Bacterial Infection Induces Delirium in Healthy, Aging Rats, Study Says

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Activation of the immune system by the Escherichia coli infection may temporarily disrupt formation of long-term memories in older rats by reducing levels of a protein required for brain cells to make new connections, according to a new study led by Temple University researchers.

This illustration depicts a 3D computer-generated image of a group of Escherichia coli. Image credit: James Archer / CDC.

This illustration depicts a 3D computer-generated image of a group of Escherichia coli. Image credit: James Archer / CDC.

Cognitive decline in old age is thought to be gradual, as in Alzheimer’s disease.

However, an abrupt or more rapid deterioration of brain function called delirium is also common in aging, but much less studied.

Although most individuals will recover from periods of delirium, these episodes, which can be triggered by an exaggerated immune response, may increase risk of dementia.

Dr. Susan Patterson from the Temple University’s Department of Biology and her colleagues from Columbia University, New York Psychiatric Institute, Temple University and the University of Colorado, Boulder, previously found that 24-month-old rats infected with Escherichia coli bacteria have a prolonged immune response and memory impairments compared to 3-month-old rats.

The scientists have now extended these findings to show that the immune response in older rats persists for 8-14 days and is associated with reduced levels of brain-derived neurotrophic factor (BDNF), a protein that enables the hippocampus to create long-term memory.

“The rodent model of delirium described in the study could inform future research to understand how surgery, infection, and injury — factors that activate the immune system — affect cognitive function in elderly humans,” Dr. Patterson and colleagues said.

The findings appear online this week in the journal eNeuro.

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Naoto Tanaka et al. Aging and an Immune Challenge Interact to Produce Prolonged, but Not Permanent Reductions in Hippocampal L-LTP and mBDNF in a Rodent Model with Features of Delirium. eNeuro, published online May 28, 2018; doi: 10.1523/ENEURO.0009-18.2018