Direct activation of the ventral striatum in anticipation of aversive stimuli

The brain "reward" system, centered on the limbic ventral striatum, plays a critical role in the response to pleasure and pain. The ventral striatum is activated in animal and human studies during anticipation of appetitive/pleasurable events, but its role in aversive/painful events is less clear. Here we present data from three human fMRI studies based on aversive conditioning using unpleasant cutaneous electrical stimulation and show that the ventral striatum is reliably activated. This activation is observed during anticipation and is not a consequence of relief after the aversive event. Further, the ventral striatum is activated in anticipation regardless of whether there is an opportunity to avoid the aversive stimulus or not. Our data suggest that the ventral striatum, a crucial element of the brain "reward" system, is directly activated in anticipation of aversive stimuli.     

The abundance of additional N-acetyllactosamine units in N-linked tetraantennary oligosaccharides of human Tamm-Horsfall glycoprotein is a donor-specific feature

Previously, treatment of Tamm-Horsfall glycoprotein (THp) from different donors with endo-beta-galactosidase has been shown to liberate a tetra- and a Sd(a)-active pentasaccharide, concluding the presence of N-linked carbohydrate chains containing additional N - acetyllactosamine units. These type of oligosaccharides were not found in a detailed structure elucidation of the carbohydrate moiety of THp of one male donor, suggesting a donor-specific feature for these type of structures. Therefore, THp was isolated from four healthy male donors and each subjected to endo-beta-galactosidase treatment in order to release these tetra- and Sd(a)-active pentasaccharide. Differences were observed in the total amount of released tetra- and Sda-active pentasaccharide of the used donors (42, 470, 478, 718 microg/100 mg THp), indicating that the presence of repeating N-acetyllactosamine units incorporated into the N-glycan moiety of THp is donor specific. Furthermore, a higher expression of the Sd(a) determinant on antennae which display N-acetyllactosamine elongation was observed, suggesting a better accessibility for the beta-N-acetylgalactosaminyltransferase. In order to characterize the N-glycans containing repeating N- acetyllactosamine units, carbohydrate chains were enzymatically released from THp and isolated. The tetraantennary fraction, which accounts for more than 33% of the total carbohydrate moiety of THp, was used to isolate oligosaccharides containing additional N - acetyllactosamine units. Five N-linked tetraantennary oligosaccharides containing a repeating N-acetyllactosamine unit were identified, varying from structures bearing four Sd(a) determinants to structures containing no Sd(a) determinant (see below). One compound was used in order to specify the branch location of the additional N- acetyllactosamine unit, and it appeared that only the Gal-6' and Gal-8' residues were occupied by a repeating N -acetyllactosamine unit.      

The effects of grazers on the performance of individuals and populations of scarlet gilia,Ipomopsis aggregata

Summary I. aggregata exhibits considerable powers of regrowth following removal of its primary shoot by herbivores, but we found no evidence of overcompensation (i.e. of significantly higher plant performance where plants were exposed to ungulate herbivory) in a comparison between individuals on grazed and ungrazed sides of exclosure fences, in a comparison between artificially clipped and control plants in one population in the Okanagan National Forest, or in comparisons between grazed and ungrazed plants in 14 natural populations. We tested whether ungulate grazing affects the population size of Ipomopsis aggregata by comparing populations inside and outside deer exclosures at 7 sites in the Western United States. We found consistent, highly significant differences in plant population density on the grazed and ungrazed sides of these exlosure fences. Plant density was a modal 25-fold higher on the protected side of the fence, suggesting that exposure to ungulate grazing increases plant death rates at some stage in the life cycle. Our results show that the presence of ungulate grazers leads to a substantial decrease in plant density despite the fact that grazing on young bolting shoots has very little influence on fruit production. Since this decrease in population density is not correlated with a decrease in the fecundity of individuals, it must instead be due to other direct and indirect effects of ungulate grazers.     

