The Effects of Neuraminidase and Gangliosides on Ovarian LH/hCG Receptors During Rat Development

Ovaries of neonatal rats are not endowed with specific LH/hCG receptors up to 6–8 days of age. Treatment of ovarian membranes of the neonatal rat with neuraminidase results in a specific binding of radioactively labeled hCG, while an increase of hormone binding is observed after neuraminidase treatment of ovarian membranes of the 21-day-old rat. These changes in hormone receptor sites in the ovary are dependent on the neuraminidase concentration used and are due to a receptor with a dissociation constant (K_D) of about 10⁻⁹ M. The K_D of the receptor in the LH/hCG sensitive ovary without neuraminidase treatment is about 10⁻¹⁰ M. These results indicate the presence of two different LH/hCG receptors in the ovarian membrane. The unmasking effect of neuraminidase onto LH/hCG receptors indicate that ganglioside-like structures are responsible for the masking of receptors in the neonatal, insensitive rat ovary and also in the 21-day-old sensitive ovary. Ganglioside preparations are able to inhibit the binding, and the fractionation of ovary gangliosides results in a fraction with a rather high inhibition potency of LH/hCG binding to the receptor. It is hypothesized that the masked receptors in the sensitive period represent a store of receptors for the reconstitution of the ovarian cells with active receptors after internalization of the hormone-receptor complex. Thus the masking of the receptors in the early postnatal rat ovary could be a prerequisite for the female differentiation of hypothalamic centers. The observed neuraminidase effect in vitro could reflect a physiologic situation. Neuraminidase was found in the ovary, and during early postnatal development the neuraminidase activity pattern coincides with that of the ovarian LH/hCG receptor changes.     

Two new stoloniferous species of Viola (Violaceae) from China

Two new stoloniferous species of Viola (Violaceae) from southern China are described and illustrated. Viola nitida is recognizably different from V. fargesii as the plant is evergreen and glabrous throughout, the leaf blade adaxially nitid, base cuneate or shallowly cordate, and margin serrate. Viola maoershanensis is different from V. diffusa as the leaf blade is serrate, base cordate and not decurrent to petiole, the petiole wingless, the flowers larger, the petals bluish violet or pinkish white, and the lower petal obtuse at the apex. The chromosome numbers of the two new species were counted as 2n = 24 (V. nitida) and 2n = 44 (V. maoershanensis). The taxonomic positions of the two species are discussed. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 349–356.     

SPATIAL PATTERNING AND COMPETITION IN AN ASPEN-WHITE PINE SUCCESSIONAL SYSTEM

The spatial patterning of and competition between established large-toothed aspen (Populus grandidentata) and invading white pine (Pinus strobus) were examined in a 65-yr-old forest system at the AuSable Trails Institute of Environmental Studies, Kalkaska County, Michigan. Density, diameter, and distance measures were recorded for tree species on two 40 × 40 m grids containing 64 quadrats each 5 × 5 m. Several indices of dispersion were used to assess pattern and regression analysis of nearest neighbor distance to tree diameter provided an index of competition. The results indicate strong aggregation for both aspen and pine on a large scale, but regularity of pattern for pines in relation to their nearest neighbor. This regularity appears to be due to competition with established aspens and suggests that the spatial patterning of the aspens acts to control the spacing and subsequent development of the invading white pines.