Cage Mates Research Articles

Mirror Perception in Mice: Preference For and Stress Reduction by Mirrors

I measured the amount of time mice spent in a compartment with either a mirror or an opaque screen and found that mice stayed longer in the compartment with the mirror. This finding suggests that mice prefer mirrors. They also showed a preference for the mirror over unfamiliar live mice but did not show a differential preference for the mirror over a familiar live mouse (cage mate). Restraint stress caused hyperthermia (known as stress-induced hyperthermia) in the mice. When cage mates received the restraint stress together, the hyperthermia was reduced. Placement of mirrors instead of the cage mates also showed stress-reducing effects, while restraint with unfamiliar mice did not reduce the hyperthermia. These results suggest that mirrors have familiar cage mate-like social effects in mice.

Common experience modifies the reinforcing properties of methamphetamine-injected cage mates but not morphine-injected cage mates in C57 mice.

The aim of this study was to determine whether previous exposure to a drug affects the social facilitation of conditioned place preference (CPP) for a drug-injected cage mate. Twenty-two male C57/BL6J mice received drug injections (methamphetamine or morphine) and 22 male C57/BL6J mice received saline injections. All 44 mice then received CPP training, during which one compartment of a conventional CPP apparatus was associated with a drug-injected cage mate (stimulus mouse) and the other compartment was associated with a saline-injected cage mate (stimulus mouse). The subject mice did not receive any drug injection during this CPP training. Time spent in the compartment associated with the drug-injected cage mate was measured before and after training. Subject mice that had previously received methamphetamine injections showed an increase in the time spent in the compartment associated with the methamphetamine-injected cage mate after CPP training. This effect was not observed in subject mice that had previously received saline injections. Subject mice did not show an increase in the time spent in the compartment associated with the morphine-injected cage mate irrespective of whether they had previously received morphine or saline injections. Therefore, in agreement with previous reports, common experience with methamphetamine induced reinforcing properties, but that with morphine did not.

Predicting direct and indirect breeding values for survival time in laying hens using repeated measures.

BackgroundMinimizing bird losses is important in the commercial layer industry. Selection against mortality is challenging because heritability is low, censoring is high, and individual survival depends on social interactions among cage members. With cannibalism, mortality depends not only on an individual’s own genes (direct genetic effects; DGE) but also on genes of its cage mates (indirect genetic effects; IGE). To date, studies using DGE–IGE models have focussed on survival time but their shortcomings are that censored records were considered as exact lengths of life and models assumed that IGE were continuously expressed by all cage members even after death. However, since dead animals no longer express IGE, IGE should ideally be time-dependent in the model. Neglecting censoring and timing of IGE expression may reduce accuracy of estimated breeding values (EBV). Thus, our aim was to improve prediction of breeding values for survival time in layers that present cannibalism.MethodsWe considered four DGE–IGE models to predict survival time in layers. One model was an analysis of survival time and the three others treated survival in consecutive months as a repeated binomial trait (repeated measures models). We also tested whether EBV were improved by including timing of IGE expression in the analyses. Approximate EBV accuracies were calculated by cross-validation. The models were fitted to survival data on two purebred White Leghorn layer lines W1 and WB, each having monthly survival records over 13 months.ResultsIncluding the timing of IGE expression in the DGE–IGE model reduced EBV accuracy compared to analysing survival time. EBV accuracy was higher when repeated measures models were used. However, there was no universal best model. Using repeated measures instead of analysing survival time increased EBV accuracy by 10 to 21 and 2 to 12 % for W1 and WB, respectively. We showed how EBV and variance components estimated with repeated measures models can be translated into survival time.ConclusionsOur results suggest that prediction of breeding values for survival time in laying hens can be improved using repeated measures models. This is an important result since more accurate EBV contribute to higher rates of genetic gain.Electronic supplementary materialThe online version of this article (doi:10.1186/s12711-015-0152-2) contains supplementary material, which is available to authorized users.

