidative reactions affecting DNA, proteins and lipids, and is also immunosuppressive. Recently, visible light and infrared radiation (IR) have been associated with oxidative damage and IR has been additionally linked to adverse heat effects on skin. Numerous other extrinsic factors, related to environment and lifestyle, also affect the appearance of skin, precipitating ageing. New molecular mechanisms linking sun and environmental factors to skin ageing have been identified: IR affects mitochondrial integrity and specific heat receptors also mediate some of its effects, tryptophan is a chromophore for UVB, and the aryl hydrocarbon receptor (AhR) is activated by light and xenobiotics to alter skin physiology. Integrating all these new elements is changing the way we think about skin extrinsic ageing. Is UVA/UVB sunscreen protection still enough for our skin?R esum e Depuis les temps anciens, lesêtres humains ont essay e de prot eger leur peau contre les effets n efastes du soleil. Depuis les ecrans minraux d'abord utilis es par les Egyptiens, aux filtres solaires organiques sophistiqu es actuels (UVA/UVB), des progr es ont et e r ealis es en termes de protection contre le soleil, et une connaissance approfondie de la physiologie cutan ee a et e acquise durant ce temps. Le spectre solaire est compos e de radiations de longueurs d'onde diff erentes poss edant des effets sp ecifiques, ainsi que des effets redondants sur la peau. Les UVB sont les principaux responsables des coups de soleil et de la formation de dim eres d'ADN qui peuvent conduire a une mutation. Les UVA g en erent des r eactions d'oxydation qui affectent l'ADN, des prot eines, et les lipides, et agissent egalement comme immunosuppresseur. R ecemment, les rayonnements de la lumi ere visible et de l'infrarouge (IR) ont et e associ es a des dommages oxydatifs, et l'IR a et e en outre li e a des effets ind esirables de la chaleur sur la peau. De nombreux autres facteurs extrins eques li es a l'environnement et au mode de vie affectent aussi l'aspect de la peau, acc el erant le vieillissement. De nouveaux m ecanismes mol eculaires reliant le soleil et les facteurs environnementaux au vieillissement de la peau ont et e identifi es: l'IR affecte l'int egrit e mitochondriale; des r ecepteurs thermiques sp ecifiques servent egalement de m ediateur de certains de ses effets; le tryptophane est un chromophore UVB; le r ecepteur d'hydrocarbures aryles (AhR) est activ e p...

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyzes biosynthesis of progesterone (P) and all precursors of glucocorticoids, mineralocorticoids, androgens, and estrogens. Despite the broad interest raised by neurosteroids, the cellular localization of 3 beta-HSD has never been investigated in the brain. We took advantage of the availability of an antiserum raised against human placental 3 beta-HSD to determine the distribution of 3 beta-HSD-immunoreactive structures in the brain of the frog Rana ridibunda by the indirect immunofluorescence technique. Three populations of 3 beta-HSD-immunoreactive cell bodies were observed in the hypothalamus, namely, in the rostral region of the preoptic nucleus, the dorsal infundibular nucleus, and the dorsal part of the ventral infundibular nucleus. A dense network of 3 beta-HSD-immunoreactive nerve fibers was visualized in the dorsal area of the diencephalon, that is, in the lateral neuropil, the corpus geniculatus lateralis, and the nucleus posterolateralis thalami. Reversed-phase HPLC analysis of frog hypothalamic extracts combined with RIA detection showed the presence of substantial amounts of immunoreactive steroids coeluting with P and 17-hydroxyprogesterone (17OH-P). The synthesis of delta 4-3-keto-steroids in the frog hypothalamus was investigated using the pulse-chase technique with 3H-pregnenolone (3H-delta 5P) as a precursor. The formation of five tritiated metabolites of 3H-delta 5P was observed, one of which coeluted with 17OH-P. Conversion of 3H-delta 5P into this radioactive metabolite was significantly reduced by trilostane, a specific inhibitor of 3 beta-HSD. Immunodetection of newly synthesized steroids in HPLC fractions of hypothalamic extracts, using 17OH-P antibodies, revealed the existence of an immunoreactive steroid that exhibited the same retention time as synthetic 17OH-P. The present study provides the first immunocytochemical mapping of 3 beta-HSD, a key enzyme of the steroid biosynthetic pathway, in the CNS of a vertebrate. The data also demonstrate for the first time biosynthesis of neurosteroids in the brain of a nonmammalian vertebrate.

, T. bergoT, T. elias, r. Tardif, d. Carrer, P. CHazeTTe, M. ColoMb, P. drobinski, e. duPonT, J.-C. duPonT, l. goMes, l. Musson-genon, C. PieTras, a. Plana-faTTori, a. ProTaT, J. rangognio, J.-C. rauT, s. réMy, d. riCHard, J. sCiare, and X. zHang A field experiment covering more than 100 fog and near-fog situations during the winter of 2006-07 investigated the dynamical, microphysical, and radiative processes that drive the life cycle of fog.

The fine modulation of gonadotropin gene expression and secretion is well recognized to be regulated by sex steroids through their direct action both at the anterior pituitary level and on the pulsatile pattern of GnRH secretion at the hypothalamic level. Since the influence of sex steroids on hypothalamic GnRH mRNA levels remains to be elucidated, quantitative in situ hybridization was used to study the effect of sex steroids on cellular levels of pro-GnRH mRNA in adult rats of both sexes. The effects of 14-day gonadectomy as well as administration of 17 beta-estradiol (E2, 0.25 micrograms) or dihydrotestosterone (DHT, 100 micrograms) twice a day during 14 days to gonadectomized animals were evaluated. In addition, the effect of progesterone (P, 2 mg, twice daily) alone or in the presence of E2 was also studied in ovariectomized animals. Hybridization was performed using a 35S-labeled cDNA probe encoding rat pro-GnRH and the corresponding mRNA levels were assessed by counting the number of silver grains overlying labeled neurons. In male rats, castration induced a highly significant 65% increase (compared to intact rats) in the mean number of grains per neuron. Administration of E2 or DHT to castrated animals completely prevented the post castration rise in pro-GnRH mRNA levels. In female animals, the effect of ovariectomy was less striking than in the male, a 25% increase (P less than 0.001) being observed. Treatment with E2 or DHT also completely prevented the increase in pro-GnRH mRNA levels induced by ovariectomy. Moreover, treatment with P in ovariectomized animals markedly potentiated the inhibitory effect of E2 on pro-GnRH mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)