A lead-gill binding model to predict acute lead toxicity to rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss, approximately 2 g) were exposed to 0.6-1.0 microM Pb (125-200 microgl(-1)) for 3 h in ion-poor water. Complexing ligands (citrate, ethylenediamine, organic matter (OM)) or competing cations (Ca, Mg, Na) were added to the water. After exposure, trout gills were removed and analyzed for accumulated Pb. From these exposures, a conditional equilibrium binding constant (K) for Pb-gill binding was calculated (log K(Pb-gillPb)=6.0), plus conditional binding constants for cationic competition at the Pb binding sites and for Pb binding to OM in the water. These log K values were entered into the MINEQL+ aquatic chemistry equilibrium program, to calculate binding of Pb by trout gills. Two versions of the Pb-gill binding model were generated, one of which took into account OM quality as indicated by a simple measure of OM aromaticity, the specific absorption coefficient. The two model versions were tested against acute Pb toxicity (as the time to reach 50% fish mortality; LT50) during 1-week exposures of trout to 3.9 microM Pb in water collected from across southern Ontario. Both versions of the model generated highly significant correlations between the LT50 values and gill Pb concentrations calculated from measured exposure water chemistry, with the OM quality version correlating slightly better. Water pH also correlated well with the LT50 values, because the Pb exposures were in the pH range (7-8) where there is a nearly linear relationship between water pH and inorganic complexation of Pb. Advantages of the Pb-gill binding model include its completeness and the flexibility inherent in its conceptual framework, for example the inclusion of competition by Ca and H(+) for Pb binding sites on gills, and inclusion of complexation of Pb in the water column by natural OM and by carbonate.     

A difference in optomotor behaviour of two Antarctic nototheniid fishes is correlated with the presence of a choroid<Emphasis Type="Italic"> rete mirabile</Emphasis> and Root effect

The hypothesis that fish vision is influenced by the presence of a choroid rete mirabile (an oxygen-concentrating apparatus in the eye) and the Root effect was tested using the optomotor response in two nototheniid species from Antarctica. Pagothenia borchgrevinki, an active cryopelagic zooplanktivore, does not exhibit a major Root effect and the rete is absent. In contrast, the sluggish, benthic nototheniid, Trematomus bernacchii, possesses both a rete and a significant Root effect. Whole-eye ocular PO2 was higher in T. bernacchii (18.6 kPa) than in P. borchgrevinki (18.1 kPa) and the optomotor response of T. bernacchii was positively influenced by subtended angle on a moving background whereas P. borchgrevinki did not respond to any subtended angle (0–600 min of arc). The optomotor response of T. bernacchii may therefore have been facilitated by elevated ocular PO2 due to the presence of the choroid rete and the Root effect.     

Patch-clamp experiments with porins extracted from a marine bacterium (Photobacterium profundum strain SS9) and reconstituted in liposomes

The reconstitution of bacterial porins in liposome bilayers for patch-clamp recording is well established. However, the solutions used in the dehydration, rehydration, and osmotic swelling of the liposomes have been developed for porins from enteric bacteria. Porins from marine bacteria normally function in contact with seawater whose ionic composition and osmotic pressure would appear to be incompatible with the established methods. Here, we show that, contrary to expectation, an established reconstitution and patch-clamp method works well with porins, mainly OmpH and OmpL, extracted from the deep-sea marine bacterium Photobacterium profundum strain SS9 and that seawater can be introduced at a supplementary stage.     

Rabies in Zimbabwe: reservoir dogs and the implications for disease control.

Using detailed field study observations of the side-striped jackal (Canis adustus) and a simple stochastic model of the transmission dynamics of the virus and host demography, we discuss the epidemiology of rabies virus infection in the jackal population of Zimbabwe. Of the two jackal species in Zimbabwe, the other being the black-backed jackal (Canis mesomelas), the bulk of notified rabies cases are in side-striped jackals. Specifically, we show that the side-striped jackal population itself does not seem able to support rabies infection endemically, i.e. without frequent reintroduction from outside sources of infection. We argue that this is probably because the overall average jackal population density is too low to maintain the chain of infection. This study suggests that the disease is regularly introduced to jackals by rabid dogs from populations associated with human settlements. Given the rapidly rising dog population in Zimbabwe, estimates are derived of the future incidence of jackal rabies based on different dog-vaccination scenarios.     

