Capacity In Rodents Research Articles

Critical Velocity, Maximal Lactate Steady State, and Muscle MCT1 and MCT4 after Exhaustive Running in Mice.

Although the critical velocity (CV) protocol has been used to determine the aerobic capacity in rodents, there is a lack of studies that compare CV with maximal lactate steady state intensity (iMLSS) in mice. As a consequence, their physiological and molecular responses after exercise until exhaustion at CV intensity remain unclear. Thus, we aimed to compare and correlate CV with iMLSS in running mice, following different mathematical models for CV estimation. We also evaluated their physiological responses and muscle MCT1 and MCT4 after running until exhaustion at CV. Thirty C57BL/6J mice were divided into two groups (exercised-E and control-C). Group E was submitted to a CV protocol (4 days), using linear (lin1 and lin2) and hyperbolic (hyp) mathematical models to determine the distance, velocity, and time to exhaustion (tlim) of each predictive CV trial, followed by an MLSS protocol. After a running effort until exhaustion at CV intensity, the mice were immediately euthanized, while group C was euthanized at rest. No differences were observed between iMLSS (21.1 ± 1.1 m.min-1) and CV estimated by lin1 (21.0 ± 0.9 m.min-1, p = 0.415), lin2 (21.3 ± 0.9 m.min-1, p = 0.209), and hyp (20.6 ± 0.9 m.min-1, p = 0.914). According to the results, CV was significantly correlated with iMLSS. After running until exhaustion at CV (tlim = 28.4 ± 8,29 min), group E showed lower concentrations of hepatic and gluteal glycogen than group C, but no difference in the content of MCT1 (p = 0.933) and MCT4 (p = 0.123) in soleus muscle. Significant correlations were not found between MCT1 and MCT4 and tlim at CV intensity. Our results reinforce that CV is a valid and non-invasive protocol to estimate the maximal aerobic capacity in mice and that the content of MCT1 and MCT4 was not decisive in determining the tlim at CV, at least when measured immediately after the running effort.

Incrementing non-matching- but not matching-to-sample is rapidly learned in an automated version of the odor span task.

The odor span task (OST) is frequently used to assess memory capacity in rodents. Odor stimuli are presented in a large arena and choices of session-novel odors produce food reward. The procedure can be described as an incrementing non-matching-to-sample contingency because on each trial one new stimulus is presented along with one or more previously presented (non-reinforced) comparison odors. An automated version of this task has recently been developed in which odors are presented with an olfactometer in an operant chamber using a successive conditional discrimination procedure. The present study compared the acquisition of matching- vs. non-matching-to-sample versions of the task with six rats tested under each procedure. All six rats trained on the non-matching variation showed rapid acquisition of the discrimination with high rates of responding to odor stimuli when they were session-novel and low rates of responding to subsequent presentations of those odors. However, only three of the six rats trained on the matching variation met acquisition criteria, and two of the three that did acquire the task required extensive training to do so. These results support findings from the OST that rats can differentiate between stimuli that are session-novel and those previously encountered, but alsothat a matching contingency is more difficult to learn than a non-matching arrangement. These findings parallel differences observed between acquisition of simple matching- and non-matching-to-sample tasks, but accounts such as novelty preference or the oddity preference effect may not be sufficient to explain the present results.

Plasticity of non-shivering thermogenesis and brown adipose tissue in high-altitude deer mice.

