Diffusion tensor imaging of rat spinal cord in vivo

Magnetic resonance imaging, with its exquisite soft tissue contrast, is an ideal modality for investigating spinal cord pathology. While conventional MRI techniques are very sensitive for spinal cord pathology, their specificity is somewhat limited. Diffusion MRI is an advanced technique which is a very sensitive and specific indicator of the integrity of white matter tracts. Diffusion imaging has been shown to detect early ischemic changes in white matter, while conventional imaging demonstrates no change. By acquiring the complete apparent diffusion tensor (ADT), tissue diffusion properties can be expressed in terms of quantitative and rotationally invariant parameters. ^ Systematic study of SCI in vivo requires controlled animal models such as the popular rat model. To date, studies of spinal cord using ADT imaging have been performed exclusively in fixed, excised spinal cords, introducing inevitable artifacts and losing the benefits of MRI's noninvasive nature. In vivo imaging reflects the actual in vivo tissue properties, and allows each animal to be imaged at multiple time points, greatly reducing the number of animals required to achieve statistical significance. Because the spinal cord is very small, the available signal-to-noise ratio (SNR) is very low. Prior spin-echo based ADT studies of rat spinal cord have relied on high magnetic field strengths and long imaging times—on the order of 10 hours—for adequate SNR. Such long imaging times are incompatible with in vivo imaging, and are not relevant for imaging the early phases following SCI. Echo planar imaging (EPI) is one of the fastest imaging methods, and is popular for diffusion imaging. However, EPI further lowers the image SNR, and is very sensitive to small imperfections in the magnetic field, such as those introduced by the bony spine. Additionally, The small field-of-view (FOV) needed for spinal cord imaging requires large imaging gradients which generate EPI artifacts. The addition of diffusion gradients introduces yet further artifacts. ^ This work develops a method for rapid EPI-based in vivo diffusion imaging of rat spinal cord. The method involves improving the SNR using an implantable coil; reducing magnetic field inhomogeneities by means of an autoshim, and correcting EPI artifacts by post-processing. New EPI artifacts due to diffusion gradients described, and post-processing correction techniques are developed. ^ These techniques were used to obtain rotationally invariant diffusion parameters from 9 animals in vivo, and were validated using the gold-standard, but slow, spinecho based diffusion sequence. These are the first reported measurements of the ADT in spinal cord in vivo . ^ Many of the techniques described are equally applicable toward imaging of human spinal cord. We anticipate that these techniques will aid in evaluating and optimizing potential therapies, and will lead to improved patient care. ^

Role of cytochrome P450 in DNA damage produced by treatment of colon cells with 1,2-dimethylhydrazine

The study of colon cancer has taken advantage of the development of a model in animals in which tumors in the colon are easily induced by chemical treatment. When 1,2-dimethylhydrazine (DMH) is injected into rats tumor growth is observed in colon in preference to other tissues. This observation led us to investigate the Cytochrome P450 system in colon and its participation in the particular “colon sensitivity” to DMH. It has been established that the Cytochrome P450 system participates in the metabolism of DMH and the methyl carbonium product of Cytochrome P450 activation of DMH is responsible for DNA damage which is considered an initial step to carcinogenesis. The Cytochrome P450 system is a reasonable place to search for an explanation of this organotropic effect of DMH and we feel that the knowledge obtained from this study can take us closer to understanding the development of colonic malignancy. In our study we used a human colon cell line (LS174T) treated with DMH. The Cytochrome P450 system in the cells was manipulated with inducers of different isoforms of Cytochrome P450. The effect of DMH on colon cells was measured by determination of O-6-methylguanine which is a DNA adduct derived from the metabolism of this chemical and is associated with development of tumors. Our results support the hypothesis that Cytochrome P450 plays an important role in the damage to cellular DNA by DMH. This damage is increased after induction of Cytochromes P450 1A1 and 2E1. The effect of inhibition of the methyltransferase and glutathione systems on protection against DMH damage in colon demonstrated the importance of the protective role of the former and the lack of effective protection of the latter system. ^

