During the past decade, possible advancement in timing of puberty has been reported in the United States. In addition, early pubertal development and an increased incidence of sexual precocity have been noticed in children, primarily girls, migrating for foreign adoption in several Western European countries. These observations are raising the issues of current differences and secular trends in timing of puberty in relation to ethnic, geographical, and socioeconomic background. None of these factors provide an unequivocal explanation for the earlier onset of puberty seen in the United States. In the formerly deprived migrating children, refeeding and catch-up growth may prime maturation. However, precocious puberty is seen also in some nondeprived migrating children. Attention has been paid to the changing milieu after migration, and recently, the possible role of endocrine- disrupting chemicals from the environment has been considered. These observations urge further study of the onset of puberty as a possible sensitive and early marker of the interactions between environmental conditions and genetic susceptibility that can influence physiological and pathological processes.

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Abstract. In this article a series of results concerning Yang-Mills fields over the euclidean sphere and other locally homogeneous spaces are proved using differential geometric methods. One of our main results is to prove that any weakly stable Yang-Mills field over S ~ with group G = SU 2, SU 3 or U 2 is either self-dual or anti-self-dual. The analogous statement for SO~-bundles is also proved. The other main series of results concerns gap-phenomena for YangMills fields. As a consequence of the non-linearity of the Yang-Mills equations, we can give explicit C°-neighbourhoods of the minimal Yang-Mills fields which contain no other Yang-Mills fields. In this part of the study the nature of the group G does not matter, neither is the dimension of the base manifold constrained to be four.

In this article a geometric process to compare spinors for different metrics is constructed. It makes possible the extension to spinor fields of a variant of the Lie derivative (called the metric Lie derivative), giving a geometric approach to a construction originally due to Yvette Kosmann. The comparison of spinor fields for two different Riemannian metrics makes the study of the variation of Dirac operators feasible. For this it is crucial to take into account the fact that the bundle in which the sections acted upon by the Dirac operators take their values is changing. We also give the formulas for the change in the eigenvalues of the Dirac operator. We conclude by giving a few cases in which an eigenvalue is stationary.

Based on these observations, we hypothesize that gonadoblastomas originate from surviving OCT3/4-positive germ cells in areas of undifferentiated gonadal tissue within the dysgenetic gonad. Supportive evidence was obtained that carcinoma in situ arises in regions with testicular differentiation.

Puberty presents remarkable individual differences in timing reaching over 5 years in humans. We put emphasis on the two edges of the age distribution of pubertal signs in humans and point to an extended distribution towards earliness for initial pubertal stages and towards lateness for final pubertal stages. Such distortion of distribution is a recent phenomenon. This suggests changing environmental influences including the possible role of nutrition, stress and endocrine disruptors. Our ability to assess neuroendocrine effects and mechanisms is very limited in humans. Using the rodent as a model, we examine the impact of environmental factors on the individual variations in pubertal timing and the possible underlying mechanisms. The capacity of environmental factors to shape functioning of the neuroendocrine system is thought to be maximal during fetal and early postnatal life and possibly less important when approaching the time of onset of puberty.

Endocrine Society, Ralph S French Charitable Foundation, and Broad Reach Foundation.

In order to evaluate the involvement of gonadotropin-releasing hormone (GnRH) in the effects of neuroexcitatory amino acids on luteinizing hormone (LH) secretion, N-methyl-D,L-aspartate (NMDA; 30 mg/kg s.c.) was administered to 50-day-old male rats. The in vitro release of GnRH from the hypothalamus showed a maximal increase (4.6-fold) in animals sacrificed 7.5 min after NMDA injection, while serum LH levels rose concomitantly. Incubation of rat hypothalami in vitro with kainate or NMDA concentrations > 0.1 mM resulted in a dose-related release of GnRH, NMDA being twofold more potent than kainate. Quisqualate (10 mM) did not affect the release of GnRH. On a molar basis, quinolinate (50 mM), a possible endogenous ligand for NMDA receptors, was the most effective in inducing GhRH secretion (34.9 ± 4.9 pg/7.5 min, mean increment ± SEM, n= 10). The effects of kainate and NMDA were mediated through different types of receptors, since GnRH response to kainate was unchanged in the absence of glycine or in the presence of increased concentrations of Mg²⁺ (2 mM) or Ca²⁺ (5.8 mM). In contrast, the GnRH response to NMDA was reduced by Ca²⁺ (5.8 mM) and abolished in the absence of glycine or in the presence of Mg²⁺ (2 mM). In addition, DL-amino-5-phosphonopentanoic acid (AP5), a competitive antagonist of NMDA receptors, prevented the NMDA-induced release of GnRH. The permissive effect of glycine on GnRH response to NMDA was 2.7-fold more important using glycine concentrations of 0.01 µM than when concentrations >100 µM were used. Intermittent incubation with NMDA in vitro (every other 7.5-min period) did not affect the amplitude of GnRH response, while continuous exposure to NMDA resulted in an initial and transient increase in GnRH release followed by a prolonged desensitization period. It is concluded that different neuroexcitatory amino acids acting through distinct receptor types may be involved in the hypothalamic control of LH release by regulating the secretion of GnRH.