Social factors modulate restraint stress induced hyperthermia in mice

Stress-induced hyperthermia (SIH) was examined in three different social conditions in mice by thermographic measurement of the body surface temperature. Placing animals in cylindrical holders induced restraint stress. I examined the effect of the social factors in SIH using the thermograph (body surface temperature). Mice restrained in the holders alone showed SIH. Mice restrained in the holders at the same time as other similarly restrained cage mates (social equality condition) showed less hyperthermia. Interestingly, restrained mice with free moving cage mates (social inequality condition) showed the highest hyperthermia. These results are consistent with a previous experiment measuring the memory-enhancing effects of stress and the stress-induced elevation of corticosterone, and suggest that social inequality enhances stress.

Streptococcus pneumoniae Enhances Human Respiratory Syncytial Virus Infection In Vitro and In Vivo.

Human respiratory syncytial virus (HRSV) and Streptococcus pneumoniae are important causative agents of respiratory tract infections. Both pathogens are associated with seasonal disease outbreaks in the pediatric population, and can often be detected simultaneously in infants hospitalized with bronchiolitis or pneumonia. It has been described that respiratory virus infections may predispose for bacterial superinfections, resulting in severe disease. However, studies on the influence of bacterial colonization of the upper respiratory tract on the pathogenesis of subsequent respiratory virus infections are scarce. Here, we have investigated whether pneumococcal colonization enhances subsequent HRSV infection. We used a newly generated recombinant subgroup B HRSV strain that expresses enhanced green fluorescent protein and pneumococcal isolates obtained from healthy children in disease-relevant in vitro and in vivo model systems. Three pneumococcal strains specifically enhanced in vitro HRSV infection of primary well-differentiated normal human bronchial epithelial cells grown at air-liquid interface, whereas two other strains did not. Since previous studies reported that bacterial neuraminidase enhanced HRSV infection in vitro, we measured pneumococcal neuraminidase activity in these cultures but found no correlation with the observed infection enhancement in our model. Subsequently, a selection of pneumococcal strains was used to induce nasal colonization of cotton rats, the best available small animal model for HRSV. Intranasal HRSV infection three days later resulted in strain-specific enhancement of HRSV replication in vivo. One S. pneumoniae strain enhanced HRSV both in vitro and in vivo, and was also associated with enhanced syncytium formation in vivo. However, neither pneumococci nor HRSV were found to spread from the upper to the lower respiratory tract, and neither pathogen was transmitted to naive cage mates by direct contact. These results demonstrate that pneumococcal colonization can enhance subsequent HRSV infection, and provide tools for additional mechanistic and intervention studies.

Rats don't leave their friends to sink or swim

In 2011, Peggy Mason of the University of Chicago and her colleagues showed that rats would free cage mates it they were trapped in a distressing restrainer apparatus. That experiment provided evidence that rats could empathize with another's discomfort, but the possibility remained that they freed others to acquire a playmate, rather than just to help. To test this, Nobuya Sato of Kwansei Gakuin University in Japan put some rats in unpleasantly wet chambers and others in dry ones. For both types of chamber, a second rat was placed in an adjacent, dry chamber, from where they could free the first rat by opening a door. The rats only helped others that were soaked and distressed, and did so more quickly if they themselves had been soaked once before

Behavioral, Cognitive and Biochemical Consequences of Witnessing Maternal Abuse: Insights from an Animal Model

Recent studies from our lab have shown that post‐traumatic stress disorder (PTSD)‐like behaviors are triggered not only in rats that physically experienced traumatic events of social defeat, but also in rats that witnessed their cage mates undergo traumatic exposure. Extending this line of research we have attempted to establish a rat model to study the consequences of early‐life exposure of witnessing maternal abuse (MAW). In this MAW model we introduced a female Spraugue‐Dawley rat (mother) into the cage of a male Long Evans (LE) rat. The female rat undergoes defeat from the LE rat. Natural litters at postnatal day 21 were placed in separate chambers surrounding the cage to witness 3 attacks per day, for 7 consecutive days. One month later, when the pups became 60 day old (considered adults), cognitive and behavioral outcomes of witnessing maternal abuse during early life were examined. MAW rats exhibited depression‐like behavior (examined via forced‐swim test) when compared to age matched controls. No changes were noted in anxiety‐like behavior (examined via open‐field and elevated plus maze tests) or learning and memory function (Radial arm water maze test) in MAW rats. Elevated levels of oxidative stress correlate with depressive phenotype of MAW rats. Studies to investigate the underlying neurobiology of MAW phenotype are currently ongoing.