High altitude environments challenge small mammals with persistent low ambient temperatures that require high rates of aerobic heat production in face of low O2 availability. An important component of thermogenic capacity in rodents is non-shivering thermogenesis (NST) mediated by uncoupled mitochondrial respiration in brown adipose tissue (BAT). NST is plastic, and capacity for heat production increases with cold acclimation. However, in lowland native rodents, hypoxia inhibits NST in BAT. We hypothesize that highland deer mice (Peromyscus maniculatus) overcome the hypoxic inhibition of NST through changes in BAT mitochondrial function. We tested this hypothesis using lab born and raised highland and lowland deer mice, and a lowland congeneric (Peromyscus leucopus), acclimated to either warm normoxia (25°C, 760 mmHg) or cold hypoxia (5°C, 430 mmHg). We determined the effects of acclimation and ancestry on whole-animal rates of NST, the mass of interscapular BAT (iBAT), and uncoupling protein (UCP)-1 protein expression. To identify changes in mitochondrial function, we conducted high-resolution respirometry on isolated iBAT mitochondria using substrates and inhibitors targeted to UCP-1. We found that rates of NST increased with cold hypoxia acclimation but only in highland deer mice. There was no effect of cold hypoxia acclimation on iBAT mass in any group, but highland deer mice showed increases in UCP-1 expression and UCP-1-stimulated mitochondrial respiration in response to these stressors. Our results suggest that highland deer mice have evolved to increase the capacity for NST in response to chronic cold hypoxia, driven in part by changes in iBAT mitochondrial function.

Assaying Reproductive Capacity in Female Rodents.

It is an important part of many rodent studies to assess reproductive capacity in the female. Animal models that involve exposure to organic compounds, teratogenicity studies, or exposure to suboptimal environments during early development often result in deficits in female fertility. In addition to longitudinal physiology assays of fecundity, there are several molecular biology approaches to assessing female reproductive potential that can be performed to provide a "snapshot" of fertility potential at a single time-point. Here we describe some of the most useful ways to assess female reproductive capacity in rodents.

The effects of ghrelin on sleep, appetite, and memory, and its possible role in depression: A review of the literature

ObjectivesGhrelin is an orexigenic digestive hormone that plays a role in sleep and memory. Our work aims is to synthesize the effects of ghrelin on appetite, sleep and memory, and also to evidence its role in depressive disorders. MethodsA systematic search was carried out on PubMed with no time boundaries. The following MeSH terms were used: ghrelin AND (appetite regulation OR obesity), (sleep wake disorders OR sleep) (memory OR cognition disorders) (depression OR depressive disorder OR mood disorder). ResultsGhrelin triggers appetite and alters meal patterns by making them longer and richer. This can lead to pathologies, obesity and insulin-resistance. Ghrelin seems to have a favourable effect on sleep in human beings. It tends to make sleep more efficacious and better quality. Finally, it seems to have an effect on synaptic plasticity in the zones involved in memory and it has been shown to improve memory capacity in rodents. Regarding depression, the administration of ghrelin leads to an anti-depressive effect in animals and in humans. Conversely, post anti-depressant ghrelin titrations have generally shown a decrease in ghrelin levels. Resistant patients seem to retain high levels. Finally, the seriousness of depression could be related to ghrelin levels. ConclusionGhrelin plays a probable part in depression, especially for particular endophenotypes. A better understanding of ghrelin in depression could potentially help to optimize future therapeutic treatments.

Interactions between medial prefrontal cortex and dorsomedial striatum are necessary for odor span capacity in rats: role of GluN2B-containing NMDA receptors.

Working memory is involved in the maintenance and manipulation of information essential for complex cognition. While the neural substrates underlying working memory capacity have been studied in humans, considerably less is known about the circuitry mediating working memory capacity in rodents. Therefore, the present experiments tested the involvement of medial prefrontal cortex (mPFC) and dorsal striatum (STR) in the odor span task (OST), a task proposed to assay working memory capacity in rodents. Initially, Long Evans rats were trained to dig in scented sand for food following a serial delayed nonmatching-to-sample rule. Temporary inactivation of dorsomedial (dm) STR significantly reduced span in well trained rats. Inactivation of mPFC or contralateral disconnection of the mPFC and dmSTR also reduced span. Infusing the GluN2B-containing NMDA receptor antagonist Ro 25-6981 into mPFC did not affect span; however, span was significantly reduced following bilateral Ro 25-6981 infusions into dmSTR or contralateral disconnection of mPFC (inactivation) and dmSTR (Ro 25-6981). These results suggest that span capacity in rats depends on GluN2B-containing NMDA receptor-dependent interactions between the mPFC and the dmSTR. Therefore, interventions targeting this circuit may improve the working memory capacity impairments in patients with schizophrenia, Alzheimer's disease, and Parkinson's disease.

