Individual housing of mice--impact on behaviour and stress responses

Monoacylglycerol lipase inhibition-induced changes in plasma corticosterone levels, anxiety and locomotor activity in male CD1 mice

The hypothalamus-pituitary-adrenal-axis is strongly controlled by the endocannabinoid system. The specific impact of enhanced 2-arachidonoylglycerol signaling on corticosterone plasma levels, however, was not investigated so far. Here we studied the effects of the recently developed monoacylglycerol lipase inhibitor JZL184 on basal and stress-induced corticosterone levels in male CD1 mice, and found that this compound dramatically increased basal levels without affecting stress responses. Since acute changes in corticosterone levels can affect behavior, JZL184 was administered concurrently with the corticosterone synthesis inhibitor metyrapone, to investigate whether the previously shown behavioral effects of JZL184 are dependent on corticosterone. We found that in the elevated plus-maze, the effects of JZL184 on "classical" anxiety-related measures were abolished by corticosterone synthesis blockade. By contrast, effects on the "ethological" measures of anxiety (i.e. risk assessment) were not affected by metyrapone. In the open-field, the locomotion-enhancing effects of the compound were not changed either. These findings show that monoacylglycerol lipase inhibition dramatically increases basal levels of corticosterone. This endocrine effect partly affects the anxiolytic, but not the locomotion-enhancing effects of monoacylglycerol lipase blockade.

Short-term weight loss attenuates local tissue inflammation and improves insulin sensitivity without affecting adipose inflammation in obese mice

Obesity is a major cause of insulin resistance, and weight loss is shown to improve glucose homeostasis. But the underlying mechanism and the role of inflammation remain unclear. Male C57BL/6 mice were fed a high-fat diet (HFD) for 12 wk. After HFD, weight loss was induced by changing to a low-fat diet (LFD) or exercise with continuous HFD. The weight loss effects on energy balance and insulin sensitivity were determined using metabolic cages and hyperinsulinemic euglycemic clamps in awake mice. Diet and exercise intervention for 3 wk caused a modest weight loss and improved glucose homeostasis. Weight loss dramatically reduced local inflammation in skeletal muscle, liver, and heart but not in adipose tissue. Exercise-mediated weight loss increased muscle glucose metabolism without affecting Akt phosphorylation or lipid levels. LFD-mediated weight loss reduced lipid levels and improved insulin sensitivity selectively in liver. Both weight loss interventions improved cardiac glucose metabolism. These results demonstrate that a short-term weight loss with exercise or diet intervention attenuates obesity-induced local inflammation and selectively improves insulin sensitivity in skeletal muscle and liver. Our findings suggest that local factors, not adipose tissue inflammation, are involved in the beneficial effects of weight loss on glucose homeostasis.

Chronic social stress during adolescence: interplay of paroxetine treatment and ageing

Exposure to chronic stress during developmental periods is a risk factor for a number of psychiatric disorders. While the direct effects of stress exposure have been studied extensively, little is known about the long-lasting effects and the interaction with ageing. The same holds true for the treatment with selective serotonin reuptake inhibitors (SSRIs), which have been shown to prevent or reverse some stress-induced effects. Here, we studied the direct and long-lasting impact of chronic social stress during adolescence and the impact of chronic treatment with the SSRI paroxetine in adulthood and aged animals. Therefore, male CD1 mice at the age of 28 days were subjected to 7 weeks of chronic social stress. Treatment with paroxetine was performed per os with a dosage of 20 mg/g BW. We were able to reverse most of the effects of chronic social stress in adult mice (4 months old) and to some extend in aged animals (15 months old) with the SSRI treatment. Especially the regulation of the HPA axis seems to be affected in aged mice with a shift to the use of vasopressin. Our results demonstrate that chronic stress exposure and antidepressant treatment at the end of the developmental period can have a significant and long-lasting impact, highly relevant for healthy ageing.

