Amygdala circuit transitions supporting developmentally-appropriate social behavior

Dopamine type II receptors in amygdala along with oxytocin in hypothalamus regulate social behavior in male mandarin voles

The amygdala dopamine (DA) system and hypothalamic oxytocin (OT) play important roles in emotion regulation, and emotions are important in regulating social behavior. However, it is unclear whether DA in the amygdala is involved in the regulation of social behavior, and whether OT in the hypothalamus is also involved in this process. In this study, we examined the release of DA in the medial amygdala (MeA) during different social interactions and the effect of injecting the dopamine II receptor (D2R) agonist quinpirole and the D2R antagonist raclopride into the MeA on social behavior and OT in the paraventricular nucleus (PVN) and supraoptic nucleus (SON), as well as in the blood of male mandarin voles (Microtus mandarinus). The results showed that the DA in the MeA increased in the process of social behavior, and the DA in the face of strangers was higher than that in the face of familiars. In addition, the injection of D2R antagonists in the MeA reduced attacking and escaping behaviors but increased physical contact and investigating behaviors, increased the number of OT-IR neurons in the PVN and SON, and increased OT levels in the blood. While injection of D2R agonists in the MeA increased attacking and escaping behaviors but reduced physical contact and investigating behaviors, it also reduced OT-IR neurons in the SON. In conclusion, D2R in the medial amygdala and oxytocin in the hypothalamus regulate social behavior.

Depression in adolescence and young adulthood: the difficulty to integrate motivational/emotional systems

Depression is presented as a multi-factorial bio-psycho-social expression that has evolved primarily as an effect of stressors related to the motivational/emotional systems that regulate the BrainMind in our relationship with conspecifics. These stressors may be caused by two sources of threat, firstly, the loss of bonding with the caregiver and later with a partner and/or group which relates to the SEPARATION (PANIC/GRIEF) system, secondly, social defeat as an expression of the social competition and social dominance. The sexual maturity drives the individual to social competition and social dominance, even if the latter often occurs before sexual maturity, e.g., chickens, dogs, non-human primates, and humans. Depression is an evolutionarily conserved mechanism in mammals to terminate both separation anxiety, so as to protect the vulnerable social brain from the consequences of prolonged separation anxiety, and the stress of social competition when social defeat is predictable. Adolescence and Young adulthood are particularly susceptible to these two types of threat because of human developmental characteristics that are summarized by the term neoteny. This refers to the slowing down of growth and development, resulting in both a prolonged period of dependence on a caring/protective adult and the persistence of juvenile characteristics throughout life. Therefore, neoteny makes the transition from childhood to sexual maturity more dramatic, making the integration of the SEPARATION (PANIC/GRIEF) system with the dynamics of social competition and dominance more stressful and a source of depression. Stress is an expression of the HPA-Hypothalamic-Pituitary-Adrenal axis that articulates with other systems, mainly the autonomic nervous system and the immune-inflammatory system. The latter is believed to be one of the most significant components in the dynamics of depressive processes, connected to the prodromes of its activation in childhood, under the pressure of environmental and relational stressors which can lead to learned helplessness. The recurrence of stressors makes it easier for the immune-inflammatory system to be activated in later life, which could make a significant contribution to the establishment of a depressive disease. The possible contribution of children's identification processes with their parents' depressive personalities through observational learning is considered.

Developmental Shifts in Amygdala Function

Mammals have evolved with strategies to optimize survival and thrive in their native environment. This includes both physical and behavioral adaptations, and extends to their social environment. However, within a social context, the roles of an animal change across development, and their behavior and biology must update to match these changes. The amygdala has a key role in social and emotional processing and expression, and displays developmental changes in early juvenile, adolescent, and adult transitions. Furthermore, the amygdala is highly sensitive to the social environment. This chapter will describe the primary amygdala developmental changes, how this maps onto major changes in social and emotional domains, and propose a framework where developmental stage of intra-amygdala circuits and its regulation by cortical inputs biases the animal toward developmentally appropriate social and emotional behavior. This developmental plasticity also presents an opportunity for retuning the developmental trajectory in the presence of ongoing challenges during maturation, such as constant threat or resource scarcity, so there can be realignment of behavior to match environmental demands.

Neurons for infant social behaviors in the mouse zona incerta

Understanding the neural basis of infant social behaviors is crucial for elucidating the mechanisms of early social and emotional development. In this work, we report a specific population of somatostatin-expressing neurons in the zona incerta (ZISST) of preweaning mice that responds dynamically to social interactions, particularly those with their mother. Bidirectional neural activity manipulations in pups revealed that widespread connectivity of preweaning ZISST neurons to sensory, emotional, and cognitive brain centers mediates two key adaptive functions associated with maternal presence: the reduction of behavior distress and the facilitation of learning. These findings reveal a population of neurons in the infant mouse brain that coordinate the positive effects of the relationship with the mother on an infant's behavior and physiology.

Synaptic pruning during adolescence shapes adult social behavior in both males and females

Evolutionarily conserved, peer-directed social behaviors are essential to participate in many aspects of human society. These behaviors directly impact psychological, physiological, and behavioral maturation. Adolescence is an evolutionarily conserved period during which reward-related behaviors, including social behaviors, develop via developmental plasticity in the mesolimbic dopaminergic "reward" circuitry of the brain. The nucleus accumbens (NAc) is an intermediate reward relay center that develops during adolescence and mediates both social behaviors and dopaminergic signaling. In several developing brain regions, synaptic pruning mediated by microglia, the resident immune cells of the brain, is important for normal behavioral development. We previously demonstrated that during adolescence, in rats, microglial synaptic pruning shapes the development of NAc and social play behavior in males and females. In this report, we hypothesize that interrupting microglial pruning in NAc during adolescence will have persistent effects on male and female social behavior in adulthood. We found that inhibiting microglial pruning in the NAc during adolescence had different effects on social behavior in males and females. In males, inhibiting pruning increased familiar exploration and increased nonsocial contact. In females, inhibiting pruning did not change familiar exploration behavior but increased active social interaction. This leads us to infer that naturally occurring NAc pruning serves to reduce social behaviors toward a familiar conspecific in both males and females.

Multiple routes of communication within the amygdala-mPFC network: A comparative approach in humans and macaques

The network formed by the amygdala (AMG) and the medial Prefrontal Cortex (mPFC), at the interface between our internal and external environment, has been shown to support some important aspects of behavioral adaptation. Whether and how the anatomo-functional organization of this network evolved across primates remains unclear. Here, we compared AMG nuclei morphological characteristics and their functional connectivity with the mPFC in humans and macaques to identify potential homologies and differences between these species. Based on selected studies, we highlight two subsystems within the AMG-mPFC circuits, likely involved in distinct temporal dynamics of integration during behavioral adaptation. We also show that whereas the mPFC displays a large expansion but a preserved intrinsic anatomo-functional organization, the AMG displays a volume reduction and morphological changes related to specific nuclei. We discuss potential commonalities and differences in the dialogue between AMG nuclei and mPFC in humans and macaques based on available data.