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Survival into adult life in patients with aortic coarctation is typical following surgical and catheter-based techniques to relieve obstruction. Late sequelae are recognised, including stroke, hypertension, and intracerebral aneurysm formation, with the underlying mechanisms being unclear. We hypothesised that patients with a history of aortic coarctation may have abnormalities of cerebral blood flow compared with controls.
Patients with a history of aortic coarctation underwent assessment of cerebral vascular function. Vascular responsiveness of intracranial vessels to hypercapnia and degree of cerebral artery stiffness using Doppler-derived pulsatility indices were used. Response to photic stimuli was used to assess neurovascular coupling, which reflects endothelial function in response to neuronal activation. Patient results were compared with age- and sex-matched controls.
A total of 13 adult patients (males=10; 77%) along with 13 controls underwent evaluation. The mean age was 36.1±3.7 years in the patient group. Patients with a background of aortic coarctation were noted to have increased pulse pressure on blood pressure assessment at baseline with increased intracranial artery stiffness compared with controls. Patients with a history of aortic coarctation had less reactive cerebral vasculature to hypercapnic stimuli and impaired neurovascular coupling compared with controls.
Adult patients with aortic coarctation had increased intracranial artery stiffness compared with controls, in addition to cerebral vasculature showing less responsiveness to hypercapnic and photic stimuli. Further studies are required to assess the aetiology and consequences of these documented abnormalities in cerebral blood flow in terms of stroke risk, cerebral aneurysm formation, and cognitive dysfunction.
Empirical evidence for the effectiveness of community treatment orders (CTOs) is at best mixed. We examine CTOs through the prism of human rights and discrimination, bearing the evidence in mind, and argue that a necessary condition for their use is that a person lacks decision-making capacity.
Several states in the Midwestern United States are using risk assessment to determine the invasiveness of introduced plant species, and each assessment process is different. This may lead to differences in results for the same species between states, creating concern about credibility by those using the assessments. In this study, risk assessments for six Midwestern states were compared, examining format, content, and assessment committee membership. Case studies were conducted for four species for which at least five of the six states in the study completed a risk assessment; results were compared in the context of general differences in assessment content and those specific to each species. Furthermore, 14 species for which only four of the six states completed assessments were briefly examined for outcome differences only, and possible reasons for these inconsistencies. Overall, differences in assessments did not result in incompatible conclusions for the species compared, suggesting that unique assessments in each state can provide consistent and credible results. We propose that these Midwestern states share species resources with each other to further improve consistency between the assessments.
Surgical activity is probably the most important component of surgical training. During the first year of surgical residency, there is an early opportunity for the development of surgical skills, before disparities between the skill sets of residents increase in future years. It is likely that surgical skill is related to operative volumes. There are no published guidelines that quantify the number of surgical cases required to achieve surgical competency. The aim of this study was to describe the current trends in surgical activity in a recent cohort of first-year Canadian neurosurgical trainees.
This study utilized retrospective database review and survey methodology to describe the current state of surgical training for first-year neurosurgical trainees. A committee of five residents designed this survey in an effort to capture factors that may influence the operative activity of trainees.
Nine out of a cohort of 20 first-year Canadian neurosurgical trainees that began training in July of 2008 participated in the study. The median number of cases completed by a resident during the initial three month neurosurgical rotation was 66, within which the trainee was identified as the primary surgeon in 12 cases. Intracranial hemorrhage and cerebrospinal fluid diversion procedures were the most common operations to have the trainee as primary surgeon.
Based on this pilot study, it appears that the operative activity of Canadian first-year residents is at least equivalent to the residents of other studied training systems with respect to volume and diversity of surgical activity.
