Growing up and how

Growing up and how the metamorphosis of a child into an adolescent is no longer a natural wonder as scien-tists have found new insights into the body mechanism, which provide clues to the onset of puberty. Researchers of the University of Califor-nia propose that leptin (a protein secreted by the adipose cells), famed for its role in controlling body fat, is a major initiator of puberty.

A long-standing theory, called the, 'critical fat hypothesis', infers that a girl must reach a certain weight before her brain feels comfortable and she is capable of conceiving; thus unleashing the cascade of events culminating in sexual maturity. The latest results lend credence to the hypothesis by suggesting that the brain monitors blood levels of leptin to trigger reproduction. The results are based on pre-vious experiments done on genetically altered mice lacking the leptin gene. Such mice became obese and turned out to be sterile. In the current experiments, normal mice with the normal complement of leptin genes were injected with extra doses of leptin. This resulted in the mice growing very lean as their brains responded to the fake fat signal by prompting them to eat less, and they also matured early. Their ovaries and uteri grew larger, reproductive tracts opened, levels of sex hormones soared and they began bearing at an earlier age.

If leptin proves to be a major puberty signal in humans, it must operate not by starting something new but by resuscitating something old. Puberty occurs through a surprising process of disinhibition. In a sense, puberty begins in the foetus with all the mechanisms for sexual maturity in place in the brain before mid-gestation. By age three, these neural mechanisms are shut down, to be revived later at adolescence.

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