Are 50-khz calls used as play signals in the playful interactions of rats? III. The effects of devocalization on play with unfamiliar partners as juveniles and as adults

When playing, rats emit 50-kHz calls which may function as play signals. A previous study using devocalized rats provides support for the hypothesis that 50-kHz function to promote and maintain playful interactions (Kisko et al., 2015). However, in that study, all pairs were cage mates and familiar with each other’s playful tendencies that could have attenuated the role of play signals. The present study uses unfamiliar pairs to eliminate any chance for such attenuation. Four hypotheses about how 50-kHz calls could act as play signals were tested, that (1) they maintain the playful mood of the partner, (2) they are used to locate partners, (3) they attract play partners and (4) they reduce the risk of playful encounters from escalating to serious fights. Predictions arising from the first three hypotheses, tested in juveniles, were not supported, suggesting that, for juveniles, 50-kHz calls are not facilitating playful interactions as play signals. The fourth hypothesis, however, was supported in adults, but not in juveniles, in that unfamiliar adult males were more likely to escalate playful encounters into serious fights when one partner was devocalized. These findings suggest that vocalizations at most have a minor role in juvenile play but serve a more central role in modulating adult interactions between strangers, allowing for the tactical mitigation of the risk of aggression.

Early-life risperidone administration alters maternal–offspring interactions and juvenile play fighting

Risperidone is an antipsychotic drug that is approved for use in childhood psychiatric disorders such as autism. One concern regarding the use of this drug in pediatric populations is that it may interfere with social interactions that serve to nurture brain development. This study used rats to assess the impact of risperidone administration on maternal–offspring interactions and juvenile play fighting between cage mates. Mixed-sex litters received daily subcutaneous injections of vehicle or 1.0 or 3.0mg/kg of risperidone between postnatal days (PNDs) 14–42. Rats were weaned and housed three per cage on PND 21. In observations made between PNDs 14–17, risperidone significantly suppressed several aspects of maternal–offspring interactions at 1-hour post-injection. At 23h post-injection, pups administered risperidone had lower activity scores and made fewer non-nursing contacts with their moms. In observations of play-fighting behavior made once a week between PNDs 22–42, risperidone profoundly decreased many forms of social interaction at 1h post-injection. At 23h post-injection, rats administered risperidone made more non-social contacts with their cage mates, but engaged in less social grooming. Risperidone administration to rats at ages analogous to early childhood through adolescence in humans produces a pattern of abnormal social interactions across the day that could impact how such interactions influence brain development.

Effect of hypochlorous acid solution on the eradication and prevention of Pseudomonas aeruginosa infection, serum biochemical variables, and cecum microbiota in rats.

In this study, hypochlorous acid solution, a weak acid, provided as drinking water to rats, was evaluated for its ability to eradicate and prevent Pseudomonas aeruginosa infection, while monitoring its simultaneous effect on serum biochemical variables and microbiota in the rat cecum. The results suggest that the solution could not eliminate the bacteria in the experimentally infected rats; however, the administration of a 10-parts-per-million (ppm) hypochlorous acid solution as drinking water was effective in inhibiting horizontal spread of P. aeruginosa infection among cage mates. Additionally, exposure to hypochlorous solution did not have any effect on serum biochemical variables of the rat including levels of total cholesterol, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), albumin, total bilirubin, lipase, amylase, urea nitrogen, total protein, calcium (Ca), phosphorus (P), sodium (Na), chlorine (Cl), except for potassium (K) levels. The most frequently isolated bacteria in the rat cecum included species belonging to Bacteroidales, Lactobacillus, Clostridiales, Erysipelotrichaceae, Akkermansia, Coriobacteriales, and Firmicutes. The ratio of the terminal restriction fragment length polymorphism (T-RFLP) peaks did not differ across rats administered with 5 and 10 ppm weak acid solution as compared to the control group for any of the bacteria, except for Erysipelotrichaceae and Firmicutes, where the ratio of T-RFLP peaks was higher in the 5 ppm group for Erysipelotrichaceae and in the 10 ppm group for Firmicutes than that in the control group (P<0.01). The results suggest that the weak acid hypochlorous solution could not eradicate P. aeruginosa completely from rats. The solution was effective in preventing infection without affecting serum biochemical variables; however, some of bacterial microbiota may have changed due to administration of the solution.

