Dual nature of Leydig cells of the human testis

This review is devoted to the human Leydig cell, and systematizes published and own unpublished results from studies performed during the last decade. Leydig cells are the main cell type in the testis that produce androgens which are important for the development of the male genital organs, secondary sex characteristics and behavior as well as for the processing and maintenance of spermatogenesis. A lot of information accumulated provides evidence that Leydig cells of the human testis and the testis of some other species express or possess immunoreactivities for numerous marker substances characteristic for nerve and neuroendocrine cells. It is shown that human Leydig cells, beside of markers for steroidogenic activity, possess: neuronal markers, synaptic and storage vesicle proteins, neural cytoskeletal proteins, 5-hydroxytryptamine, enzymes involved in the synthesis of catecholamines, neurohormones and/or their receptors, neuropeptides, calcium-binding proteins, cell adhesion molecules, glial cell antigens, components of the nitric oxide/cyclic guanosine monophosphate system, components of the renin/angiotensin system, and numerous growth factors and their receptors. These results provide new evidence for the neuroendocrine nature of Leydig cells. As consequence, two main questions arise: (i) the origin of Leydig cells and (ii) their functional significance as neuroendocrine cells. The presumption that Leydig cells originate from mesenchymal-like cells of the mesonephros is the most common view in the literature. However, no data are provided concerning the origin of the stem cells from which the Leydig cell lineage develops. Mesenchyme comprises the embryonic connective tissue cells that may have mesodermal, ectodermal and neuroectodermal (neural crest) origin. In this relation and based on the recently established neuroendocrine feature, we speculate that Leydig stem cells may detach from unknown regions of the neural crest and migrate to the mesonephric and gonadal anlage at early stages of development. The functional significance of Leydig cells as neuroendocrine cells is also illustrated on the basis of the nitric oxide/cyclic guanosine monophosphate system. Accordingly, Leydig cells may regulate their steroidogenic activity by an intracrine or autocrine fashion. Furthermore, they are probably able to synchronize the activity of the cells in a Leydig cell cluster by a paracrine way. Leydig cells may influence the contractile activity of the smooth muscle cells of blood vessels, thus regulating the blood flow rate and the permeability for hormones and nutritive substances. Also, Leydig cells may regulate the contractile state of peritubular myofibroblasts and myofibroblasts and smooth muscle cells of the tunica albuginea. Similarly, Leydig cells may communicate with Sertoli cells and germ cells of the seminiferous tubules. Leydig cells are a relatively stable, heterogeneous population of cells in the human testis which persists even in cases of impaired spermatogenesis, fibrosis and different pathological changes of the testis. This fact suggests that Leydig cells survive under unusual conditions due to precise regulatory systems which make them to a larger extent independent from the local homeostasis.Biomedical Reviews 1996; 6: 11-41

Silicon nanoparticles and interstellar extinction

To examine a recently proposed hypothesis that silicon nanoparticles are the source of extended red emission (ERE) in the interstellar medium, we performed a detailed modeling of the mean Galactic extinction in the presence of silicon nanoparticles. For this goal we used the appropriate optical constants of nanosized Si, essentially different from those of bulk Si due to quantum confinement. It was found that a dust mixture of silicon nanoparticles, bare graphite grains, silicate core-organic refractory mantle grains and three-layer silicate-water ice-organic refractory grains works well in explaining the extinction and, in addition, results in the acceptable fractions of UV/visible photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions barely agree with the fraction of UV/visible photons needed to excite the observed ERE, we conclude that the intrinsic photon conversion efficiency of the photoluminescence by silicon nanoparticles must be near 100%, if they are the source of the ERE.Comment: Latex2e, uses emulateapj.sty (included), multicol.sty, epsf.sty, 6 pages, 3 figures (8 Postscript files), accepted for publication in ApJ Letters, complete Postscript file is also available at http://physics.technion.ac.il/~zubko/eb.html#SNP

The 3D Geometry of Reflection Nebulae IC 59 and IC 63 with their illuminating Star Gamma Cas

The early-type star $\gamma$ Cas illuminates the reflection nebulae IC 59 and IC 63, creating two photo-dissociation regions (PDRs). Uncertainties about the distances to the nebulae and the resulting uncertainty about the density of the radiation fields incident on their surfaces have hampered the study of these PDRs during the past three decades. We employed far-UV -- optical nebula -- star colour differences of dust-scattered light to infer the locations of the nebulae relative to the plane of the sky containing $\gamma$ Cas, finding IC 63 to be positioned behind the star and IC 59 in front of the star. To obtain the linear distances of the nebulae relative to $\gamma$ Cas, we fit far-infrared archival $\textit{Herschel}$ flux data for IC 59 and IC 63 with modified blackbody (MBB) curves and relate the resulting dust temperatures with the luminosity of $\gamma$ Cas, yielding approximate distances of 4.15 pc for IC 59 and 2.3 pc for IC 63. With these distances, using updated far-UV flux data in the 6 eV - 13.6 eV range for $\gamma$ Cas with two recent determinations of the interstellar extinction for $\gamma$ Cas, we estimate that the far-UV radiation density at the surface of IC 63 takes on values of $G_0$ = 58 or $G_0$ = 38 with respective values for E(B-V) for $\gamma$ Cas of 0.08 and 0.04 mag. This is a substantial reduction from the range 150 $\le$ $G_0$ $\le$ 650 used for IC 63 during the past three decades. The corresponding, even lower new values for IC 59 are $G_0$ = 18 and $G_0$ = 12.Comment: Accepted for publication on January 4th, 2024 by the Monthly Notices of the Royal Astronomical Societ

Benefits of repeated book readings in children with SLI

In this pilot study, we ask whether repeated storybook reading is also beneficial for word learning in children diagnosed with specific language impairment (SLI). We compared 3-year-old German learning children diagnosed with SLI to typically developing children matched on age and socioeconomic status (SES). One week later, children with SLI retained the target words from the stories just as well as their peers, although they did perform significantly worse on immediate recall