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Tracking the effects of childhood stress
Why do mistreated children so often demonstrate antisocial or aggressive behavior later in life? Alexa Veenema, an assistant professor of psychology at Boston College, looks for answers at the molecular level, in the chemicals that help the brain regulate social behavior.
As Veenema wrote in a 2009 article in the journal Frontiers in Neuroendocrinology, many studies have established a link in humans between “early social deprivation or trauma” (physical abuse, for instance, or the loss of a parent) and a heightened incidence of “conduct disorders, personality disorders, major depression, posttraumatic stress disorder, schizophrenia, and anxiety disorders.” A core symptom of most, if not all, of those afflictions is aggression, she notes.
To study the neurobiological connection between early-life stress and later aggression, Veenema uses a method common in her field—subjecting newborn male rats to a pattern of “maternal separation.” For the first 14 days of their lives, the infant rats are kept from their mothers for three hours a day. In various experiments, Veenema and her colleagues have found that newborn rats that experience this deprivation go on to exhibit abnormally aggressive behavior—biting and nape attacks—as adults. The results have led Veenema to suppose that increased aggression is tied to changes in how the rats’ brains process social information. But when do such changes occur—and how?
In a study published last year in Psychoneuroendocrinology, Veenema and a team of four colleagues set out to determine the extent to which previously separated rats are able to distinguish between rats that are strangers and rats they’ve encountered before, as compared with a control group. Testing both juveniles and adults, she introduced a known and an unknown rat into each subject’s cage, then timed the identification process—accomplished by rats, as by dogs, through sniffing. The expectation was that familiarization would occur more quickly with prior acquaintances. The results showed that juvenile separated rats performed similarly to the control group; the adult separated rats, however, had more difficulty recognizing acquaintances. Veenema’s conclusion: “Certain behavioral effects of early-life stress” may only emerge “later in life.”
“Now it becomes very interesting for us,” Veenema says, recounting the experiment in her McGuinn Hall office. Studies show that a small protein or neuropeptide called vasopressin, which is synthesized and released in the brains of rats and humans, plays a key role in regulating emotional and social behavior. Veenema set out to monitor vasopressin levels in separated and control rats, tracking changes that occurred as the rats underwent her identification test over time.
By inserting a tiny microdialysis probe—a monitoring device that simulates a capillary—into the rats’ brains, Veenema and her colleagues were able to track (and alter) the amounts of vasopressin present. They found that among five-week-old, prepubescent juveniles—whether in the separated or control group—the levels of the protein were similar. Among 16-week-old adult separated rats, however, the levels were depressed. When Veenema gave rats in this group an injection of vasopressin via the probe, their social discrimination skills surfaced, for the moment, intact.
Veenema is now investigating the different effects of vasopressin, and of another neuropeptide called oxytocin, with regard to gender. Manipulating vasopressin levels can produce opposite effects in male and female rats, and oxytocin is known to play an important role in social development in female brains. Veenema says these chemicals may relate to the well-documented differences in the incidence of certain psychiatric disorders reported between males and females. “Autism is a good example,” she says, “where boys have a four times higher chance of developing autism than girls do.”
In early 2011, Veenema, who joined the Boston College psychology department last fall, was awarded a Young Investigator Award from the Brain and Behavior Research Foundation (formerly the National Alliance for Research on Schizophrenia and Depression). She says she and the five members of her laboratory will use the two-year, $60,000 grant to investigate the role of vasopressin and oxytocin in regulating juvenile behavior in male and female rats, as a way of furthering their understanding of “possible mechanisms” underlying the sex-bias in human psychiatric disorders.