Ebola virus transmission in guinea pigs.

Ebola virus (EBOV) transmission is currently poorly characterized and is thought to occur primarily by direct contact with infectious material; however transmission from swine to nonhuman primates via the respiratory tract has been documented. To establish an EBOV transmission model for performing studies with statistical significance, groups of six guinea pigs (gps) were challenged intranasally (i.n.) or intraperitoneally (i.p.) with 10,000 times the 50% lethal dose (LD50) of gp-adapted EBOV, and naive gps were then introduced as cage mates for contact exposure at 1 day postinfection (p.i.). The animals were monitored for survival and clinical signs of disease and quantitated for virus shedding postexposure. Changes in the duration of contact of naive gps with infected animals were evaluated for their impact on transmission efficiency. Transmission was more efficient from i.n.- than from i.p.-challenged gps, with 17% versus 83% of naive gps surviving exposure, respectively. Virus shedding was detected beginning at 3 days p.i. from both i.n.- and i.p.-challenged animals. Contact duration positively correlated with transmission efficiency, and the abrogation of direct contact between infected and naive animals through the erection of a steel mesh was effective at stopping virus spread, provided that infectious animal bedding was absent from the cages. Histopathological and immunohistochemical findings show that i.n.-infected gps display enhanced lung pathology and EBOV antigen in the trachea, which supports increased virus transmission from these animals. The results suggest that i.n.-challenged gps are more infectious to naive animals than their systemically infected counterparts and that transmission occurs through direct contact with infectious materials, including those transported through air movement over short distances. Ebola is generally thought to be spread between humans though infectious bodily fluids. However, a study has shown that Ebola can be spread from pigs to monkeys without direct contact. Further studies have been hampered, because an economical animal model for Ebola transmission is not available. To address this, we established a transmission model in guinea pigs and determined the mechanisms behind virus spread. The survival data, in addition to microscopic examination of lung and trachea sections, show that mucosal infection of guinea pigs is an efficient model for Ebola transmission. Virus spread is increased with longer contact times with an infected animal and is possible without direct contact between an infected and a naive host but can be stopped if infectious materials are absent. These results warrant consideration for the development of future strategies against Ebola transmission and for a better understanding of the parameters involved in virus spread.

Bite marks in mink—Induced experimentally and as reflection of aggressive encounters between mink

For many years, bite marks have been used as an indicator for aggression in mink production systems. However, the validity of bite marks as indicator of aggression has recently been questioned. We therefore tested the following hypotheses: (1) experimentally applied pressure to, or penetration of, the pelt during the growth phase of the winter coat will produce marks that can be recognized as bite marks at pelting, (2) bite marks applied experimentally by use of an artificial tooth or occurring due to social/aggressive interactions (bites) between mink are only visible if pressure/bite on the mink skin is applied during the active growth phase of the winter coat prior to time when matured, (3) bite marks will be easier to detect on dark mink than on mink with light coloured fur and (4) the number of bite marks accumulates and increases with time mink are housed in groups. The experimental mink were of the brown colour type (N=140) and the white colour type (N=60). Twenty brown and 20 white mink (housed in pairs since weaning) were housed individually at the age of 16 weeks. Every second week (at the age of 20, 22, 24, 25 and 28 weeks), four brown and four white mink were subjected to pressure by an artificial tooth. Before pressure was applied, each mink was anaesthetized and pain treated.In order to investigate when bite marks from cage mates are inflicted and to what extend they accumulate over time, 120 brown and 40 white juvenile mink were placed in groups of four in climbing cages after weaning. Every second week (at the age of 20, 22, 24, 26 and 28 weeks) group housed mink were moved to single housing in standard cages in order to prevent further bites from cage mates.At the age of 29 weeks, all mink were killed individually by CO2 and the pelts were examined for bite marks.The results showed that: (1) experimentally applied pressure on the skin can be recognized as bite marks in brown mink at pelting, (2) bite marks are easier to detect on brown mink than on white coloured mink (P<0.001), (3) bite marks applied experimentally by use of an artificial tooth or occurring due to social/aggressive interactions (bites) between mink are only visible if pressure/bite on the mink skin is applied during the active growth phase of the winter coat prior to time when matured, and (4) the longer time mink are kept in groups, the more bite marks can be observed on the skin (P<0.001).The study has shown that bite marks are a valid and useful welfare indicator for quantifying the social tolerance of dark mink and consequently the risk for serious bite wounds.

