Group-housed Male Mice Research Articles

Effects of repeated social stress on leukocyte distribution in bone marrow, peripheral blood and spleen

Leukocyte trafficking between the various body compartments has an important surveillance function that ensures the detection of antigen and enables the immune system to initiate a rapid and effective response. Repeated social defeat of group-housed male mice induced by daily, acute encounters with an aggressive conspecific substantially altered leukocyte trafficking and led to a gradual redistribution of immune cells in bone marrow, peripheral blood and spleen. Recurrent exposure to the stressor over a period of 2, 4 or 6 consecutive days was associated with cell mobilization and increased myelopoiesis in the bone marrow that was paralleled by an accumulation of neutrophils and monocytes in circulation and spleen. Substantial depletion of B cells in bone marrow and blood was associated with an increase in splenic B cells indicating a redirection of this cell type to the spleen. In contrast, T cells were markedly reduced in these immune compartments. The recruitment of CD11b + leukocytes (i.e., monocytes/macrophages and neutrophils) from the bone marrow to the spleen might play a critical role in the development of functional glucocorticoid resistance in the murine spleen that was reported in context with repeated social defeat.

Strain‐specific aggressive behavior of male mice submitted to different husbandry procedures

AbstractSevere aggression within groups of male laboratory mice can cause serious welfare problems. Previous experiments have shown that the transfer of specific olfactory cues during cage cleaning and the provision of nesting material decrease aggression and stress in group‐housed male mice. In this study, the combined effect of these husbandry procedures was tested for their long‐term effect on aggression in two strains of male mice (BALB/c and CD‐1). We used postcleaning aggressive behavior, wound counts, and testosterone levels as indicators of aggressiveness. Physiological responses to social challenge were investigated through urinary corticosterone and adrenal tyrosine‐hydroxylase measurements. Furthermore, the aggression‐modulating effects of two enrichment items (ShepherdShack/DesRes and PVC tube) were explored. Marked differences were found between the two strains. CD‐1 mice were more aggressive, had higher testosterone levels but lower corticosterone levels, and had fewer wounds than BALB/c mice. However, in neither of the two strains was long‐term enrichment with nesting material and its transfer after cage cleaning effective in lasting reduction of intermale aggression. This may be explained by the fact that aggression levels were generally low. It seems that housing mice in small, socially stable groups or keeping social disturbances to a minimum considerably modulates aggression in group‐housed male mice. Mice of both strains housed in cages enriched with nesting material had lower urinary corticosterone levels than standard‐housed mice. We therefore conclude that the long‐term provision of nesting material, including the transfer of nesting material during cage cleaning, may enhance the welfare of laboratory mice. Aggr. Behav. 29:69–80, 2003. © 2002 Wiley‐Liss, Inc.

Social stress alters splenocyte phenotype and function

Social stress of group-housed male mice induced a state of functional glucocorticoid (GC) resistance in splenocytes. The following studies examined the effects of paired-fighting (PF) stress on immune cell distribution and function in spleens of male mice. Following six daily PF stress sessions, splenic monocytes and neutrophils increased and lymphocytes decreased. PF also altered the distribution of CD62L and CD11b positive monocytes. Additionally, PF augmented proliferation and lowered the sensitivity of LPS-stimulated splenocytes to the antiproliferative effects of corticosterone, suggesting that PF induced a state of GC resistance in splenocytes. Together, these findings indicate that social stress altered phenotype and function of splenic immune cells. These findings may have implications for the healing of bite wounds that are often associated with social stress in rodents.

Effect of low doses of clozapine on behaviour of isolated and group-housed male mice in the elevated plus-maze test

Clozapine is effective over a low and narrow dose range in the treatment of the negative symptoms of schizophrenia. Its efficacy is said to reflect an anxiolytic property of the neuroleptic. This study examined the effects of a low dose range of clozapine (0.1, 0.2 and 0.4 mg/kg) administered to isolated (7 days) and group-housed male mice on their behaviour in the elevated plus-maze. The results using this model of anxiety showed no dose-dependent effect on behaviour after treatment with low doses of clozapine. Some doses (0.1 and 0.4 mg/kg), however, reduced the duration and frequency of open arm entries compared to control-treated mice in the group-housed animals. This might indicate a slight anxiogenic effect. Support for this view is provided by some of the ethological measures, particularly head-dipping (HD). Seven days of isolation did not alter the main anxiety indices in controls. Nevertheless, some measures (e.g. closed entries and duration in the closed arm) were modified by the clozapine treatment (0.2 mg/kg) in a manner suggesting a mild anxiogenic action. The effects of the drug in individually and group-housed male mice were certainly different.

