Melatonin inhibits GnRH-1, GnRH-3 and GnRH receptor expression in the brain of the European Sea Bass, Dicentrarchus labrax

Several evidences supported the existence of melatonin effects on reproductive system in fish. In order to investigate whether melatonin is involved in the modulation of GnRH systems in the European sea bass, we have injected melatonin (0.5 μg/g body mass) in male specimens. The brain mRNA transcript levels of the three GnRH forms and the five GnRH receptors present in this species were determined by real time quantitative PCR. Our findings revealed day–night variations in the brain expression of GnRH-1, GnRH-3 and several GnRH receptors (dlGnRHR-II-1c, -2a), which exhibited higher transcript levels at mid-light compared to mid-dark phase of the photocycle. Moreover, an inhibitory effect of melatonin on the nocturnal expression of GnRH-1, GnRH-3, and GnRH receptors subtypes 1c, 2a and 2b was also demonstrated. Interestingly, the inhibitory effect of melatonin affected the expression of hypophysiotrophic GnRH forms and GnRH receptors that exhibit day–night fluctuations, suggesting that exogenous melatonin reinforce physiological mechanisms already established. These interactions between melatoninergic and GnRH systems could be mediating photoperiod effects on reproductive and other rhythmic physiological events in the European sea bass.

Experimental demonstration of tomographic slit technique for measurement of arbitrary intensity profiles of light beams

We demonstrate experimentally an optical imaging method that makes use of a slit to collect tomographic projection data of arbitrarily shaped light beams; a tomographic backprojection algorithm is then used to reconstruct the intensity profiles of these beams. Two different implementations of the method are presented. In one, a single slit is scanned and rotated in front of the laser beam. In the other, the sides of a polygonal slit, which is linearly displaced in a x-y plane perpendicular to the beam, are used to collect the data. This latter version is more suitable than the other for adaptation at micrometer-size scale. A mathematical justification is given here for the superior performance against laser-power fluctuations of the tomographic slit technique compared with the better-known tomographic knife-edge technique.

Ballistic, diffusive, and localized transport in surface-disordered systems: two-mode waveguide

This paper presents an analytical study of the coexistence of different transport regimes in quasi-one-dimensional surface-disordered waveguides (or electron conductors). To elucidate main features of surface scattering, the case of two open modes (channels) is considered in great detail. Main attention is paid to the transmission in dependence on various parameters of the model with two types of rough-surface profiles (symmetric and antisymmetric). It is shown that depending on the symmetry, basic mechanisms of scattering can be either enhanced or suppressed. As a consequence, different transport regimes can be realized. Specifically, in the two-mode waveguide with symmetric rough boundaries, there are ballistic, localized and coexistence transport regimes. In the waveguide with antisymmetric roughness of lateral walls, another regime of the diffusive transport can arise. Our study allows to reveal the interplay between all relevant scattering mechanisms, in particular, the role of the so-called square-gradient scattering which is typically neglected in literature, however, can give a strong impact to the transmission.

Discrimination between two mechanisms of surface scattering in a single-mode waveguide

Transport properties of a single-mode waveguide with rough boundary are studied by discrimination between two mechanisms of surface scattering, the amplitude and square-gradient ones. Although these mechanisms are generically mixed, we show that for some profiles they can separately operate within nonoverlapping intervals of wave numbers of scattering waves. This effect may be important in realistic situations due to inevitable long-range correlations in scattering profiles.