Investigating short-term disruption of social bonds in prairie voles with emphasis on depression-relevant behaviors and altered autonomic regulation of the heart

Social relationships positively influence psychological and biological function. The disruption of social bonds through separation or death often results in social isolation and can adversely impact mental and cardiovascular health. Prairie voles (Microtus ochrogaster) are rodents that form monogamous pair bonds and regulate cardiac function similar to humans. Using this species, previous investigations of social environment disruption have yielded depression-relevant behaviors, increased basal heart rate, heart rhythm dysfunction, and sympathovagal imbalance characterized by increased sympathetic and decreased parasympathetic input to the heart. Importantly, these same biomarker changes (e.g. cardiac and autonomic dysregulation) are observed in both depression and cardiovascular disease in humans. Thus, the prairie vole species is a useful animal model for investigating the neurobiological basis of social behavior, cardiovascular function, and the adverse changes resulting from stress. The present study investigated the behavioral, cardiac (heart rate and heart rate variability), and autonomic nervous system consequences of acute disruption of social bonds between male and female prairie voles. Adult male prairie voles were implanted with a wireless radiofrequency transmitter for electrocardiographic recordings. Following recovery, all male prairie voles were paired with a novel adult female. After five days, half of the males were separated from the female partner, while the other half remained paired (control). Five days following the separation, male prairie voles were exposed to a forced swim test. Forty-eight hours after the forced swim test, autonomic nervous system function was assessed using pharmacological receptor blockade. The isolated male prairie voles displayed higher resting heart rate and lower respiratory sinus arrhythmia as compared to control male prairie voles. In addition, isolated male prairie voles displayed depression-relevant behavior and increased HR during the forced swim test. Peripherally selective pharmacological autonomic nervous system receptor blockade yielded changes in heart rate indicative of autonomic nervous system imbalance in the isolated group. These findings provide insight into the underlying neurobiological mechanisms linking social environment disruptions to an increased risk of depression and cardiovascular dysfunction.