Oswald Biological Sciences Second Place: RNA Degradation is Elevated with Age-, but not Disuse-Associated Skeletal Muscle Atrophy

Aging and inactivity are both associated with decreased muscle size and protein content. The possible role of RNA degradation in the loss of protein has not yet been investigated. Therefore, we hypothesized that RNA degradation was elevated with muscle atrophy in aging and disuse. Brown Norway/Fisher344 male rats at 6 and 32 months were hindlimb suspended (HS) for 14 days to induce muscle atrophy or remained weight bearing (WB). Cytosolic extracts from gastrocnemius muscles were prepared for Western analysis of DCP-2 protein (marker of p-bodies) and RNA degradation assay. In vitro total RNA decay assay was performed using 30ug of total RNA (from tibialis anterior) incubated with 20ug of S15 extracts from gastrocnemius. RNA integrity was determined using the Agilent Technologies algorithm to calculate the RNA Integrity Number (RIN); decay rate and half-life were calculated for each sample. Results indicated an increase in DCP-2 protein at 32 months of age in both HS and WB groups. In addition, an almost 2-fold increase in decay rate and 48% decrease in half-life of total RNA was observed in muscle from 32 month old rats. However, no significant difference in decay rate and half-life was observed with disuse at either 6 or 32 months. We conclude that muscle atrophy associated with aging, but not disuse, may be due to a decrease in total RNA because of increased RNA degradation

Pulmonary effects of inhalation of spark-generated silver nanoparticles in Brown-Norway and Sprague-Dawley rats

The increasing use of silver nanoparticles (AgNPs) in consumer products is concerning. We examined the potential toxic effects when inhaled in Brown-Norway (BN) rats with a pre-inflammatory state compared to Sprague-Dawley (SD) rats.We determined the effect of AgNPs generated from a spark generator (mass concentration: 600-800 μg/mm(3); mean diameter: 13-16 nm; total lung doses: 8 [Low] and 26-28 [High] μg) inhaled by the nasal route in both rat strains. Rats were sacrificed at day 1 and day 7 after exposure and measurement of lung function.In both strains, there was an increase in neutrophils in bronchoalveolar lavage (BAL) fluid at 24 h at the high dose, with concomitant eosinophilia in BN rats. While BAL inflammatory cells were mostly normalised by Day 7, lung inflammation scores remained increased although not the tissue eosinophil scores. Total protein levels were elevated at both lung doses in both strains. There was an increase in BAL IL-1β, KC, IL-17, CCL2 and CCL3 levels in both strains at Day 1, mostly at high dose. Phospholipid levels were increased at the high dose in SD rats at Day 1 and 7, while in BN rats, this was only seen at Day 1; surfactant protein D levels decreased at day 7 at the high dose in SD rats, but was increased at Day 1 at the low dose in BN rats. There was a transient increase in central airway resistance and in tissue elastance in BN rats at Day 1 but not in SD rats. Positive silver-staining was seen particularly in lung tissue macrophages in a dose and time-dependent response in both strains, maximal by day 7. Lung silver levels were relatively higher in BN rat and present at day 7 in both strains.Presence of cellular inflammation and increasing silver-positive macrophages in lungs at day 7, associated with significant levels of lung silver indicate that lung toxicity is persistent even with the absence of airway luminal inflammation at that time-point. The higher levels and persistence of lung silver in BN rats may be due to the pre-existing inflammatory state of the lungs

Home Cage Compared with Induction Chamber for Euthanasia of Laboratory Rats

This study compared behavioral and physiologic changes in Sprague-Dawley and Brown Norway rats that were euthanizedby using a 30% volume displacement rate of CO2 in either their home cage or an induction chamber; rats euthanized in thehome cage were hypothesized to demonstrate a higher level of animal wellbeing. No significant differences were detectedin the physiologic responses to home cage versus induction chamber euthanasia groups. A few strain-related behavioraldifferences occurred. The number of digs per second was higher in Brown Norway compared with Sprague-Dawley rats when in the home cage, where a digging substrate was present. Rearing frequency was higher in both Brown Norway and Sprague-Dawley rats in the induction chamber compared with the home cage. This study demonstrated that although strainspecific differences were associated with the process of euthanasia, there were no significant differences between the treatment groups of home cage compared with induction chamber. This finding suggests that-from the perspective of a rat-either the home cage or an induction chamber can be used for euthanasia, with likely extension of this conclusion to use of either method to the induction of anesthesia

