Fine-scale population differentiation and gene flow in a terrestrial salamander (Plethodon cinereus) living in continuous habitat.

Several recent studies have shown that amphibian populations may exhibit high genetic subdivision in areas with recent fragmentation and urban development. Less is known about the potential for genetic differentiation in continuous habitats. We studied genetic differentiation of red-backed salamanders (Plethodon cinereus) across a 2-km transect through continuous forest in Virginia, USA. Mark-recapture studies suggest very little dispersal for this species, whereas homing experiments and post-Pleistocene range expansion both suggest greater dispersal abilities. We used six microsatellite loci to examine genetic population structure and differentiation between eight subpopulations of red-backed salamanders at distances from 200 m to 2 km. We also used several methods to extrapolate dispersal frequencies and test for sex-biased dispersal. We found small, but detectable differentiation among populations, even at distances as small as 200 m. Differentiation was closely correlated with distance and both Mantel tests and assignment tests were consistent with an isolation-by-distance model for the population. Extrapolations of intergenerational variance in spatial position (sigma(2)<15 m(2)) and pair-wise dispersal frequencies (4 Nm < 25 for plots separated by 300 m) both suggest limited gene flow. Additionally, tests for sex-biased dispersal imply that dispersal frequency is similarly low for both sexes. We suggest that these low levels of gene flow and the infrequent dispersal observed in mark-recapture studies may be reconciled with homing ability and range expansion if dispersing animals rarely succeed in breeding in saturated habitats, if dispersal is flexible depending on the availability of habitat, or if dispersal frequency varies across the geographic range of red-backed salamanders.

Methods and materials for the measurement of subjective and objective measurements of image quality.

The evaluation of medical imaging systems may be performed using both subjective (e.g. high contrast limiting resolution, and low contrast detail detectability), and objective/physical (e.g. characteristic curve, signal-to-noise ratio, modulation transfer function, and Wiener spectra) indices of image quality. For the purposes of Quality Assurance subjective measurements currently have a wider usage in the clinical environment due to the inherent simplicity of the measurements; however, more rigorous objective approaches are gaining acceptability, and represent a paradigm for possible future QA measurements. Both approaches have their advantages and disadvantages. There is currently wide debate as to the interpretation of these measurements. However, there appears to be a lack of standardisation among scientists in the various approaches to making these measurements, and especially so in the case of objective indices; furthermore, the measurement protocol used must have a bearing on the interpretation of subsequent results. The purpose of this paper is to (i) present the most fundamental indices in the characterisation of 'image quality', and (ii) recommend approaches to the measurement of these indices.

Effects of moderate and high doses of alcohol on attention, impulsivity, discriminability, and response bias in immediate and delayed memory task performance.

BACKGROUND: Prior studies that examined the effects of alcohol on Continuous Performance Test (CPT) performance have resulted in inconsistent outcomes. Most studies that examined the effects of alcohol on concentrated attention tasks (like the CPT) found little effect of alcohol on performance measures, even when doses that exceeded 0.8 g/kg were used. One likely reason for these inconsistencies is the varying difficulty (and sensitivity) of the task used, and as a result, comparisons between studies are difficult. This study is one in a series that examines the effects of alcohol on attention by using a difficult version of the CPT (Immediate and Delayed Memory Task--IMT/DMT). Our purpose for these studies has been two-fold, examining the effects of alcohol (1) on concentrated attention (i.e., correct detections) and (2) on errors (i.e., commission errors) previously correlated with impulsive behaviors. The first is important because previous studies have shown little effect of alcohol on attention, and the second is important because commission errors have been related to impulsive behaviors. METHODS: In the IMT/DMT, participants respond to a briefly displayed number when it is identical to the one displayed before it. The procedure includes immediate and delayed conditions where successive stimuli to be matched are delayed by 0.5 sec or by 3.5 sec. The three stimulus types included target (identical match), catch (four of five digits match), and filler (no match) stimuli. Twenty subjects completed this task after consuming either a placebo drink or a drink that contained 0.5 g/kg or 1.0 g/kg of alcohol on different days. RESULTS: The main findings were that (1) alcohol decreased the percentage of correct identifications of target stimuli; (2) alcohol increased the percentage of commission errors in relation to the number of correct target responses; and (3) alcohol decreased discriminability whereas response bias became more conservative. CONCLUSIONS: These results clearly demonstrated a time-course effect of the 1.0 g/kg alcohol dose on attention, impulsivity, discrimination, and response criteria when a variety of dependent measures are used.

