Gonadal hormones and intrasexual aggressive behavior in female bank voles (Clethrionomys glareolus)

The effects of gonadal hormones on aggressive behavior in the female bank vole was investigated in 10 min home cage tests. Ovariectomized (ovx) or intact females injected with oil, with progesterone (P), with a mixture of progesterone and estrogen (P+E), or with testosterone (T) alone were confronted in a resident-intruder test with unfamiliar, nonoperated females as intruders. Intact females showed aggressive behavior more frequently than ovx females. Ovx females injected with P, with P+E, or with T made significantly more attacks, and these attacks lasted longer than those observed for oil-treated voles. The results indicate that P, the typical female hormone, is responsible for aggressive behavior in female bank voles; however, only T increased the duration of interfemale aggression. Aggr. Behav. 24:63–70, 1998. © 1998 Wiley-Liss, Inc.     

Genetic differences in the mouse defense test battery

The mouse defense test battery (MDTB) has been designed to examine anxiogenic- or anxiolytic-like properties of psychoactive drugs through effects on specific defensive behaviors. In the present study, the MDTB was used to evaluate the potential contribution of genetic factors to these behaviors. The data revealed pronounced differences in several defense reactions among four inbred strains (BALB/c, C57BL/6, CBA, DBA/2) and one outbred (Swiss) mouse line. Thus, when subjects were introduced into the apparatus, Swiss and C57BL/6 displayed the highest levels of horizontal and vertical activities, while BALB/c and DBA/2 mice showed intermediate and CBA low activity rates. When subjects were chased by the rat, C57BL/6 mice used flight as the dominant defense strategy, while the defensive responses of BALB/c, C57BL/6, and DBA/2 mice consisted of flight reactions and risk assessment activities. However, when flight or escape was not possible, risk assessment became the predominant feature of the defense repertoire in the C57BL/6 mice. When defensive threat/attack behaviors were required, Swiss, BALB/c, DBA/2, and C57BL/6 mice showed very similar reactions in terms of the magnitude of the responses observed. CBA mice were poorly defensive in all these test situations. Finally, after the rat was removed from the test apparatus, Swiss, DBA/2, and C57BL/6 mice displayed more vertical activities than BALB/c mice. These latter, however, showed an increased level of ambulation compared to the activity recorded before the rat exposure. Together, these findings indicate that genetic factors contribute to defensive behaviors in this animal model of anxiety. The different behavioral profiles displayed by the strains used here may provide the means to obtain a better insight into the neurobehavioral mechanisms involved in anxiety-related disorders. Aggr. Behav. 23:19–31, 1997. © 1997 Wiley-Liss, Inc.     

Dominance and age-related changes in the play fighting of intact and post-weaning castrated male rats (Rattus norvegicus)

The play fighting behaviour of male rats (Rattus norvegicus) castrated at weaning was compared to that of intact controls during the juvenile and post-pubertal phases of development. Following puberty, both the castrated and intact animals exhibited an age-related change in their play fighting; the frequency of initiating play fighting decreased and juvenile patterns of playful defense were replaced by more adult-like patterns. As these changes occurred even in the absence of the pubertal surge of gonadal hormones, they were more likely to result from the organizational effects of gonadal hormones in the perinatal period than the activational effects of these hormones at puberty. Although the castrated animals exhibited the age-related changes in behaviour, they did not exhibit the asymmetries in play associated with dominance relationships. As demonstrated in previous studies, in pairs of intact rats, the animal that attacks the most and uses more juvenile defenses during play fighting and weighs the least is typically the subordinate. In the castrates, asymmetries in weight and playful defense are not related to play frequency, indicating the absence of a dominance relationship. Although the characteristic changes in male play fighting at puberty are independent of the activational effects of gonadal hormones, dominance relationships and their associated changes in play fighting are dependent on these hormones. Therefore, in the perinatal period gonadal hormones most likely organize the age-related changes in play behaviour, whereas post-pubertally gonadal hormones activate dominance relationships and thus, indirectly modify play fighting by affecting dominance-associated assymetries in behaviour. © 1996 Wiley-Liss, Inc.     

Life spans in mice from strains selected for high or low aggression

The present study assessed the life spans in two lines of mice selectively bred for high (Turku Aggressive, TA) and low (Turku Nonaggressive, TNA) levels of aggression. The maintained parental Swiss albino strain (N), normally distributed with regard to aggression, served as a control line. It was found that the TNA males had a significantly shorter life span than the other lines of mice of both sexes. The relative early death of the TNA males was discussed in terms of male age-related decline of inherited low levels of catecholamine and androgenous hormone concentrations. © 1996 Wiley-Liss, Inc.     

