Listen Up: That Birdsong You’re Enjoying Is Courtesy of Estrogens
December 17, 2012
by Robin Tricoles
Next time you hear a bird sing, consider that this aural pleasure is courtesy of estrogens. Although estrogens are often thought of as female hormones, that concept is incomplete. It’s true that estrogens are produced in the ovaries, but they’re also produced in the adrenal glands, liver—and the brain, in both males and females.
But it’s the abundance of estrogens produced in songbirds’ brains that may help them sing, learn songs and respond to them. “Birds that learn songs have a high capacity for estrogen production in the brain, just like humans,” says Luke Remage-Healey, a behavioral physiologist. Scientists, including Remage-Healey, strongly suspect that estrogens are important for learning.
So he and his colleagues developed a way to measure the concentrations of estrogens in various regions of the brain of zebra finches, a highly social songbird. What they found: part of the bird’s auditory cortex synthesizes estrogens. And that appears to be the case in other songbird species as well.
“In male songbirds, the estrogens are produced almost entirely in the brain,” says Remage-Healey. In females, the estrogens are produced in the brain and also in the ovaries. So, if a circuit needs estrogens to help process information, the male does it by synthesizing estrogen locally. The female does it by synthesizing some estrogen in the brain but also peripherally.
With that in mind, Remage-Healey wanted to find out what would happen if he inhibited the enzyme in finches’ brains that synthesizes estrogens. And what he found was that the birds’ ability to respond behaviorally to song was disrupted. “Recordings of the neurons in the regions of their brain that encode song showed that these circuits are also clearly disrupted,” he says.
“This and other ongoing animal research programs show that there’s something non-reproductive about estrogen in the brain,” says Remage-Healey. “This means there’s potentially an association here between learning and estrogen production locally in the brain.”
In fact, some species of juvenile songbirds that produce lots of estrogens in their brain have a discrete span of time in which adult birds teach them to sing. The young birds practice these elements just the way young human infants do when they babble, says Remage-Healey. “And gradually song emerges similar to how human speech emerges.”
Remage-Healey says researchers are beginning to understand the role cortical estrogens play in the cognitive function of a variety of animals, including humans. For example, scientists now know that neurodegeneration can be associated with diminished estrogen production. So researchers are hoping they can tap into that phenomenon to design treatments for diseases that are affected by a lack or overproduction of estrogens.
“It’s interesting from a basic perspective that a molecule we originally understood to be a reproductive hormone is now considered more of a neurotransmitter-like molecule,” says Remage-Healey. “The question is what does that mean for how we understand the brain.”
Luke Remage-Healey, PhD, is a behavioral physiologist who focuses on the neural basis of natural behavior. He studies songbirds as a model for understanding vocal learning and brain plasticity. He and and his colleagues are interested in how local neurochemicals modulate neural circuits for vocal communication, such as singing, song learning, and song memory. Remage-Healey is an assistant professor of psychology at UMass Amherst, and his work is supported by the National Institutes of Health.