Ever since Prozac first came on the market in 1987, the pharmaceutical industry has spent millions of dollars a year marketing – both to doctors and their patients – that clinical depression is a genetically based biochemical imbalance. The specific disorder is “serotonin deficiency” – best treated (according to the pharmaceutical companies by a dozen or so enormously profitable Selective Serotonin Reuptake Inhibitors (SSRIs ) and related drugs. While antidepressants can be literally life saving for some people, approximately 50% of patients who take them never achieve full recovery. And in the eyes of the medical community, a 50% response rate is a definite embarrassment. This poor response rate also suggests that factors other than “biochemical imbalance” are causing Americans to become depressed.
Animal Models of Depression
The other argument against a strictly biochemical cause of clinical depression is the reality that other mammals – including primates – don’t experience genetically based serotonin deficiency. In order to study the effect of new antidepressants in laboratory animals, depressive disorders have to be artificially created because they don’t exist in nature. Given the high prevalence of depression in human beings, coupled with the fact that the human and chimpanzee genomes are 99% identical, one would expect great apes to show some evidence of genetic, biochemically based depression – if this were a genuine medical disorder.
What (U.S.) Epidemiological Studies Show
- 5.3% of adults are depressed on any given day
- 12% of women and 7% of men will experience depression in any given year
- 20% of women will experience depression in their lifetime (the prevalence of depression in men is more difficult to estimate, as they are less likely to acknowledge feeling depression or to seek help.
How Researchers Make Animals Depressed
There are six approaches to artificially inducing depressive disorders in animals, all based on environmental influences known to trigger depression in people. These include
1. massive, unrelenting stress
2. social isolation
3. premature separation of pups from their mother
4. brain injury
5. neurotransmitter depleting drugs, such a reserpine (an old blood pressure medication) and tetrabenazine (used to treat movement disorders)
6. amphetamine withdrawal (rats are “addicted” to amphetamine and become profoundly depressed when it’s withdrawn). All six experimental designs have been shown to cause depression by depleting brain neurotransmitters (mainly serotonin and norepinephrine).
Creating Depression via Genetic Engineering
Recently a strain of mice (the Flinders Sensitive Line) has been deliberately inbred and a second strain (HPA Transgenic) genetically engineered to develop depressive symptoms – for use in testing new antidepressants.
Nevertheless most animal testing of new antidepressants is based on the “learned helplessness” model and involves submitting mice and rats to traumatic stress levels of stress. In the most common experiment, mice are dropped into a large vat of water and the researcher times how long they keep swimming before they give up. After taking a dose of Prozac, they keep swimming longer.
Newer methodologies involve hanging mice by their tails – those given antidepressants struggle longer before giving up on trying to escape – and teaching mice to avoid an electric shock by pushing a lever. The researcher then inactivates the lever, and the mice continue to push it anyway, even though they still get shocked. Mice under the influence of antidepressants keep pushing it longer.
At What Point Do We Look for Other Causes?
Although I don’t consider myself an animal rights activist (I am much more concerned about the horrible things we do to human beings), there is something incredibly sad about the drug companies’ persistence in torturing small animals. It’s also well past time for them to admit that mammals do not experience genetic, biochemically caused depression – despite a 25 year, multibillion dollar campaign to convince us that they do. That the time has come to give a serious look at other potential causes (and cures), including, among other possibilities, nutritional deficiencies, environmental toxins and the systematic degradation of American family and community life.