Does aerobic exercise training promote changes in structural and biomechanical properties of the tendons in experimental animals? A systematic review

To develop a systematic review to evaluate, through the best scientific evidence available, the effectiveness of aerobic exercise in improving the biomechanical characteristics of tendons in experimental animals. Two independent assessors conducted a systematic search in the databases Medline/PUBMED and Lilacs/BIREME, using the following descriptors of Mesh in animal models. The ultimate load of traction and the elastic modulus tendon were used as primary outcomes and transverse section area, ultimate stress and tendon strain as secondary outcomes. The assessment of risk of bias in the studies was carried out using the following methodological components: light/dark cycle, temperature, nutrition, housing, research undertaken in conjunction with an ethics committee, randomization, adaptation of the animals to the training and preparation for the mechanical test. Eight studies, comprising 384 animals, were selected; it was not possible to combine them into one meta-analysis due to the heterogeneity of the samples. There was a trend to increasing ultimate load without changes in the other outcomes studied. Only one study met more than 80% of the quality criteria. Physical training performed in a structured way with imposition of overloads seems to be able to promote changes in tendon structure of experimental models by increasing the ultimate load supported. However, the results of the influence of exercise on the elastic modulus parameters, strain, transverse section area and ultimate stress, remain controversial and inconclusive. Such a conclusion must be evaluated with reservation as there was low methodological control in the studies included in this review.

Individual housing of female mice: influence on postsurgical behaviour and recovery

Individual housing of laboratory mice may increase vulnerability to surgical stress, and interfere with postsurgical recovery. To analyse the effect of housing conditions on recovery, pair- and single-housed female C57BL/6J mice underwent a minor laparotomy +/− analgesia, anaesthesia only or no treatment. Animals were monitored using non-invasive methods during the immediate postsurgical period to assess pain and general impairment. While no appearance or posture abnormalities were observed postexperiment, home cage behaviours were affected distinctly. Discriminant analysis identified self-grooming, locomotion, climbing and resting as mainly responsible for experimental group separation. Behavioural rhythmicity was disrupted, and behaviours related to wellbeing, such as nest building, climbing and burrowing, decreased. Behavioural pain signs (e.g. press) increased. Most behavioural alterations showed a gradation between treatments, e.g. burrowing latency ranged from an intermediate level following anaesthesia only and surgery with analgesia, to pronounced prolongation after surgery without analgesia. Significantly lower burrowing performance after surgery without analgesia in individually-housed animals indicates better recovery in pairs. Social interaction in pairs – an important component of normal behaviour (64%) and a potential indicator for direct social support – was nearly absent (0.3–0.5%). While anaesthesia and surgery resulted in clear changes in behaviour, differences between housing conditions were minor. Hence, despite a tendency towards better recovery in pairs, we found no distinct negative effect of individual housing. In conclusion, both housing conditions are acceptable during the period immediately following minor surgery, though social housing is always preferable in female mice.

A guide to analysis of mouse energy metabolism

We present a consolidated view of the complexity and challenges of designing studies for measurement of energy metabolism in mouse models, including a practical guide to the assessment of energy expenditure, energy intake and body composition and statistical analysis thereof. We hope this guide will facilitate comparisons across studies and minimize spurious interpretations of data. We recommend that division of energy expenditure data by either body weight or lean body weight and that presentation of group effects as histograms should be replaced by plotting individual data and analyzing both group and body-composition effects using analysis of covariance (ANCOVA).

Forebrain CRF₁ modulates early-life stress-programmed cognitive deficits

Childhood traumatic events hamper the development of the hippocampus and impair declarative memory in susceptible individuals. Persistent elevations of hippocampal corticotropin-releasing factor (CRF), acting through CRF receptor 1 (CRF₁), in experimental models of early-life stress have suggested a role for this endogenous stress hormone in the resulting structural modifications and cognitive dysfunction. However, direct testing of this possibility has been difficult. In the current study, we subjected conditional forebrain CRF₁ knock-out (CRF₁-CKO) mice to an impoverished postnatal environment and examined the role of forebrain CRF₁ in the long-lasting effects of early-life stress on learning and memory. Early-life stress impaired spatial learning and memory in wild-type mice, and postnatal forebrain CRF overexpression reproduced these deleterious effects. Cognitive deficits in stressed wild-type mice were associated with disrupted long-term potentiation (LTP) and a reduced number of dendritic spines in area CA3 but not in CA1. Forebrain CRF₁ deficiency restored cognitive function, LTP and spine density in area CA3, and augmented CA1 LTP and spine density in stressed mice. In addition, early-life stress differentially regulated the amount of hippocampal excitatory and inhibitory synapses in wild-type and CRF₁-CKO mice, accompanied by alterations in the neurexin-neuroligin complex. These data suggest that the functional, structural and molecular changes evoked by early-life stress are at least partly dependent on persistent forebrain CRF₁ signaling, providing a molecular target for the prevention of cognitive deficits in adults with a history of early-life adversity.

