Some people marvel at the supposed miracle of childbirth. Others claim that our bodies are evidence of intelligent design. Some arguments against the theory of evolution point to the eye as a supposedly amazing piece of engineering (even though a look at the cell layers that light has to pass thru to reach the rods and cones seem like poor engineering to me - to say nothing about widespread problems with sight and focus). Another example of poor human body engineering comes from a new report from the Medical College of Georgia that after giving birth to babies many women suffer from post partum depression as a result of an after effect of chemical signals that the fetus sent to ensure an adequate blood supply.
That crosstalk allows the mother's blood to flow out of the uterine artery and get just a single cell layer away from the fetus' blood, says Dr. Puttur D. Prasad, biochemist in the Medical College of Georgia School of Medicine.
That controlled exchange between the blood of mother and fetus is courtesy of the placenta regulating levels of serotonin, a neurotransmitter commonly associated with depression. But platelets that enable blood clotting also secrete serotonin which prompts platelets to aggregate and the placenta to want to get rid of it.
The same serotonic transporter mechanism that works in neurons gets used to control placental blood flow. This dual use of a component causes huge amounts of mental pain among new mothers.
"If there were no proper control here, blood leaving the mother's blood vessel would trigger release of serotonin, platelets would aggregate, vessels constrict and the fetus wouldn't get what it needs," says Dr. Prasad. An MCG research team led by Dr. Vadivel Ganapathy first reported evidence of serotonin transporter gene expression in the placenta back in 1989 in the Journal of Biological Chemistry. Now they know the gene plays an important role in the crosstalk that forestalls clotting until after birth.
If you were going to intelligently design an organism would you reuse the same transporter mechanism both for brain functioning and for feeding a developing fetus? The interleukin-1 beta that is used to stimulate serotonin transporters in the uterus also travels to the brain and as a side effect causes neurons all over the brain to make too many serotonin transporters.
When the fetus and placenta are gone, blood continues flowing from the mother's uterine artery until platelets move in to stop it, Dr. Prasad explains. Serotonin levels begin to rise and interact with receptors on the smooth muscle of the uterus. This stimulates production of interleukin-1 beta which the MCG researchers found regulates expression of serotonin-hoarding transporters. Interleukin-1 beta gets in the mother's bloodstream, crosses the blood brain barrier and creates more serotonin transporters on the neurons when they are not needed.
This lousy design is a product of evolution. The alternative is that the design is the product of an intelligent designer who isn't intelligent enough to make a really good design. It worked well enough to propagate the species and so the genetic sequences that code for this mechanism survived.
Until interleukin-1 beta levels normalize, there's too little communication between serotonergic neurons and moms get the blues, says Dr. Prassad. "We believe that 80 percent of women experience postpartum blues because of this effect of interleukin-1 beta. If our hypothesis holds true, lowering interleukin-1 beta levels may be a better treatment option." He notes that while serotonin reuptake inhibitors, commonly used for depression, work well in these women, transferring the drug to the baby during nursing can be problematic.
A woman pines to have a baby for many years. She finally finds Mr. Right, they work hard and save up enough money, get a decent house, they try to start a pregnancy, out comes the baby, and then due to poor genetic design of regulatory systems she spends weeks or even months suffering depression. Natural selection also brings us many genetic diseases too. Nature is cruel.
|Share |||Randall Parker, 2008 August 09 12:06 AM Brain Depression|