Acute social isolation and regrouping cause short- and long-term molecular changes in the rat medial amygdala.

Social isolation poses a severe mental and physiological burden on humans. Most animal models that investigate this effect are based on prolonged isolation, which does not mimic the milder conditions experienced by people in the real world. We show that in adult male rats, acute social isolation causes social memory loss. This memory loss is accompanied by significant changes in the expression of specific mRNAs and proteins in the medial amygdala, a brain structure that is crucial for social memory. These changes particularly involve the neurotrophic signaling and axon guidance pathways that are associated with neuronal network remodeling. Upon regrouping, memory returns, and most molecular changes are reversed within hours. However, the expression of some genes, especially those associated with neurodegenerative diseases remain modified for at least a day longer. These results suggest that acute social isolation and rapid resocialization, as experienced by millions during the COVID-19 pandemic, are sufficient to induce significant changes to neuronal networks, some of which may be pathological.

The effects of acute social isolation on long-term social recognition memory.

The abilities to recognize individual animals of the same species and to distinguish them from other individuals are the basis for all mammalian social organizations and relationships. These abilities, termed social recognition memory, can be explored in mice and rats using their innate tendency to investigate novel social stimuli more persistently than familiar ones. Using this methodology it was found that social recognition memory is mediated by a specific neural network in the brain, the activity of which is modulated by several molecules, such the neuropeptides oxytocin and vasopressin. During the last 15 years several independent studies have revealed that social recognition memory of mice and rats depends upon their housing conditions. Specifically, long-term social recognition memory cannot be formed as shortly as few days following social isolation of the animal. This rapid and reversible impairment caused by acute social isolation seems to be specific to social memory and has not been observed in other types of memory. Here we review these studies and suggest that this unique system may serve for exploring of the mechanisms underlying the well-known negative effects of partial or perceived social isolation on human mental health.