Female mucopolysaccharidosis IIIA mice exhibit hyperactivity and a reduced sense of danger in the open field test

Reliable behavioural tests in animal models of neurodegenerative diseases allow us to study the natural history of disease and evaluate the efficacy of novel therapies. Mucopolysaccharidosis IIIA (MPS IIIA or Sanfilippo A), is a severe, neurodegenerative lysosomal storage disorder caused by a deficiency in the heparan sulphate catabolising enzyme, sulfamidase. Undegraded heparan sulphate accumulates, resulting in lysosomal enlargement and cellular dysfunction. Patients suffer a progressive loss of motor and cognitive function with severe behavioural manifestations and premature death. There is currently no treatment. A spontaneously occurring mouse model of the disease has been described, that has approximately 3% of normal enzyme activity levels. Behavioural phenotyping of the MPS IIIA mouse has been previously reported, but the results are conflicting and variable, even after full backcrossing to the C57BL/6 background. Therefore we have independently backcrossed the MPS IIIA model onto the C57BL/6J background and evaluated the behaviour of male and female MPS IIIA mice at 4, 6 and 8 months of age using the open field test, elevated plus maze, inverted screen and horizontal bar crossing at the same circadian time point. Using a 60 minute open field, we have demonstrated that female MPS IIIA mice are hyperactive, have a longer path length, display rapid exploratory behaviour and spend less time immobile than WT mice. Female MPS IIIA mice also display a reduced sense of danger and spend more time in the centre of the open field. There were no significant differences found between male WT and MPS IIIA mice and no differences in neuromuscular strength were seen with either sex. The altered natural history of behaviour that we observe in the MPS IIIA mouse will allow more accurate evaluation of novel therapeutics for MPS IIIA and potentially other neurodegenerative disorders.

Evaluation of social and physical enrichment in modulation of behavioural phenotype in C57BL/6J female mice

Housing conditions represent an important environmental variable playing a critical role in the assessment of mouse behaviour. In the present study the effects of isolation and nesting material on the behaviour of female C57BL/6J mice were evaluated. The mice were subjected to different rearing conditions from weaning (at the age of 3 weeks). The study groups were group- and single-housed mice, divided further into groups with or without nesting material (species-specific enrichment). After 8 weeks spent in respective conditions the behavioural testing began. Both factors (social conditions and nesting material) appeared to have a significant impact on the behavioural phenotype. However, it is important to stress that the interaction between the factors was virtually absent. We established that isolation increased locomotor activity and reduced anxiety-like behaviour in several tests of exploration. In contrast, absence of nesting material increased anxiety-like behaviour. Neither factor affected rota-rod performance, nociception and prepulse inhibition. Contextual fear memory was significantly reduced in single-housed mice, and interestingly, in mice with nesting material. Cued fear memory was reduced by single-housing, but not affected by enrichment. Mice from enriched cages displayed faster and better learning and spatial search strategy in the water maze. In contrast, isolation caused significant impairment in the water maze. In conclusion, both isolation and species-specific enrichment have profound effects on mouse behaviour and should be considered in design of the experiments and in assessment of animal welfare issues.