Path tortuosity of Eurasian badgers (<Emphasis Type="Italic">Meles meles</Emphasis>) in a heterogeneous Mediterranean landscape

Movement is the process by which individual organisms are displaced over time to eat, reproduce and defend resources. Fractal analysis is a technique used to study animal movement that measures spatial complexity of path tortuosity; here, we apply it to characterize the movement patterns of the Eurasian badger (Meles meles) in a Mediterranean landscape. We calculated path tortuosity overall and seasonally, and for individuals of different sexes and social groups. The influence of variables related to badgers’ resources (food, shelter, water), human infra-structures and weather conditions were analysed with respect to the tortuosity of each badger’s path. A total of 55 search paths from six badgers were considered for this study. Although badgers generally displayed convoluted movement, there were two exceptions: (a) males overall and (b) all badgers in summer; for both, movements had a lower fractal value, i.e. were less tortuous. The convoluted movement pattern generally observed is probably adapted to the clumped distribution of food in the study area. Nevertheless, our results suggest that the use of dens and latrines were the principal determinants of tortuosity of badgers’ paths while foraging.     

Cyclic AMP-dependent protein kinase decreases GABAA receptor current in mouse spinal neurons

GABA, the major inhibitory neurotransmitter in the mammalian brain, binds to GABAA receptors, which form chloride ion channels. The predicted structure of the GABAA receptor places a consensus phosphorylation site for cAMP-dependent protein kinase (PKA) on an intracellular domain of the channel. Phosphorylation by various protein kinases has been shown to alter the activity of certain ligand- and voltage-gated ion channels. We have examined the role of phosphorylation by the catalytic subunit of PKA in the regulation of GABAA receptor channel function using whole-cell and excised outside-out patch-clamp techniques. Inclusion of the catalytic subunit of PKA in the recording pipettes significantly reduced GABA-evoked whole-cell and single-channel chloride currents. Both heat inactivation of PKA and addition of the specific protein kinase inhibitor peptide prevented the reduction of GABA-evoked currents by PKA. Neither mean channel open time nor channel conductance was affected by PKA. The reduction in GABA receptor current by PKA was primarily due to a reduction in channel opening frequency.     

Phylogeographic evidence for two mesic refugia in a biodiversity hotspot

Phylogeographic studies of flora in species-rich south-western Australia point to complex evolutionary histories, reflecting patterns of persistence and resilience to climatic changes during the Pleistocene. We asked whether coastal areas of the mid-west and south, as well as granite outcrops and inland ranges, have acted as major refugia within this region during Pleistocene climatic fluctuations by analysing phylogeographic patterns in the shrub Calothamnus quadrifidus R.Br. (Myrtaceae). We determined variation in chloroplast DNA data for 41 populations across the geographic range. Relationships and major clades were resolved using parsimony and Bayesian analyses. We tested for demographic and spatial expansion of the major clades and estimated clade divergence dates using an uncorrelated, lognormal relaxed clock based on two conservative chloroplast mutation rates. Two distinct phylogeographic clades were identified showing divergence during the Pleistocene, consistent with other phylogeographic studies of south-west Australian flora, emphasising the impact of climatic oscillations in driving divergence in this landscape. The southern clade was more diverse, having higher haplotype diversity and greater genetic structure, while the northern clade showed evidence of fluctuation in population size. Regions of high haplotype diversity with adjacent areas of low diversity observed in each clade indicated the locations of two coastal refugia: one on the south coast and another along the mid-west coast. This is the first evidence for major Pleistocene refugia using chloroplast genetic data in a common, widespread species from this region.     

Scaffold hopping from pyridones to imidazo[1,2-a]pyridines. New positive allosteric modulators of metabotropic glutamate 2 receptor

Imidazo[1,2-a]pyridines were identified via their shape and electrostatic similarity as novel positive allosteric modulators of the metabotropic glutamate 2 receptor. The subsequent synthesis and SAR are described. Potent, selective and metabolically stable compounds were found representing a promising avenue for current further studies.