REGULATORY ROLE OF OX22HIGH T-CELLS IN MERCURY-INDUCED AUTOIMMUNITY IN THE BROWN NORWAY RAT

The monoclonal antibody OX22 defines a functional split within CD4+ T cells in the rat, with OX22high cells mainly producing interleukin 2 (IL-2) and interferon γ and responsible for delayed-type hypersensitivity responses, and OX22low cells mainly producing IL-4 and -5 and responsible for providing B cell help. There are reciprocal interactions between OX22high and OX22low cells, and it has been suggested that the OX22low subset has a role in the prevention of autoimmunity. We have used OX22 in vivo to define the role of these subsets in mercuric chloride-induced autoimmunity in the Brown Norway rat. In this model, there is polyclonal B cell activation and animals develop widespread tissue injury. Treatment of thymectomized animals with OX22 led to a profound reduction in the number of OX22high T cells in the peripheral blood. OX22-treated animals consistently developed more severe tissue injury than controls given an irrelevant antibody of the same isotype. Control animals pretreated with broad spectrum antimicrobial drugs showed milder tissue injury, but this protective effect of antimicrobials was lost in OX22-treated animals. Transfer of naive T cells to OX22-treated animals provided protection, but if T cells were depleted in vitro of OX22high cells before transfer, this effect was lost. These data provide evidence for a protective immunoregulatory role for OX22high T cells in mercuric chloride-induced autoimmunity.link_to_subscribed_fulltex

Large-scale structure of brown rat (Rattus norvegicus) populations in England: effects on rodenticide resistance

The brown rat (Rattus norvegicus) is a relatively recent (<300 years) addition to the British fauna, but by association with negative impacts on public health, animal health and agriculture, it is regarded as one of the most important vertebrate pest species. Anticoagulant rodenticides were introduced for brown rat control in the 1950s and are widely used for rat control in the UK, but long-standing resistance has been linked to control failures in some regions. One thus far ignored aspect of resistance biology is the population structure of the brown rat. This paper investigates the role population structure has on the development of anticoagulant resistance. Using mitochondrial and microsatellite DNA, we examined 186 individuals (from 15 counties in England and one location in Wales near the Wales–England border) to investigate the population structure of rural brown rat populations. We also examined individual rats for variations of the VKORC1 gene previously associated with resistance to anticoagulant rodenticides. We show that the populations were structured to some degree, but that this was only apparent in the microsatellite data and not the mtDNA data. We discuss various reasons why this is the case. We show that the population as a whole appears not to be at equilibrium. The relative lack of diversity in the mtDNA sequences examined can be explained by founder effects and a subsequent spatial expansion of a species introduced to the UK relatively recently. We found there was a geographical distribution of resistance mutations, and relatively low rate of gene flow between populations, which has implications for the development and management of anticoagulant resistance

Modeling Reveals the Dependence of Hippocampal Neurogenesis Radiosensitivity on Age and Strain of Rats

