12 March 2007

Sex and Violence--Beware the Teenaged Girl

Teenagers are typically impulsive. But many teens are also quite volatile in mood--cycling from seductive to violent in very short order. Researchers at SUNY Downstate have followed up on earlier research to show in a female mouse model that adolescent brains (CA1 region of hippocampus) react paradoxically to a hormone that is soothing in adults and children.
The team reports in Nature Neuroscience that allopregnanolone (THP), a chemical that normally helps soothe the activity of brain cells in adults and children by binding to receptors that inhibit accelerating electrical activity, actually becomes an antagonist during puberty.

...."Puberty is certainly a time when there are huge changes in hormones," senior study author Sheryl Smith says. "When we looked at the time of puberty, we found that the steroid THP completely flipped to the opposite effect."

THP is a steroid created in the body when progesterone, the female sex hormone, is metabolized. Typically, THP is released in the brain in response to stress, and quiets the neural system within 30 minutes of escalation. THP works by binding to so-called GABA receptors on the surfaces of neurons, or nerve cells. Smith notes that GABA (gamma-aminobutyric acid) is the primary inhibitory neurotransmitter in the brain, and that "any sedative like tranquilizers, anesthetics and alcohol all act on the GABA receptor."

...To determine if the special receptors were linked to behavioral differences, the researchers stressed out young, pubescent and adult mice by trapping them in a plastic tube for 45 minutes. They then removed them and gave them 20 minutes to settle down before placing them in another stressful situation—a maze that is known to make the animals anxious. The 20 minutes of downtime was enough time for the young and adult mice to relax but the adolescents remained hyped up.

The team later determined in vitro that the alpha4-beta2-delta receptors in the CA1 behave differently than normal GABA receptors, absorbing a current of chloride ions, rather than expelling them. "Normally, chloride is flowing out," Smith explains, "and THP enhances the GABA receptors which enhance [the] inhibition" of out-of-control neural activity. During puberty, THP instead slows desensitizes GABA receptors, allowing spiking brain activity to carry on unchecked.

In other words, instead of promoting normal GABA-ergic inhibition post-stress, the DHT in adolescent females allowed the brain to remain in the excited, or stressed state.

Tetrahydroprogesterone (THP or allopregnanolone) has been known for years to be an anxiolytic neurosteroid. THP is also important in mediating the sexual behaviour of female animals. The connection between sex and violence seen in some young women may very well be mediated by this hormone (or precursors/metabolites).

Certainly inexplicable violence and rage attacks sometimes seen in adolescence and young adulthood may in some instances be related to altered receptor activity to these neuro-steroids.

When one combines the delayed development of pre-frontal cortical centers (and pathways) with altered stress and possibly sex receptor activity, one may be able to begin to make more sense of adolescent proclivities.

However, one can not truly understand current behaviours of adolescents and university aged students without taking into account the cultural pressures toward psychological neoteny in most western young people. The absence of meaningful life responsibility until well into the twenties, for many youth, quite possibly alters the gene expression controlling behaviour.

The old saw that states: " if you are not a leftist at twenty, you have no heart; but if you are still a leftist at thirty, you have no brain"--takes on new significance when contemplating some of the important neuro-physiologic differences between adolescents and mature adults.

Much of the anger seen in protest movements--that sometimes ignites into violence--can certainly be explained by increased volatility and reduced judgment present in the immature brain.

Some of these young brains may very well become "frozen" in an immature state if the proper maturational triggers are not pulled during the appropriate critical period of development.

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