Amnestic drugs in the odor span task: Effects of flunitrazepam, zolpidem and scopolamine

The odor span task is an incrementing non-matching–to-sample procedure designed to provide an analysis of working memory capacity in rodents. The procedure takes place in an arena apparatus and rats are exposed to a series of odor stimuli in the form of scented lids with the selection of new stimuli reinforced. This procedure makes it possible to study drug effects as a function of the number of stimuli to remember. In the present study, the non-selective positive allosteric GABAA receptor modulator flunitrazepam impaired odor span performance at doses that did not affect a control odor discrimination. In contrast, the alpha-1 selective positive GABAA receptor modulator zolpidem and the cholinergic receptor antagonist scopolamine only impaired odor span at doses that produced more global impairment, including decreased accuracy in the control discrimination and increased response omissions in the both the odor span and control discrimination procedures. Even though the effects of flunitrazepam were selective to odor span performance, they did not depend on the number of stimuli to remember—the same degree of impairment occurred regardless of the memory load. These findings suggest that flunitrazepam interfered selectively with conditional discrimination performance rather than working memory and tentatively suggest that flunitrazepam’s selective effects in the odor span task relative to the control odor discrimination are mediated by one or more non-alpha1 GABAA receptor subtypes.

The GH/IGF-1 axis in a critical period early in life determines cellular DNA repair capacity by altering transcriptional regulation of DNA repair-related genes: implications for the developmental origins of cancer.

Experimental, clinical, and epidemiological findings support the concept of developmental origins of health and disease (DOHAD), suggesting that early-life hormonal influences during a sensitive period around adolescence have a powerful impact on cancer morbidity later in life. The endocrine changes that occur during puberty are highly conserved across mammalian species and include dramatic increases in circulating GH and IGF-1 levels. Importantly, patients with developmental IGF-1 deficiency due to GH insensitivity (Laron syndrome) do not develop cancer during aging. Rodents with developmental GH/IGF-1 deficiency also exhibit significantly decreased cancer incidence at old age, marked resistance to chemically induced carcinogenesis, and cellular resistance to genotoxic stressors. Early-life treatment of GH/IGF-1-deficient mice and rats with GH reverses the cancer resistance phenotype; however, the underlying molecular mechanisms remain elusive. The present study was designed to test the hypothesis that developmental GH/IGF-1 status impacts cellular DNA repair mechanisms. To achieve that goal, we assessed repair of γ-irradiation-induced DNA damage (single-cell gel electrophoresis/comet assay) and basal and post-irradiation expression of DNA repair-related genes (qPCR) in primary fibroblasts derived from control rats, Lewis dwarf rats (a model of developmental GH/IGF-1 deficiency), and GH-replete dwarf rats (GH administered beginning at 5weeks of age, for 30days). We found that developmental GH/IGF-1 deficiency resulted in persisting increases in cellular DNA repair capacity and upregulation of several DNA repair-related genes (e.g., Gadd45a, Bbc3). Peripubertal GH treatment reversed the radiation resistance phenotype. Fibroblasts of GH/IGF-1-deficient Snell dwarf mice also exhibited improved DNA repair capacity, showing that the persisting influence of peripubertal GH/IGF-1 status is not species-dependent. Collectively, GH/IGF-1 levels during a critical period during early life determine cellular DNA repair capacity in rodents, presumably by transcriptional control of genes involved in DNA repair. Because lifestyle factors (e.g., nutrition and childhood obesity) cause huge variation in peripubertal GH/IGF-1 levels in children, further studies are warranted to determine their persisting influence on cellular cancer resistance pathways.

