Stress and anxiety are part of life—but while a little bit of stress (good stress) may keep us active and alert, and sometimes even motivate us, the long-term type (bad stress or chronic stress) can have negative effects on our health. Chronic stress “is the grinding stress that wears people away day after day, year after year. Chronic stress destroys bodies, minds and lives. It wreaks havoc through long-term attrition. It’s the stress of poverty, of dysfunctional families, of being trapped in an unhappy marriage or in a despised job or career. Chronic stress comes when a person never sees a way out of a miserable situation. It’s the stress of unrelenting demands and pressures for seemingly interminable periods of time. With no hope, the individual gives up searching for solutions.” Broadly speaking, chronic stress can be mentally visualized as the perception of environmental demands that are believed to exceed one’s resources for adapting to the situation.
Chronic stress leads to the development of so-called “stress-related disorders.” Elevated blood pressure, heart disease, psychological impairments and depression are just some examples of these disorders. Scientists have known for years that chronic stress influences the inflammatory response—our first line of defense against infectious microbes. It is the inflammatory response that, in turn, may worsen heart disease, increase the risk of heart attack and stroke, and lead to cognitive disorders— those that affect learning, memory, perception, and problem solving.
Now, results from a new study show that chronic psychosocial stress promotes short-term memory loss. The study (Neuroinflammatory Dynamics Underlie Memory Impairments after Repeated Social Defeat), published a few days ago (March 2, 2016) in the Journal of Neuroscience, was carried out using a mouse model known to recapitulate the key physiological, immunological, and behavioral changes that humans undergo when exposed to chronic psychosocial stress.
For the study, mouse were exposed to repeated social defeat stress: non-aggressive mice were repeatedly subjected to bouts of social defeat by a larger and aggressive mouse placed in the same cage. The results show that mice that were repeatedly exposed to the aggressive intruder had a hard time recalling where the escape hole was in a maze they had mastered prior to the stressful period. Jonathan Godbout, senior author of the study, said in a press release: ““The stressed mice didn’t recall it. The mice that weren’t stressed, they really remembered it.”
Repeated social defeat stress promoted inflammation in the hippocampus, a region of the brain involved in the formation, organization and storage of new memories. Presence of inflammation was characterized on the basis of proinflammatory gene expression, monocyte trafficking, and activation of microglia. Microglia are the primary immune cells of the central nervous system, and are highly similar to peripheral macrophages. John Sheridan, one of the study co-authors, said in the press release: “Stress releases immune cells from the bone marrow and those cells can traffic to brain areas associated with neuronal activation in response to stress. They’re being called to the brain, to the center of memory.”
Minocycline, an anti-inflammatory agent and purported microglia inhibitor that was given to the mice, prevented memory loss and recruitment of monocytes. The study authors conclude that, together, their findings open up possibilities for novel immune interventions in the treatment of cognitive and mood disturbances