Effects of chemical lipid extraction and arithmetic lipid correction on stable isotope ratios of fish tissues

For accurate interpretation of fish trophodynamics from carbon stable isotope data it is necessary to extract tissue lipids. This is because lipid content varies within and among tissues in both space and time, and because lipids are 13C-depleted relative to proteins. However, lipid extraction may affect delta15N, thus requiring costly and time-consuming separation of delta13C and delta15N analyses. These problems have prompted the development of arithmetic correction techniques for delta13C, but the techniques and their underlying assumptions have not been systematically tested. This study compared the effects of lipid extraction and arithmetic correction techniques on delta13C and delta15N of European sea bass (Dicentrarchus labrax) tissues. Following Folch lipid extraction from muscle and liver, there was a mean increase in delta15N of 0.77 per thousand, but enrichment varied with lipid content such that effects on delta15N were hard to predict. Changes in delta13C and C:N between untreated and lipid-extracted samples reflected the quantity of lipid removed. The arithmetic correction techniques of mass balance and lipid correction were sensitive to the C:N of the lipid-extracted tissue and to the assumed depletion of lipid delta13C relative to protein delta13C. However, the mass balance approach was appropriate for the mathematical correction of bulk tissue data in most circumstances, provided that the C:N of lipid-extracted tissue could be determined for a small proportion of samples. Application of mass balance arithmetic correction can lead to significant time and cost savings in trophodynamic studies, because the majority of delta13C and delta15N analyses would not need to be run separately.

Tissue and fixative dependent shifts of delta13C and delta15N in preserved ecological material

Carbon and nitrogen stable isotope analyses are routinely used to investigate aquatic food webs, and have potential application in retrospective investigations using archived materials. However, such analyses assume that storage does not alter isotopic signatures of materials preserved, or that changes in isotopic composition during storage are predictable. Here we examine preservation shifts on cod (Gadus morhua) muscle, roe and liver tissue over 21 months following preservation in 80% ethanol, in 4% formaldehyde, and by freezing. Preservation shifts were not consistent among tissues. High protein tissues exhibited greater delta(15)N shifts than low protein tissues in 4% formaldehyde, while greater delta(13)C shifts occurred in relatively higher fat tissues when preserved in alcohol. Freezing did not change isotopic signatures. Responses of delta(15)N and delta(13)C are explained by differences in the preservative's isotopic signature and the reaction properties and biochemical composition of the tissues preserved. The results clarify some of the processes that lead to isotopic change during preservation.

The long Bain breathing system: an investigation into the implications of remote ventilation

A long version of the Bain breathing system is commonly used when remote anaesthesia is required, such as during magnetic resonance imaging or radiotherapy. We compared the static compliance and distal pressures over a range of flows in a 1.6 and 9.6 m Bain system. We examined the effect on ventilation of increasing the length of the Bain system in lung models for 10, 20 and 70 kg patients. We found that static compliance was increased in the long Bain system. We found that with matched peak inspiratory ventilator pressures there was a reduction in peak inspiratory pressures at the patient end with the longer system (p < 0.001). A reduction in tidal volume was found with the 9.6 m Bain (p < 0.001), and positive end-expiratory pressure was increased (p = 0.01). Although the effect on tidal volume was proportionally small in the 70 kg simulation (660 and 617 ml in 1.6 and 9.6 m systems, respectively) it increases in significance in children, with a 23% reduction in tidal volume in the 10 kg mock lung (95 and 73 ml in 1.6 and 9.6 m systems, respectively). Anaesthetists should be aware of the reduction in tidal volume and increased positive end-expiratory pressure. During remote anaesthesia with a long Bain system, the ventilator should be adjusted to compensate.

Beta-amyloid precursor protein (beta APP) as a marker for axonal injury after head injury

It has been demonstrated recently that beta-amyloid protein (beta AP), generally associated with the plaques of Alzheimer's disease, can also be found in the brains of survivors of head injury. In this study the distribution of the beta AP precursor protein (beta APP) was examined immunohistochemically to determine if it is colocalized with beta AP in such cases. beta APP immunoreactivity was observed in neuronal perikarya in the neocortex and in dystrophic neurites surrounding beta AP immunoreactive plaques i.e. in a distribution similar to that seen in Alzheimer's disease. In addition, beta APP immunoreactivity was noted within white matter tracts where it marked damaged axons. However, no colocalisation of beta APP with beta AP was observed in any white matter region. These results indicate that processing of beta APP to produce beta AP occurs in the synaptic terminal field of axons and illustrate the utility of beta APP immunoreactivity as a general marker for axonal injury.