Maize with enhanced provitamin A carotenoids (biofortified), accomplished through conventional plant breeding, maintains vitamin A (VA) status in Mongolian gerbils (Meriones unguiculatus). Two studies in gerbils compared the VA value of β-cryptoxanthin with β-carotene. Study 1 (n 47) examined oil supplements and study 2 (n 46) used maize with enhanced β-cryptoxanthin and β-carotene. After 4 weeks' depletion, seven or six gerbils were killed; remaining gerbils were placed into weight-matched groups of 10. In study 1, daily supplements were cottonseed oil, and 35, 35 or 17·5 nmol VA (retinyl acetate), β-cryptoxanthin or β-carotene, respectively, for 3 weeks. In study 2, one group of gerbils was fed a 50 % biofortified maize diet which contained 2·9 nmol β-cryptoxanthin and 3·2 nmol β-carotene/g feed. Other groups were given equivalent β-carotene or VA supplements based on prior-day intake from the biofortified maize or oil only for 4 weeks. In study 1, liver retinol was higher in the VA (0·74 (sd 0·11) μmol) and β-cryptoxanthin (0·65 (sd 0·10) μmol) groups than in the β-carotene (0·49 (sd 0·13) μmol) and control (0·41 (sd 0·16) μmol) groups (P < 0·05). In study 2, the VA (1·17 (sd 0·19) μmol) and maize (0·71 (sd 0·18) μmol) groups had higher liver retinol than the control (0·42 (sd 0·16) μmol) group (P < 0·05), whereas the β-carotene (0·57 (sd 0·21) μmol) group did not. Bioconversion factors (i.e. 2·74 μg β-cryptoxanthin and 2·4 μg β-carotene equivalents in maize to 1 μg retinol) were lower than the Institute of Medicine values.
So far, we have concentrated on the techniques for manipulating the genome of E. coli. However, it is very likely that we will need to work with other organisms, too. We might be interested in some aspect of the biology of another species and want to study the effect of modifying it in some way. We might want to make genetically altered versions of commercially important species, such as crop plants, to improve their value. Or we might want to produce a protein in a form that requires some post-translational modification that E. coli is unable to accomplish. The principles that we have seen for E. coli apply in exactly the same way. We need to have suitable vectors, a means of getting the DNA into the organism and ways to select transformants. We may also need to take steps to increase expression. Often, we first clone DNA from one organism in E. coli and identify a recombinant containing a particular gene of interest. We then transfer that gene into some other host species to alter the host's properties. An organism containing a gene derived from elsewhere is said to be transgenic.
In this chapter we will look at the vectors and transformation systems available for a range of other organisms. We will look first at bacteria, and then we will consider fungi, plants (including algae) and animals.
So far, we have seen how to clone particular sequences and identify them. In Chapter 8 we will look at how these clones can be put to use directly at the DNA level or to direct the synthesis of RNA or protein. However, it is often the case that we need to modify sequences before using them. Here are just three of the many situations in which we may need to do this:
(a) We are trying to identify promoters and regulatory sequences, and need to make a mutation in a putative promoter or regulatory sequence to see whether that actually affects the efficiency of transcription initiation.
(b) We are interested in how the primary and higher order structures of a protein determine its function. It might, therefore, be necessary to modify the codon for an amino acid we believe to be at the active site of an enzyme and then assess the effects of that change on catalytic activity. Directed alteration of particular parts of proteins as a way of probing the relationship between structure and function or altering the function in a controlled way is often termed protein engineering.
(c) Genes are often cloned without our fully understanding the role that the proteins they encode have in the cell. Assessing that role may be possible by inactivating the endogenous gene in an organism to generate a mutant strain. This approach is often called reverse genetics, to emphasize the contrast with the traditional approach whereby a strain carrying a mutation with specific effects is characterized first and the relevant gene cloned and analysed subsequently.
Later chapters will describe the techniques for the amplification of DNA sequences by propagation inside cells. However, it is often possible to amplify specific sequences more simply and quickly by a direct enzymatic process called the polymerase chain reaction or PCR. The basic procedure is outlined in Figure 2.1. In the simplest case, PCR amplification requires that we know a small amount of nucleotide sequence at each end of the region to be amplified. Oligonucleotides complementary to that sequence are synthesized, typically 20 or so nucleotides long. These oligonucleotides are used as primers for enzymatic amplification.
A reaction mixture is set up containing a sample of DNA that includes the region to be amplified, the primers in large molar excess, deoxynucleoside triphosphates (dNTPs) and a heat-stable DNA polymerase. The most common enzyme for this purpose is the Taq polymerase, which is a DNA polymerase isolated from the thermophilic bacterium Thermus aquaticus, which can be grown routinely in the laboratory at 75°C or more. This enzyme, which the bacterium uses for cellular DNA synthesis, has a temperature optimum of at least 80°C and is not readily denatured by the repeated heating and cooling cycles that we shall see are needed in the amplification process. There are many other thermophilic bacteria, and their polymerases can also be used, as discussed below.