Factors influencing maternal attack on conspecific intruders by lactating female “TO” strain mice

Factors regulating maternal attack in “TO” strain mice were investigated to determine 1) optimal conditions for inducing this behaviour and 2) the likely utility of this activity. Lactating females were more likely to attack male intruders than female intruders. The mate's presence reduced maternal attack in this strain, or (putting it conversely) aggression was generated in the male's absence. Removal of the mothers from their litters for four to five hours also suppressed maternal attack. Investigation of the bite targets in the maternal attack suggested that it is a defensive, rather than an offensive, response.     

Effects of neonatal cyproterone acetate administration on isolation-induced fighting behavior and mounting behavior in male and female TO strain albino mice

The effects of a single dose (1 mg) of cyproterone acetate administered on either day 1 or day 20 of life on the adult behaviors of male and female TO strain albino mice were studied. The mice were tested both in a “standard opponent”-type situation and in a similar test using a hormonally primed receptive female, after being gonadectomized and maintained with testosterone propionate as adults. Neonatal treatment with this compound had little effect on subsequent fighting behavior in either sex, but clear evidence was produced that this treatment masculinized the sexual behavioral potentialities of the females, an effect which was apparent in animals which had been injected on either day 1 or day 20 of life. Indications were obtained that females treated neonatally with cyproterone acetate were capable of differentiating between the male and female “opponents” in a manner similar to the male. The effects of this treatment on fighting behavior consequently appear to be dissimilar to the effects of neonatal castration in this species. However, the effects on mounting behavior in the females, evidenced in adulthood, seem Likely to be a consequence of the weak androgenic properties of the antiandrogen. The administration of cyproterone acetate neonatally appears to have a more dramatic effect on the adult weights of endocrine organs in females than in mates.     

The role of endocrines in isolation-induced intermale fighting in albino laboratory mice. I: PITUITARY-ADRENOCORTICAL INFLUENCES

Recent experiments concerning the possible role of components of the pituitary–adrenocortical axis (ACTH and glucocorticoids) in isolation-induced intermale fighting behavior in laboratory strains of mice are reviewed. A series of experiments which investigate factors that may influence the successful demonstration of this relationship are described. Differences in performances in standard-opponent tests of some outbred strains of albino mice are indicated, as well as an interesting positive correlation between the aggressiveness and the relative adrenal weights of the strains employed. Long-acting preparations of both ACTH and ACTH 4–10, injected throughout a period of isolation, suppressed fighting behavior in intact TO-strain mice in subsequent standard-opponent and trained-fighter tests. After it had been confirmed that vigorous isolation-induced fighting could be obtained in bilaterally castrated mice which had been subcutaneously implanted with testosterone pellets, the effects of long-acting preparations of ACTH, ACTH 4–10, ACTH 1–10, and ACTH 4–10 D-phe on the fighting behavior of such animals were studied. A significant suppression of fighting behavior was evident only with respect to ACTH, suggesting that ACTH 4–10 may have its action on this behavior in a manner rather different from that of the parent molecule. Some evidence was also obtained indicating that the zinc used in the preparation of long-acting injections of ACTH and its analogs may also cause a decline in the level of fighting behavior, in a standard-opponent test, in TO-strain mice which had been castrated and testosterone implanted. While such a finding does not affect the validity of the recorded behavioral influences of ACTH and ACTH 4–10 described earlier, it does seem likely that the presence of this substance in placebo injections would make the demonstration of the actions of the pep tides difficult, as there would be a low level of fighting in all categories. Rather less impressive results were obtained with respect to the influences of ACTH preparations and zinc on castrated—implanted CFW mice. The studies identify a number of the factors which may influence the successful demonstration of a relationship between the functioning of the pituitary—adrenocortical axis and isolation-induced agonistic behavior in the mouse. A number of general, if tentative, conclusions may also be listed. It seems likely, in spite of the interpretational difficulties caused by what seems to be a complex and rather unstable relationship, that ACTH and glucocorticoids may have profound influences on this type of fighting behavior in this species. One may also conclude that the evidence for an extraadrenal influence of ACTH on this behavior appears stronger as a result of these and related studies and that the actions of ACTH and its analogs on murine fighting behavior may be logically related to the actions of these compounds on the acquisition and extinction of conditioned avoidance reactions in hypophysectomized rats. The possible utility of such actions to the natural territorial habit of the adult male mouse is also indicated.     

Attack by female mice on “Strangers”

In this study the aggressive responses directed by small groups of female mice towards virgin, pregnant, and lactating female strangers, which were individually introduced into their cages, were compared. The results obtained show that, except when lactating, pregnant females are neither attacked much more often nor any more severely than virgin mice. It is suggested that only the state of lactation favors the production of stimuli (olfactory) which release attack by female mice.     

Activity of creatine kinase in mice under various “Stress” conditions

“Stress” induced by swimming, immobilization, and fighting in male albino mice results in a significant increase of creatine kinase (CK) activity in blood obtained by decapitation. The increase partially depends on motor activity as shown in fighting animals. Males show higher CK values than females. Isolation and even immobilization also lead to higher CK activity, the latter to a similar extent as swimming and fighting. We believe that CK activity is regulated by processes additional to motor activity.     