Influence of pharmacological manipulations of NMDA and cholinergic receptors on working versus reference memory in a dual component odor span task

Developed as a tool to assess working memory capacity in rodents, the odor span task (OST) has significant potential to advance drug discovery in animal models of psychiatric disorders. Prior investigations indicate OST performance is impaired by systemic administration of N-methyl-d-aspartate receptor (NMDA-r) antagonists and is sensitive to cholinergic manipulations. The present study sought to determine whether an impairment in OST performance can be produced by systemic administration of the competitive NMDA-r antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP; 3, 10, 17 mg/kg i.p.) in a unique dual-component variant of the OST, and whether this impairment is ameliorated by nicotine (0.75 mg/kg i.p.). Male Sprague-Dawley rats were trained to asymptotic level of performance on a 24-trial two-comparison incrementing nonmatching to sample OST. In addition, rats were administered a two-comparison olfactory reference memory (RM) task, which was integrated into the OST. The RM task provided an assessment of the effects of drug administration on global behavioral measures, long-term memory and motivation. Several measures of working memory (span, longest run, and accuracy) were dose dependently impaired by CPP without adversely affecting RM. Analysis of drug effects across trial blocks demonstrated a significant impairment of performance even at low memory loads, suggesting a CPP-induced deficit of olfactory short-term memory that is not load-dependent. Although nicotine did not ameliorate CPP-induced impairments in span or accuracy, it did block the impairment in longest run produced by the 10 mg/kg dose of CPP. Overall, our results indicate that performance in our 24 odor two-comparison OST is capacity dependent and that CPP impaired OST working, but not reference, memory.

Fenvalerate, A Pyrethroid Insecticide, Adversely Affects Sperm Production and Storage in Male Rats

The aim of this study was to investigate the potential estrogenic activity of fenvalerate by examining reproductive and fertility capabilities in Wistar rats. Adult male animals were treated for 30 d with 20 or 40 mg/kg/d fenvalerate or corn oil (vehicle) by oral gavage. Further, a possible estrogenic activity of fenvalerate (0.4, 1, 4, 8, or 40 mg/kg) was tested after a 3-d treatment of immature female rats using the uterotrophic assay. Exposure to the higher dose of fenvalerate was toxic to testis and epididymis as shown by a decrease in the absolute weights and sperm counts in both organs. Although the sperm counts were reduced, the fertility and sexual behavior were similar in control rats and rats treated with 40 mg/kg pesticide. Fenvalerate did not exert estrogenic activity in vivo at the tested doses. Data suggest that fenvalerate treatment in this study failed to compromise fertility, possibly due to enhanced reproductive capacity in rodents compared to humans.

Effects of seed abundance on seed scatter-hoarding of Edward’s rat (Leopoldamys edwardsi Muridae) at the individual level

Mast seeding is a common phenomenon, and has important effects on seed dispersal and hoarding by animals. At population level, the predator satiation hypothesis proposes that the satiating effect of a large amount of seeds on a relatively small number of predators benefits seed survival in mast-seeding years. However, the effect of mast seeding on the scatter-hoarding of rodents at the individual level is largely unknown. In this study, we investigated the effects of seed abundance (by simulating mast seeding and non-mast seeding) on the removal, consumption and scatter-hoarding of seeds of Camellia oleifera (Theaceae) by Edward's rat Leopoldamys edwardsi (Muridae) in seminatural enclosures in southwest China. We wanted to test the masting-enhanced hoarding hypothesis, which suggests that rodents tend to scatter-hoard more seeds in mast-seeding years in order to occupy more food resources. Our results indicate that L. edwardsi tended to disperse and scatter-hoard more seeds of C. oleifera per night with increasing seed abundance, and to eat less seeds per night when there was a high level of seed abundance in the enclosure experiments. These results support the masting-enhanced hoarding hypothesis. This capacity of rodents may be an evolutionary adaptation to the mast-seeding phenomenon. Our results suggest that mast seeding benefits forest regeneration not only through the predator satiation effect at the population level, but also through increased hoarding by animals at the individual level.

