Obesity-inducing lesions of the central nervous system alter leptin uptake by the blood-brain barrier.

Leptin regulates body adiposity by decreasing feeding and increasing thermogenesis. Obese humans and some obese rodents are resistant to peripherally administered leptin, suggesting a defect in the transport of leptin across the blood-brain barrier (BBB). Defective transport of exogenous leptin occurs in some models of obesity, but in other models transport is normal. This shows that factors other than obesity are associated with impairment of leptin transport across the BBB. In order to further investigate these factors, we determined leptin transport in rats made obese by lesioning of the ventromedial hypothalamus (VMH), paraventricular nucleus (PVN), or posterodorsal amygdala (PDA). These regions all contain leptin receptors and lesions there induce obesity and hyperleptinemia and alter the levels of many feeding hormones which might participate in leptin transporter regulation. We measured the uptake of radioactively labeled leptin by the BBB by multiple-time regression analysis which divides uptake into a reversible phase (Vi, e.g., receptor/transporter binding to the brain endothelial cell) and an irreversible phase (Ki, complete transport across the BBB). Leptin uptake was not affected in rats with VMH lesions. No significant change occurred in the entry rate (Ki) for any group, although Ki declined by over 35% in rats with PVN lesions. Decreased uptake was observed in rats with PVN lesions and with PDA lesions. This was primarily due to a reduced Vi (about 21% for the PDA). This decreased uptake is most likely explained by decreased binding of leptin to the brain endothelial cell, which could be because of decreased binding by either receptors or transporters. This suggests that some of the feeding hormones controlled by the PVN and PDA may participate in regulating leptin uptake by the BBB.     

Geographic isolation and evolution of Mediterranean endemic Cyclamen: insights from chloroplast trnL (UAA) intron sequence variation

 In this study we construct a phylogenetic hypothesis for the relatedness among disjunct subspecies of Cyclamen repandum and its two allopatric congeners, C. creticum and C. balearicum in order to examine the evolutionary divergence of currently isolated populations across the western Mediterranean. The most parsimonious phylogenetic tree obtained from sequencing the cpDNA trnL (UAA) intron suggests a major phylogeographic divide in southern Greece between two clades. The first clade comprises samples of C. repandum subsp. peloponnesiacum (from the Peloponnese) and C. creticum (from Crete). The second comprises samples of C. repandum subsp. repandum (from Croatia, Italy, southern France, Corsica, Sardinia and Sicily), C. repandum subsp. rhodense (from Rhodes and Kos) and C. balearicum (from the Balearic Islands and southern France). These data suggest that C. creticum has evolved in allopatry from C. repandum subsp. peloponnesiacum and that C. balearicum and C. repandum ssp. rhodense have diverged from C. repandum subsp. repandum at its western and eastern distribution limits. At one small site on Corsica, a population of C. repandum may have introgressed with relictual populations of C. balearicum. These divergence patterns illustrate how a phylogenetic perspective can be used to better understand the evolution of endemism in the Mediterranean flora. Received February 19, 2001 Accepted August 22, 2001     

DIATOM SILICA BIOMINERALIZATION: AT NANOSCALE LEVEL A CHEMICALLY UNIFORM PROCESS

Using a high-brilliance synchrotron X-ray source, combined small- and wide-angle X-ray scattering (SAXS and WAXS) was applied to study nanoscale characteristics, in particular pore size in the range of 3 to 65 nm, of a variety of unialgal cultures of centric and pennate diatoms, and of mixed diatom populations sampled in the field. Results of scattering analysis were compared with details of pore size, structure and orientation visible at the electron microscopic level. WAXS patterns did not reveal any crystalline phase or features of microcrystallinity (resolution 0.07 to 0.51 nm), which implies a totally amorphous character of the SiO₂ matrix of the frustule material. SAXS data (resolution 3 to 65 nm) provided information on geometry, size, and distribution of pores in the silica. Overall, two pore regions were recognized that were common to the silica of all samples: the smallest (d less than 10 nm) regularly spaced and shaped spherically, the larger (up to 65 nm) being cylinders or slits. Apparently, at a nanoscale level diatomaceous silica is quite homologous among species, in agreement with the chemical principles of silica polymerization under the conditions of pH and precursor concentrations inside the silicon deposition vesicle. The final frustule "macro"-morphology is of course species-specific, being determined genetically. Synthetically-derived MCM-type silicas have a similarly organized pore distribution in an amorphous silica matrix as we found in all diatom species studied. We therefore suggest that organic molecules of a kind used as structure-directing agents to produce these artificial silicas play a role in the nucleation of the silica polymerization reaction and the shaping of pore morphology inside the silicon deposition vesicle of diatoms. Structure-directing molecules now await isolation from the SDV, followed by identification and characterisation by molecular techniques.     

Molecular determinants of visual pigment function.

Mutagenesis studies and comparisons of natural variants of rhodopsin and related visual pigments have led to new insights concerning photoreceptor function. The studies identify domains important for receptor folding, the residues that set the wavelength of absorption for the ligand 11-cis retinal, and residues, that when mutated, trigger the cell death of photoreceptors.     

DNA sequence analysis of serologically detected ELA class II haplotypes at the equine DQP locus

The genetic diversity at the ELA DQβ locus was investigated using polymerase chain reaction and DNA sequencing. Based upon serological methods 16 class II homozygous animals were selected and their genomic DNA was used. A DQβ gene from an equine cDNA library was also sequenced. Our methology and the similarity between the genomic and the cDNA sequences suggest that the studied locus is expressed on equine lymphocytes. In the predicted amino acid sequence the most extensive variation is located at residues 56–60. The pattern of these five amino acids is strongly correlated to the serological ELA class II specificities (W13, W22, W23, Be200). The alleles corresponding to the W23 specificity are the most divergent among the equine DQβ alleles and also from other mammalian DQβ sequences.     

The effects of Heterosigma akashiwo on juvenile Oncorhynchus tshawytscha and its implications for fish culture

The effects of natural blooms of Heterosigma akashiwo on freshwater-and saltwater-acclimated juvenile chinook salmon were assessed. Rates of fish mortality in the blooms were independent of acclimation of fish to seawater and the ambient oxygen levels, but were dependent on concentration of algae and ambient water temperatures. No pathological abnormality to gills or other internal organs in the fish were evident. Aeration or oxygenation of fish cages did not enhance or inhibit fish survival in a H. akashiwo bloom. Cause of death was considered to be due to a labile ichthyotoxic agent.