A Kiss with Consequences

Ready for a kiss? The neurotransmitter kisspeptin may be a key trigger for puberty.

Puberty may begin with a kiss. A new study indicates that a neurotransmitter, which carries the whimsical name kisspeptin, provides a powerful signal to the neurons that control the onset of sexual maturation. The find is one of the first to explain the initial steps that set off the hormonal whirlwind of puberty.

Human babies produce relatively high levels of sex hormones--baby boys have testosterone levels similar to those of grown men. Somehow, the hormones are then shut down for more than a decade, until the onset of puberty. What turns this system on and off has long puzzled researchers.

Recent discoveries have provided tantalizing clues. In 2003, two groups reported independently that mutations in a neuronal receptor called GPR54 could explain the failure of children in several families to enter puberty (ScienceNOW, 22 October 2003). The receptor responded to proteins called kisspeptins (originally discovered and named by cancer researchers), but it wasn't clear whether that signal played any role in puberty.

To test the question, Tony Plant of the University of Pittsburgh School of Medicine and colleagues treated prepubescent monkeys with a protein fragment called kisspeptin-10. Within 30 minutes, the monkeys' levels of luteinizing hormone, a key marker of puberty, increased 25-fold. This suggested to the researchers that kisspeptin is a powerful trigger for the chemical cascade that drives puberty. The team, which reported its findings online this week in the Proceedings of the National Academy of Sciences, also showed that kisspeptin levels increase during puberty in the brains of both female and male monkeys.

The observation is the first solid evidence for a molecular signal that prompts the release of puberty's hormones, says Robert Steiner oft the University of Washington, Seattle. The peptide is effective "in infinitesimal amounts," he notes, and appears to be one of the strongest triggers ever discovered for GnRH neurons, which are known to orchestrate the release of sex hormones. Ape and human reproductive systems are extremely similar, he says, so it is likely that the protein plays a similar role in the human brain.

Related sites
Tony Plant's Web site
Puberty information from the NIH
Abstract of PNAS paper

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