July 23 (HealthDay News) -- A natural brain protein may make people less susceptible to depression and other emotional disorders, a new study suggests.

Previous research on mice has shown that a brain protein called deltaFosB increases in response to stress.

The current study, which was expected to be published in the July 19 issue of Neuron, used mice to explore the role of deltaFosB in coping with stress.

In the study, a team led by Eric Nestler, of the University of Texas Southwestern Medical Center at Dallas, exposed mice to random shocks from which the animals could not escape. Then they measured the lag time for the mice to escape subsequent shocks when they were given the chance to do so. This lag time represents the animals' level of "behavioral despair."

This experimental approach is often used to model human emotional disorders, including depression, post-traumatic stress disorder (PTSD) and bipolar disorder. Like humans with such disorders, behavioral despair in mice responds to antidepressants.

The mice with the shortest lag time (i.e., the least despair) also had higher levels of deltaFosB in a brain region involved in processing of pain signals and defense responses. The animals with longer escape times or failure to escape, however, showed lower deltaFosB levels.

The researchers also found that introducing higher levels of the gene for deltaFosB into the mice reduced the animals' level of despair.

Furthermore, increased levels of deltaFosB were associated with decreased activity of the gene for a protein called substance P, which is known to regulate mood, pain sensitivity, anxiety and stress.

The researchers hope that their future research will test the theory that antidepressants may enhance resiliency to stress by improving a person's ability to cope with chronic stress.