Novel humanized recombinant T cell receptor ligands protect the female brain after experimental stroke.

Transmigration of peripheral leukocytes to the brain is a major contributor to cerebral ischemic cell death mechanisms. Humanized partial major histocompatibility complex class II constructs (pMHC), covalently linked to myelin peptides, are effective for treating experimental stroke in males, but new evidence suggests that some inflammatory cell death mechanisms after brain injury are sex-specific. We here demonstrate that treatment with pMHC constructs also improves outcomes in female mice with middle cerebral artery occlusion (MCAO). HLA-DR2 transgenic female mice with MCAO were treated with RTL1000 (HLA-DR2 moiety linked to human MOG-35-55 peptide), HLA-DRa1-MOG-35-55, or vehicle (VEH) at 3, 24, 48, and 72 h after reperfusion and were recovered for 96 h or 2 weeks post-injury for measurement of histology (TTC staining) or behavioral testing. RTL1000- and DRa1-MOG-treated mice had profoundly reduced infarct volumes as compared to the VEH group, although higher doses of DRa1-MOG were needed for females vs. males evaluated previously. RTL1000-treated females also exhibited strongly improved functional recovery in a standard cylinder test. In novel studies of post-ischemic ultrasonic vocalization (USV), as measured by animal calls to their cage mates, we modeled in mice the post-stroke speech deficits common in human stroke survivors. The number of calls was reduced in injured animals relative to pre-MCAO baseline regardless of RTL1000 treatment status. However, call duration was significantly improved by RTL1000 treatment, suggesting benefit to the animal’s recovery of vocalization capability. We conclude that both the parent RTL1000 molecule and the novel non-polymorphic DRα1-MOG-35-55 construct were highly effective immunotherapies for treatment of transient cerebral ischemia in females.

Huddling facilitates expression of daily torpor in the large Japanese field mouse Apodemus speciosus

Small endotherms employ multiple adaptations to maintain energy balance in winter, including spontaneous daily torpor and simultaneous huddling. The relationships between these adaptations have been discussed in several previous studies, but it has not been well-established if huddling actually affects the expression of torpor in small endotherms. We examine whether and how huddling affects the expression of torpor in the large Japanese field mouse Apodemus speciosus, which is known to become torpid under artificial winter conditions. The mice were found to adjust expression of torpor in response to the number of cage mates. Torpor frequency and minimum torpid body temperature were both significantly elevated when the number of cage mates was increased, but there was no significant change in torpor bout length. Rewarming rate on arousal was lower when the number of cage mates was increased, suggesting reduction in endogenous rewarming due to exogenous passive rewarming. Food consumption per mouse decreased significantly with increasing number of cage mates. Thus, our study demonstrates that social thermoregulatory behaviors such as huddling can facilitate expression of spontaneous daily torpor in small rodents. These findings suggest that energy constraints, such as ambient temperature and food availability may not be the only modulating factors on the expression of daily torpor.

Mating compatibility between Bactrocera invadens and Bactrocera dorsalis (Diptera: Tephritidae).

