Diminished pheromone-induced sexual behavior in neurokinin-1 receptor deficient (TACR1(-/-)) mice

Studies in mice with targeted deletions of tachykinin genes suggest that tachykinins and their receptors influence emotional behaviors such as aggression, depression and anxiety. Here, we investigated whether TAC1- and TAC4-encoded peptides (substance P and hemokinin-1, respectively) and the neurokinin-1 receptor (NK-1R) are involved in the modulation of sexual behaviors. Male mice deficient for the NK-1R (TACR1 (-/-)) exhibited decreased exploration of female urine in contrast to C57BL/6 control mice and mice deficient for NK-1R ligands such as TAC1 (-/-), TAC4 (-/-) and the newly generated TAC1 (-/-) /TAC4 (-/-) mice. In comparison to C57BL/6 mice, mounting frequency and duration were decreased in male TACR1 (-/-) mice, while mounting latency was increased. Decreased preference for sexual pheromones was also seen in female TACR1 (-/-) mice. Furthermore, administration of the NK-1R-antagonist L-703,606 decreased investigation of female urine by male C57BL/6 mice, suggesting an involvement of NK-1R in urine sniffing behavior. Our results provide evidence for the NK-1R in facilitating sexual approach behavior, as male TACR1 (-/-) mice exhibited blunted approach behavior toward females following the initial interaction compared with C57BL/6 mice. NK-1R signaling may therefore play an important role in pheromone-induced sexual behavior.     

A model of emotional stress‐induced binge eating in female mice with no history of food restriction

Overeating is a major contributing factor to obesity and related health complications. For women, in particular, negative emotions such as stress strongly influence eating behavior and bingeing episodes. Modeling this type of binge eating in rodents presents challenges: firstly, stress‐induced anorexia is commonly observed in rodents therefore a mild stressor is required in order to observe an orexigenic effect. Second, many studies report using calorie restriction to observe the required behavior; yet this does not necessarily reflect the human condition. Thus, the aim of this study was to develop a model of emotional stress‐induced bingeing independent of caloric restriction. Female and male C57BL/6J mice were divided into ad libitum (n = 20 per sex) and food‐restricted (n = 20 per sex) groups which were both further split into a control group and a group exposed to frustration stress (n = 10 per group). All mice were provided intermittent access to a highly palatable food in 2 cycles. At the end of each cycle the stress group was subjected to a 15‐minute frustration episode where highly palatable food was within the home cage but inaccessible. Both groups were then given free access for 15 minutes. Frustrated female mice from the ad libitum displayed binge‐like behavior compared with controls (P = .0001). Notably, this behavior was absent in males. Ovariectomy had no impact on binge‐like behavior. Collectively, these data validate a novel model of emotional stress‐induced binge eating specific to female mice which does not require caloric restriction and is not driven by ovarian hormones.     

Transgenerational inheritance of chronic adolescent stress: Effects of stress response and the amygdala transcriptome

Adolescent stress can impact health and well‐being not only during adulthood of the exposed individual but even in future generations. To investigate the molecular mechanisms underlying these long‐term effects, we exposed adolescent males to stress and measured anxiety behaviors and gene expression in the amygdala—a critical region in the control of emotional states—in their progeny for two generations, offspring and grandoffspring. Male C57BL/6 mice underwent chronic unpredictable stress (CUS) for 2 weeks during adolescence and were used to produce two generations of offspring. Male and female offspring and grandoffspring were tested in behavioral assays to measure affective behavior and stress reactivity. Remarkably, transgenerational inheritance of paternal stress exposure produced a protective phenotype in the male, but not the female lineage. RNA‐seq analysis of the amygdala from male offspring and grandoffspring identified differentially expressed genes (DEGs) in mice derived from fathers exposed to CUS. The DEGSs clustered into numerous pathways, and the “notch signaling” pathway was the most significantly altered in male grandoffspring. Therefore, we show that paternal stress exposure impacts future generations which manifest in behavioral changes and molecular adaptations.     

Effects of corticotropin releasing factor and sauvagine on social behavior of isolated mice

Corticotropin releasing factor (CRF) and sauvagine (SVG) when injected ICV both reduced aggressive behavior and sociability while increasing defensive behavior in isolated DBA/2 mice interacting with a group-housed intruder. SVG was more effective than CRF in producing such behavioral effects. These results add further evidence to the similarity between CRF and SVG, and are discussed in terms of the involvement of these peptides in emotional reactivity in the laboratory mouse.     

