Childhood Stress Boosts Harmful Brain Hormone

July 10, 2001 -- Neglect and abuse during early childhood can cause memory loss and impaired cognitive abilities later in life by boosting the production of a hormonethat harms the brain's learning and memory center, scientistssaid Monday.

In an experiment involving laboratory rats, researchers atthe University of California at Irvine's College of Medicineshowed that these stress-related dysfunctions were caused by abrain hormone called corticotropin-releasing hormone (CRH).

Until now, scientists had assumed that steroid stress hormonesproduced by the adrenal glands were responsible.

Dr. Tallie Baram, who led the study, said pinpointing themechanism at work could lead to new types of treatments forstress-related damage to the brain. The study appears in theProceedings of the National Academy of Sciences.

The researchers studied what happened in the brains of ratsin an attempt to gain a better understanding of how stress inearly childhood, including emotional neglect and abuse,produces enduring negative consequences in people.

"It's been shown in children and infants and also in animalmodels that chronic, early-life stress leads to a decline incognitive function, particularly cognitive function that'srelated to the part of the brain called the hippocampus," Baramsaid in an interview.

"That part of the brain is responsible for learning andmemory. What's been really not clear is how that happens."

Cell Death and Memory Impairment

Baram's team used a single injection of CRH, a hormone thatregulates the nervous system's responses to stress, to mimicearly-life stress in rats that were about two weeks old.

The rats given the injection experienced significant braincell death — a loss of between one-tenth and one-fifth of thecells in a section of the hippocampus associated withstress-related damage.

Rats injected with the hormone were less able to performspatial memory and object-recognition tests later in life thanrats that did not receive the injections.

While the injections were given only once early in life,cell death in the hippocampus and memory problems worsened withage, the study found.

"What we are finding is that not only are we killing cellsin the hippocampus, but there's also reorganization — newconnections to the existing cells that make them morevulnerable," Baram said. "We create, if you will, a viciouscycle in which stress early in life can have very persistenteffects throughout life."

The researchers ruled out steroid stress hormones — whoselevels shoot up during stressful events — as responsible forthe cell death. They said rats that had been altered to preventthem from producing these adrenal hormones still showed thememory loss and cell death produced by the CRH injection.

Baram said if scientists can find a method to block theimpact of CRH on the brain, it would be possible to create newways to prevent cognitive impairment later in life whentreating certain human stress-related disorders.