Relationship of biomedical science content acquisition performance to students' level of PBL group interaction: are students learning during PBL group?

This study assessed biomedical science content acquisition from problem-based learning (PBL) and its relationship to students' level of group interaction. We hypothesized that learning in preparation for exams results primarily from individual study of post-case learning objectives and that outcomes would be unrelated to students' group involvement. During dental curricular years 1 and 2, student-generated biomedical learning issues (LIs) were identified from six randomly chosen PBL cases. Knowledge and application of case concepts were assessed with quizzes based on the identified LIs prior to dissemination of the learning objectives. Students and facilitators were surveyed on students' level of group involvement for the assessed LI topics. Year 1 students had significantly higher assessment scores (p=0.0001). For both student classes, means were significantly higher for the recall item (Q1) than for the application item (Q2). Q1 scores increased along with the student's reported role for Year 1 (p=0.04). However, there was no relationship between the student's reported role and Q1 for Year 2 (p=0.20). There was no relationship between the student's reported role and Q2 for Year 1 (p=0.09) or Year 2 (p=0.19). This suggests that students' level of group involvement on the biomedical learning issues did not significantly impact students' assessment performance.     

Interplay between fluoride and abrasivity of dentifrices on dental erosion–abrasion

Objectives

Eroded teeth are more susceptible to toothbrushing wear than sound teeth. We tested the hypothesis that fluoride and abrasivity of dentifrices can interact, modulating the development of erosive–abrasive lesions.

Methods

Human enamel and root dentin specimens were submitted to cycles of demineralization, remineralization and toothbrushing using six dentifrices formulated with three different abrasivity levels: low (L), medium (M) and high (H); with (+F) and without (−F) fluoride. Surface loss was quantified by optical profilometry and compared among groups (α = 0.05).

Results

In dentin, it was ranked: L < M < H, for both +F and −F dentifrices. In enamel, +F dentifrices had similar results; however for −F formulations, M and H did not differ. Fluoride reduced surface loss in enamel, at all abrasive levels. In dentin, the same fluoride effect was observed but only for the low abrasive formulation.

Conclusions

Both fluoride and abrasivity were important modulators of enamel surface loss, while abrasivity had a higher impact than fluoride on dentin.     

Treatment with 3‐aminobenzamide during ex vivo lung perfusion of damaged rat lungs reduces graft injury and dysfunction after transplantation

Ex vivo lung perfusion (EVLP) with pharmacological reconditioning may increase donor lung utilization for transplantation (LTx). 3‐Aminobenzamide (3‐AB), an inhibitor of poly(ADP‐ribose) polymerase (PARP), reduces ex vivo lung injury in rat lungs damaged by warm ischemia (WI). Here we determined the effects of 3‐AB reconditioning on graft outcome after LTx. Three groups of donor lungs were studied: Control (Ctrl): 1 hour WI + 3 hours cold ischemia (CI) + LTx; EVLP: 1 hour WI + 3 hours EVLP + LTx; EVLP + 3‐AB: 1 hour WI + 3 hours EVLP + 3‐AB (1 mg^.mL^?1) + LTx. Two hours after LTx, we determined lung graft compliance, edema, histology, neutrophil counts in bronchoalveolar lavage (BAL), mRNA levels of adhesion molecules within the graft, as well as concentrations of interleukin‐6 and 10 (IL‐6, IL‐10) in BAL and plasma. 3‐AB reconditioning during EVLP improved compliance and reduced lung edema, neutrophil infiltration, and the expression of adhesion molecules within the transplanted lungs. 3‐AB also attenuated the IL‐6/IL‐10 ratio in BAL and plasma, supporting an improved balance between pro‐ and anti‐inflammatory mediators. Thus, 3‐AB reconditioning during EVLP of rat lung grafts damaged by WI markedly reduces inflammation, edema, and physiological deterioration after LTx, supporting the use of PARP inhibitors for the rehabilitation of damaged lungs during EVLP.     

Superficial- and deep-tissue temperature increases in anesthetized dogs during exposure to high specific absorption rates in a 1.5-T MR imager

Superficial- and deep-tissue heating was measured in five dogs during high-specific-absorption-rate radiofrequency (RF) irradiation to see whether significant temperature changes could be produced by a 1.5-T clinical magnetic resonance imager. The RF power output employed was 6.3 times that required for routine imaging. Temperature probes were placed in both deep and superficial tissues, and temperatures were recorded before, during, and after exposure. In each dog, there was a linear temperature increase of several degrees during RF exposure; the maximal average change was 4.6 degrees C in the urinary bladder. The temperature increase was slightly greater in deep tissues than in superficial tissues. The calculated specific absorption rate, based on the temperature change, averaged 7.9 W/kg for all five dogs. These findings argue for continued caution in the design and operation of imagers capable of high specific absorption rates, particularly when they are used for imaging infants or patients with altered thermoregulatory capability.     