Behaviors of Swiss-Webster and C57/BL/6N sin mice in a fear/defense test battery

When confronted by an approaching threat stimulus (experimenter or laboratory rat), Swiss-Webster mice show initial flight, followed by freezing and defensive vocalization and biting, the latter only when escape is blocked. These defense patterns resemble those of the wild rat, suggesting that mice of this strain do not show the reductions in flight and defensive threat/attack that are typical of laboratory rats. C57/BL/6N Sin strain mice showed fewer avoidances to an approaching predator, as well as reduced vocalization and defensive biting, a pattern more similar to that of laboratory rats. As with rats, female mice appeared to be more defensive to a predator. They showed greater reactivity to dorsal contact and more frequent defensive biting and jump attacks than males of the same strains. These patterns of defensive behaviors suggest that, although strain differences in defense are substantial, laboratory mice are suitable for, and may offer several advantages in, the study of the genetic, endocrine, and pharmacological basis of antipredator defense. © 1995 Wiley-Liss, Inc.     

Anger and aggression during role-playing: Gender differences between hormonally treated male and female transsexuals and controls

A role-playing study on anger was conducted in order to identify the influence of sex hormones on individual and gender differences in irritation, anger arousal, and aggression. Different groups were studied: female-to-male and male-to-female transsexuals, with either group tested after 3 months of cross-sex hormone treatment, and untreated control women and men. All subjects were exposed to a 35-min videotape of an individual tested in an aversive, physically stressful, and frustrating situation in the laboratory. While watching, subjects were asked to imagine being in the same situation. Meanwhile, cardiovascular responses were registered and the intensity of moods and aggressive behaviour were assessed. Apart from a clear effect upon cardiovascular arousal and anger-related moods, there were also some interesting differences between the four groups, the most interesting one being a stronger aggressive response in the female-to-male transsexuals. Furthermore, interesting information was gathered with respect to the issue of whether role-playing and actual experimentation provide valid tests of anger and aggression in real life. © 1995 Wiley-Liss, Inc.     

Effects of age at differential housing and the duration of individual housing/grouping on lntermale fighting behavior and adrenocortical activity in TO strain mice

A study of the effects of the duration of individual and group housing on intermale fighting and adrenocortical activity was conducted in TO strain mice. It was found that fighting and threat increased with progressive isolation up to an asymptote at 56–58 days. ‘Basal’ adrenocortical function differed little under the 2 housing conditions, but after ‘stress,’ mice isolated for short periods, which had not fought when tested for aggression, had lower titers than group-housed counterparts. However, mice that had been isolated for longer periods, and had fought in aggression tests, had higher corticosterone titers than comparable group-housed animals. The effects of a short duration (28–30 days) of differential housing, commencing at different ages, were also studied. The shorter duration adrenocortical changes were largely confirmed. In general, the earlier the age at which the differential housing was imposed, the greater the behavioral differences between animals under each housing condition. It is suggested that this is largely a consequence of a loss of behavioral plasticity in older mice. The data provides little support for the concept of the “isolation stress syndrome,” or for the view that the characteristic fighting exhibited by individually housed mice is a consequence of “social deprivation”.     

尼莫地平改善高钙所致记忆障碍的脑内突触机制

海马内微量注射高钙造成小鼠记忆障碍后,观察了尼莫地平（腹腔注射）对记忆障碍的改善作用,并用透射电镜和图像分析仪对海马CA3区Gray I型突触界面结构参数进行了观测和定量分析,进一步探讨尼莫地平改善高钙所致记忆障碍的脑内突触机制。结果表明,尼莫地平确能改善高钙所致记忆障碍,并能显著逆转高钙所致的小鼠海马CA3区突触间隙宽度显著增大,PSD极显著变薄,平坦型突触显著增多,凹型和穿孔型突触显著减少等一系列突触界面结构的病理性变化。提示海马CA3区Gray I型突触界面结构参数的逆转可能是钙拮抗剂尼莫地平改善高钙所致记忆障碍的形态学基础     

Differences between two strains of mice,selectively bred for high and low aggressiveness,in the capacity of male odors to affect aggressive behavior

The connection between a genetic disposition for aggressive behavior and the odor signal system in male mice was studied. The males belonged to two strains of mice which have been developed by selective breeding for high- (TA) and low aggressiveness (TNA). Urine from the high aggressive strain (TA), when applied to castrates, stimulated the aggressiveness of NMRI males while TA-soiled bedding suppressed their aggressiveness. In response to male odors from the low aggressive strain (TNA), the NMRI males showed quite contrasting reactions. The results provide evidences of a correlation between the hereditarily determined disposition for aggressive behavior and the odor signal system in TA- and TNA males.     

Activation of intermale aggression by combined estrogen-androgen treatment

Adult CD-1 male mice were gonadectomized and tested for their response to the aggression-promoting property of androgens, estrogens, or combined androgen-estrogen treatment. The results showed that the combined treatment was the most effective, although androgens alone were sufficient for behavioral restoration. These findings suggest that testosterone may activate aggression through both its androgenic and estrogenic metabolites.