Influence of cage enrichment on aggressive behaviour and physiological parameters in male mice

From welfare perspective group housing of mice is preferred over individual housing. Group housing of male laboratory mice, however, often leads to problems due to excessive aggressive behaviour. In our search for management and housing modifications to decrease aggression in group-housed male laboratory mice, we have tested the effect of two types of environmental enrichment—nesting material and shelter—on aggressive behaviour after cage cleaning and after a 1 h isolation period. Severity of wounds, urinary corticosterone levels, body weight, food and water intake and several post-mortem parameters were also monitored. The results indicated that type of enrichment strongly affected both aggressive behaviour and physiological parameters. Overall, nesting material reduced aggressive behaviour, while a shelter increased aggressive behaviour compared to control housing. This effect was also reflected in the number of wounds counted. Furthermore, during shelter housing mice gained less body weight, drank less and showed higher corticosterone levels, while in housing conditions with nesting material, mice ate less. We conclude that providing male mice with nesting material reduces aggression between male mice, and may, thus, be promoted as being beneficial to their physical health and psychological well-being.

Modulation of aggression in male mice: influence of group size and cage size

Aggression in group-housed male mice is known to be influenced by both cage size and group size. However, the interdependency of these two parameters has not been studied yet. In this study, the level of aggression in groups of three, five, or eight male BALB/c mice housed in cages with a floor size of either 80 or 125 cm 2/animal was estimated weekly after cage cleaning for a period of 14 weeks. Furthermore, urine corticosterone levels, food and water intake, body weight, and number of wounds were measured weekly. At the end of the experiment, tyrosine hydroxylase (TH) activity, testosterone levels, and weight of spleen, thymus, testes, and seminal vesicles were determined. Results indicate a moderate increase of intermale aggression in larger cages when compared to the smaller cages. Aggression in groups of eight animals was considerably higher than in groups of three animals. The increase of agonistic behavior was observed both in dominant and subordinate animals. Physiological parameters indicate differences in stress levels between dominant and subordinate animals. It is concluded that aggressive behavior in group-housed male BALB/c mice is best prevented by housing the animals in small groups of three to five animals, while decreasing floor size per animal may be used as a temporary solution to decrease high levels of aggression in an existing social group.

Do Male Mice Prefer or Avoid Each Other's Company? Influence of Hierarchy, Kinship, and Familiarity

In the laboratory, individual housing of male mice who otherwise show aggression is common practice. Because mice are a social species, the question arises whether this procedure is right from the animals' point of view. This study tested the preference of subordinate animals for their dominant cagemate, and vice versa, and the preference of subordinate animals for an unknown subordinate partner. Experiments that allowed male mice with different histories to choose either an inhabited or an empty cage have shown that the mice preferred the proximity of another male over individual housing. No differences in this respect were found between dominant and subordinate males, or between littermates and nonlittermates. The preference was most obvious when mice who were previously housed together were tested. The study concludes that separation and single housing for mice are not attractive solutions for overcoming aggression in group-housed male mice and that alternative approaches, such as improving the housing conditions, should be explored as a way of tempering intermale aggression.

Effect of repeated administration of the antioxidant stobadine on the behavior of singly-housed male mice in intraspecies conflict.

The aim of the present study was to assess the effect of repeated oral administration of stobadine (70 mg/kg) on the occurrence of selected behavioral elements during exposure to an intraspecies conflict between singly-housed and group-housed male mice. Isolation induced timidity (defensive-escape behavior without attacks) in most mice (87%). This isolation-induced timidity was reduced after stobadine treatment. In the stobadine-treated group, sociable activities (following, climbing) were also decreased. After discontinuation of the treatment (18 days), aggressive behavior tended to increase in the stobadine-treated group. The results of this study are indicative of an inhibitory effect of repeated administration of stobadine on some behavioral activities of singly-housed male mice in an intraspecies conflict.