The invasive fruit fly, Bactrocera invadens Drew, Tsuruta & White, is a highly polyphagous fruit pest that occurs predominantly in Africa yet has its origins in the Indian subcontinent. It is extremely morphologically and genetically similar to the Oriental fruit fly, Bactrocera dorsalis (Hendel); as such the specific relationship between these two species is unresolved. We assessed prezygotic compatibility between B. dorsalis and B. invadens using standardized field cage mating tests, which have proven effectiveness in tephritid cryptic species studies. These tests were followed by an assessment of postzygotic compatibility by examining egg viability, larval and pupal survival, and sex ratios of offspring produced from parental and subsequent F1 crosses to examine for hybrid breakdown as predicted under a two-species hypothesis. B. dorsalis was sourced from two countries (Pakistan and China), and each population was compared with B. invadens from its type locality of Kenya. B. invadens mated randomly with B. dorsalis from both localities, and there were generally high levels of hybrid viability and survival resulting from parental and F1 crosses. Furthermore, all but one hybrid cross resulted in equal sex ratios, with the single deviation in favor of males and contrary to expectations under Haldane's rule. These data support the hypothesis that B. dorsalis and B. invadens represent the same biological species, an outcome that poses significant implications for pest management and international trade for sub-Saharan Africa.

Modelling of feather pecking behavior in beak-trimmed and non-beak-trimmed crossbred laying hens: Variance component and trait-based approach

Because of a ban on the use of beak trimming in some European countries, feather pecking is becoming a substantial problem in the layer industry, both from animal welfare and economic points of view. The feather condition score (FCS) as a measure of feather damage has been shown to be closely related to feather pecking behavior in laying hens housed in groups. To obtain a better understanding of genetic and other biological mechanisms underlying feather pecking behavior, data on FCS of a population of 2,724 female offspring from crossing 50 male W1 and 907 female WB purebred lines were used. The offspring of 25 sires were beak-trimmed, and the offspring of another 25 sires were non-beak-trimmed. Titers of plasma natural antibody (NAb) isotypes IgM and IgG binding keyhole limpet hemocyanin at 24 wk of age were measured. Feather condition was scored at 53 wk of age. In the first part of the present study, we estimated genetic parameters for FCS with 2 variance components models: a traditional linear animal model and a model combining direct and associative genetic effects. In the second part of the present study, a trait-based analysis for FCS was conducted to investigate whether NAb isotype titers can explain variation in FCS among individuals, by fitting a linear mixed model. Though the estimated associative genetic variance was substantial, associative effects for FCS were not statistically significant in both populations (P = 0.09 in beak-trimmed birds, and P = 0.08 in non-beak-trimmed birds). This suggests an insufficient number of records on FCS. Individual's NAb isotypes titers did not show direct effect for FCS of itself, but individual's IgG titers showed a suggestive effect on the FCS of cage mates (associative effect) in beak-trimmed laying hens, which need further confirmation.

The influence of poststress social factors on hormonal reactivity in prepubertal male rats

Following a variety of stressors, prepubertal animals display significantly longer hormonal stress responses than adults. Although the mechanisms that mediate this pubertal-related difference in stress reactivity are unclear, previous studies have shown that social interactions are differentially affected by stress in animals before and after puberty. Given the influence of social factors on stress reactivity, we hypothesize the protracted stress-induced hormonal response in prepubertal animals may be in part mediated by aspects of their poststress social environment. We explored this hypothesis by measuring plasma ACTH and corticosterone in prepubertal male rats 15, 30, and 45 min after a 30 min session of restraint stress exposed to one of three social conditions: recovering in the presence of a stressed cage mate; recovering in the presence of a nonstressed cage mate; and recovering in the absence of a cage mate. We report here that although prepubertal and adult animals display different hormonal responses following restraint, the presence or absence of stressed cage mates has little impact on the poststress hormonal response in prepubertal males. We do, however, show that social factors can alter HPA reactivity in prepubertal animals, in that significant hormonal responses are evoked in nonstressed animals exposed to a stressed cage mate, an effect not found in adults. Collectively, these data indicate that although the poststress social environment does not play a role in mediating the protracted hormonal response in prepubertal animals, the social context can significantly influence HPA activation in otherwise unstressed animals prior to puberty.