Low dose zolmitriptan as a 5-HT neuroendocrine challenge agent in humans.

The 5-HT1B/D agonist sumatriptan has been used in a number of studies as a neuroendocrine challenge agent. Whether its neuroendocrine effects are centrally mediated is unclear, however, since sumatriptan shows minimal penetration of the central nervous system. Zolmitriptan shows a greater penetration into the central nervous system than sumatriptan, and has recently been shown to be an effective challenge agent. In order to determine the neuroendocrine, temperature and side effects of a 2.5 mg oral dose of zolmitriptan, 17 healthy volunteers underwent a placebo controlled, repeated measures, double blind neuroendocrine challenge. Zolmitriptan or placebo were administered, and cortisol, growth hormone, prolactin, blood pressure and temperature, were measured over four hours after the dose of zolmitriptan. Zolmitriptan at this dose was well tolerated by all subjects, with minimal side effects and only minor effects on blood pressure. There was a significant increase in serum growth hormone after zolmitriptan compared to placebo, however there were no significant effects on cortisol, prolactin or oral temperature. The neuroendocrine effects of 2.5 mg of orally administered zolmitriptan are similar to previously reported effects of sumatriptan, with minimal side effects.

Effects of inter-pond distance on the breeding ecology of tungara frogs.

Habitat and resource distributions can influence the movement and aggregation of individuals and thus have important effects on breeding behavior and ecology. Though amphibians have been model systems for the study of breeding behavior and sexual selection, most studies have examined breeding behavior within a single pond. As a result, little is known about how inter-pond distance affects breeding amphibians. We studied the effects of inter-pond distance on the breeding ecology of the tungara frog, Physalaemus pustulosus, in replicated pond arrays in which distance was varied from 0 to 50 m. We predicted that male site fidelity and male aggregation within arrays would increase with inter-pond distance, and that the opportunity for mate choice and oviposition site selectivity by females would decrease with the distance between ponds. Male site fidelity did increase with inter-pond distance. However, male aggregation decreased with distance, such that males tended to be more evenly spaced among ponds when ponds were farther apart. The opportunity for mate choice by females, measured as the number of males within the phonotactic radius of females, also decreased with inter-pond distance. Each of these three responses was consistent with a threshold effect between 5 m and 10 m in inter-pond distance. This threshold corresponded to the maximum distance at which females in laboratory choice experiments exhibited phonotaxis toward the "whine" call of a tungara male, suggesting that phonotactic limits may play an important role in tungara movements and spacing patterns. The distribution of egg masses among ponds, a potential correlate of oviposition site selectivity, did not vary with inter-pond distance. Multiple egg masses deposited on the same night were significantly overdispersed in all distance treatments, implying that females may select oviposition sites to avoid conspecific egg masses over distances of at least 50 m. Collectively, these results demonstrate that inter-pond distance may indeed affect amphibian breeding and movement behavior, and that consideration of multiple habitat patches and their spatial distributions can provide new insights into even the most well-understood mating systems.

Alcohol increases commission error rates for a continuous performance test.

BACKGROUND: Studying the effects of alcohol on Continuous Performance Test (CPT) performance was of interest for two reasons, i.e., (1) perhaps because of the ease of the task used in previous experiments, alcohol has not been found to impair performance, and (2) CPT commission errors (described below) have been related to impulsive behavior. METHODS: In this study, the CPT featured both an Immediate Memory Task (IMT) and a more difficult Delayed Memory Task (DMT). We compared the performance of 18 subjects under both alcohol and placebo conditions, using a within-subject design. Both the IMT (0.5-sec delay) and the DMT (3.5-sec delay, with distracter stimuli at 0.5-sec intervals) required the subject to respond if a briefly displayed number was identical to the one presented before it. Stimuli included target (identical match), catch (4 of 5 digits matched), and novel (random number) stimuli. On 2 separate days, subjects performed between administrations of three hourly placebo drinks or three hourly drinks containing 0.20 g/kg of alcohol (producing peak breath alcohol concentrations of approximately 0.035%). RESULTS: The main finding was that alcohol consumption increased responses to catch stimuli (i.e., commission errors) in the DMT. In contrast, performance in the IMT (the easier task) was unaffected by alcohol. Commission errors measured during peak breath alcohol concentrations were significantly correlated with scores on the Barratt Impulsivity Scale for both the IMT and DMT. Discriminability (A') between target and catch stimuli was reduced by alcohol for the DMT only. CONCLUSIONS: These data indicate that even small amounts of alcohol can produce measurable changes in CPT performance parameters if the task is of sufficient difficulty and that commission errors can be increased by alcohol consumption.

