Scientists have found the first instance of melatonin directly acting on a neuropeptide in the vertebrate brain, they reported February 7 online in PNAS.

"This suggests if melatonin can do this on one neuropeptide system, it could do it on other neuropeptide systems," coauthor George Bentley of the University of California at Berkeley told The Scientist.

In 2000, Kazuyoshi Tsutsui at Hiroshima University in Japan and colleagues discovered a neuropeptide dubbed GnIH that inhibited gonadotropin release, serving as the missing antagonist for gonadotropin-releasing hormone, the primary agonist controlling reproduction in vertebrates. In searching for regulatory mechanisms governing GnIH expression, the investigators noted melatonin was implicated in seasonal gonadotropin secretion.

To explore any link between melatonin and GnIH, the researchers focused on quail, which are highly photoperiodic, and removed their major sources of melatonin, the eyes and pineal gland. They quantified expression of GnIH precursor mRNA via competitive polymerase chain...

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