The discovery that depressed female monkeys and humans show similar clinical and central nervous system characteristics may improve testing of possible therapies for depression, according to an article in the April issue of the Archives of General Psychiatry.

“Brain scans of depressed female monkeys revealed the same underlying neurobiological changes that are found in the brains of depressed people,” said Carol A. Shively, PhD, from Wake Forest University School of Medicine. “This is further evidence that these animal models can help researchers understand depression, develop new treatments and test their effectiveness.”

The positron emission tomography (PET) scans looked at the 5-HT1a serotonin receptor in 11 areas of the brain. A tracer that binds to the serotonin receptor was injected into a vein of each subject. The regions with tracer binding showed as a bright yellow color during the scan. The depressed monkeys had lower serotonin receptor binding in all areas of the brain examined, consistent with previous studies in depressed people.

This supports earlier studies showing that depressed female monkeys have similar physical characteristics to women who are depressed, including low activity levels, disruptions in hormones and higher heart rates.

“Even though women are twice as likely as men to experience clinical depression and are at increased risk for depression during premenstrual, postpartum and perimenopausal times in their lives, we have never had any female animal models of depression,” said Shively, a professor of comparative medicine. “Monkeys offer a special opportunity for research because they are among the few animals that have menstrual cycles and complex cognitive function.”

In addition, the animals have never been exposed to psychotropic medications, alcohol, tobacco or illegal drugs. Monkey models can be used to develop new treatments and test their effectiveness, Shively said, through observing behavior and using brain scans to reveal if treatments or medications are actually working.

“Another way we’d like to see the model used is to investigate the cognitive aspects of depression,” Shively said. “The way that many of our pharmaceutical products got onto the market was that they were tested on rodents. But when they were used by humans, we found side effects that caused cognitive dysfunction like lack of concentration. Depressed people do not need more cognitive dysfunction. This animal model could be used to test treatments that alleviate cognitive problems associated with depression rather than making them worse.”

Shively pointed out that there are very few places in the country that have both a primate center and an imaging center that made this study possible. “This research cannot be done without having both centers here.”