Molecular mechanism of PUVA-induced apoptosis in mouse epidermal cells

A combination of psoralens and ultraviolet-A radiation referred to as PUVA, is widely used in the treatment of psoriasis. PUVA therapy is highly effective in killing hyperproliferative cells, but its mechanism of action has not been fully elucidated. Psoralen binds to DNA, and upon photoactivation by UVA, it forms monofunctional adducts and interstrand cross-links. PUVA treatment has been shown to be mutagenic and to produce tumors in animals. In addition, epidemiological studies have reported a 10 to 15 percent increased risk of developing squamous cell carcinoma in individuals treated chronically with PUVA. However, it remains a treatment for skin disorders such as psoriasis because its benefits outweigh its risks. The widespread use of PUVA therapy and its associated cancer risk requires us to understand the molecular mechanisms by which PUVA induces cell death. Immortalized JB6 mouse epidermal cells, p53−/− mice, and Fas Ligand−/− (gld) mice were used to investigate the molecular mechanism by which PUVA kills cells. Treatment of JB6 cells with 10 μg/ml 8-methoxypsoralen followed by irradiation with 20 kJ/m2 UVA resulted in cell death. The cells exhibited morphological and biochemical characteristics of apoptosis such as chromatin condensation, DNA ladder formation, and TUNEL-positivity. PUVA treatment stabilized and phosphorylated p53 leading to its activation, as measured by nuclear localization and induction of p21Waf/Cip1, a transcriptional target of p53. Subsequent in vivo studies revealed that there was statistically significantly less apoptosis in p53 −/− mice than in p53+/+ mice at 72 hours after PUVA. In addition, immunohistochemical analysis revealed more Fas and FasL expression in p53+/+ mice than in p53−/− mice, suggesting that p53 is required to transcriptionally activate Fas, which in turn causes the cells to undergo apoptosis. Studies with gld mice confirmed a role for Fas/FasL interactions in PUVA-induced apoptosis. There was statistically significantly less apoptosis in gld mice compared with wild-type mice 24, 48, and 72 hours after PUVA. These results demonstrate that PUVA-induced apoptosis in mouse epidermal cells requires p53 and Fas/FasL interactions. These findings may be important for designing effective treatments for diseases such as psoriasis without increasing the patient's risk for skin cancer. ^

Role of entorhinal cortical plasticity in spatial and contextual memory

It is well accepted that the hippocampus (HIP) is important for spatial and contextual memories, however, it is not clear if the entorhinal cortex (EC), the main input/output structure for the hippocampus, is also necessary for memory storage. Damage to the EC in humans results in memory deficits. However, animal studies report conflicting results on whether the EC is necessary for spatial and contextual memory. Memory consolidation requires gene expression and protein synthesis, mediated by signaling cascades and transcription factors. Extracellular-signal regulated kinase (ERK) cascade activity is necessary for long-term memory in several tasks, including those that test spatial and contextual memory. In this work, we explore the role of ERK-mediated plasticity in the EC on spatial and contextual memory. ^ To evaluate this role, post-training infusions of reversible pharmacological inhibitors specific for the ERK cascade that do not affect normal neuronal activity were targeted directly to the EC of awake, behaving animals. This technique provides spatial and temporal control over the inhibition of the ERK cascade without affecting performance during training or testing. Using the Morris water maze to study spatial memory, we found that ERK inhibition in the EC resulted in long-term memory deficits consistent with a loss of spatial strategy information. When animals were allowed to learn and consolidate a spatial strategy for solving the task prior to training and ERK inhibition, the deficit was alleviated. To study contextual memory, we trained animals in a cued fear-conditioning task and saw an increase in the activation of ERK in the EC 90 minutes following training. ERK inhibition in the EC over this time point, but not at an earlier time point, resulted in increased freezing to the context, but not to the tone, during a 48-hour retention test. In addition, animals froze maximally at the time the shock was given during training; similar to naïve animals receiving additional training, suggesting that ERK-mediated plasticity in the EC normally suppresses the temporal nature of the freezing response. These findings demonstrate that plasticity in the EC is necessary for both spatial and contextual memory, specifically in the retention of behavioral strategies. ^

Effectiveness of healthcare waste management interventions in developing countries