Short term effects of a ketogenic diet on body weight, energy expenditure and exercise capacity in rodents

Short term effects of a ketogenic diet on body weight, energy expenditure and exercise capacity in rodents

Behavioral Tests for Preclinical Intervention Assessment

Select functional outcome tests commonly used for evaluating sensorimotor and cognitive capacity in rodents with focal intracerebral ischemic or hemorrhagic injury are described, along with upgrades and issues of concern for translational research. An emphasis is placed on careful quantitative and qualitative assessment of acute and long-term behavioral deficits, and on avoidance of frequent pitfalls. Methods for detecting different degrees of injury and treatment-related improvements are included. Determining the true potential of an intervention requires a set of behavioral analyses that can monitor compensatory learning. In a number of preclinical outcome tests, animals can develop remarkably effective "tricks" that are difficult to detect but frequently lead to dramatic improvements in performance, particularly with repeated practice. However, some interventions may facilitate learning without promoting brain repair, but these may not translate into a meaningful level of benefit in the clinic. Additionally, it is important to determine whether there are any preinjury functional asymmetries in order to accurately assess damage-related changes in behavior. This is illustrated by the fact that some animals have chronic endogenous asymmetries and that others, albeit infrequently, can sustain a spontaneous cerebral stroke, without any experimental induction, that can lead to chronic deficits as reflected by behavioral, imaging, and histological analyses. Finally, a useful new modification of the water maze that involves moving the platform from trial to trial within the target quadrant is reviewed, and its advantages over the standard version are discussed.

Tolerance to the anhedonic effects of lipopolysaccharide is associated with changes in syntaxin immunoreactivity in the nucleus accumbens.

The bacterial endotoxin lipopolysaccharide (LPS) produces a host of effects in mammals known collectively as 'sickness' behaviours. Acute treatment with LPS also results in a loss of hedonic capacity in rodents that can be measured by changes in responding for reinforcing electrical stimulation of the lateral hypothalamus. In contrast, repeated exposure to LPS typically leads to the development of tolerance to many of the physiological and behavioural effects of endotoxin, although the effect of chronic treatment with LPS on anhedonia remains unknown. In the present experiment, rats were trained to respond on an ascending-series current-intensity intracranial self-stimulation (ICSS) protocol, and were then treated with either acute or sub-chronic LPS (100 microg). Compared to vehicle-treated subjects, acute exposure to LPS induced a dramatic loss of ICSS responding; however, with repeated exposure to LPS, rats developed a behavioural tolerance to its anhedonic effects. To investigate a potential molecular substrate for the anhedonic effects of LPS, quantitative immunohistochemistry was used to measure levels of the synaptic proteins syntaxin, SNAP-25 and synaptophysin in the dorsal and ventral striatum of rats treated acutely and sub-chronically with LPS. A single injection of LPS produced a significant decrease in syntaxin immunoreactivity in the nucleus accumbens core and shell, while similar treatment in chronically treated rats that displayed behavioural tolerance had no effect. These results demonstrate a novel molecular substrate for the effects of LPS, and imply that the underlying physiology of the transient anhedonic effects of LPS may differ from that involved in chronic psychiatric disorders in humans.

An Orphan No More?

Nuclear receptors are a superfamily of proteins that function as ligand-activated transcription factors. Among these proteins are the so-called "orphan receptors," such as the retinoid X receptor (RXR), for which the endogenous activating ligands have not been identified. Using a cell-based screening assay, Mata de Urquiza et al. show that docosahexaenoic acid (DHA), an abundant polyunsaturated fatty acid in mammalian brain, is a potent activator of RXR. DHA deficiency has previously been linked to defects in spatial learning capacity in rodents. The new data raise the possibility that DHA's effects are mediated through an RXR signaling pathway. Mata de Urquiza, A., Liu, S., Sjöberg, M., Zetterström, R., Griffiths, W., Sjövall, J., and Perlmann, T. (2000) Docosahexaenoic acid, a ligand for the retinoid X receptor in mouse brain. Science 290 : 2140-2144. [Abstract] [Full Text]

An Orphan No More?

Nuclear receptors are a superfamily of proteins that function as ligand-activated transcription factors. Among these proteins are the so-called "orphan receptors," such as the retinoid X receptor (RXR), for which the endogenous activating ligands have not been identified. Using a cell-based screening assay, Mata de Urquiza et al. show that docosahexaenoic acid (DHA), an abundant polyunsaturated fatty acid in mammalian brain, is a potent activator of RXR. DHA deficiency has previously been linked to defects in spatial learning capacity in rodents. The new data raise the possibility that DHA's effects are mediated through an RXR signaling pathway.Mata de Urquiza, A., Liu, S., Sjöberg, M., Zetterström, R., Griffiths, W., Sjövall, J., and Perlmann, T. (2000) Docosahexaenoic acid, a ligand for the retinoid X receptor in mouse brain. Science 290: 2140-2144.[Abstract][Full Text]

Chronic K-supplementation decreases myocardial [Na,K-ATPase] and net K-uptake capacity in rodents.

