The role of endocrines in isolation-induced lntermale fighting in albino laboratory mice. II. Sex steroid influences in aggressive mice

Isolation-induced intermale fighting in laboratory mice can be dramatically reduced under most circumstances by castration. This behavior in castrates may, however, be restored, or even accentuated, by androgen replacement. Experiments on the effects of sex steroids on such fighting in castrated mice, which, for want of a better term, are designated as “aggressive,” have been recently described. These mice are housed with a female until 10 days after siring a litter and are, thereafter, housed individually for a further 14 days before castration and subsequent hormone treatment. Such mice show substantial levels of fighting in “standard-opponent” tests even before isolation. Although castration results in reduced fighting in these mice, this behavior is rarely completely abolished in all individuals. It seems likely that steroid treatment of aggressive mice maintains or intensifies an already present motivation. Treatments in these studies consisted of daily oil-based intramuscular injections for 14 days preceding and throughout behavioral testing. The standard-opponent tests were 7 min encounters with adult, subordinate, grouped males in the cleaned home cages of experimental mice. The steroids investigated included estradiol benzoate (EB), 19-hydroxytestosterone (19-OHT), androstenedione (A), testosterone (T), and Sα-dihydrotestosterone (DHT), either singly or in combination. The results suggest that (a) on a dosage basis, estrogens were at least as effective as androgens in maintaining fighting in castrated aggressive mice; (b) 19-OHT (one of the metabolic intermediates between testosterone and 17 β-estradiol) was also effective but somewhat less so than the same dose of EB; (c) the three naturally occurring androgens investigated all effectively maintained fighting at comparatively low doses (50 μg/day) which compares with a replacement dose of 500 μg/day of T in some studies in traditional castrated mice (e.g., Luttge and Hall, 1973); (d) aromatization is not essential for a behavioral action of androgens as DHT, a nonaromatizable androgen, maintained fighting in these mice; (e) whereas a two-site (central motivational and peripheral penile) action seems probable in the influence of androgens on sexual behavior in castrated rats (e.g., Parrott, 1975), DHT did not augment the action of EB on fighting in castrated aggressive mice, indicating that only a central action of steroids was required in the aggressor.     

Effects of early exposure to mating on adult sexual behavior in male mice varying in their genetic disposition for aggressive behavior

This study examined whether the sexual behavior of adult male mice is influenced by exposure in early postnatal life to brief episodes of mating. Another focus of interest was the interplay between a genetic disposition for aggressive behavior and the early exposure experiences. The subjects used in the study were male mice of the fiftysixth generation of selection for high (Turku aggressive, TA) and low (Turku non-aggressive, TNA) levels of aggressiveness. Moderately aggressive males of the parental strain (normal, N) were also used. Subjects of each strain were exposed from 21 to 32 days of age to mating mice behind a wire mesh screen. Control subjects were placed in a comparable enclosure, but were exposed to nothing. The results showed that male mice exposed to mating early in life showed a higher rate of activities in the sexuality tests, including aggressive responses. A genetic potential for aggressive behavior was related to a higher degree of sexual activity, and the early exposures optimized the hereditary attributes. The relation between sexual and aggressive behavior is discussed. © 1994 Wiley-Liss, Inc.     

Crossfostering in mice selectively bred for high and low levels of open-field thigmotaxis

The main purpose of this research was to investigate whether the difference in open-field (OF) thigmotaxis between mice selectively bred for high and low levels of wall-seeking behavior originated from genetic or acquired sources. Unfostered, infostered, and crossfostered mice were compared in two experiments in which the effects of strain, sex, and fostering on ambulation, defecation, exploration, grooming, latency to move, radial latency, rearing, thigmotaxis, and urination were studied. These experiments revealed that OF thigmotaxis was unaffected by the foster condition and thus genetically determined. The selected strains of mice also diverged repeatedly with regard to exploration and rearing. The findings are in line with the previously described existence of an inverse relationship between emotionality and exploration.     