Long-term individual housing in C57BL/6J and DBA/2 mice: assessment of behavioral consequences

The aim of the present study was to investigate the effects of individual housing on mouse behavior. The male mice of the C57BL/6J and DBA/2 strains were separated at the age of 4 weeks and kept in individual housing for 7 weeks until behavioral testing began. Their behavior was compared to the group-housed mice in a battery of tests during the following 7 weeks. The single-housed mice were hyperactive and displayed reduced habituation in the tests assessing activity and exploration. Reduced anxiety was established in the elevated plus-maze, but an opposite effect was observed in the dark-light (DL) and hyponeophagia tests. Immobility in the forced swimming test was reduced by social isolation. The DBA mice displayed higher anxiety-like behavior than the B6 mice in the plus-maze and DL exploration test, but hyponeophagia was reduced in the DBA mice. Moreover, all effects of individual housing on the exploratory and emotional behavior were more evident in the DBA than in the B6 mice. Novel object recognition and fear conditioning (FC) were significantly impaired in the single-housed mice, whereas water-maze (WM) learning was not affected. Marked strain differences were established in all three learning tests. The B6 mice performed better in the object recognition and FC tasks. Initial spatial learning in the WM was faster and memory retention slightly enhanced in the B6 mice. The DBA mice displayed lower preference to the new and enhanced preference to the old platform location than the B6 mice after reversal learning in the WM. We conclude that individual housing has strong strain- and test-specific effects on emotional behavior and impairs memory in certain tasks.     

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 × 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.     

Influence of sex and genetic background on anxiety-related and stress-induced behaviour of prodynorphin-deficient mice

The role of dynorphin/kappa opioid receptors in epilepsy and addiction are well accepted, but their function in emotional control is not yet fully understood. Data obtained from different strains of prodynorphin (Pdyn)- and kappa opioid receptor (KOP)-deficient mice do not provide a consistent picture of the functions of Dyn/KOP in anxiety, suggesting the influence of testing conditions and/or genetic background. Therefore, we investigated the behaviour and neurochemistry of male and female Pdyn KO mice on the balb/c and C57Bl/6N background. Consistent with our results obtained from male mice on the C57bl/6N background, we observed a less anxious phenotype in the elevated plus maze, open-field and light-dark test in male mice on the balb/c background. Female mice on the balb/c background also displayed less anxiety like behaviour; however these data reflect high trait anxiety and inter-individual differences. In contrast, female mice on the C57Bl/6N background displayed low trait anxiety and a paradigm-dependent reduction of anxiety. No differences were observed in the forced swim test, while balb/c Pdyn KO mice displayed prolonged immobility in the tail suspension test. In line with our previous results, we observed reduced CRH mRNA in the central amygdala in all groups of mice. In contrast, the recently observed CRH mRNA reduction in the hypothalamic paraventricular nucleus appears restricted to male, but not female mice. Our data support previous data suggesting a pronounced impact of endogenous prodynorphin-derived peptides on anxiety. Moreover, our data support the idea that the less anxious phenotype manifests only at elevated stress levels.     

Learning of submissive behavior in mice: A new model

The experience of winning or loosing fights plays an important role in subsequent aggressive or submissive behaviors. In this study agonistic behavior of male mice was chosen to investigate learning mechanisms in the context of a biologically meaningful situation.An ICR mouse introduced into a group of five C57BL/6 mice was attacked by mice of high social status (Fighter, F), but not by lower ranking animals (Non-Fighter, NF). On this basis the following model was developed to study learning of submissive behavior. Day 1 (baseline trial): An ICR mouse was introduced to a single NF-C57 mouse. Few submissive behaviors (crouch) were observed in naive ICR mice upon contact with NF-C57 mice. Day 2 (learning trial): The same ICR mouse was defeated by an F-C57 mouse until it showed defensive upright posture upon approach. This criterion was reached after a mean latency of 3.5 min and after being exposed to a mean number of 14 bites. Day 3 (retest trial): The same pairs as on day 1 confronted each other. Without being attacked, the ICR mouse showed a significant increase of submissive behavior (crouch, defensive sideways and upright) upon mere contact with the NF-C57 mouse when compared to day 1 and to control mice on day 3. Controls, confronted on all three days with NF-C57 mice, showed no increase in submissive behaviors.The results are discussed in terms of acquisition, memory, retrieval and extinction of learned submissive behavior. It is suggested that the mechanisms underlying learning of submissive behavior include generalization of conditioning and specific extinction processes. The further use of the learning scheme to assess drug effects is illustrated.     

