Stress, opioid peptides, the immune system, and cancer.

Our results indicate that a particular form of footshock stress can suppress immune function in rats and decrease their resistance to tumor challenge. These effects appear to be mediated by opioid peptides released by stress, and they can be mimicked by high doses of morphine given systemically or by a vastly smaller dose delivered intracerebroventricularly. Such findings fit well into the emerging field of behavioral neuroimmunology and reinforce continuing efforts to elucidate the neural and neurohumoral mechanisms by which the environment can affect the organism's immune system.