Cognitive dysfunction following radiation treatment for brain cancers in both children and adults have been correlated to impairment of neurogenesis in the hippocampal dentate gyrus. Various species and strains of rodent models have been used to study radiation-induced changes in neurogenesis and these investigations have utilized only a limited number of doses, dose-fractions, age and time after exposures conditions. In this paper, we have extended our previous mathematical model of radiation-induced hippocampal neurogenesis impairment of C57BL/6 mice to delineate the time, age, and dose dependent alterations in neurogenesis of a diverse strain of rats. To the best of our knowledge, this is the first predictive mathematical model to be published about hippocampal neurogenesis impairment for a variety of rat strains after acute or fractionated exposures to low linear energy transfer (low LET) radiation, such as X-rays and γ-rays, which are conventionally used in cancer radiation therapy. We considered four compartments to model hippocampal neurogenesis and its impairment following radiation exposures. Compartments include: (1) neural stem cells (NSCs), (2) neuronal progenitor cells or neuroblasts (NB), (3) immature neurons (ImN), and (4) glioblasts (GB). Additional consideration of dose and time after irradiation dependence of microglial activation and a possible shift of NSC proliferation from neurogenesis to gliogenesis at higher doses is established. Using a system of non-linear ordinary differential equations (ODEs), characterization of rat strain and age-related dynamics of hippocampal neurogenesis for unirradiated and irradiated conditions is developed. The model is augmented with the description of feedback regulation on early and late neuronal proliferation following radiation exposure. Predictions for dose-fraction regimes compared to acute radiation exposures, along with the dependence of neurogenesis sensitivity to radiation on age and strain of rats are discussed. A major result of this work is predictions of the rat strain and age dependent differences in radiation sensitivity and sub-lethal damage repair that can be used for predictions for arbitrary dose and dose-fractionation schedules

Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats

This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other vessels), and describes techniques for evaluating tissue perfusion using Laser Doppler Flowmetry (LDF) and microvessel density utilizing fluorescently labeled Griffonia simplicifolia (GS1) lectin. Current methods for studying isolated resistance arteries at transmural pressures encountered in vivo and in the absence of parenchymal cell influences provide a critical link between in vivo studies and information gained from molecular reductionist approaches that provide limited insight into integrative responses at the whole animal level. LDF and techniques to selectively identify arterioles and capillaries with fluorescently-labeled GS1 lectin provide practical solutions to enable investigators to extend the knowledge gained from studies of isolated resistance arteries. This paper describes the application of these techniques to gain fundamental knowledge of vascular physiology and pathology in the rat as a general experimental model, and in a variety of specialized genetically engineered designer rat strains that can provide important insight into the influence of specific genes on important vascular phenotypes. Utilizing these valuable experimental approaches in rat strains developed by selective breeding strategies and new technologies for producing gene knockout models in the rat, will expand the rigor of scientific premises developed in knockout mouse models and extend that knowledge to a more relevant animal model, with a well understood physiological background and suitability for physiological studies because of its larger size

Ventilatory Phenotypes among Four Strains of Adult Rats.

Our purpose in this study was to identify different ventilatory phenotypes among four different strains of rats. We examined 114 rats from three in-house, inbred strains and one outbred strain: Brown Norway (BN;n = 26), Dahl salt-sensitive (n = 24), Fawn-hooded Hypertensive (FHH: n = 27), and outbred Sprague-Dawley rats (SD; n = 37). We measured eupneic (room air) breathing and the ventilatory responses to hypoxia (12% O2-88% N2), hypercapnia (7% CO2), and two levels of submaximal exercise. Primary strain differences were between BN and the other strains. BN rats had a relatively attenuated ventilatory response to CO2 (P \u3c 0.001), an accentuated ventilatory response to exercise (P \u3c 0.05), and an accentuated ventilatory roll-off during hypoxia (P \u3c 0.05). Ventilation during hypoxia was lower than other strains, but hyperventilation during hypoxia was equal to the other strains (P \u3e 0.05), indicating that the metabolic rate during hypoxia decreased more in BN rats than in other strains. Another strain difference was in the frequency and timing components of augmented breaths, where FHH rats frequently differed from the other strains, and the BN rats had the longest expiratory time of the augmented breaths (probably secondary to the blunted CO2 sensitivity). These strain differences not only provide insight into physiological mechanisms but also indicate traits (such as CO2 sensitivity) that are genetically regulated. Finally, the data establish a foundation for physiological genomic studies aimed at elucidating the genetics of these ventilatory control mechanisms