July 16, 1997 July 10, 1997
Contact: Kate Egan,404-727-7709, email: kegan @rmy.emory.edu
Biology of a Monogamous Bond
Findings reported in Hormones and Behavior help explain social attachment, provide clues for autistic behavior
As a youngster, he's a tad timid but he gets along well enough with others. He doesn't fight much. Then something happens. He meets an attractive female and mates with her. Within 24 hours, he becomes quite aggressive, actively excluding all others save for her. Why the sudden change?
Apparently, says Thomas R. Insel, MD, Director of the Yerkes Regional Primate Research Center of Emory University, this kind of behavior among prairie voles is part of a larger network of social behaviors that preserve the bond between the lovebirds, while excluding all others. The couple is held together like glue by a mutual interest that favors staying together.
Dr. Insel, a self-described "psychiatrist turned neuroscientist," has spent years figuring out how this bond is formed and maintained, neurobiologically speaking. His research focuses on the mechanisms underlying affiliative behaviors, which he hopes will help in developing treatments for autism and even schizophrenia, both of which result in social isolation and detachment. There is currently no therapy or cure for these problems. The antipsychotic drugs used currently are useful only for symptoms like hallucinations or self injurious behaviors; they do not help social deficits.
Specifically, Dr. Insel and his research team examine the peptide hormones vasopressin (AVP) and oxytocin (OT) and their vital roles in influencing complex social behaviors such as affiliation, parental care, territorial aggression, and several behaviors associated with monogamy (pair bonding, paternal care, mate guarding).
To demonstrate how OT and AVP influence these behaviors, Dr. Insel compares neuropeptide pathways in two rodent species: the prairie vole and the montane vole. Although the two species are 99% genetically identical, they exhibit very different social behaviors. The prairie vole is highly social and forms lasting, monogamous pair bonds after mating. A prairie male prefers the company of its mate and shows aggression toward other males once he has bonded with a female. The breeding pair nests together and both parents provide extensive and prolonged parental care, with the offspring remaining in the parental nest for several weeks beyond weaning. Manipulating their exposure to AVP and OT will drastically alter these behaviors.
In contrast, the montane vole typically nests in isolation and breeds promiscuously. Montane breeding partners do not form a pair bond after mating, the males are notparental, and females abandon the offspring soon after birth.
Why such a difference? It's all in the wiring. The neural wiring, that is, deep inside the brain. It turns out that the receptors for vasopressin (in males) and oxytocin (in females) are distributed in different areas of the brain in the two species. Dr. Insel and his colleagues, Larry Young, Ph.D, and Zuoxin Wang, Ph.D., think they have an idea why: the promoter portion of the AVP receptor gene, which possibly instructs the gene where in the brain it should be expressed, is configured differently in the two species. "This difference in receptor distribution is what we think makes the species respond differently to AVP," says Dr. Insel. "It's not just that prairie voles have more AVP than montane voles. Montanes just act differently, even when we inject AVP directly into the brain."
Drs. Insel's lab has carefully mapped out the specific locations of the receptors in the brain. The next step is to determine which aspect of social behavior each area is responsible for ----and if and how behavior is altered when the receptors are blocked or otherwise manipulated. For instance, is one location associated with pair bonding, and another with aggression? Or perhaps paternal care?
To study the question further, Drs. Insel and Young are using a mouse that has been genetically altered to contain the prairie vole's AVP and OT receptor genes. Their work is described in the June issue of Hormones and Behavior.
"Hopefully, this will result in a mouse with altered receptor distribution," explains Dr. Young. "Then we'll look at behavior." Will the mouse's social behavior mimic that of a vole? Will the mouse become more monogamous?
Dr. Young's theory is that every species has different receptor distribution----which leads to different social patterns. "Throughout evolution, AVP and OT receptor distribution has changed. When it changes behavior favorably, it is selected for," explains Dr. Young. "Now we are trying to determine whether we can modify social behavior in the laboratory the same way evolution has over millions of years."
Dr. Insel and his team eventually plan to map the receptors for AVP and OT in the rhesus monkey. These studies will reveal much about the evolution of monogamy and the the neuroendocrine basis of affiliation. The obvious question is what impact might this have for humans? How similar is the human biology of attachment? It is hoped that these studies will improve understanding of the determinants of human social bond formations, as well as provide clues to the social deficits characteristic of devastating human diseases such as autism and schizophrenia.
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The above story is based on materials provided by Yerkes Primate Research Center.
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