Randomized pharmacodynamic and pharmacogenetic trial of dronabinol effects on colon transit in irritable bowel syndrome-diarrhea

Background Genetic variation in endocannabinoid metabolism is associated with colonic transit in irritable bowel syndrome (IBS) with diarrhea (IBS‐D). The nonselective cannabinoid (CB) receptor agonist, dronabinol (DRO), reduced fasting colonic motility in nonconstipated IBS. FAAH and CNR1 variants influenced DRO’s effects on colonic motility. Our aims were: (i) to compare dose‐related effects of DRO to placebo (PLA) on gut transit in IBS‐D, and (ii) to examine influence of genetic variations in CB mechanisms on DRO’s transit effects. Methods Thirty‐six IBS‐D volunteers were randomized (double‐blind, concealed allocation) to twice per day PLA (n = 13), DRO 2.5 mg (n = 10), or DRO 5 mg (n = 13) for 2 days. We assessed gastric, small bowel, and colonic transit by validated radioscintigraphy and genotyped the single nucleotide polymorphisms CNR1 rs806378 and FAAH rs324420. Data analysis utilized a dominant genetic model. Key Results Overall treatment effects of DRO on gastric, small bowel, or colonic transit were not detected. CNR1 rs806378 CT/TT was associated with a modest delay in colonic transit at 24 h compared with CC (P = 0.13 for differential treatment effects on postminus pretreatment changes in colonic transit by genotype). No significant interaction of treatment with FAAH rs324420 was detected. Conclusions & Inferences Overall, DRO 2.5 or 5 mg twice per day for 2 days had no effect on gut transit in IBS‐D. There appears to be a treatment‐by‐genotype effect, whereby DRO preferentially delays colonic transit in those with the CNR1 rs806378 CT/TT genotypes. Further study of CB pharmacogenetics may help identify a subset of IBS‐D patients most likely to benefit from CB agonist therapy.     

Enriched environment exposure regulates excitability, synaptic transmission, and LTP in the dentate gyrus of freely moving rats

Performance in hippocampus-dependent and other tasks can be improved by exposure to an enriched environment (EE), but the physiological changes in neural function that may mediate these effects are poorly understood. To date, there have been conflicting reports regarding potential mechanisms, such as an increase in basal synaptic transmission, an increase in cell excitability, or altered synaptic plasticity. Here, we reexamined in freely moving animals the conditions under which varying degrees of EE exposure might lead to increases in synaptic or neural function in the dentate gyrus of the hippocampus. Adult male Sprague-Dawley rats were chronically implanted with stimulating and recording electrodes in the perforant path and dentate gyrus, respectively, and housed singly in standard cages. After stable recordings were established for field excitatory postsynaptic potentials (fEPSPs) and population spikes (PSs), the effects of various degrees of periodic novel environment exposure for 19 days were assessed. Exposure to an EE increased fEPSPs, but only when animals were kept in nominally low-stress housing conditions. An increase in granule-cell excitability, as evidenced by PS increases, was induced by all environmental treatments with the greatest effect being induced by overnight EE exposure. EE exposure did not change the level of long-term potentiation (LTP) induced by a moderate high-frequency tetanus, but continued EE exposure post-tetanus produced a significantly faster decay of LTP relative to control animals. These results suggest that, in adult animals, EE exposure may augment hippocampal information processing, but may also speed turnover of information in the hippocampus during the maintenance period.     

Digital imaging of the chest

During the past several years, image acquisition in nuclear medicine, computed tomography, ultrasonography, subtraction angiography, and magnetic resonance has been by digitization. Despite these advances, research in the development of digital imaging in conventional radiography has lagged behind. Although studies with a variety of digital techniques have been carried out on several fronts, we still do not possess a method that has captured the imagination of the majority of radiologists and other physicians to a point where it could replace conventional screen-film imaging. This article reviews the current status and general principles of the technology, focusing on the four digital radiographic techniques that have shown the greatest promise - film digitization, an image intensifier - based system, photostimulable phosphor plates, and a scanned projection system. The physical aspects of each of the four systems and the clinical results that have been reported to date, as well as the advantages and disadvantages of each system, are presented.     

Stabilization of mitochondrial function by Ginkgo biloba extract (EGb 761)

A large body of data emphasizes the central role of mitochondrial dysfunction during aging and as an early event in neurodegenerative diseases. In this study we used PC12 cells and dissociated mice brain cells, as well as isolated mitochondria to investigate the effects of EGb 761 on mitochondrial functions. We mimicked mitochondrial abnormalities during aging by using external factors (nitrosative stress, serum deprivation and complexes inhibitors) consequently altering mitochondrial processes, such as energy metabolism. As markers for the function of mitochondria, ATP levels and mitochondrial membrane potential were measured. EGb 761 alleviated mitochondrial functions in vitro at concentrations as low as 0.01 mg/ml. Treating two different age groups of mice with EGb 761 (100mg/kg body weight for 14 days) showed beneficial effects on complexes I, IV and V of the mitochondrial respiratory chain and against nitrosative stress. Interestingly, these effects were only observed in the aged mice group, proving higher efficacy of EGb 761 during aging. The single components of EGb 761 showed in both cell models protection of the mitochondrial membrane potential indicating that a complementary action of the components is responsible for the versatile actions of EGb 761.