Understanding the Role of the Blood-Brain Barrier in Behavior

The blood-brain barrier, which provides a protective covering for the brain, can be thought of as a tightly controlled lock-box, responsible for letting in only a very select group of molecules.

The Blood-Brain Barrier: A Controlled Environment

“The blood-brain barrier controls what reaches the brain,” said Brigitte Dauwalder, associate professor of biology and biochemistry at the University of Houston. “The brain needs to be in a very controlled environment, or else the neurons will misfire. For that reason, the environment needs to be isolated to maintain the necessary conditions for it to function.”

The blood-brain barrier is what makes certain diseases, such as meningitis, so deadly. Under normal conditions, the blood-brain barrier prevents most substances from crossing into the brain. However, if a pathogen manages to slip past these defenses, this protection becomes a double-edged sword, as the drugs needed to treat this infection cannot cross the blood-brain barrier. This aspect of the blood-brain barrier also makes treating other brain disorders, such as Alzheimer’s or Parkinson’s, more difficult.

Beyond Barrier Functions: Behavioral Studies

In a four-year, $700,000 grant from the National Science Foundation, Dauwalder’s research group will look at the role of the blood-brain barrier in regulating courtship behavior in the fruit fly Drosophila melanogaster.

“Very little is known about the blood-brain barrier beyond its function as a barrier, for example its role in regulating complex behaviors.” Dauwalder said.

During their attempts at mating, male Drosophila exhibit a highly scripted set of courtship behaviors. Simply put, the male flies do a strictly choreographed dance, to which the females might respond, or might not. These behaviors, which are well-characterized, have been shown to be under the control of sex-specific factors.

Given that the majority of genes within the Drosophila genome are also found in humans, Drosophila is an ideal system for studying how the blood-brain barrier functions. Drosophila have short life spans, and over the years, scientists have developed a number of genetic tools to study them. Given the highly stereotypical mating behaviors, scientists also have a clear way of recognizing when something changes.

Hormonal Signaling Crossing the Barrier

While in the process of studying these behaviors, Dauwalder found something unusual. She expected that signaling inside the brain would be entirely responsible for the control of the courtship circuits in the brain. Instead, she found that many of the required male-specific signals and hormones originated outside the brain, which raised the question of how this signaling manages to cross the seemingly impenetrable blood-brain barrier.

“We don’t know if hormonal signaling is happening within the blood-brain barrier,” Dauwalder said.

With the new grant, Dauwalder’s research group will look at two hormones in Drosophila, called ecdysone and juvenile hormone. They will ask the question of what role the blood-brain barrier plays in transferring these signals from one side to the other, and how this influences brain function.

“The more we understand about how the blood-brain barrier functions and influences the brain, the more knowledge we have for when things go wrong,” Dauwalder said.

- Rachel Fairbank, College of Natural Sciences and Mathematics