Inefficiencies during the management of healthcare waste can give rise to undesirable health effects such as transmission of infections and environmental pollution within and beyond the health facilities generating these wastes. Factors such as prevalence of diseases, conflicts, and the efflux of intellectual capacity make low income countries more susceptible to these adverse health effects. The purpose of this systematic review was to describe the effectiveness of interventions geared towards better managing the generation, collection, transport, treatment and disposal of medical waste, as they have been applied in lower and middle income countries.^ Using a systematic search strategy and evaluation of study quality, this study reviewed the literature for published studies on healthcare waste management interventions carried out in developing countries, specifically the low and lower middle income countries from year 2000 to the current year. From an initially identified set of 829 studies, only three studies ultimately met all inclusion, exclusion and high quality criteria. A multi component intervention in Syrian Arab Republic, conducted in 2007 was aimed at improving waste segregation practice in a hospital setting. There was an increased use of segregation boxes and reduced rates of sharps injury among staff as a result of the intervention. Another study, conducted in 2008, trained medical students as monitors of waste segregation practice in an Indian teaching hospital. There was improved practice in wards and laboratories but not in the intensive care units. The third study, performed in 2008 in China, consisted of modification of the components of a medical waste incinerator to improve efficiency and reduce stack emissions. Gaseous pollutants emitted, except polychlorodibenzofurans (PCDF) were below US EPA permissible exposure limits. Heavy metal residues in the fly ash remained unchanged.^ Due to the paucity of well-designed studies, there is insufficient evidence in literature to conclude on the effectiveness of interventions in low income settings. There is suggestive but insufficient evident that multi-component interventions aimed at improving waste segregation through behavior modification, provision of segregation tools and training of monitors are effective in low income settings.^

AN INVESTIGATION OF THE MODIFYING EFFECTS OF VITAMIN A AND HYPOXIC CELL SENSITIZERS IN RADIATION CARCINOGENESIS IN MICE

The effect of vitamin A (retinyl acetate) and three hypoxic cell sensitizers (metronidazole, misonidazole and desmethylmisonidazole) on lung tumor development in strain A mice exposed to radiation was assessed.^ In experiments involving vitamin A, two groups of mice were fed a low vitamin A diet (< 100 IU/100g diet) while the two other groups were fed a high vitamin A diet (800 IU/100g diet). After two weeks one group maintained on the high vitamin A diet and one group maintained on the low vitamin A diet were given an acute dose of 500 rad of gamma radiation to the thoracic region. The circulating level of plasma vitamin A in all four groups of mice was monitored. A difference in circulating vitamin A in the mice maintained on high and low vitamin A diet became evident by 20 weeks and continued for the duration of the experiment. Mice were killed 18, 26, and 40 weeks post irradiation, their lungs were removed and the number of surface adenomas were counted. There was a significant increase in the number of mice bearing lung tumors and the mean number of lung tumors per mouse in the irradiated group maintained on the high vitamin A diet at 40 weeks post irradiation as compared to the irradiated group maintained on a low vitamin A diet (p < 0.05). Under the conditions of this experiment the development of pulmonary adenomas in irradiated strain A mice appears to relate directly to circulating levels of vitamin A.^ In the other experiment two dose levels of the hypoxic cell sensitizers, 0.2mg/g and 0.6mg/g, were used either alone or in combination with 900 rad of gamma radiation in a fractionated dose schedule of twice a week for three weeks. In the groups of mice which received hypoxic cell sensitizers only, the prevalence and the mean number of lung tumors per mouse were somewhat increased (p < 0.10) in the higher dose group (0.6mg/g) of misonidazole but was not significantly different from the control animals in the other two sensitizer groups. The combination of hypoxic cell sensitizer and radiation did not show any significant enhancement of lung tumor response when compared with the group which received radiation only. The dose of radiation used in this study significantly enhanced lung tumor formation in mice when compared with the control group. Thus, under the experimental exposure conditions used in this investigation, which were very similar to the exposure conditions occurring in clinical treatment, all three hypoxic cell sensitizers did not sensitize the mouse to the carcinogenic effects of gamma radiation.^

2005 ACIP recommendations effect on newborn hepatitis B vaccination rates and the factors affecting the successful implementation of the recommendations in the US