Effects of the blockade of the system of opioid peptides on changes in emotional/behavioral reactions of rats induced by the action of extrahigh-frequency electromagnetic radiation in the norm and under conditions of hypokinetic stress

We studied the effects of pharmacological blockade (by injections of naloxone) of the system of opioid peptides on changes in emotional/behavioral reactions of rats in the open-field test. These changes were caused by the isolated action of low-intensity electromagnetic radiation (EMR) of extrahigh frequency (EHF) and its combination with experimentally induced hypokinetic stress. We conclude that one of the mechanisms of physiological effects of low-intensity EHF EMR is an increase in the functional activity of the system of regulatory opioid peptides; this results in adaptive modifications of the emotional/behavioral reactions under new conditions of the open-field test and provide an anti-stress effect under conditions of hypokinetic stress. Neirofiziologiya/Neurophysiology, Vol. 38, No. 1, pp. 52–60, January–February, 2006.     

Diurnal behavioral and endocrine effects of chronic shaker stress in mice

Experiments were performed in C57BL/6J male mice to determine 1) light/dark effects of acute and chronic shaker stress on open field behavioral patterns and 2) light/dark effects of chronic stress on plasma corticosterone and oxytocin. Shaker stress was applied acutely (15 min) or chronically (3 or 7 days). Mice were tested in the open field in the light or dark phase of the circadian cycle. For the endocrine study, mice were exposed to 3 days of intermittent shaker stress and sacrificed after the last stress event (09:00 or 19:00 h). Acute or chronic shaker stress had no significant effects on intensity of motor activity and rearing of mice tested under either light condition. Mice tested in the dark phase had higher motor activity and exhibited lower anxiety-like behavior as expressed by central zone activities and had higher emotionality as expressed by increased defecation. Chronic stress increased corticosterone with a greater absolute increase in the dark period. However, the percentage stress-induced increase was not different between the day and night periods. The oxytocin response to stress was observed only during the light phase with no change seen at dark phase. These results show that there is a marked difference in the light/dark pituitary stress response with no alteration in stress induced behavioral changes. They also suggest that there are circadian interactions in the endocrine stress axis that are without consequences for open field behavior.     

Yokukansan,a traditional Japanese herbal medicine,alleviates the emotional abnormality induced by maladaptation to stress in mice

The aim of the present study was to examine the effect of yokukansan, a traditional Japanese herbal medicine that is composed of Atractylodis lanceae Rhizoma, Poria, Cnidii Rhizoma, Uncariae Uncis cum Ramulus, Angelicae Radix, Bupleuri Radix and Glycyrrhizae Radix, on the emotional abnormality induced by maladaptation to stress in mice. Mice were exposed to repeated restraint stress for 60 or 240 min/day for 14 days. From the 3rd day of stress exposure, mice were given yokukansan orally (p.o.) or the 5-HT_1A receptor agonist flesinoxan intraperitoneally (i.p.) immediately after the daily exposure to restraint stress. After the final exposure to restraint stress, the emotionality of mice was evaluated using an automatic hole-board apparatus. A single exposure to restraint stress for 60 min induced a decrease in head-dipping behavior in the hole-board test. This emotional stress response disappeared in mice that had been exposed to repeated restraint stress for 60 min/day for 14 days, which confirmed the development of stress adaptation. In contrast, mice that were exposed to restraint stress for 240 min/day for 14 days did not develop this stress adaptation, and still showed a decrease in head-dipping behavior. The decreased emotionality observed in stress-maladaptive mice was significantly recovered by chronic treatment with yokukansan (1000 mg/kg, p.o.) as well as flesinoxan (0.25 and 0.5 mg/kg, i.p.) immediately after daily exposure to stress. These findings suggest that yokukansan may have a beneficial effect on stress adaptation and alleviate the emotional abnormality under conditions of excessive stress.     

