The effect of oxalate on gluconeogenesis by isolated chicken hepatocytes. Increased sensitivity to inhibition as a result of biotin deficiency

Addition of varying concentrations of oxalate to isolated chicken hepatocytes reduced gluconeogenesis from lactate in a manner indicating that pyruvate carboxylase was not the rate-limiting step. With hepatocytes from biotin-deficient chicks, sensitivity to inhibition was increased, and was consistent with pyruvate carboxylase being rate-limiting. Administration of biotin to deficient chicks overnight restores sensitivity to oxalate to normal.     

Synthesis, SAR exploration, and X-ray crystal structures of factor XIa inhibitors containing an alpha-ketothiazole arginine

Using an alpha-ketothiazole arginine moiety as a key recognition element, a series of small peptidomimetic molecules was designed and synthesized, and their co-crystal structures with factor XIa were studied in an effort to develop smaller, less peptidic inhibitors as antithrombotic agents.     

Invasive plant species thresholds in the forests of Robinson Crusoe Island,Chile

Background: Invasion by exotic plants worldwide can lead to the loss of native species, particularly on islands with a high proportion of endemic plants, such as Robinson Crusoe Island (RCI).

Aims: We studied the two most invasive exotic plant species occurring in the forest of RCI: Aristotelia chilensis and Rubus ulmifolius. We aimed at establishing thresholds for environmental and microsite variables related to invasion.

Methods: Environmental and forest understorey variables, including canopy gaps and invasive species cover were measured in non-invaded and invaded forest sites. We expected more invasion in plots located close to invasive shrublands, and in large gaps with high solar radiation.

Results: We found no relationship between the distance to invasive shrublands and invasion probability. Solar radiation tended to be slightly related with a higher cover of R. ulmifolius, the most abundant invasive exotic plant in RCI forests. Overall, the cover of native ferns appeared to inhibit invasion.

Conclusions: The identification of variable thresholds related to invasion can be useful for guiding management decisions. Our results suggest that management should consider monitoring forest canopy gap formation and promote the establishment of ferns to reduce the probability of invasive species establishing.     

Excitatory inputs to spiny cells in layers 4 and 6 of cat striate cortex

The principal target of lateral geniculate nucleus in the cat visual cortex is the stellate neurons of layer 4. In previously reported work with intracellular recording and extracellular stimulation in slices of visual cortex, three general classes of fast excitatory synaptic potentials (EPSPs) in layer 4a spiny stellate neurons were identified. One of these classes, characterized by large and relatively invariant amplitudes (mean 1.7 mV, average coefficient of variation (CV) 0.083) were attributed to the action of geniculate axons because, unlike the other two classes, they could not be matched by intracortical inputs, using paired recording. We have examined in detail the properties of this synaptic input in twelve examples, selecting for study those EPSPs where there was secure extracellular stimulation of the single fibre input to a pair of stimuli 50 ms apart. In our analysis, we conclude that the depression that these inputs show to the second stimulus is entirely postsynaptic, since the evidence strongly suggests that the probability of transmitter release at the synaptic site(s) remains 1.0 for both stimuli. We argue that the most plausible explanation for this postsynaptic depression is a reduction in the average probability of opening the synaptic channels. Using a simple biochemical analysis (c.f. Sigworth plot), it is then possible to calculate the number of synaptic channels and their probability of opening, for each of the 12 connections. The EPSPs had a mean amplitude of 1.91 mV (+/- 1.3 mV SD) and a mean CV of 0.067 (+/- 0.022). The calculated number of channels ranged from 20 to 158 (59.4 +/- 48.7) and their probability of opening to the first EPSP had an average of 0.83 (+/- 0.09), with an average depression of the probability to 0.60 for the second EPSP. Geniculate afferents also terminate in layer 6. Intracellular recordings were also made in the upper part of this layer and a total of 51 EPSPs were recorded from pyramidal cells of three principal types. Amongst this dataset we sought EPSPs with similar properties to those characterized in layer 4a. Three examples were found, which is a much lower percentage (6%) than the incidence of putative geniculate EPSPs found in layer 4a (42%).     

Adaptation of the Blood Antioxidant Defence Mechanisms of Sheep with a Genetic Lesion Resulting in Low Red Cell Glutathione Concentrations

Finnish Landrace sheep with a genetic lesion which results in restricted cysteine transport across the red cell membrane have total glutathione concentrations in their red blood cells that are approximately 40% of those in normal sheep of the same breed. However, dimethyldisulphide-challenged red blood cells from both phenotypes produce an ESR-spin adduct at similar rates. The resistance of the low glutathione phenotype red cells to oxidant challenge is reflected by increases in the activities of antioxidant enzymes. Sheep with a genotypic disorder in cysteine transport may be a suitable model for studying the genetic expression of antioxidant enzymes in response to oxidant loads.