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

Caroline Perinazzo Da Veiga,Bruno Carlo Cerpa Aranda,Klaus A Miczek,Dirson Stein,Rosa Maria Martins De Almeida,Celso Rodrigues Franci,Aldo Bolten Lucion

doi:10.3922/j.psns.2011.1.012

Abstract

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. Keywords: social instigation, lactating rats, corticosterone, male, HPA axis

Highlights

The postpartum period constitutes a complex suite of physiological and behavioral processes that are important to offspring growth and development (Lonstein, 2005)
The experiments revealed that lactating rats subjected to social instigation or aggressive confrontation in the presence of their pups showed lower plasma corticosterone levels, and this response was valid when oxytocin, prolactin, and progesterone levels were assessed
Previous studies demonstrated that lactating rats have an attenuated HPA axis response, reducing plasma corticosterone levels in response to both physical and emotional stressors (Lescoat & Maniey, 1976; Lightman & Young, 1987, 1989; Lightman et al, 2001; Myers et al, 1975; Neumann et al, 1998; Thoman et al, 1970; Stern & Levine, 1972; Stern et al, 1973; Smotherman et al, 1976; Walker et al, 1992, 1995; Windle et al, 1997), but few studies have used the maternal defense test or residentintruder test to assess the stress responses of lactating rats (Deschamps, Woodside, & Walker, 2003; Neumann et al, 2001; Neumann, 2003)

Summary

Introduction

The postpartum period constitutes a complex suite of physiological and behavioral processes that are important to offspring growth and development (Lonstein, 2005). Social instigation is an experimental protocol used to heighten species-typical aggressive behaviors Aldo Bolten Lucion, Departamento de Fisiologia, Programa de Pós-Graduação em Neurociências, Miczek, Lucion, & De Almeida, 2007; Veiga et al, 2011). This procedure is highly effective in increasing aggressive behavior in animals by instigating the resident with its proximity to an opponent (Potegal, 1991). One of the advantages of using social instigation is that it engenders basal levels of aggression, facilitating the use of some compounds to assess their effects on aggression

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Conclusion