Influence of trait hostility on tryptophan depletion-induced laboratory aggression.

Previous research has indicated that laboratory aggression in men increases after temporarily reducing the synthesis and neurotransmission of serotonin (5-HT) in the brain using the plasma L-tryptophan (Trp) depletion technique. Further research indicates that male subjects selected for high trait hostility are particularly prone to increased aggression following plasma Trp depletion. In a recent study of laboratory aggression in male control subjects, we demonstrated that laboratory aggression increased following ingestion of a Trp-depleting beverage, but not after ingestion of a Trp-containing beverage nor under food-restricted conditions. We report here that the increases in aggression under Trp-depleted conditions were specific to men who scored the highest on the Buss-Perry Aggression Questionnaire. These preliminary data support earlier findings that compared to non-hostile men, hostile men may be more prone to behavior change induced by the perturbation of the 5-HT neurotransmitter system.

Plasma L-tryptophan depletion and aggression.

There is a well-established relationship between aggression and lowered serotonin neuro-transmission. Recently developed methodologies for manipulating L-tryptophan levels (and brain serotonin) have been applied to human laboratory studies of aggression. Collectively, these studies provide further evidence for the serotonin-aggression relationship. Two important findings have been made recently: (1) subsets of individuals (e.g., persons self-rating high on aggressive or hostility scales) may differ in their susceptibility to aggression produced through plasma tryptophan depletion; and (2) alcohol in combination with L-tryptophan depletion has an additive effect on aggression. All previous studies have been conducted with men. Extending these studies to women appears to be the much-needed next step given that serotonergic levels appear to vary both as a function of the menstrual cycle phase and menstrual symptomatology.

Quality assurance programme applied to mobile C-arm fluoroscopy systems.

The importance of quality assurance (QA) of X-ray equipment in diagnostic imaging departments is well recognised. However, practically no attention has been paid in the literature to the application of QA programmes to mobile C-arm fluoroscopy systems. This equipment is sometimes omitted from these programmes because it is often "off-site" from the main radiological facility and suitable QA protocols are unavailable. The need for QA can be substantiated by the fact that these systems are finding greater clinical use in orthopaedic, vascular and cardiac applications. Hence, there is a growing awareness among users for the need of good image quality and low patient radiation dose. In view of this, the objective of this study was to review the existing literature, design a suitable QA protocol for this equipment and use it to survey 10 C-arms in clinical use. The protocol was designed to address mechanical and electrical safety in addition to radiation safety and image quality. Results indicate substantial performance differences between systems with significant variations in input air kerma rate to the image receptor. The authors believe that such a protocol is necessary with a view to establishing optimal performance levels and assist in the development of suitable "write-off" criteria for such systems.

A comparison of radiation dose in examination of the abdomen using different radiological imaging techniques.

Typical radiation doses for abdominal examinations were determined for field sizes and entrance doses commonly selected on image intensifier based digital radiographic systems. In addition, measurements were also performed using conventional film-screen methods, a 100 mm camera combination and a phosphor storage computed radiography system. Both antero-posterior and postero-anterior projections were assessed. An anthropomorphic phantom loaded with lithium fluoride thermoluminescent dosimeters was used to measure entrance surface doses. Organ equivalent doses, deduced using normalized organ dose data, were used to calculate effective dose and effective dose equivalent. A comparison of the imaging techniques on the basis of effective dose indicated that significant dose reductions (by approximately a factor of 3) may be expected if the abdomen is imaged using a postero-anterior rather than an antero-posterior projection for a given imaging system. If digital imaging systems are used instead of a conventional film-screen technique, patient effective dose for a given projection can be lower by at least a factor of 5.

An investigation into the radiation dose associated with different imaging systems for chest radiology.

With the advent of digital imaging there now exists a range of imaging techniques which may be used to acquire chest images. The purpose of this investigation was to determine typical radiation doses associated with the use of a conventional film-screen system, 100 mm film technique, large-field digital image intensifier radiography, computed radiography and a scanning slit system (AMBER, Oldeft, Netherlands). Radiation doses to relevant organs were assessed using direct measurements made with lithium fluoride thermoluminescent dosemeters, together with calculations made using normalized dose data. Typical doses were assessed using anthropomorphic phantoms for both postero-anterior and lateral projections. The risk-related quantities, i.e. effective dose and effective dose equivalent, were then calculated from these organ doses. When compared on the basis of effective dose equivalent, certain imaging techniques were seen to offer the potential for significant dose reduction, possibly at the expense of image quality.