Effects of castration on aggression and levels of serum sex hormones and their central receptors in mandarin voles (Microtus mandarinus)

Abstract

Aggression in socially monogamous mandarin vole (Microtus mandarinus) was observed after castration. Levels of serum sex hormones and their central receptors were also measured using enzyme-linked immunosorbent assay and immunohistochemistry methods. The data indicate that adult males showed higher levels of aggression after castration. However, castration significantly reduced levels of serum testosterone, and the number of androgen receptor immunoreactive neurons in the anterior hypothalamus, bed nucleus of the stria terminalis, medial amygdaloid nucleus (P<0.01) and lateral septal nucleus (P<0.05). In addition, levels of estrogen receptor β in the anterior hypothalamus and medial amygdaloid nucleus (P<0.05), bed nucleus of the stria terminalis and lateral septal nucleus (P<0.01) declined to varying degrees at weekly intervals. In contrast, serum 17β-estradiol concentrations were up-regulated by castration and castration did not change levels of estrogen receptor α in the medial amygdaloid nucleus and lateral septal nucleus, but increased it in the anterior hypothalamus 3 weeks after castration (P<0.05). We suggest that higher levels of aggression induced by castration may be independent of serum testosterone and androgen receptors, and may be associated with high serum 17β-estradiol concentrations, stable estrogen receptor α immunoreactive neurons in some brain regions and the relative ratio of the two estrogen receptors.

Perinatal stress effects on later anxiety and hormone secretion in male mandarin voles.

“…We found a negative association between prenatal restraint stress and E 2 levels in serum (see Figure 5), which is inconsistent with our previous work showing a positive association between prenatal treatment and estrogen levels in serum (He, Tai, et al, 2012). This may be because the previous experiment used female offspring and involved ethanol exposure as the stressor.…”

“…The control group (N ϭ 20) was left undisturbed in their cages. One to five pups were produced in each litter, and the sex ratio was 1.87 females to 1 male (He, Tai, et al, 2012;Tai, Wang, & Zhao, 1999). To exclude litter effects, only one male pup was chosen from each litter: The 20 male pups from the treatment group were denoted as PS, and the 20 male pups from the control group as prenatal control (PC).…”

“…The mandarin vole (Microtus mandarinus) is a monogamous rodent that engages in pair bonding, affiliation, and biparental care (Guo et al, 2011;Tai, Wang, & Zhou, 2001). Social-bonding and pair-bonding formation are critical components of mental health (Young, Gobrogge, Liu, & Wang, 2011), and mandarin voles have emerged as a model for the study of social-emotional behaviors such as those associated with anxiety (He, 2014) and depression (He, Tai, Zhang, & Zhang, 2012). Previous experiments by our group have shown that PS (e.g., exposure to ethanol) increases anxiety and decreases central AR expression in adult mandarin voles (He, 2014).…”

Postnatal separation prevents the development of prenatal stress‐induced anxiety in association with changes in oestrogen receptor and oxytocin immunoreactivity in female mandarin vole (Microtus mandarinus) offspring

“…The formation of social bonds and pair bonds is dominant components of mental health (Johnson & Young, ). Mandarin voles ( Microtus mandarinus ) have been proposed as a model for the investigation of social–emotional behaviour related to anxiety and depression (He et al ., , ) because it is monogamous and associated with pair bonding, affiliation and biparental care (Tai et al ., ). Prenatal stress enhances depressive‐like behaviour and reduces central ERα and OT distribution in adult female mandarin voles (He et al ., ), while the increase in anxiety‐like behaviour was associated with significantly lower E 2 and more ERα in adult male offspring (He et al ., ).…”

Effects of cocaine on aggression and associated central ERα and oxytocin expression in ovariectomized and intact mandarin voles

“…These results indirectly support the proposal by Trainor et al (2006a) that estrogen acts in a specific subset of a complex network of nuclei to affect aggressive behavior. He et al (2012) proposed that aggressive behavior and gonadal hormones have a complex relationship, and the effects of gonadal hormones on aggression are species dependent. Thus, the relationship between ovariectomy and aggressive behaviors may be species typical and variable.…”