Assessing learning and memory in pigs

In recent years, there has been a surge of interest in (mini) pigs (Sus scrofa) as species for cognitive research. A major reason for this is their physiological and anatomical similarity with humans. For example, pigs possess a well-developed, large brain. Assessment of the learning and memory functions of pigs is not only relevant to human research but also to animal welfare, given the nature of current farming practices and the demands they make on animal health and behavior. In this article, we review studies of pig cognition, focusing on the underlying processes and mechanisms, with a view to identifying. Our goal is to aid the selection of appropriate cognitive tasks for research into pig cognition. To this end, we formulated several basic criteria for pig cognition tests and then applied these criteria and knowledge about pig-specific sensorimotor abilities and behavior to evaluate the merits, drawbacks, and limitations of the different types of tests used to date. While behavioral studies using (mini) pigs have shown that this species can perform learning and memory tasks, and much has been learned about pig cognition, results have not been replicated or proven replicable because of the lack of validated, translational behavioral paradigms that are specially suited to tap specific aspects of pig cognition. We identified several promising types of tasks for use in studies of pig cognition, such as versatile spatial free-choice type tasks that allow the simultaneous measurement of several behavioral domains. The use of appropriate tasks will facilitate the collection of reliable and valid data on pig cognition.

Voluntary Ethanol Consumption Induced by Social Isolation Reverses the Increase of α(4)/δ GABA(A) Receptor Gene Expression and Function in the Hippocampus of C57BL/6J Mice

Post-weaning social isolation (SI) is a model of prolonged mild stress characterized by behavioral and neurochemical alterations. We used SI in C57BL/6J mice to investigate the effects of ethanol (EtOH) in the free-choice drinking paradigm on gene expression and function of γ-aminobutyric acid type A receptors (GABA_ARs) and the role of neuroactive steroids in the actions of EtOH in the hippocampus. SI stress induced a marked reduction in hippocampal 3α-hydroxy-5α-pregnan-20-one (3α,5α-TH PROG) and was associated with molecular and functional changes of the GABA_AR. The gene expression of the α₄ and δ subunits was increased in the hippocampus of SI C57BL/6J mice; the expression of the γ₂ subunit was decreased whereas that of the α₁ did not change. Patch-clamp recordings in dentate gyrus (DG) granule cells obtained from SI C57BL/6J mice revealed a greater enhancement of tonic currents induced by α-(4,5,6,7-tetrahydroisoxazolo[5,4-c] pyridin-3-ol (THIP) compared to that in control C57BL/6J mice. These neurochemical, molecular and functional changes observed in SI C57BL/6J mice were associated with an increased EtOH intake and EtOH preference. Nevertheless, the increase in EtOH consumption did not restore the reduction in hippocampal 3α,5α-TH PROG induced by SI. EtOH self-administration blocked the changes in gene expression of the α₄ subunit but not those of the δ and γ₂ subunits induced by SI. In addition, EtOH self-administration did not block the SI-induced changes in GABA_AR-mediated tonic inhibition in hippocampal granule cells but increased the frequency of basal GABAergic sIPSCs in DG granule cells. We conclude that self-administration of EtOH selectively abolishes the increase of α₄ subunit but not other neurochemical, molecular, and functional modifications induced by SI prolonged mild stress.

Enhanced Sensitivity to Ethanol-Induced Inhibition of LTP in CA1 Pyramidal Neurons of Socially Isolated C57BL/6J Mice: Role of Neurosteroids

Ethanol (EtOH) induced impairment of long-term potentiation (LTP) in the rat hippocampus is prevented by the 5α-reductase inhibitor finasteride, suggesting that this effect of EtOH is dependent on the increased local release of neurosteroids such as 3α,5α-THP that promote GABA-mediated transmission. Given that social isolation (SI) in rodents is associated with altered plasma and brain levels of such neurosteroids as well as with an enhanced neurosteroidogenic action of EtOH, we examined whether the inhibitory effect of EtOH on LTP at CA3-CA1 hippocampal excitatory synapses is altered in C57BL/6J mice subjected to SI for 6 weeks in comparison with group-housed (GH) animals. Extracellular recording of field excitatory postsynaptic potentials (fEPSPs) as well as patch-clamp analysis were performed in hippocampal slices prepared from both SI and GH mice. Consistent with previous observations, recording of fEPSPs revealed that the extent of LTP induced in the CA1 region of SI mice was significantly reduced compared with that in GH animals. EtOH (40 mM) inhibited LTP in slices from SI mice but not in those from GH mice, and this effect of EtOH was abolished by co-application of 1 μM finasteride. Current-clamp analysis of CA1 pyramidal neurons revealed a decrease in action potential (AP) frequency and an increase in the intensity of injected current required to evoke the first AP in SI mice compared with GH mice, indicative of a decrease in neuronal excitability associated with SI. Together, our data suggest that SI results in reduced levels of neuronal excitability and synaptic plasticity in the hippocampus. Furthermore, the increased sensitivity to the neurosteroidogenic effect of EtOH associated with SI likely accounts for the greater inhibitory effect of EtOH on LTP in SI mice. The increase in EtOH sensitivity induced by SI may be important for the changes in the effects of EtOH on anxiety and on learning and memory associated with the prolonged stress attributable to SI.

