Research on tumor development has implications for humans and cancer

Female rats that are apprehensive of new experiences as infants maintain that temperament and die earlier from mammary and pituitary tumors than do their more adventuresome sisters, according to new research by a team based at the Institute for Mind and Biology at the University.

The apprehensive rats were more likely to have irregular reproductive cycles than adventuresome rats, and that disruption could account for hormonal differences linked to the early development of tumors, the scholars found. However, there was no difference in the length of time between onset of cancer and death in the two sets of rats.

Because the findings have identified a difference in temperament that is associated with the onset of tumor development, the findings may have implications for research on the development of cancer in humans, said Martha McClintock, the David Lee Shillinglaw Distinguished Service Professor in Psychology. McClintock is a member of the team that reported its findings in the paper “Infant Temperament Predicts Life Span in Female Rats that Develop Spontaneous Tumors” published in the current issue of Hormones and Behavior.

Current human studies on the relationship between cancer and personality primarily focus on survival once a tumor has been identified.

“Human studies may need to consider more basic behavior traits than those already considered,” McClintock explained. By understanding the development of basic traits, researchers will be better equipped to link the connections between personality and cancer development, the team suggested.

The team found that the links between behavior traits and tumor development and survival in rats are striking.

“This is the first evidence that infant temperament among rats predicts the time at which these tumors appear and the age at which the females will die,” said lead author Sonia Cavigelli, a former University researcher who now is an assistant professor of biobehavioral health at Pennsylvania State University. Jason Yee, a graduate student in Comparative Human Development, also is an author of the paper.

For their study, the researchers selected 81 female Sprague-Dawley rat pups. The breed is prone to development of breast and pituitary tumors. In order to minimize the differences in temperament that are accountable to differences between rat families, the researchers compared behavior among sisters.

The rats were tested at 20 days and 11 months of age in a cage to see how willing they were to explore a new environment that contained non-threatening items, such as toys. The researchers measured the rats’ adventurousness by recording how far the rats wandered in the environment.

They found that by the age of 390 days, middle age for rats, 80 percent of the fearful rats had palpable mammary tumors while only 38 percent of the adventuresome rats did. The fearful rats had a life span of 573 days versus 850 days for the adventuresome rats. They found similar life span results for females with the onset of pituitary tumors.

The researchers also monitored ovarian cycles daily from the time the rats were 55 days old until they were 450 days old. In studying their ovarian cycles, the researchers found that during puberty the fearful rats were twice as likely as the adventuresome rats to have irregular cycles (52 percent versus 22 percent). The cycles stabilized after the rats reached adulthood, and then became differentiated again during middle age with the fearful rats having irregular cycles more often. The aging effects on reproduction also were accelerated in the fearful rats.

In an earlier study, University researchers looked at the life span of male rats and found that the adventuresome males lived longer. Because the male rats died of a variety of diseases, they could not establish a reason for the differences. This study links personality specifically with the development of tumors.