Background. Hepatitis B virus infection is one of major causes of acute and chronic hepatitis, cirrhosis of the liver, and primary hepatocellular carcinoma. Hepatitis B and its long term consequences are major health problems in the United States. Hepatitis B virus can be vertically transmitted from mother to infant during birth. Hepatitis B vaccination at birth is the most effective measure to prevent the newborn from HBV infection and its consequences, and is part of any robust perinatal hepatitis B prevention program following ACIP recommendations. Universal vaccination of the new born will prevent HBV infection during early childhood and, assuming that children receive the three dosages of the vaccine, it will also prevent adolescent and adult infections. Hepatitis B vaccination is now recommended as part of a comprehensive strategy to eliminate HBV transmission in the United States. ^ Objective. (1)To assess if the hepatitis B vaccination rates of newborn babies have improved after the 2005 ACIP recommendations. (2) To identify factors that affects the implementation of ACIP recommendation for hepatitis B vaccination in newborn babies. These factors will encourage ongoing improvement by identifying successful efforts and pinpointing areas that fall short and need attention. Additional focus areas may be identified to accelerate progress in eliminating perinatal HBV transmission.^ Methods. This review includes information from all pertinent articles, reviews, National immunization survey (NIS) surveys, reports, peer reviewed literature and web sources that were published after 1991.The key words to be used for selecting the articles are: "Perinatal Hepatitis B Prevention program", "Universal Hepatitis B vaccination of newborn babies", "ACIP Recommendations." The data gathered will be supplemented with an analysis of vaccination rates using the National Immunization Survey (NIS) birth dose coverage data.^ Results. The data collected in the NIS of 2009 reveals that the national coverage for birth dose of HepB increased to 60.8% from 50.1% in 2006. The largest increase observed for the birth dose in the past 5 years is from 2008 which increased from 55.3 % to 60.8% in 2009. By state, coverage ranged from 22.8% in Vermont to 80.7% in Michigan. %. Overall, in 2009 the estimated vaccination rates are in higher ranges for most states compared to the estimated vaccination rates in 2006. States vary widely in hepatitis B vaccination rates and in their compliance with the 2005 ACIP recommendation. There are many factors at various stages that might affect the successful implementation of the new ACIP recommendation as revealed in literature review. ^ Conclusions. HBV perinatal transmission can be eliminated, but it requires identifying the gaps and measures taken to increase the current vaccination coverage, ensuring timely administration of post exposure immunoprophylaxis and continued evaluations of the impact of immunization recommendations.^

TRPV1 Channels Contribute to Behavioral Hypersensitivity and Spontaneous Activity in Nociceptors After Spinal Cord Injury

A majority of persons who have sustained spinal cord injury (SCI) develop chronic pain. While most investigators have assumed that the critical mechanisms underlying neuropathic pain after SCI are restricted to the central nervous system (CNS), recent studies showed that contusive SCI results in a large increase in spontaneous activity in primary nociceptors, which is correlated significantly with mechanical allodynia and thermal hyperalgesia. Upregulation of ion channel transient receptor vanilloid 1 (TRPV1) has been observed in the dorsal horn of the spinal cord after SCI, and reduction of SCI-induced hyperalgesia by a TRPV1 antagonist has been claimed. However, the possibility that SCI enhances TRPV1 expression and function in nociceptors has not been tested. I produced contusive SCI at thoracic level T10 in adult, male rats and harvested lumbar (L4/L5) dorsal root ganglia (DRG) from sham-treated and SCI rats 3 days and 1 month after injury, as well as from age-matched naive control rats. Whole-cell patch clamp recordings were made from small (soma diameter <30 >μm) DRG neurons 18 hours after dissociation. Capsaicin-induced currents were significantly increased 1 month, but not 3 days, after SCI compared to neurons from control animals. In addition, Ca2+ transients imaged during capsaicin application were significantly greater 1 month after SCI. Western blot experiments indicated that expression of TRPV1 protein in DRG is also increased 1 month after SCI. A major role for TRPV1 channels in pain-related behavior was indicated by the ability of a specific TRPV1 antagonist, AMG9810, to reverse SCI-induced hypersensitivity of hindlimb withdrawal responses to heat and mechanical stimuli. Similar reversal of behavioral hypersensitivity was induced by intrathecal delivery of oligodeoxynucleotides antisense to TRPV1, which knocked down TRPV1 protein and reduced capsaicin-evoked currents. TRPV1 knockdown also decreased the incidence of spontaneous activity in dissociated nociceptors after SCI. Limited activation of TRPV1 was found to induce prolonged repetitive firing without accommodation or desensitization, and this effect was enhanced by SCI. These data suggest that SCI enhances TRPV1 expression and function in primary nociceptors, increasing the excitability and spontaneous activity of these neurons, thus contributing to chronic pain after SCI.