小鼠的记忆与脑内突触结构参数变化的相关性

比较不同月龄小鼠学习记忆力与脑内突触结构参数变化的相关性。选用１月龄和６月龄小鼠,用Ｙ－迷宫检测分辨学习能力,用一次性被动回避反应检测记忆力。然后杀鼠取脑,进行超微结构观察和定量分析测定。结果表明：（１）１月龄小鼠的分辨学习能力优于６月龄小鼠,记忆力也有优于６月龄小鼠的趋势。（２）无论在海马或大脑皮层体区,有两种结构参数有一致性增龄变化,即６月龄小鼠突触界面曲率都比１月龄小鼠显著和极显著增大;而６月龄小鼠上述两脑区的突触后致密物质厚度都极显著地小于１月龄小鼠。实验结果提示,脑内突触界面结构的增龄性变化可能是学习记忆力增龄性变化的结构基础。     

情绪唤醒影响记忆巩固过程的神经生理机制

白鼠和人类都对情绪唤醒的经历有更好的记忆。情绪唤醒影响记忆巩固的神经生理机制主要有以下几种方式:(a)情绪唤醒或急性应激,会引发个体内部应激激素的释放,从而增强其记忆巩固过程。(b1)杏仁核的激活对情绪唤醒影响记忆巩固过程十分重要,杏仁核内部去甲肾上腺素(NE)的释放影响记忆巩固过程。(b2)杏仁核投射到负责不同类型记忆加工的脑区,如海马和皮层,从而影响记忆。(c)应激激素影响记忆巩固的过程中,杏仁核内NE的激活在这一过程中扮演着重要角色。综上,情绪唤醒影响记忆巩固的过程,涉及到激素调节、神经调节及二者的共同作用。     

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

Severe 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.     

Habituation of aggressive behavior in mice: A parametric study

The decline of aggression as a result of repeated episodes of fighting may represent a habituation phenomenon. The frequency of biting and sideways threat by male mice toward conspecific intruders declined over ten 5-min confrontations. Aggression returned to about 50% of original levels when a new intruder was introduced. Variations in length or frequency of confrontation indicated that the rate of decline of attack bites and sideways threats depended on these confrontation parameters. The condition that provided the fewest opportunities to fight provided the least decline in the frequency of attack and threat. The frequency of attack bites and sideways threats elicited by the presentation of a new intruder after repeated confrontations was greater than the frequency of attack bite and sideways threat in the last confrontation with the original intruder, when the resident and intruder were relatively inexperienced. Spontaneous recovery of attack and threat occurred but rate of recovery did not depend on confrontation parameters. The results indicate that the decrement of aggression in mice in repeated confrontations may be the result of habituation but fatigue is an important cofactor.     

Baby babbling at five months linked to sex hormone levels in early infancy

Gender-dependent differentiation of the brain at morphological, neurochemical and functional levels of organization have been shown to be primarily controlled by sex differences in gonadal hormone concentrations during pre- and early postnatal development. Indeed, previous studies have reported that pre- and perinatal hormonal environments influence brain development and, consequently, affect sex specific long-term language outcomes.Herein, we investigated whether postnatal surges of estrogen (estradiol) and androgen (testosterone) may predict properties of pre-speech babbling at five months. This study is the first attempt to investigate a possible correlation between sex hormones and infants’ articulatory skills during the typical postnatal period of extended hormonal activity known as ‘mini-puberty.’ A hierarchical, multiple regression approach revealed a significant, robust positive relationship between 4-week concentrations of estradiol and individual articulatory skills. In contrast, testosterone concentrations at five months negatively correlated with articulatory skills at the same age in both boys and girls. Our findings reinforce the assumption of the importance of sex hormones for auditory–vocal development towards language in human infants.     

睾酮对价值加工的影响——基于“累积前景”理论框架的决策行为研究

较多研究支持睾酮和决策中的风险寻求行为呈正相关,但是也有其他的研究未能发现这种关系。基于决策的累计前景理论,本研究使用动态估计参数估计任务(DEEP),结合计算模型的方法,对120名双盲给药、有安慰剂对照的被试进行睾酮对价值加工过程作用的探究。结果显示,睾酮减少了个体的概率扭曲以及增加了损失规避,但是没有引发明显的风险寻求行为,研究结果表明睾酮对个体的价值加工过程产生了影响,使个体对概率的感知更接近于客观值并且增加了对损失的敏感性。