An enzyme-linked immunosorbent assay for N-acetylglucosaminyltransferase-V

The development of an enzyme-linked immunosorbent assay (ELISA) for uridine 5'-diphospho-N-acetyl-glucosamine: alpha mannoside beta 1----6 N-acetylglucosaminyltransferase (GnT-V) is reported. The assay quantitates the enzymatic conversion of the specific synthetic GnT-V acceptor GlcNAc beta 1----2Man alpha 1----6Man beta-R (5) to the product GlcNAc beta 1----2[GlcNAc-beta 1----6]Man alpha 1----6Man beta-R (6) when these oligosaccharide structures were covalently attached to bovine serum albumin which was then coated on microtiter wells. Conversion of 5 to 6 was detected using a polyclonal antiserum raised against the product 6 and from which antibodies cross-reacting with acceptor 5 had been removed by affinity adsorption. GnT-V activity detected by ELISA was linearly proportional to both enzyme concentration and time under appropriate experimental conditions where 50-300 fmol of product was formed per microtiter well. GnT-V activity could be measured by ELISA in Triton X-100 extracts of hamster kidney acetone powder and in human serum. The twofold increase in GnT-V activity which is known to accompany Rous sarcoma virus transformation of baby hamster kidney cells could also be quantitated using the ELISA.     

Spatially structured population dynamics in feral oilseed rape

We studied the population dynamics of feral oilseed rape (Brassica napus) for 10 years (1993-2002) in 3658 adjacent permanent 100 m quadrats in the verges of the M25 motorway around London, UK. The aim was to determine the relative importance of different factors affecting the observed temporal patterns of population dynamics and their spatial correlations. A wide range of population dynamics was observed (downward or upward trends, cycles, local extinctions and recolonizations), but overall the populations were not self-replacing (lambda < 1). Many quadrats remained unoccupied throughout the study period, but a few were occupied at high densities for all 10 years. Most quadrats showed transient oilseed rape populations, lasting 1-4 years. There were strong spatial patterns in mean population density, associated with soil conditions and the successional age of the plant community dominating the verge, and these large-scale spatial patterns were highly consistent from year to year. The importance of seed spilled from trucks in transit to the processing plant at Erith in Kent was confirmed: rape populations were significantly higher on the 'to Erith' verge than the 'from Erith' verge (overall mean 2.83-fold greater stem density). Quadrats in which lambda > 1 were much more frequent in the 'to Erith' verge, indicating that seed immigration can give the spurious impression of self-replacing population dynamics in time-series analysis. There was little evidence of a pervasive Moran effect, and climatic forcing did not produce widespread large-scale synchrony in population dynamics for the motorway as a whole; just 23% of quadrats had significant rank correlations with the mean time-series. There was, however, significant local spatial synchrony of population dynamics, apparently associated with soil disturbance and seed input. This study draws attention to the possibility that different processes may impose population synchrony at different scales. We hypothesize that synchrony in this system is driven by at least three processes: small-scale, local forcing caused by soil disturbance, intermediate-scale forcing as a result of seed input, and large-scale climatic forcing (e.g. winter rainfall) that affects the motorway as a whole.     

Uptake kinetics of 99Tc in common duckweed

The uptake of the nuclear waste product technetium-99 was studied in common duckweed (Lemna minor). In addition to measurements, a model involving two compartments in duckweed with different chemical forms of technetium was derived. The model was tested by chemical speciation, i.e. differentiating between reduced Tc-compounds and Tc(VII)O(4)(-). The TcO(4)(-) concentrations measured were in good agreement with those predicted by the model. Two processes determine technetium uptake: (1) transport of Tc(VII)O(4)(-) across the cell membrane, and (2) reduction of Tc(VII). The TcO(4)(-) concentration in duckweed reaches a steady state within 2 h while reduced Tc-compounds are stored, as a result of absence of release or re-oxidation processes. Bioaccumulation kinetic properties were derived by varying 99Tc concentration, temperature, nutrient concentrations, and light intensity. The reduction of technetium in duckweed was highly correlated with light intensity and temperature. At 25 degrees C the maximum reduction rate was observed at light intensities above 200 μmol m(-2) s(-1) while half of the maximum transformation rate was reached at 41 μmol m(-2) s(-1). Transport of TcO(4)(-) over the cell membrane requires about 9.4 kJ mol(-1), indicating an active transport mechanism. However, this mechanism behaved as first-order kinetics instead of Michaelis-Menten kinetics between 1x10(-14) and 2.5x10(-5) mol l(-1) TcO(4)(-). Tc uptake could not be inhibited by 10(-3) mol l(-1) nitrate, phosphate, sulphate or chloride.