Predator detection and avoidance by starlings under differing scenarios of predation risk

Practically all animals must find food while avoiding predators.An individual's perception of predation risk may depend on manyfactors, such as distance to refuge and group size, but it isunclear whether individuals respond to different factors ina similar manner. We tested whether flocks of foraging starlingsresponded in the same way to an increased perception of predationrisk by assessing three factors: (1) neighbor distances, (2)habitat obstruction, and (3) recent exposure to a predator.We found that in all three scenarios of increased risk, starlingsreduced their interscan intervals (food-searching bouts), whichincreased the frequency of their vigilance periods. We thenexamined how one of these factors, habitat obstruction, affectedescape speed by simulating an attack with a model predator.Starlings were slower to respond in visually obstructed habitats(long grass swards) and slower when they had their head downin obstructed habitats than when they had their head down inopen habitats. In addition, reaction times were quicker whenstarlings could employ their peripheral fields of vision. Ourresults demonstrate that different sources of increased riskcan generate similar behavioral responses within a species.The degree of visibility in the physical and social environmentaffects both the actual and perceived risk of predation.     

Metabolism of glucose by human embryos

Glucose turnover, as measured by CO2 production, lactate accumulation and carbon incorporation from [U-14C]glucose as sole energy substrate, was low on the 2nd day of culture of human embryos resulting from in-vitro fertilization but above that of unfertilized oocytes. In general, all parameters of metabolism increased substantially during the following 2 days of development but the rate of increase in lactate production was greater than that of CO2, especially between Days 3 and 4. Within developing embryos, no correlation was evident between the metabolic turnover of glucose and the method of patient stimulation, the morphological quality of embryos or the apparent rate of cleavage in culture. The results indicate that, before Day 3 of development, glucose is not effective as an energy source for the human embryo because of a blockade to glycolysis similar to that in mouse embryos.     

Development of mouse embryos cryopreserved by vitrification

Eight-cell mouse embryos were cryopreserved by vitrification in a concentrated solution of dimethylsulphoxide, acetamide, propylene glycol and polyethylene glycol. This solution (designated VS1) does not crystallize when cooled to subzero temperatures but instead forms a glassy transparent solid. Embryos were exposed in three steps to a stock VS1 solution or a saline solution containing 90% of the cryoprotectants in the stock VS1 (90% VS1) and then the suspensions were vitrified by rapid cooling in liquid nitrogen. Of 568 embryos vitrified in 90% VS1, 80% developed in vitro and 98 normal fetuses or young (17% of the total) were produced after transfer to pseudopregnant recipients. By contrast, 22% of 153 embryos vitrified in the stock VS1 developed in vitro, but only one normal fetus was obtained after transfer. These results demonstrate that normal fetuses and young can be produced from embryos cryopreserved by the simple and rapid method of vitrification.     

Characteristics and epitope mapping of a cloned human autoantigen La

The La (SS-B) polypeptide is a ribonucleoprotein against which high titer antinuclear antibodies (ANA) react in the human autoimmune disease primary Sj?gren's syndrome. To identify the autoepitopes with which the ANA anti-La (anti-SS-B) reacts, we isolated a 1.4-kb cDNA clone for La from a lambda gt10 library made from a human Burkitt's cell line. This clone contained an open reading frame of 1065 bp, encoding a 40.1-kDa polypeptide that corresponded to the carboxyl-terminal end of the La protein. The predicted polypeptide sequence of the recombinant protein was highly charged and unrelated to any previously published sequence. We also compared this clone to a previously published cDNA sequence for La and demonstrated significant differences, particularly that the open reading frame in our cDNA continued for 926 additional bases 3' to a putative termination codon in the previously reported sequence. The recombinant La protein was expressed in Escherichia coli and tested for reactivity with 200 sera containing ANA of various specificities. Only the sera containing anti-La antibodies reacted with the cloned La. By expressing subclones of the La cDNA as fusion proteins with beta-galactosidase, we have localized at least one epitope for the binding of anti-La antibodies to the carboxyl-terminal 103 amino acids of the La protein. No anti-La binding could be demonstrated to the region of the La protein that had previously been predicted to contain an autoepitope for the binding of anti-La (SS-B) antibodies. Studies of cloned autoepitopes could provide important clues to the role ANA play in disease and lead to targeted intervention in the treatment of primary Sj?gren's syndrome.     

Effect of dibutyryl cyclic adenosine monophosphate on granulosa cell proliferation, oocyte growth and meiotic maturation in isolated mouse primary ovarian follicles cultured in collagen gels.

