Why men are more aggressive

Why Men Are More Aggressive: What A Mother Should Know

Aggression in men may be due to variations in one of two genes involved
in the activity of the neurotransmitter serotonin, according to results
of a study reported at the 6th International Congress of
Neuroendocrinology (ICN 2006), which takes place June 19 - 22 at the
David L. Lawrence Convention Center in downtown Pittsburgh.

However, men with the "aggression" genes aren't necessarily all
cads; genetics appears to be predictive only if men have hostile
attitudes and fathers who never completed high school. Moreover, a
genetic predisposition toward aggression could be rebuffed by a mother
who nurtures her infant, suggests another study involving primates.

Summaries of these studies' findings and research revealing new
information about the molecular and biophysical mechanisms that
determine sexual arousal and sexual behavior follow:

No argument here: Research determining why some men are more aggressive

What pushes some men to the outer limits of machismo, to be more
confrontational or apt to get into scuffles and arguments? According to
results of a study involving 531 white men of European descent,
belligerence may be attributable to variations in one of two genes
involved in the activity of the neurotransmitter serotonin. However,
men with the "aggression" genes aren't necessarily all cads,
cautions Stephen Manuck, Ph.D., professor of psychology at the
University of Pittsburgh, who led the research. Genetics appears to be
predictive of aggression only if men also have more cynical and hostile
attitudes toward others or fathers who never completed high school.

The Pitt study is the first to look at whether aggression in
"normal" men may, in part, be attributed to the same
serotonin-related genetic alterations that have been associated with
aggressive behaviors in certain psychiatric and criminal populations.
Indeed, the study found those who reported past fights, conflicts with
authority figures or breaking objects in bouts of anger were more
likely to carry the "low activity" MAOA gene variant that's been
linked to criminal violence.

Monoamine oxidase-A, or MAOA, is an enzyme that inactivates serotonin,
helping to keep its levels in proper balance. Yet the low activity MAOA
gene was only associated with aggressive "acting out" among men
with oppositional attitudes. Variation in another serotonin gene, the
serotonin 2A receptor, which is necessary for the neurotransmitter to
act, also was predictive of antagonistic behavior, but only among men
whose fathers had less than a high-school education. The same gene has
been implicated in personality and anti-social disorders and in some
criminal offenders.

Maternal buffer can prevent aggression

It can be a real jungle out there, and parents often do their best to
shield their children from the worst of influences. According to new
research, mothers can offer some added protection that fathers can't:
a buffer against the development of aggressive behavior. According to
primate studies, those with a genetic susceptibility for hostile
behavior can grow up to be docile in nature, provided they had loving
and caring mothers as infants.

Up to 10 percent of rhesus monkeys living in the wild are overly
aggressive and react inappropriately even in the most benign
situations, a trait they typically develop at a young age and seldom
grow out of. Moreover, researchers have recently found, these
aggressive animals have lower levels of the brain chemical serotonin,
an observation noted through adulthood. Like their wild counterparts,
monkeys studied in the laboratory that have a variation of a certain
serotonin-related gene also make less serotonin and are more impulsive
and aggressive, but only if they had mothers who did not bond with them
as infants. As Stephen J. Suomi, Ph.D., chief, Laboratory of
Comparative Ethology at the National Institute of Child Health & Human
Development, has demonstrated, monkeys with the same gene-based
serotonin deficiency who were reared by more nurturing mothers avoid
developing aggressive behaviors. "Maternal buffering," he suggests,
can trump genetics. The same may be true in humans.

Getting to the essential mechanisms of brain arousal and sexual
behavior

To understand what brings about arousal of the central nervous system
leading to sexual behavior, scientists have had to discover specific
biochemical reactions within a select group of neurons in the
hypothalamus, says Donald Pfaff, Ph.D., professor and head of the
Laboratory of Neurobiology and Behavior at Rockefeller University. The
process involves a complement of sex steroid hormones, perhaps as many
as 120 genes and a host of environmental variables (not least among
them, arousing stimuli and a suitable mate).

In these brain mechanisms, interactions between genes and the immediate
environment play an essential part. Other, longer-term interactions
stem from an animal's treatment about the time of birth. Those
longer-term interactions are hypothesized to depend on chemical
modification of either DNA through a process called methylation or of
proteins covering the DNA. These so-called epigenetic mechanisms can
produce heritable changes in behaviors without changing the animal's
DNA sequence. Dr. Pfaff's new results reveal some of the molecular
and biophysical mechanisms that dictate when and how chemical messages
for generalized arousal affect the neurons in the hypothalamus that
control sexual arousal and sexual behaviors.

Held in a different part of the world every four years under the
auspices of the International Neuroendocrine Federation, this year's
congress - Bridging Neuroscience and Endocrinology - is being
sponsored by the American Neuroendocrine Society and the University of
Pittsburgh School of Medicine. The first full day of the program, June
20, is being held in conjunction with the 10th Annual Meeting of the
Society for Behavioral Neuroendocrinology.

Formerly the International Society of Neuroendocrinology, the
International Neuroendocrine Federation consists of six member
societies and seven regional groups, representing all parts of the
world. The federation's president is John A. Russell, MBChB, Ph.D.,
chair of neuroendocrinology, University of Edinburgh. The chair of the
ICN 2006 scientific program is Iain J. Clarke, Ph.D., professorial
fellow in the department of physiology at Monash University in
Australia. Tony Plant, Ph.D., professor of cell biology and physiology
and director of the Center for Research in Reproductive Physiology,
University of Pittsburgh School of Medicine, is chair of the local
organizing committee.

Source: University of Pittsburgh Medical Center
http://www.sciencedaily.com/releases/2006/06/060621162228.htm

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