Animal models of social stress: the dark side of social interactions.

Social stress occurs in all social species, including humans, and shape both mental health and future interactions with conspecifics. Animal models of social stress are used to unravel the precise role of the main stress system - the HPA axis - on the one hand, and the social behavior network on the other, as these are intricately interwoven. The present review aims to summarize the insights gained from three highly useful and clinically relevant animal models of psychosocial stress: the resident-intruder (RI) test, the chronic subordinate colony housing (CSC), and the social fear conditioning (SFC). Each model brings its own focus: the role of the HPA axis in shaping acute social confrontations (RI test), the physiological and behavioral impairments resulting from chronic exposure to negative social experiences (CSC), and the neurobiology underlying social fear and its effects on future social interactions (SFC). Moreover, these models are discussed with special attention to the HPA axis and the neuropeptides vasopressin and oxytocin, which are important messengers in the stress system, in emotion regulation, as well as in the social behavior network. It appears that both nonapeptides balance the relative strength of the stress response, and simultaneously predispose the animal to positive or negative social interactions.

Behavioral and neurochemical characterization of maternal care effects on juvenile Sprague-Dawley rats.

Maternal care represents a major constituent of early life environment and has the potential to modulate critical neurobehavioral responses to stress. The aim of the present study was to determine the effects of naturally occurring variations in maternal care on behavioral and neurochemical responses of juvenile Sprague-Dawley rats. A group of dams were classified based on their licking behavior in high and low licking-grooming mothers. Afterwards, the male offspring was tested in a series of behavioral tests: open field test (OFT), elevated plus maze (EPM) and forced swimming test (FST). Additionally, monoamine concentrations were determined post-mortem in three brain regions: hippocampus, ventral striatum and prefrontal cortex. Our findings suggest that maternal care variations have an effect on several anxiety-related behaviors in OFT and EPM but not in depression-like behaviors in FST. Such behavioral differences could be related to an increased DOPAC concentration and 5-HT turnover in prefrontal cortex. These evidences suggest that natural variations in maternal care modified some behavioral and neurochemical parameters related with anxiety and stress in this strain.

Maternal behavior as an early modulator of neurobehavioral offspring responses by Sprague-Dawley rats.

Maternal care plays an important role as an early modeler of neurodevelopment and brain function, and its effects remain until adulthood. Such modeling or programming has shown to influence the stress response and represents a key susceptibility factor in the development of mood disorders. In order to characterize such process which is still not clear, male offspring were classified in animals with low, medium and high licking/grooming (LG) according to the maternal behavior. Juvenile animals were subjected to the open field test (OFT) and the forced swimming test (FST), and offspring of low and high LG mothers were compared. Seven days after the FST, neurochemical and gene expression analyses were carried out in order to identify possible changes on relevant targets. Maternal care did determine locomotor behaviors in the OFT, supporting an anxiogenic effect of low maternal investment. This effect seems to be associated with the serotonergic systems in both nucleus accumbens (NAc) and hippocampus (HPC), since offspring of low LG mothers showed decreased 5-HT neurotransmission in those brain regions compared with animals of high LG mothers. Furthermore, TrkB expression was higher in offspring of high LG compared to the group of low LG mothers, supporting its influence as a mechanistic intermediate of such effect, at least in the NAc. Taken together, these findings strongly support the influence of differential maternal care on the neurodevelopment and responsivity of juvenile rats.