Equal but different

Sometimes it’s the things that make us different are what end up making us the same

Dr. Geert deVries of Georgia State’s Neuroscience Institute is conducting research on hormonal differences between male and female brain chemistry in mammals and the effect these differences have on behavior. .

Chemical differences in male and female brains might be the body’s way of creating behavioral similarities for opposite sexes.

“I had no idea about differences in the brain between male and females. So I looked at animals irrespective or whether they were males or females. I got very messy results,” deVries said. “I found that in some animals the system that I was looking at developed quite early and in other animals it just lagged behind. It was so messy that I thought it would be hard to publish. We did something wrong.”

It was not until he separated the data into male and female groups that he noticed the clear distinction. He discovered the system that produces the hormone vasopressin develops much earlier in males than it does in females.

This was the first report on differences between the neurotransmitter systems between male and female brains. Dr. deVries was fascinated by this discovery and has been studying it ever since.

He has found that male mammals may produce higher levels of vasopressin than females. This high level of production may be regulating behavior and compensating for a lack of hormones that are produced by females during pregnancy.

deVries began his work studying the brain back in the early 1970’s, primarily working with freshwater snails. It was not until 1980 that he became interested in studying sex-based hormonal differences in brain chemistry after accidentally discovering a distinct dimorphic difference in the production of the hormone vasopressin in the brains of mammals.

“It was by me doing a dumb experiment. I had looked at the development of a system in the brain that makes vasopressin. It may regulate social behaviors, but nobody thought along those lines at the time. It was a really a novel idea that vasopressin was made in the brain to control all areas of the brain,”  deVries said.

At that time, neuroscientists knew vasopressin played a large role in the body’s ability to filter fluid through the kidneys and made sure that fluids were re-absorbed into the body after filtration process that moved toxins into the urine for disposal. Vasopressin was also known to play a part in blood pressure regulation, but it was not commonly thought to regulate brain functions.

In Holland, where deVries began his studies, it had been suggested that vasopressin was somehow connected to learning and memory. Already with experienced in studying brain development, deVries was asked by the institute he worked at in Holland to look at the development of vasopressin synthesis or vasopressin expression in the brain. It was by happy accident that deVries made the connection between sex and vasopressin production.

In 1994, deVries began working with prairie voles, a species of vole that exhibited the highest level of difference between male and female brain chemistry that had been studied to date.

“You look through the life cycle and you see not many changes in females but in the males the vasopressin content goes up and down. So we know that this big drop in vasopressin is matched by an actual increase in the message for vasopressin. So what you see is these cells dumping vasopressin in order to get something going.” deVries said.

When deVries theorized that the production of vasopressin in males may be preventing behavioral difference rather than causing it, things started to make sense.

By blocking the hormone in the brains of the male prairie voles, deVries was able to demonstrate that the hormone had a link to paternal behavior. Voles with blocked hormones were suddenly hostile towards vole pups.

Rodent females often go through pregnancy in their life cycle, and voles are no different. Female voles will only begin to exhibit maternal tendencies after her first litter of pups. Female voles that have not gone through pregnancy will exhibit hostile behavior towards pups until they themselves give birth. Since male voles are not able to give birth, compensating for a hormone that they cannot produce may be the root of why their brains produce an apparent excess of vasopressin.

Compensation for differences between the sexes is not unheard of.

“So I tried to push my colleagues to think that if you find a sex difference in the brain maybe your first thought should be that it’s doing something very similar as to the production of XIST RNA[X chromosomes females produce]… you have this huge sex difference set up probably for only one reason: to make sure that male cells and female cells act the same way.” deVries said.

DeVries said although men and women may operate differently on a hormonal level, our similarities far outnumber our differences.

“There are sex differences that we don’t understand, what I’ve been saying is part of why we don’t understand them is because we want to put a label on it that it causes a difference in function. Maybe you should start thinking about it at the other end as well. You should have two alternative hypotheses, one that it can cause a difference and one that it might prevent one.”