A discrete-time logistic model of frond dynamics for Mazzaella parksii (Rhodophyta, Gigartinales)

Mathematical modelling is useful in population ecology and resource management. Logistic models have traditionally been applied to unitary organisms, but it is unclear whether they could be used at the frond (ramet) level for clonal seaweeds. This study shows that frond dynamics for the clonal seaweed Mazzaella parksii (=M. cornucopiae) can be described by a discrete-time logistic model. The model is realistic in that it includes density-dependence, which was previously demonstrated experimentally for this species, and only necessitates data on frond density measured at discrete time intervals. This may constitute a useful tool for the management of clonal seaweeds of economic importance that occur in dense stands. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in Antioxidant Defense Enzymes after d-amphetamine Exposure: Implications as an Animal Model of Mania

Studies have demonstrated that oxidative stress is associated with amphetamine-induced neurotoxicity, but little is known about the adaptations of antioxidant enzymes in the brain after amphetamine exposure. We studied the effects of acute and chronic amphetamine administration on superoxide dismutase (SOD) and catalase (CAT) activity, in a rodent model of mania. Male Wistar rats received either a single IP injection of d-amphetamine (1 mg/kg, 2 mg/kg, or 4 mg/kg) or vehicle (acute treatment). In the chronic treatment rats received a daily IP injection of either d-amphetamine (1 mg/kg, 2 mg/kg, or 4 mg/kg) or vehicle for 7 days. Locomotor behavior was assessed using the open field test. SOD and CAT activities were measured in the prefrontal cortex, hippocampus, and striatum. Acute and to a greater extent chronic amphetamine treatment increased locomotor behavior and affected SOD and CAT activities in the prefrontal cortex, hippocampus and striatum. Our findings suggest that amphetamine exposure is associated with an imbalance between SOD and CAT activity in the prefrontal cortex, hippocampus and striatum.     

Lipopolysaccharide-induced fever alters Hering–Breuer reflex in anesthetized rats

The aim of the study was to test the hypothesis that control of breathing via Hering–Breuer reflex (HB) is influenced by lipopolysaccharide (LPS)-induced fever in rats. Animals were injected intraperitoneally with LPS and control group with an equivalent volume of saline. HB reflex was elicited by inflations of the lungs followed by occlusion of the airways under control of esophageal pressure. Duration of HB reflex (T_apnoe) was continuously reduced as body temperature rose during experiment. Compared to normothermic controls, animals with fever had significant shortening of T_apnoe at 240 min and 300 min after LPS administration. Fever was further accompanied by a reduction in the strength of HB reflex (inhibitory ratio, IR). In comparison with controls, significant decrease of IR was observed at 300 min after LPS injection. Conclusion: altered neural control of breathing demonstrated by decreased power of Hering–Breuer inflation reflex in conditions of LPS-induced fever may facilitate thermal tachypnoea and/or play a role in the origin of respiratory instability accompanying febrile response.     

Refining predictions of climate change impacts on plant species distribution through the use of local statistics

Bioclimate envelope models are often used to predict changes in species distribution arising from changes in climate. These models are typically based on observed correlations between current species distribution and climate data. One limitation of this basic approach is that the relationship modelled is assumed to be constant in space; the analysis is global with the relationship assumed to be spatially stationary. Here, it is shown that by using a local regression analysis, which allows the relationship under study to vary in space, rather than conventional global regression analysis it is possible to increase the accuracy of bioclimate envelope modelling. This is demonstrated for the distribution of Spotted Meddick in Great Britain using data relating to three time periods, including predictions for the 2080s based on two climate change scenarios. Species distribution and climate data were available for two of the time periods studied and this allowed comparison of bioclimate envelope model outputs derived using the local and global regression analyses. For both time periods, the area under the receiver operating characteristics curve derived from the analysis based on local statistics was significantly higher than that from the conventional global analysis; the curve comparisons were also undertaken with an approach that recognised the dependent nature of the data sets compared. Marked differences in the future distribution of the species predicted from the local and global based analyses were evident and highlight a need for further consideration of local issues in modelling ecological variables.