Changes in behavior and ultrasonic vocalizations during antidepressant treatment in the maternally separated Wistar-Kyoto rat model of depression

Genetic predisposition and stress are major factors in depression. The objective of this study was to establish a robust animal model of depression by selecting the appropriate substrain of the Wistar-Kyoto (WKY) rat, and subjecting these rats to the stress of maternal separation during the early stages of development. The initial experiment identified WKY/NCrl as the appropriate substrain of WKY to use for the study. In the second part of the study, depression-like behavior and ultrasonic vocalizations (USVs) were recorded in WKY/NCrl and maternally separated WKY/NCrl rats during the course of reversal of depression-like behavior. Wistar rats served as the reference strain. In adulthood, non-separated WKY/NCrl, maternally separated WKY/NCrl and Wistar rats were injected intraperitoneally with either saline or desipramine (15mg/kg/day) for 15days and their behavior recorded. Desipramine decreased immobility and increased active swimming and struggling behavior of WKY/NCrl in the FST and also decreased their USVs in response to removal of cage mates. The USVs in this study appeared to signal an attempt to re-establish social contact with cage mates and provided a measure of social dependence. Maternally separated WKY/NCrl rats displayed more anxiety than normally reared WKY/NCrl rats and responded to the anxiolytic effects of desipramine. The present findings support the use of WKY/NCrl as an animal model of depression. Maternal separation increased the anxiety-like behavior of the WKY/NCrl, thus providing a robust model to study depression- and anxiety-related behavior.

Social transmission of Pavlovian fear: fear-conditioning by-proxy in related female rats

Pairing a previously neutral conditioned stimulus (CS; e.g., a tone) to an aversive unconditioned stimulus (US; e.g., a foot-shock) leads to associative learning such that the tone alone will elicit a conditioned response (e.g., freezing). Individuals can also acquire fear from a social context, such as through observing the fear expression of a conspecific. In the current study, we examined the influence of kinship/familiarity on social transmission of fear in female rats. Rats were housed in triads with either sisters or non-related females. One rat from each cage was fear conditioned to a tone CS+ shock US. On day two, the conditioned rat was returned to the chamber accompanied by one of her cage mates. Both rats were allowed to behave freely, while the tone was played in the absence of the foot-shock. The previously untrained rat is referred to as the fear-conditioned by-proxy (FCbP) animal, as she would freeze based on observations of her cage-mate’s response rather than due to direct personal experience with the foot-shock. The third rat served as a cage-mate control. The third day, long-term memory tests to the CS were performed. Consistent with our previous application of this paradigm in male rats (Bruchey et al. in Behav Brain Res 214(1):80–84, 2010), our results revealed that social interactions between the fear conditioned and FCbP rats on day two contribute to freezing displayed by the FCbP rats on day three. In this experiment, prosocial behavior occurring at the termination of the cue on day two was significantly greater between sisters than their non-sister counterparts, and this behavior resulted in increased freezing on day three. Our results suggest that familiarity and/or kinship influences the social transmission of fear in female rats.

Risk assessment of H2N2 influenza viruses from the avian reservoir.

H2N2 influenza A viruses were the cause of the 1957-1958 pandemic. Historical evidence demonstrates they arose from avian virus ancestors, and while the H2N2 subtype has disappeared from humans, it persists in wild and domestic birds. Reemergence of H2N2 in humans is a significant threat due to the absence of humoral immunity in individuals under the age of 50. Thus, examination of these viruses, particularly those from the avian reservoir, must be addressed through surveillance, characterization, and antiviral testing. The data presented here are a risk assessment of 22 avian H2N2 viruses isolated from wild and domestic birds over 6 decades. Our data show that they have a low rate of genetic and antigenic evolution and remained similar to isolates circulating near the time of the pandemic. Most isolates replicated in mice and human bronchial epithelial cells, but replication in swine tissues was low or absent. Multiple isolates replicated in ferrets, and 3 viruses were transmitted to direct-contact cage mates. Markers of mammalian adaptation in hemagglutinin (HA) and PB2 proteins were absent from all isolates, and they retained a preference for avian-like α2,3-linked sialic acid receptors. Most isolates remained antigenically similar to pandemic A/Singapore/1/57 (H2N2) virus, suggesting they could be controlled by the pandemic vaccine candidate. All viruses were susceptible to neuraminidase inhibitors and adamantanes. Nonetheless, the sustained pathogenicity of avian H2N2 viruses in multiple mammalian models elevates their risk potential for human infections and stresses the need for continual surveillance as a component of prepandemic planning.