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Brain uptake of iron-59 and iodine-125-labelled transferrin from blood in the adult rat has been investigated using graphical analysis to determine the blood-brain barrier permeability to these tracers in experiments that lasted between 5 min and 8 days. The blood-brain barrier permeability (K(in)) to 59Fe was 89 x 10(-5) ml/min/g compared to the value of 7 x 10(-5) ml/min/g for 125I-transferrin, which is similar to that of albumin, a plasma marker. The autoradiographic distribution of these tracers in brain was also studied to determine any regional variation in brain uptake after the tracers had been administered either systemically or applied in vitro. No regional uptake was seen for 125I-transferrin even after 24 h of circulation. In contrast, 59Fe showed selective regional uptake by the choroid plexus and extra-blood-brain barrier structures 4 h after administration. After 24 h of circulation, 59Fe distribution in brain was similar to the transferrin receptor distribution, as determined in vitro, but was unlike the distribution of nonhaem iron determined histochemically. The data suggest that brain iron uptake does not involve any significant transcytotic pathway of transferrin-bound iron into brain. It is proposed that the uptake of iron into brain involves the entry of iron-loaded transferrin to the cerebral capillaries, deposition of iron within the endothelial cells, followed by recycling of apotransferrin to the circulation. The deposited iron is then delivered to brain-derived transferrin for extracellular transport within the brain, and subsequently taken up via transferrin receptors on neurones and glia for usage or storage.

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In 1975, Isnard and Zeeman proposed a cusp catastrophe model for the polarization of a social group, such as the population of a democratic nation. Ten years later, Kadyrov combined two of these cusps into a model for the opinion dynamics of two "nonsocialist" nations. This is a nongradient dynamical system, more general than the double-cusp catastrophe studied by Callahan and Sashin [1987]. Here, we present a computational study of the nongradient double cusp, in which the degeneracy of Kadyrov's model is unfolded in codimension eight. Also, we develop a discrete-time cusp model, study the corresponding double cusp, establish its equivalence to the continuous-time double cusp, and discuss some potential applications. We find bifurcations for multiple critical-point attractors, periodic attractors, and (for the discrete case) bifurcations to quasiperiodic and chaotic attractors.

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