The effects of high K intake on plasma K, myocardial K content and Na,K-ATPase concentration and on myocardial K uptake during KCl infusion were evaluated in rodents. Myocardial Na,K-ATPase was quantified in crude homogenates by K-dependent pNPPase activity in rats, and in intact samples by3H-ouabain binding in guinea pigs. Na, K-ATPase alpha isoform distribution was assessed by immunoblotting. Plasma K was monitored in anesthetized rats during intravenous infusion of 0.75 mmol KCl/100 g body weight/h. A significant increase in plasma K was observed after 2 days of K supplementation, 4.9+/-0.2 (mean+/-s.e.m.)v 3.0+/-0.2 mmol/l in weight matched controls ( P<0.01,n=5) and this difference remained stable. After 1 day, a significant myocardial K content increase was obtained, 86. 2+/-3.0v 76.7+/-1.9 micromol/g wet weight (P<0.05, n=5); after 4 days myocardial K stabilized 4.9+/-1.2 micromol/g wet weight above control level (P<0.05,n=5). From the 4th day, a significant decrease in myocardial K-dependent pNPPase activity was observed, 1.18+/-0.04v 1. 31+/-0.01 micromol/min/g wet weight in weight matched controls (P<0. 05,n=5); after 2 weeks the decrease was 29% (P<0.05,n=5), with a reduction in alpha1-isoform abundance by 24% (P<0.05,n=5), and a tendency to a decrease in alpha2 of 10% (n.s.,n=5). The measurements were validated by 3H-ouabain binding to myocardial samples from guinea pigs K-supplemented for 2 weeks, showing a decrease of 21% (P<0.05,n=5). During KCl infusion, the myocardial K content increase rate was reduced by 52% (P<0.05) in the K-supplemented rats. The observed effects of K-supplementation on plasma K, myocardial K content and myocardial K-dependent pNPPase activity were abolished within 2 days after reallocation to chow with normal K content. In conclusion, high K-intake is associated with significantly and reversible increased plasma and myocardial K content, and decreased myocardial Na,K-ATPase concentration and net myocardial K uptake capacity. Thus, the heart is protected from major increases in intracellular K concentrations during chronically-high K-intake.

Running performance and cardiovascular capacity are not impaired in creatine-depleted rats

Several published reports have indicated that derangement of the phosphocreatine/creatine (Cr) energy-buffering system via Cr analogue feeding results in cardiomyopathy when cardiac performance is assessed in vitro. The present study was designed to examine indexes of cardiac performance in rats that have been chronically Cr depleted. Adult (180 +/- 4 g) rats were assigned to a normal diet (ND) (n = 8) or a Cr-depletion diet (CD) group (n = 10). After 61 +/- 1 days of ad libitum feeding, measurements of steady-state exercise O2 consumption were made. Hemodynamic indexes were then assessed during incremental running to peak sustained levels. Rats were then killed and the left ventricle was excised. In the CD group Cr was depleted 82% and V1 isomyosin decreased while V2 increased. O2 consumption during steady-state running was not different in CD rats. The respiratory exchange ratios of CD rats reflected a bias toward fat utilization during the latter stages of prolonged exercise. The exercise heart rates and peak systolic blood pressures of CD rats were slightly lower than those of ND rats. Both negative and positive rates of left ventricular pressure development were significantly reduced at all running speeds in the CD rats. CD rats were capable of exercise performance equal to that of ND animals. The hemodynamic and metabolic data suggest that the adaptations seen in the CD animals may be similar to those reported after endurance training. These results indicate that chronic Cr depletion does not impair either the circulatory or exercise capacity of rodents.