Inactivation of Glucocorticoid Receptor in Noradrenergic System Influences Anxiety- and Depressive-Like Behavior in Mice

The aim of this study was to investigate whether conditional inactivation of the glucocorticoid receptors (GRs) in noradrenergic neurons affects animal behavior in mice. Selective ablation of GRs in the noradrenergic system was achieved using the Cre/loxP approach. We crossed transgenic mice expressing the Cre recombinase under the dopamine beta-hydroxylase (DBH) promoter with animals harboring the floxed GR gene. The resulting GR^DBHCre mutant mice exhibited no alterations in terms of normal cage behavior, weight gain, spatial memory or spontaneous locomotor activity, regardless of gender. To assess depressive- and anxiety-like behaviors we performed the Tail Suspension Test and the Light-Dark Box Test. While male mutant animals did not show any alternations in both tests, female GR^DBHCre mutants displayed depressive- and anxiety-like behavior. Additionally, male GR^DBHCre mice were exposed to chronic restraint stress but still exhibited immobility times and anxiety statuses similar to those of non-stressed animals while stressed control mice clearly revealed depressive- and anxiety-like phenotype. Thus, in males the effects of the mutation were precipitated only after chronic restraint stress procedure. Our data reveal a possible gender-dependent role of GRs in the noradrenergic system in anxiety- and depressive-like behavior in mice.     

Effects of beta endorphin and delta-sleep inducing peptide on resistance to emotional stress

Enzyme immunoassay was used to study the contents of beta-endorphin and delta-sleep inducing peptide (DSIP) in blood and hypothalamus in rats of Wistar and August lines under acute emotional stress. The stress-resistance of the animals was determined by using preliminary behavior tests. The rats were divided into two groups and predisposed to acute emotional stress. It was found that the contents of these peptides in Wistar-rats, which are more resistant to emotional stress, were higher compared with the August-rats, which are more predisposed to emotional stress. It was shown that the contents of beta-endorphin and DSIP in Wistar-rats is higher than in predisposed Wistar-rats.     

Effect of forced swimming on the memory track retention in mice with various behavioral stereotypes

The effects of forced swimming on retrieval of the passive avoidance during its extinction were found to depend on aggressive and submissive behavior. In mice without generated behavioral stereotypes, swim stress applied before or after training stabilized retention of the memory trace retrieval. The similar improved influence of forced swimming on memory storage is revealed in submissive, but not aggressive mice. The increase of resistance against extinction under the swim stress can be connected to facilitation of emotional processes.     

Effects of different forms of environmental enrichment on behavioral,endocrinological, and immunological parameters in male mice

This study investigated effects of different forms of environmental enrichment on behavioral, endocrinological, and immunological parameters in male mice. For this purpose, animals of the inbred strain CS were kept in groups of four males under three different housing conditions: (A) nonstructured Makrolon type III laboratory cages ("standard-housing" = S); (B) equivalent laboratory cages that were enriched with a box and a scaffolding ("enriched-housing" = E); and (C) spacious terraria that were structured richly ("super-enriched-housing" = SE). Both forms of enrichment caused a sharp rise in aggressive behavior, though play behavior was increased in E and SE mice, too. Levels of sociopositive behaviors in S and SE mice were higher than those in E mice. Plasma corticosterone concentrations and adrenal tyrosine hydroxylase activities were significantly increased in male mice kept in both forms of enriched cages, indicating an activation of the pituitary-adrenocortical and the adrenomedullary systems. The behavioral and endocrinological differences were partly reflected by immunological parameters: SE mice had levels of IgG1 and ratios of IFN-gamma/IL-10 and IL-2/IL-10 significantly lower than those of S mice. Ratios of IgG2a/IgG1 were significantly higher in SE mice. The absolute percentages of CD8 cells in E-mice were significantly lower than those in S mice. Despite the elevated levels of stress hormones under both forms of enriched housing, the behavioral parameters also indicate positive effects of the enrichment, especially on SE animals. Obviously, an environmental enrichment is beneficial for male mice as long as the spatial conditions are generous enough to allow coping with the increased aggression brought about by the enrichment.     

