From: Antoun Nabhan (firstname.lastname@example.org)
Date: Thu Nov 09 2000 - 13:46:09 PPET
Well, let the momma jokes commence. The nitric oxide angle makes nitrous
balloon jokes in-range, as well.
Seriously, the mouse seems to be a decent enough model. Research like this
is frighteningly close to collapsing our vaunted notion of "free will" into
a biochemical concept, something partially if not completely modelable. On
the other hand, how predictable is a chaotic process?
Suspect List Shortens For Maternal Aggression's Brain Origins
Scientists studying the origins of aggression have highlighted areas in the
brains of mouse mothers that may generate fierce attacks on males who pose
a potential threat to their pups.
The findings will be presented by Johns Hopkins University postdoctoral
researcher Stephen Gammie at this week's annual meeting of the Society for
Neuroscience in New Orleans. Gammie says the results are an important step
towards pinning down the origins of this type of aggressive behavior in the
mouse brain, an accomplishment that could help scientists better probe
aggression's origins in humans. To prevent strange male mice from harming
their offspring, female mice with pups normally attack any such mouse who
comes into their area. A few mouse moms, however, fail to show this
response. Gammie divided mice into groups based on this distinction,
compared the two groups for presence of compounds related to brain
activity, and was able to identify four brain areas that were active in the
aggressive moms but not in the non-aggressives.
Given the mouse brain's small size, cutting down the list of suspects for
production of aggression might seem an unlikely or unimportant step. But
even the humble mouse brain has sufficient structural and biochemical
complexity to resist giving up its secrets easily, Gammie says.
"By taking advantage of natural variation in aggression, our study
decreased the odds of confusing aggression control mechanisms with other
areas of the brain activated when a strange male mouse approaches," says
Gammie. "For example, areas of the brain that are involved in seeing and
smelling the males become active in both groups of mouse moms. Areas that
become active only in the aggressive moms have a good chance of being
linked to production of the primary difference in behavior, the aggression."
Gammie's postdoctoral mentor, Hopkins psychology and neuroscience professor
Randy Nelson, was one of a group of several Hopkins scientists who
discovered a link five years ago between the brain neurotransmitter nitric
oxide and aggression in male mice. In an attempt to greatly reduce or
eliminate nitric oxide in the mice's brains, scientists had given them a
defective copy of a gene involved in nitric oxide production. They found
that this led to a dramatic increase in aggression levels among the male mice.
Working with Nelson, Gammie showed last year that the genetic change had
the opposite effect on females, decreasing their aggression when they were
exposed to strange males after giving birth.
In the new experiments, funded by the National Institutes of Health and the
National Institute of Mental Health, Gammie and Nelson exposed normal,
non-altered mouse moms to strange males and tested their brains for
transcription factors known as pCREB and cFOS. Both pCREB and cFOS have
been linked to nerve cell activity by other labs. Some of the regions
highlighted in the new experiment have shown up before in experiments by
Gammie and other researchers.
For example, the paraventricular nucleus has been linked to aggression in
related research into the behavior of prairie voles. Voles are also rodents
and look like a stout mouse or rat, but are more closely related to
lemmings and muskrats than to mice. The paraventricular nucleus is located
in the hypothalamus, a brain area where environmental stimuli are
integrated with internal signals from the brain, and a response to the
stimuli begins to be produced. "We're not there yet, but the pieces of the
puzzle are starting to come together," Gammie says. With a list of likely
suspects based on the research of Gammie and others, neuroscientists can
begin to consider more precise pharmacological manipulation of the brain to
zero in on the brain circuitry that produces aggression.
"Maternal aggression occurs in almost all mammals. It is a highly adaptive
behavior because it helps keep offspring alive," Gammie says, noting that
highly adaptive characteristics tend to be preserved by evolution. "If we
gain a detailed understanding of the neural circuitry underlying maternal
aggression in rodents, then it may be possible later on to use that
information to help understand how maternal aggression is controlled in
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