What do we know about using (activating) and overusing our internal systems that respond to stress?

Animal and human research has taught us much about our internal stress systems. When laboratory animals are exposed to a prolonged stress (usually food deprivation, mild electrical stimulation of the foot, or handling), they develop a stress syndrome. This syndrome consists of high blood pressure (hypertension), loss of appetite, weight loss, muscle wasting, gastrointestinal ulcers, loss of reproductive function, suppression of the immune system, and depression. Researchers also noticed that stress of long duration (chronic stress) sensitizes the stress system (makes it more responsive to stress). That is, the system then overresponds to new stressors. They further noticed that the administration of certain drugs, such as amphetamines or cocaine, could also sensitize the stress response. Moreover, constant stress increases the self-administration of drugs in laboratory animals. So, a vicious cycle is induced. The more stress there is, the more mice seek the drugs, and the more the sensitivity (increased responsiveness) to stress is increased!

Early separation from the mother has also been seen as another potent stressor in animals. Such separation has been linked to increased levels of the stress hormones that cause the stress syndrome, which includes depression. Studies in humans are underway to evaluate how maternal stress, even early in the pregnancy, can affect the developing fetus.

Why might maternal stress affect the fetus? The answer is the communication of the blood circulations of the mother and the fetus. From the mother's blood, the fetus gets both the good (for example, nutrients and oxygen) and the bad. The bad components of the blood can include alcohol, nicotine, illicit drugs, prescription drugs, and stress chemicals such as cortisol and norepinephrine.

These animal and human studies seem to indicate that stress leads to depression. In other words, chronic stress in the mother's womb (in utero) or early deprivation (separation from the mother) might even predispose a person to developing the psychiatric syndrome of clinical depression in later life. Furthermore, other experiments show that the administration of stress hormones can actually decrease brain connections and even the number of brain cells in crucial areas, such as the limbic system. This loss of brain connections and cells then can lead to further maladaptive (inadequate adjustment) responses to stress.

What's more, some particular kinds of stress seem to be even more detrimental than other types. That is, some types of stress can actually lead to diseases. For example, stresses that are unpredictable and uncontrollable seem to be the greatest culprits. On the other hand, stresses with which we can cope and master are not necessarily bad. In fact, we can learn from these stresses, predict their recurrence, and develop action plans to reduce or avoid them in the future. In this way, some stresses can actually trigger new personality growth and biologically induced adaptive (healthy adjustment) changes. Indeed, much of psychotherapy is empirically (guided by practical experience rather than theory) based upon this concept.