Effect of social instigation and aggressive behavior on hormone levels of lactating dams and adult male Wistar rats

Abstract

Among rodents, maternal aggression in the postpartum period represents a species-typical adaptation, but when aggressive behavior increases beyond this adaptive level, it can represent a model of excessive aggression. This study assessed the neuroendocrine response of lactating rats and socially instigated male rats. The aim of the present study was to assess neuroendocrine responses and the behavioral pattern of lactating rats and males that were subjected to an emotional stressor using the social instigation protocol. We measured plasma corticosterone levels as the key hormonal parameter of the hypothalamic-pituitary-adrenal (HPA) axis and oxytocin, prolactin, and progesterone, which are released in response to several types of stressors. Our results showed that lactating rats that were subjected to only social instigation or aggressive confrontation in the presence of their pups had lower plasma corticosterone levels, and this response was similar to oxytocin, prolactin, and progesterone levels. By contrast, male rats showed increased corticosterone levels after being subjected only to social instigation. Male rats also engaged in aggressive behavior compared with the control group. In conclusion, this study demonstrated that lactating rats subjected to social instigation exhibited an attenuation of the HPA axis response, which is considered to be crucial to the dam’s welfare so that it can care for its offspring. Thus, we can infer that lactation is a relevant factor in neuroendocrine responses to stress because of the increased levels of corticosterone in males.