Cyclic nucleotide levels in the brain of inbred mice in emotional stress exposure

The content of cAMP and cGMP in different brain regions was studied in C57Bl/6 and BALB/c mice at rest and upon exposure to emotional stress induced by open field technique. Interstrain differences in baseline nucleotide content, differences in nucleotide distribution in the brain regions and changes in their concentration after stress have been revealed.     

Pituitary-adrenal function in female mice with mutation Agouti yellow (A(y))

Agouti protein is a paracrine signaling factor modulating action of ACTH and alpha-MSH. Dominant mutation Ay causes ectopic, ubiquitous expression of Agouti protein in mice. It was shown that Ay mutation increased stress-induced hypothalamo-adrenal activity in male mice. There is a sex difference in the hypothalamo-pituitary-adrenal axis in rodents. The aim of this study was to test effects of ectopic overexpression of Agouti protein on pituitary-adrenal function in female mice. Female mice of C57Bl/6J strain with Ay mutation (Ay/alpha) and with mutation nonagouti (alpha/alpha; lack of Agouti protein) were used. Ay/alpha-females had an increased blood level of corticosterone and ACTH after 10-minute restriction as compared with alpha/alpha-females. The adrenal threshold sensitivity and reaction to exogenous ACTH in vivo suggests that increased corticosterone reaction to emotional stress is caused by increased pituitary stimulation.     

Effect of chronic corticosterone application on depression‐like behavior in C57BL/6N and C57BL/6J mice

Many studies using genetic mouse models are performed with animals on either one of the two closely related genetic backgrounds, C57BL/6J or C57BL/6N. These strains differ only in a few genetic loci, but have some phenotypic differences that also affect behavior. In order to determine the effects of chronic stress hormone exposure, which is relevant for the pathogenesis of psychiatric disorders, we investigated here the behavioral manifestations of long‐term increase in corticosterone levels. Thus, male mice from both sub‐strains were subcutaneously implanted with corticosterone (20 mg) or placebo pellets that released the hormone for a period of 21 days and resulted in significantly elevated plasma corticosterone levels. Corticosterone significantly increased food intake in B6N, but not in B6J mice. At various time points after pellet implantation, we performed tests relevant to activity and emotional behaviors. B6J mice displayed a generally higher activity in the home cage and the open field. Corticosterone decreased the activity. In B6N mice, corticosterone also decreased sucrose preference, worsened the coat state and increased forced swim immobility, while it had no effect in the B6J strain. Altogether, these results indicate that B6N mice are more sensitive to some of the effects of chronic corticosterone treatment than B6J mice.     

Social effects of the behavior of male and female mice in open field]

Canonical discriminant analysis is used to differentiate behaviors, in male and female mice, either isolated, either grouped by two, or grouped by five, and placed into two different open-fields, one of 1 m X 1 m and one of 2.5 m X 2.5 m. Social effects are experimentally demonstrated. In addition the evidenced complexity of the behavior of mice in an openfield cannot be merely reduced to a decrease or increase of an emotional or of an exploratory behavior, as it has been previously stated.     

Liver injury after an aggressive encounter in male mice

Acute and intense psychological stressors induce cell damage in several organs, including the heart and the liver. Much less is known about social stress. In male mice, aggressive behavior is the most common social stressor. It is remarkable that upon fighting, submandibular salivary glands release a number of peptides into the bloodstream including epidermal growth factor (EGF). We showed previously that released EGF protects the heart from cell damage in this particular stressful situation. Here, we studied the effect of an aggressive encounter on the liver and whether EGF has a similar effect on this organ. An aggressive encounter in male mice caused inflammatory response and a transient increase in plasma alanine and aspartate transaminase activities. At 3 h, focal infiltration of neutrophils was observed in liver parenchyma. These cells accumulate on eosinophilic hepatocytes, which may correspond to dying cells. A few hours later, evidence of necrotic lesion was observed. Surgical excision of submandibular glands, sialoadenectomy, did not prevent the rise in plasma EGF concentration and did not affect the increase in plasma transaminase activities. Neither did the administration of tyrphostin AG-1478 (inhibitor of EGF receptor kinase) alter the increase in plasma alanine transaminase activity. However, it did enhance the rise in both aspartate transaminase and creatine kinase activity, suggesting heart damage. We conclude that an aggressive encounter causes mild liver damage and that released EGF does not protect this organ, in contrast to its effect on the heart.