Modeling social influences on human health

Social interactions have long-term physiological, psychological, and behavioral consequences. Social isolation is a well-recognized but little understood risk factor and prognostic marker of disease; it can have profoundly detrimental effects on both mental and physical well-being, particularly during states of compromised health. In contrast, the health benefits associated with social support (both reduced risk and improved recovery) are evident in a variety of illnesses and injury states; however, the mechanisms by which social interactions influence disease pathogenesis remain largely unidentified. The substantial health impact of the psychosocial environment can occur independently of traditional disease risk factors and is not accounted for solely by peer-encouraged development of health behaviors. Instead, social interactions are capable of altering shared pathophysiological mechanisms of multiple disease states in distinct measurable ways. Converging evidence from animal models of injury and disease recapitulates the physiological benefits of affiliative social interactions and establishes several endogenous mechanisms (inflammatory signals, glucocorticoids, and oxytocin) by which social interactions influence health outcomes. Taken together, both clinical and animal research are undoubtedly necessary to develop a complete mechanistic understanding of social influences on health.

Behavioral characterization of A/J and C57BL/6J mice using a multidimensional test: association between blood plasma and brain magnesium-ion concentration with anxiety

Up to 29% of all adults will experience an anxiety-related disorder during their lives. Treatment of these disorders is still difficult and the exact mechanisms and pathways behind anxiety disorders remain to be elucidated. Although evidence exists for genetically based susceptibility of human psychiatric diseases, risk genes have rarely been identified up to now. Inbred mouse strains are, together with the crosses and genetic reference populations derived from them, important tools for the genetic dissection of complex behavioral traits in the mouse. Thus, inbred mouse models of human anxiety may be a potent starting tool to search for candidate genes in mice, which could then via comparative genomics be translated to the human situation. In this paper we investigate whether the A/J and C57BL/6J mouse inbred strains differ in a limited number of motivational systems (anxiety, exploration, memory, locomotion, and social affinity), but especially in anxiety-related behavior from each other. Young adult individuals from both genders of A/J and C57BL/6J strains were behaviorally phenotyped using a multidimensional test: the modified hole board. This paradigm basically is a combination of the traditional hole board and the open field test allowing to test for anxiety-related avoidance behavior, risk assessment, arousal, exploration, memory, locomotor activity, and social affinity, using just one single test. An acute, aversive stimulus (intra-peritoneal injection with saline) was applied to the animals to test for the robustness of their behavioral phenotype. In addition, presumed physiological indicators for anxiety (circulating glucose, cholesterol, and corticosterone, adrenal tyrosine hydroxylase, and blood plasma and brain magnesium) were investigated. It could be concluded that C57BL/6J and A/J mice differ with respect to almost all tested motivational systems. For some measures, including anxiety-related behavioral parameters, there were clear gender effects. The high-anxiety phenotype of A/J mice could be shown to represent a primary and robust characteristic. Further, blood plasma and brain magnesium levels were significantly correlated with several anxiety-related behavioral parameters. These results emphasize the hypothesized, and possibly causal, association between magnesium status and emotionality.

