Foraging behaviour and dispersion of eastern grey kangaroos (Macropus giganteus) in an ideal free framework

Ideal free distribution (IFD) theory predicts that animals in competitive situations should distribute themselves among available habitat patches according to the density of conspecifics and its regulatory effect on resources. To investigate the applicability of IFD models to free-ranging herbivores, we quantified the dispersion and foraging behaviour of eastern grey kangaroos Macropus giganteus among habitat patches of differing suitability, within and outside a reservoir catchment in southern Victoria, Australia. Kangaroo densities within the catchment had a regulatory effect on resource density, while surrounding farmland maintained a higher standing crop despite higher densities of competitors. This difference was slight in autumn, however, when the system was apparently close to equilibrium. Gross bite rates of individuals foraging in farmland were lower than for individuals foraging within the catchment, and vigilance behaviour occurred more frequently in farmland habitat than any other, decreasing time devoted to feeding. Interference competition occurred in only 1.9% of focal samples, although competitive differences based on phenotype were observed. Although resource gains by individual kangaroos are likely to be influenced by other factors, including resource dynamics, predation risk and phenotypic differences, IFD theory provides a valuable analytical framework for this herbivore foraging system.     

Place cells,navigational accuracy,and the human hippocampus.

The hippocampal formation in both rats and humans is involved in spatial navigation. In the rat, cells coding for places, directions, and speed of movement have been recorded from the hippocampus proper and/or the neighbouring subicular complex. Place fields of a group of the hippocampal pyramidal cells cover the surface of an environment but do not appear to do so in any systematic fashion. That is, there is no topographical relation between the anatomical location of the cells within the hippocampus and the place fields of these cells in an environment. Recent work shows that place cells are responding to the summation of two or more Gaussian curves, each of which is fixed at a given distance to two or more walls in the environment. The walls themselves are probably identified by their allocentric direction relative to the rat and this information may be provided by the head direction cells. The right human hippocampus retains its role in spatial mapping as demonstrated by its activation during accurate navigation in imagined and virtual reality environments. In addition, it may have taken on wider memory functions, perhaps by the incorporation of a linear time tag which allows for the storage of the times of visits to particular locations. This extended system would serve as the basis for a spatio-temporal event or episodic memory system.     

The effect of temperature upon the combined diffusional and kinetic parameters of tissue respiration.

The parameter of temperature has been introduced into equations which relate respiration rate and the diffusion of oxygen into respiring tissues having different geometries. A general equation has been derived having the form $\text{d = A(C)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{exp}\text{(}\text{f}\text{2RT}$), where d is a measure of the depth of tissue which can be oxygenated; C is the external oxygen partial pressure; A is a complex constant which can, however, be evaluated for any given tissue and geometry; and f is given by the relationship f =μ — (ΔH + B), where μ is the Arrhenius coefficient of energy of activation of the respiratory complex within the tissue; ΔH is the differential molar heat of the solution of oxygen in water; and B is the (empirical) temperature coefficient of the viscosity of water. The equation is evaluated for the two situations of sheets and spheres of respiring tissue.     

Pharmacological inhibition of Carbonic Anhydrase IX and XII to enhance targeting of acute myeloid leukaemia cells under hypoxic conditions

Acute myeloid leukaemia (AML) is an aggressive form of blood cancer that carries a dismal prognosis. Several studies suggest that the poor outcome is due to a small fraction of leukaemic cells that elude treatment and survive in specialised, oxygen (O₂)-deprived niches of the bone marrow. Although several AML drug targets such as FLT3, IDH1/2 and CD33 have been established in recent years, survival rates remain unsatisfactory, which indicates that other, yet unrecognized, mechanisms influence the ability of AML cells to escape cell death and to proliferate in hypoxic environments. Our data illustrates that Carbonic Anhydrases IX and XII (CA IX/XII) are critical for leukaemic cell survival in the O₂-deprived milieu. CA IX and XII function as transmembrane proteins that mediate intracellular pH under low O₂ conditions. Because maintaining a neutral pH represents a key survival mechanism for tumour cells in O₂-deprived settings, we sought to elucidate the role of dual CA IX/XII inhibition as a novel strategy to eliminate AML cells under hypoxic conditions. Our findings demonstrate that the dual CA IX/XII inhibitor FC531 may prove to be of value as an adjunct to chemotherapy for the treatment of AML.     

Kinetic Modeling of 52Fe/52mMn-Citrate at tthe Blood-Brain Barrier by Positron Emission Tomography

The kinetics of iron at the blood-brain barrier of the monkey were studied in vivo using positron emission tomography (PET) and the tracer 52Fe/52mMn-citrate. 52mMn is the beta(+)-emitting daughter nuclide of 52Fe and therefore contributes to the observed signal and background in the PET images and may influence the quantification of physiological relevant iron parameters. The kinetics of pure (52m)Mn-citrate at the blood-brain barrier of the monkey were studied experimentally, and the analysis of the data with a reasonable compartment model led to equal efflux and influx parameters for Mn (1.35 +/- 0.3 x 10(-2) min(-1)). By using complexes between Mn and diethylenetriaminepentaacetic acid, the validity of the proposed model could be confirmed. To describe the observed kinetics of 52Fe/(52m)Mn-citrate, the manganese model was coupled to an iron model, which finally allowed the quantification of two iron-specific parameters: an input rate into global brain tissue of 7.15 +/- 2.6 x 10(-4) min(-1) and a time delay of roughly 24 min to account for the observed activities. The simpler linearization procedure has been proposed and could be applied to all our data sets and is able to replace the complicated nonlinear iron/manganese tracer kinetic model neglecting any influence of manganese on the analysis.     

Human spatial navigation: cognitive maps, sexual dimorphism, and neural substrates.

Recent research on navigation has been particularly notable for the increased understanding of the factors affecting human navigation and the neural networks supporting it. The use of virtual reality environments has made it possible to explore the effect of environment layout and content on way-finding performance, and it has shown that these effects may interact with the sex and age of subjects. Functional brain imaging, combined with the use of virtual environments, has revealed strong parallels between humans and other animals in the neural basis of navigation.     

Spatial heterogeneity and function of voltage- and ligand-gated ion channels in retinal amacrine neurons.

The spatial distribution of ion channels within amacrine cells of the tiger salamander retina was studied using patch recording in the retinal slice preparation. By focally puffing kainate, GABA and glycine at amacrine cell processes in the inner plexiform layer, it was determined that the cell's glutamate receptors were located in a confined region of the processes near the soma, while glycine and GABA receptors were located throughout the processes. Likewise, similar techniques in conjunction with voltage steps demonstrated that voltage-gated sodium channels were located throughout the cell and were shown to generate sodium-dependent spikes, while only the processes contained voltage-gated calcium channels. These results suggest that this form of transient amacrine cell collects its excitatory synaptic inputs in a region confined to a central annular region near the soma, that the signal is actively propagated throughout its processes by voltage-gated sodium channels and that calcium-dependent neurotransmitter release of glycine from this neuron can occur throughout its processes. Thus, excitatory signals are collected in the processes near the soma, inhibitory signals throughout the processes and excitation is probably propagated throughout the processes of the amacrine cell.