Females are often less aggressive than males, but they exhibit high levels of agonistic behavior against an intruder in the area of the nest during lactation. This behavior is referred to as maternal aggression. In rats, maternal aggressive behavior occurs more often from postpartum day 3 (PPD 3) to PPD 12. Social instigation is an experimental protocol used to increase the levels of aggression that are typical of the species. In the present study we used social instigation to analyze the expression of a marker of neuronal activity, c-fos. Lactating rats on PPD 5, in the presence of their pups, were divided into four groups: (1) no social instigation and no aggressive behavior, (2) social instigation and no aggressive behavior, (3) no social instigation and aggressive behavior, and (4) social instigation and aggressive behavior. Sixty minutes after the aggression test we used immunohistochemistry to detect Fos in two brain regions, the ventral-orbital region of the prefrontal cortex (VO PFC) and dorsal raphe nucleus (DRN). Our results showed that rats with aggressive behavior that were provoked exhibited an increase in Fos expression in the VO PFC compared with the control group (i.e., no social instigation and no aggressive behavior). No change in Fos expression was found in the DRN. These results complement previous findings with microinjection of serotonin 5-hydroxytryptamine-1B receptor agonists into the same region, demonstrating that the VO PFC is an important region in the modulation of maternal aggressive behavior.

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.

The objective of this study was to assess the role of environmental/nest components and maternal behavior after several neonatal interventions on subsequent behavioral responses. Male Wistar rats were subjected to different neonatal interventions and were later evaluated for innate fear-like behavior in adulthood. The experimental groups included nonhandled (i.e., animals were not touched), handled (i.e., animals were separated from their mother, removed from the nest, and handled for 10 min/day), brief maternal separation (i.e., the mother was removed from the homecage for 10 min/day, and the pups remained in their cages without being touched), and tactile stimulation (i.e., the mother was removed from the homecage, and pups were stimulated with a brush for 10 min/day within the nest). The mother's behavior was recorded during the neonatal period, and the male pups were later tested in the open field as adults. The results revealed that only mothers whose pups were handled had an increase in the duration of licking behavior compared with the other groups. In the open field test, we observed decreased behavioral innate fear-like responses in male adults in the handled and brief separation groups compared with the others groups. Our results confirm that interventions during the neonatal period cause stable behavioral changes (decreased innate fear) in adulthood and that absent or excessive tactile stimulation appears to be an important factor. Both repeated disruption of the mother-infant relationship and withdrawal from the environment/nest are factors that exert profound effects on the development of the animals.

Vários estudos recentes têm demonstrado a repercussão da privação materna no desenvolvimento neurobiológico e psicológico da criança. A depressão pós-parto, quando persistente, pode favorecer a ocorrência de situações de negligência e abuso infantil. Este trabalho tem como objetivo revisar estudos publicados a partir de 1988 que demonstrem alterações no desenvolvimento neurológico, endócrino, mental e comportamental de crianças cujas mães tiveram depressão pós-parto. A importância do meio ambiente inicial foi revisada em estudos pré-clínicos com mamíferos não-humanos, demonstrando que, quando há privação ou estresse no início do desenvolvimento, ocorrem alterações persistentes em estruturas encefálicas, em secreções neuro-hormonais e na densidade de receptores específicos. Também serão descritos alguns aportes teóricos sobre a importância da relação mãe-bebê concordantes com os achados experimentais.

Many recent studies have shown that maternal deprivation has important effects on the psychological and neurobiological development of the child. Puerperal depression, when persistent, predisposes to child abuse and negligence. This paper aims at reviewing studies published as of 1988 that demonstrated changes in the neurological, endocrine, mental and behavioral development of children born from depressed puerperal women. Environmental influence was also revised, focusing on pre-clinical studies carried out with non-human mammals, which showed that deprivation or stress in early development stages predicts changes in brain structure, neuro-humoral secretions and density of specific receptors. Finally, the study also revises some theoretical aspects of the child-mother relationship importance, which are in accordance with the experimental findings.

Varios estudios recientes vienen demostrando la repercusión de la privación materna en el desarrollo neurobiológico y psicológico del niño. La depresión postparto, cuando persistente, puede favorecer la ocurrencia de situaciones de negligencia y abuso infantil. El objetivo de este trabajo es revisar estudios publicados a partir de 1988, que demuestren alteraciones en el desarrollo neurológico, endocrino, mental y comportamental de niños cuyas madres sufrieron con depresión postparto. La importancia del medio ambiente inicial ha sido revisada en estudios preclínicos con mamíferos no-humanos, demostrando que, cuando hay privación o estrés en el comienzo del desarrollo, ocurren alteraciones persistentes en estructuras encefálicas, en secreciones neuro-hormonales y en la densidad de receptadores específicos. También se describirán algunos aportes teóricos acerca de la importancia de la relación madre-niño, en concordancia a los hallazgos experimentales.