A novel chronic social stress paradigm in female mice

Major depression is one of the most prevalent stress-related psychiatric diseases. Next to environmental influences such as chronic social stress, gender is among the strongest risk factors for major depression, with women having a twice as high risk to develop the disease compared to men. While there is abundant literature on the effects of chronic social stress in male rodents, there is a serious lack of information on gender-specific effects. Especially in mice, which due to the wide availability of transgenic lines offer a unique opportunity to study gene x environment interactions, there is no existing model of chronic social stress that is applicable to both sexes. We here describe the effects of chronic social stress based on the disruption of the social network in a group-housed situation in female mice, a model that was recently described and validated for male mice. In this model, the group composition of the mice is changed twice per week for a period of 7 weeks, covering the adolescent and early adulthood period. We observed that housing in an unpredictable social environment resulted in chronic stress in female mice. The observed effects, which included increased adrenal weight, decreased thymus weight, increased corticosterone levels, and increased anxiety-like behavior, were very similar to the described effects of this paradigm in male mice. In addition, we observed a distinct expression of stress system-related genes in female mice following chronic stress exposure. Our results validate this model as a suitable approach to study chronic social stress in female mice and open up the opportunity to use this model with transgenic or knockout mouse lines.

Brain distribution of genes related to changes in locomotor activity

The relationship between genes and behavior, and particularly the hyperactive behavior, is clearly not linear nor monotonic. To address this problem, a database of the locomotor behavior obtained from thousands of mutant mice has been previously retrieved from the literature. Data showed that the percent of genes in the genome related to locomotor hyperactivity is probably more than 1.56%. These genes do not belong to a single neurotransmitter system or biochemical pathway. Indeed, they are probably required for the correct development of a specific neuronal network necessary to decrease locomotor activity. The present paper analyzes the brain expression pattern of the genes whose deletion is accompanied by changes in locomotor behavior. Using literature data concerning knockout mice, 46 genes whose deletion was accompanied by increased locomotor behavior, 24 genes related to decreased locomotor behavior and 23 genes not involved in locomotor behavior (but important for other brain functions) have been identified. These three groups of genes belonged to overlapping neurotransmitter systems or cellular functions. Therefore, we postulated that a better predictor of the locomotor behavior resulting from gene deletion might be the brain expression pattern. To this aim we correlated the brain expression of the genes and the locomotor activity resulting from the deletion of the same genes, using two databases (Allen Brain Atlas and SymAtlas). The results showed that the deletion of genes with higher expression level in the brain had higher probability to be accompanied by increased behavioral activity. Moreover the genes that were accompanied by locomotor hyperactivity when deleted, were more expressed in the cerebral cortex, amygdala and hippocampus compared to the genes unrelated to locomotor activity. Therefore, the prediction of the behavioral effect of a gene should take into consideration its brain distribution. Moreover, data confirmed that genes highly expressed in the brain are more likely to induce hyperactivity when deleted. Finally, it is suggested that gene mutations linked to specific behavioral abnormalities (e.g. inattention) might probably be associated to hyperactivity if the same gene has elevated brain expression.

Evaluation of study design variables and their impact on food-maintained operant responding in mice

Operant conditioning paradigms are useful for studying factors involved in reward, particularly when combined with the tools of genetic manipulation in mice. Published operant studies involving mice vary widely with respect to design, and insight into the consequences of design choices on performance in mice is limited. Here, we evaluated the impact of five design variables on the performance of inbred male mice in operant tasks involving solid food pellets as reinforcing agents. We found that the use of lever-press or nose-poke during FR1 sessions did not impact the performance of C57BL/6 mice, but that the lever-press approach correlated with enhanced performance during PR testing. While FR1 session duration had a notable impact on the rate of acquisition of food-maintained responding, performance during FR1 and PR sessions was largely unaffected. Higher order schedules of reinforcement (FR3 and FR5) led to elevated responding during both FR and PR sessions, and improved the correspondence between rewards earned and consumed. Single and group-housed mice performed indistinguishably during FR1 and PR sessions, while environmental enrichment combined with group housing accelerated the rate of acquisition of food-maintained responding while decreasing responding during PR testing. Finally, while C57BL/6 and 129/Sv mice exhibited comparable behavior during FR1 sessions, C57BL/6 mice tended to acquire food-maintained responding faster than 129/Sv counterparts, and exhibited elevated responding during PR testing. Altogether, our findings indicate that while operant performance for food in mice is relatively insensitive to many study parameters, experimental outcomes can be shaped predictably with proper design decisions.