Aggressive and social behavior after alprazolam withdrawal: experimental therapy with Ro 19-8022

The aim of the present study was to ascertain whether withdrawal from alprazolam can increase anxiety-like and aggressive behavior during intra species conflict in mice and, if so, whether a partial benzodiazepine agonist Ro 19-8022 is able to reverse these behavioral changes without untoward effects such as sedation. An experimental model consisting of interactions of pairs of singly-housed male mice with non-aggressive group-housed male mice was used. Alprazolam (1 mg/kg) was given orally twice daily for 8 days and once on the 9th day. When withdrawn from alprazolam (3 days after the last dose), mice reduced social investigation and increased the incidence of aggressive behavior in comparison to the pre-withdrawal level. However, the increase of aggression was moderate and occurred only in subjects with low pre-treatment levels of aggression. Ro 19-8022 (10 mg/kg) significantly antagonized the decrease of social behavior and the increase of aggression after alprazolam withdrawal without causing sedation or ataxia.

Serum Estradiol Levels and Ethanol-Induced Aggression

HILAKIVI-CLARKE, L., M. RAYGADA AND E. CHO. Serum estradiol levels and ethanol-induced aggression. PHARMACOL BIOCHEM BEHAV 58(3) 785–791, 1997.—The biological mechanisms behind ethanol-induced aggression are not known. Because gonadal hormones are linked both to aggression and ethanol, the present study examined relationships among the levels of serum estradiol (E 2), testosterone (T), and aggressive behavior in ethanol-treated male mice. We found that among group-housed male mice, serum E 2 levels were significantly elevated 30 min after a single injection of 0.6 g/kg ethanol. Serum T levels showed a nonsignificant decrease by ethanol. The E 2/T ratio, an index of aromatization of T to E 2, was significantly higher in the ethanol-treated animals when compared with the vehicle-treated animals. We also determined aggressive behavior in the resident-intruder test among isolated male mice at baseline (after a vehicle), and after an injection of 0.6 g/kg ethanol. The mice were grouped accordingly to those that increased, decreased, or remained nonaggressive in response to ethanol administration. We found that at baseline, neither serum T or E 2 levels, nor E 2/T ratio differed significantly between the increased or reduced aggressor mice. In contrast to the increase in serum E 2 levels seen in the nonaggressive mice, ethanol significantly reduced circulating E 2 levels, but did not affect aromatization of E 2 from T in the mice that became aggressive following an ethanol injection. These data suggest that mice who exhibit a paradoxical decrease in serum E 2 levels by ethanol may be particularly prone to ethanol-induced aggression.

The Influence of Mouse Housing Density on Autoimmune Reactivity

Splenic cells from C57BL/6 mice housed in groups (six per cage) or individually (one per cage) were analyzed for their ability to synthesize autoantibodies against autologous bromelain-treated erythrocytes. Group-housed male mice had a significantly lower number of autoimmune plaque forming cells (APFC) in their spleens than age matched female mice housed under similar conditions. However, when male mice were housed individually for 4 to 44 weeks, a marked increase in numbers of APFC were found in their spleens, approaching those of female control mice. Our results demonstrate that a simple environmental manipulation such as housing conditions can profoundly modulate autoimmune reactivity. Thus, alteration of the psychophysiological state determined by the quality of housing may significantly affect the development of autoimmune disease.

Deoxycorticosterone Acetate (DOCA)-Induced Sodium Appetite in Group-Housed Mice

Research investigating sodium hunger in mice has failed to produce evidence that mineralocorticoids are involved in sodium appetite. In our own laboratory, doses of deoxycorticosterone acetate (DOCA) ranging from 1 mg/kg to 20 mg/kg have failed to induce a sodium appetite. In rats, glucocorticoids have been effective in potentiating mineralocorticoid-induced sodium appetite. Recent research has suggested that the mouse, like the rat, does possess mineralocorticoid sensitivity for sodium hunger but, unlike the rat, has a strong dependency on an accompanying glucocorticoid action. The present experiment was conducted to study the effects of DOCA on sodium appetite in mice under housing conditions that attempted to eliminate the reduction of corticosterone associated with social isolation. Therefore, male GHSC mice were group-housed and were tested within two counterbalanced treatment conditions. One condition consisted of an injection of 10 mg/kg DOCA on 2 consecutive days, and the other condition consisted of an injection of the vehicle on 2 consecutive days. Group-housed male GHSC mice showed a significantly larger amount of NaCl consumption after injections of DOCA than after injections of the vehicle.

