Prothoracicotropic hormone
Prothoracicotropic hormone (PTTH) was the first insect hormone to be discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć (1922) and Vincent Wigglesworth (1934), who realized that ligation of the head of immature insects could prevent molting or pupation of the body region excluded from the head if the ligation was performed before a critical age in the lifestage was reached. After a certain point the ligation had no effect and both sections of the insect would molt or pupate. However, implantation of a conspecific brain to a sessile ligated abdomen or an abdomen under diapause would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
Jeffrey M. Friedman
When Friedman started his own laboratory at The Rockefeller University, he turned his attention to the question of weight regulation. Working with a special strain of mice, he set out to identify the hormone that normal animals use to control their appetite - a molecule that was missing in the plump rodents. After eight years—on May 8, 1994, at 5:30 a.m.—he found what he was looking for: evidence that he'd located the gene that produces the hormone he later dubbed "leptin", after the Greek word for "thin" (λεπτός "leptos"). "It was astonishingly beautiful", he says of the x-ray film that nailed the gene, a piece of data that now hangs on his office wall.