Differences in the Activation of the Mitochondrial Permeability Transition Among Brain Regions in the Rat Correlate with Selective Vulnerability

Mitochondria from different regions of the brain were prepared, and the activation of the mitochondrial permeability transition (MPT) by calcium was investigated by monitoring the associated mitochondrial swelling. In general, the properties of the MPT in brain mitochondria were found to be qualitatively similar to those observed in liver and heart mitochondria. Thus, swelling was inhibited by adenine nucleotides (AdNs) and low pH (<7.0), whereas thiol reagents and alkalosis facilitated swelling. Cyclosporin A and its nonimmunosuppressive analogue N-methyl-Val-4-cyclosporin A (PKF 220-384) both inhibited swelling and prevented the translocation of cyclophilin D from the matrix to the membranes of cortical mitochondria. However, the calcium sensitivity of the MPT differed in mitochondria from three brain regions (hippocampus > cortex > cerebellum) and is correlated with the susceptibility of these regions to ischemic damage. Depleting mitochondria of AdNs by treatment with pyrophosphate ions sensitized the MPT to [Ca2+] and abolished regional differences, implying regional differences in mitochondrial AdN content. This was confirmed by measurements showing significant differences in AdN content among regions (cerebellum > cortex > hippocampus). Our data add to recent evidence that the MPT may be involved in neuronal death.     

Site-dependent population dynamics: the influence of spatial habitat heterogeneity on individual fitness in the sedge warbler Acrocephalus schoenobaenus

During nine years of study, we detected a mechanism corresponding to site dependence operating in a population of the sedge warbler Acrocephalus schoenobaenus inhabiting a natural wetland of high within-habitat heterogeneity. Sites with a larger share of cover by tall wetland vegetation were preempted during spring settlement; they were occupied in more breeding seasons and by more experienced males. The fitness of males occupying these sites was higher in terms of local recruit production. The total area occupied by the population expanded or contracted depending on its population size. This mechanism increased or decreased the mean site quality, influencing local recruitment of young, although mainly by changing the share of unproductive sites in the total pool of occupied sites. The results indicate that population demographic rates may depend on the spatial heterogeneity of resources at the level of individuals.     

Involvement of the L-cysteine biosynthetic pathway in azide-induced mutagenesis in Salmonella typhimurium

L-Cystine and L-cysteine specifically reverse the mutagenic action of azide in Salmonella typhimurium and Escherichia coli. To establish whether the L-cysteine biosynthetic pathway is involved in azide-induced mutagenesis, several derivatives of a mutagen tester-strain of S. typhimurium bearing mutations in different cys genes were isolated. No mutagenic effect of azide was observed in a strain carrying mutation in the cysE gene, unless the incubation medium was supplemented with exogenous O-acetylserine. Out of 16 cysK mutants 14 were mutagenized by azide very poorly or not at all. These results indicate that the activity of O-acetylserine sulfhydrylase A, and the availability of O-acetylserine, one of the two co-substrates of the enzyme, are essential for the mutagenic action of azide in S. typhimurium