Wednesday, July 17, 2013

Serotonin and 5-HIAA

A group of researchers has studied the relationship between serotonergic activity and aggressiveness in a free-ranging colony of rhesus monkeys (reviewed by Howell et al., 2007). The investigators found that young male monkeys with the lowest levels of 5-HIAA showed a pattern of risk-taking behavior, including high levels of aggression directed toward animals that were older and much larger than themselves. They were much more likely to take dangerous, unprovoked long leaps from tree to tree at a height of more than 7 m (27.6 ft). They were also more likely to pick fights that they could not possibly win. Of forty-nine preadolescent male monkeys that the investigators followed for four years, 46 percent of those with the lowest 5-HIAA levels died, while all of the monkeys with the highest levels survived. (See Figure 11.7.) Most of the monkeys that died were killed by other monkeys. In fact, the first monkey to be killed had the lowest level of 5-HIAA and was seen attacking two mature males the night before his death. Clearly, serotonin does not simply inhibit aggression; rather, it exerts a controlling influence on risky behavior, which includes aggression.
Born to an alcoholic teen mother who raised him with an abusive alcoholic stepfather, Steve was hyperactive, irritable, and disobedient as a toddler…. After dropping out of school at age 14, Steve spent his teen years fighting, stealing, taking drugs, and beating up girlfriends…. School counseling, a probation officer, and meetings with child protective service failed to forestall disaster: At 19, several weeks after his last interview with researchers, Steve visited a girlfriend who had recently dumped him, found her with another man, and shot him to death. The same day he tried to kill himself. Now he’s serving a life sentence without parole (Holden, 2000, p. 580).
      By the time Joshua had reached the age of 2,… he would bolt out of the house and into traffic. He kicked and head-butted relatives and friends. He poked the family hamster with a pencil and tried to strangle it. He threw regular temper tantrums and would stage toy-throwing frenzies. “At one point he was hurting himself—banging his head against a wall, pinching himself, not to mention leaping off the refrigerator…. Showering Joshua with love… made little difference: By age 3, his behavior got him kicked out of his preschool (Holden, 2000, p. 581). - From Physiology of Behavior by Neil Carlson, 2010.

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