Differential sexual activity of isolated and group-housed male mice: Lack of substantial influence of acute or chronic naloxone administration

Influences of naloxone upon male sexual behavior were examined using two different baseline activity levels: individually and group-housed mice. In Experiment 1, single injections of 0, 12.5, or 50 μg per animal were administered before testing. Isolated mice showed more sexual activity than did grouped mice; naloxone failed to alter those differences. In Experiment 2, a similar result was obtained despite administration of 50 or 150 μg per animal of naloxone. In Experiment 3, 0 or 50 μg of naloxone was administered to isolated or grouped males daily on the 5 days before testing. Isolated mice showed performance superior to that of grouped mice, but there was no effect of the drug. In Experiment 4, doses of 0, 12.5, or 50 μg of naloxone were given to isolated or grouped males twice daily for 7 days prior to testing, producing little effect. These results suggest that the influences of prior social condition on male sexual activity are robust in the face of naloxone administration.

Differential sexual activity of isolated and group-housed male mice: Influence of acute d-Amphetamine sulfate administration

It is established that group housing can impair sexual activity of male mice, and that central catecholamines are involved in male sexual response, but it is not known whether catecholamine mechanisms are involved in sexual impairment in grouped males. Injections of 0, 0.22, 0.67, 2.0, or 6.0 mg/kg of d-amphetamine sulfate were administered 1 h before testing to individually and group-housed male C57BL/6J mice. Isolated mice showed more mounts, intromissions, and ejaculations and shorter response latencies than did group-housed mice. The latencies to first mount, intromission, and ejaculation were nonmonotonically related to dosage, being shortest at the lowest dosage in isolated mice, but significantly elevated by the higher dosages in both isolated and grouped males. The number of ejaculations was significantly elevated by moderate dosages in both isolated and grouped mice, peaking at the 2.0 mg/kg dosage in isolated mice and at 0.67 mg/kg in grouped mice. Nevertheless, amphetamine treatment generally failed to eliminate differences between males from isolated and grouped backgrounds.

Stress-induced hyperthermia in mice: Hormonal correlates

In the stress-induced hyperthermia (SIH) paradigm in group-housed male mice, the rectal temperature of last measured mice is approximately 1.5°C higher than the first measured one when the temperature of each mouse is measured sequentially with an interval of 1 min. In the present study it is demonstrated that SIH is accompanied by increases in plasma ACTH, corticosterone, and glucose levels that return to baseline more or less parallel to the temperature. The simultaneous increases in temperature and plasma stress hormones strongly support the use of the SIH paradigm in mice as an animal model to study putative anti-stress or anxiolytic properties of drugs.

Influence of lithium and rubidium on exploratory behaviour and locomotor activity in isolated male mice (author's transl)

The effect of lithium and rubidium on curiosity rearing, and locomotor activity in isolated and group-housed male mice (DBA/2 Han) was investigated. LiCl and RbCl were given with the drinking water (30 mol/l) during 3 weeks. The behaviour of the animals was tested before and after the chronical application of either lithium or rubidium. The results show that lithium was able to enhance the decreased curiosity of the isolated mice which now was no longer different from that of normal group-housed animals. The locomotor activity of the isolated animals was also increased by LiCl, while rearing was not altered. Rubidium even more decreased the already diminished curiosity of the 'fighting mice' but had no influence on rearing and locomotor activity. Three weeks after cessation of treatment the behaviour of the isolated mice returned to predrug levels. Neither lithium nor rubidium had any influence of the behaviour of animals kept in groups.

Juvenile male mice: An attempt to accelerate testis function by exposure to adult female stimuli

Two experiments were conducted in order to determine whether juvenile male mice show accelerated maturation of testis function following chronic exposure to adult female mice. Experiment 1 showed that the maturation of testis function, as measured by radioimmunoassay of plasma androgens in post-weaning group-housed (6/cage) male mice, is most rapid between 22 and 42 days of age with peak androgen levels attained by 42 days of age. Experiment 2 showed that juvenile males exposed to an adult female through a wire mesh partition from 22 to 32 days of age show accelerated growth of an androgen-dependent accessory organ, the seminal vesicles, when compared to males housed either in direct contact with an adult female, in isolation or in groups of 2 or 6. The absence of dense housing conditions (i.e., juvenile males housed in isolation or pairs) promoted, whereas social conflict (i.e., juvenile males housed in direct contact with an adult female) and dense living conditions (i.e., juvenile males housed in groups of six) inhibited, the growth of the seminal vesicles. Because plasma androgens were unaffected by the differential housing conditions, it was speculated that the pulsatile pattern of androgen release in the mouse may have obscured possible group differences in circulating hormones.