The development of territorial-induced intermale agonistic behavior in albino laboratory mice

Male mice of the CF-1 strain (Mus musculus) were allowed to take up lone residence in a small territory consisting of a 60-cm enclosure attached by a tubular runway to a standard mouse cage with food, water, and bedding. A group of ten mice, each of which resided in its own separate enclosure for 24 hours, were more aggressive toward intruders than other groups of ten mice following six-hour residence periods, or no such residence. Aggression toward intruders increased in repeated weekly tests of the six-hour residents, but after four weeks of testing did not reach the maximum stable level displayed by the 24-hour residents over four weeks of testing. In another experiment, the 24-hour residence period of groups of 20 CF-1 male mice was disturbed by briefly removing the mouse from the enclosure, before introducing the intruder, at various intervals prior to testing. Removal of the resident five minutes before testing resulted in a marked decrease in aggression toward intruders. Although lesser decreases in aggression followed intervals of 30, 45, and 60 minutes, a 180 minute interval resulted in no appreciable effects compared to undisturbed controls. It is concluded that exposure to the stimuli provided by the enclosure results in an aggressive readiness in the resident mouse which reaches a high level within a 24-hour period.     

Relationships between testosterone metabolism in the brain,other endocrine variables and intermale aggression in mice

Relationships between some endocrine variables (plasma testosterone and estradiol; in vitro gonadal biosynthesis from pregnenolone precursor and adrenocortical biosynthesis from progesterone precursor; in vitro activity of 17β-hydroxysteroid de-hydrogenase (17β-HSDH) and of aromatizing enzymes in the subcellular fractions of the brain) and isolation-induced inter-male aggressiveness were studied. A significant positive correlation was found between fighting behavior, measured by the number of wins in a series of paired encounters, and the activity of brain 17β-HSDH. A significant inverse correlation was found between fighting behavior and the activity of aromatizing enzymes in the nuclear fraction of the brain. No significant correlations were found between fighting and the other endocrine variables investigated. These results may suggest that the conversions testosterone → androstenedione and testosterone → estradiol in the brain play a role in the control of inter-male fighting in the mouse. These results may also account for the effect of repeated wins and defeats on brain steroidogenesis.     

Further Evidence that Social Interaction Reduces Conditioned Taste Aversions in Mice

Social interactions with other conspecifics affect food selection in mammals. A previous study suggested that male mice attenuate conditioned taste aversion (CTA) by lithium chloride after interacting with an unfamiliar male conspecific. The present study was designed to (a) examine whether interactions with a familiar conspecific would attenuate CTA and (b) investigate sex differences in the social attenuation of CTA in mice. Results indicated that interacting with a familiar conspecific of the same sex following poisoning attenuated conditioned taste aversions only in male mice. The results suggest that the familiarity of conspecifics was not a critical factor in the social attenuation of CTA. Discrepancies between present and previous findings are discussed.     

Pain‐induced aggression and changes in social behavior in mice

The effects of neuropathic, formalin, and acetic acid‐induced visceral pain were investigated on the social and aggressive behaviors in the Swiss male mice. Neuropathic pain was induced by tibial nerve transection (TNT). Also, somatic and visceral pain was conducted by intraplantar injection of diluted formalin (1%, 20 μl) and intraperitoneal administration of acetic acid (0.6%, 200 μl), respectively. Fourteen and twenty one days after the TNT surgery, and also, 1 and 7 days following formalin and acetic acid administration, the three‐chambered test was used to determine sociability and preference for social novelty and resident/intruder test was used for the evaluation of the aggressive behaviors. In the sociability phase of the three‐chambered test, all the three models of pain did not change the animal's sociability. However, in the social novelty preference phase, the animals in pain showed deficits in social novelty preference by a significant increase in the time spent with the familiar mice compared to the control groups. Also, animals in pain significantly showed more aggressive behaviors like biting and clinching and have much less attack latency in comparison to the control groups. Pain‐induced changes in the social novelty preference and aggressive behaviors continued in the neuropathic group until the end of the experiment. However, 7 days following the induction of both formalin and visceral pain, animals' social memory, and aggression almost returned to the standard value. These results suggest that long‐lasting pain could lead to social memory impairment and increase aggressive behaviors in mice.     

A developmental-genetic analysis of aggressive behavior in mice: IV. Genotype-environment interaction

To assess the extent of plasticity in behavioral development after directional selection for aggressive behavior, male mice were reared and tested in selected social rearing and testing conditions. After four generations of selective breeding, the lines differed in all attack measures when tested in a dyadic assessment following isolation rearing. Line-specific effects of isolation vs. group rearing were demonstrated, and longitudinal studies showed the ontogenetic pattern of difference between lines to be substantially changed by conditions of rearing and testing. The social-interactional processes that might produce the developmental genotype-environment interaction were investigated. Line-specific interaction patterns within long-established sibling groups predicted aggressive behavior in cross-situational dyadic assessments. Group rearing attenuated most line differences in aggressive measures, but the high-aggressive line was more likely than the low-aggressive line to persist in attacking over consecutive days of observation. Cross-fostering in early development did not significantly change adult aggressive behavior. Some implications of a developmental-genetic approach to the study of social interactions are discussed.