Isolated primary follicles from 10-day-old mice were cultured in a collagen gel matrix for 6 days in Minimum Essential Medium + foetal calf serum, followed by culture in unsupplemented medium (control) or in medium containing hypoxanthine (2 mM) or dibutyryl cyclic adenosine monophosphate (dbcAMP, 0.25 mM) for a further 3 or 6 days. Less than 10% of oocytes resumed meiosis during the culture period in all groups. At recovery, the diameter of oocytes at the germinal vesicle stage was recorded and their ability to resume meiosis was determined. Hypoxanthine had little effect on oocyte growth and meiotic competence, but culture in dbcAMP resulted in oocytes that were larger (60.2 +/- 0.6 microns) than those of controls (55.8 +/- 0.5 microns) and more competent to resume meiosis than were controls (42.9% and 10.8%, respectively). The addition of dbcAMP to the culture medium induced a 4-5-fold increase in the number of granulosa cells oocyte compared with controls (3757 +/- 423 and 838 +/- 93, respectively). These results indicate that increased oocyte growth and meiotic competence is primarily mediated via dbcAMP effects on the granulosa cells.     

Metabolic Stability of Hippocampal Slice Preparations During Prolonged Incubation

Abstract: Hippocampal slices were prepared under three conditions: (1) in medium containing glucose and oxygen at 4°C; (2) as in (1), but at 37°C; (3) in medium devoid of glucose and oxygen at 37°C. The rates of recovery to roughly steady-state levels and through 8 h of incubation were monitored for energy metabolite levels and related parameters. In vitro stable values are compared with in situ hippocampal levels. Regardless of the conditions under which slices were prepared, metabolite levels required up to 3 h to stabilize, and these levels were maintained or improved through 8 h of incubation. Further, the maximal concentrations of metabolites were independent of the conditions of slice preparation. Total adenylates and total creatine levels reached 55% of those in vivo. Lactate decreased from the decapitation-induced high levels, but stabilized at concentrations about twice those in rapidly frozen brain. Cyclic AMP and cyclic GMP exhibited peak levels at 30 min of incubation, and cyclic GMP remained elevated for 3 h. Although all three methods of slice preparation resulted in similar metabolite profiles on incubation, the initial decreases in high energy phosphates were delayed by chilling. Most striking, the slices prepared in the absence of glucose and oxygen exhibited much smaller orthodromic evoked potentials in the dentate gyrus. The presence of glucose and oxygen during preparation of the slices appears to be critical to the electrophysiological response of the tissue.     

Isolation and characterization of a large,neurite-associated glycoconjugate from neuroblastoma cells

A high molecular weight glycoconjugate has been isolated from neurite-producing neuronal tumor cells in culture and has been designated as I(0) based on its elution characteristics in gel filtration chromatography. This molecule cannot be found in a variety of nonneuronal cells. I(0) is found in the substratum-attached material or cell fraction of neurite-producing neuroblastoma cells, depending upon culture conditions. It is found in the substratum-bound fraction of B104 rat neuroblastoma cells during serum starvation and in the EGTA-detached cell fraction of B104 cells grown in chemically defined N2 medium. It occurs only in the cell fraction of the human neuroblastoma line Platt. Examination of behavioral variants of the B104 rat line further strengthens the association of I(0) with neurite production; the constitutive neurite-producing E(R)B9 variant contains I(0) while the non-neurite-producing E(R)A11 variant does not. I(0) is large, eluting in the void volume of sepharose-CL2B columns. Radioiodination of intact cells with lactoperoxidase shows I(0) to be a cell surface component. Metabolic radiolabeling studies show that it contains a high proportion of polysaccharide to protein, does not contain mannose, and is unsulfated. Alkaline borohydride reduction release two size classes of large polysaccharide chain. The alkaline reduction results, along with the mannose incorporation studies, show the presence of O-glycosidic linkages and few, if any, N-linkages. Resistance to nitrous acid deamination, insensitivity to glycosaminoglycan lyases, and the absence of sulfation, indicate that I(0) does not contain the glycosaminoglycans hyaluronic acid, chondroitin-, dermatan-, or heparin- sulfates. Affinity column chromatography reveals high binding affinity of I(0) to polyornithine and no binding to gelatin (collagen) or the glycosaminoglycans hyaluronate and heparin. These studies describe a unique high molecular weight glycoconjugate on the surface of neurite-producing neuroblastoma cell lines from two species.