Mice that were socially isolated before a heart attack had increased TNF-alpha levels and 5 to 8 times more brain neuron damage. (2008)
From the article:
Results showed that the mice that were socially isolated prior to the heart attack showed five to eight times more damage to their neurons compared to mice that were housed together, said Weil, who is now a post-doctoral researcher at Rockefeller University in New York.
Socially isolated mice also showed evidence of greater inflammation in the hippocampus, when compared to socially housed and control mice.
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Socially isolated mice showed increased activation of microglia, a type of immune cell in the central nervous system that responds to damaged neurons, the study found.
One of the ways microglia respond is by releasing tumor necrosis factor alpha (TNF-a), one of a large family of proteins called cytokines – chemical messengers that are mobilized when the body is injured or has an infection. These cytokines cause inflammation in their effort to repair an injured or infected area of the body.
Levels of TNF-a were elevated in isolated mice, but not in socially housed mice, compared to the control mice.
The higher levels of TNF-a in the socially isolated mice, and the inflammation it caused, was the main reason for the increased neuronal damage in these animals, Nelson said.