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.
Autopharmacology
Historically, the first approach to the concept of autopharmacology began with British physiologist and pharmacologist Henry Dale in the 1910s, discovered the role of acetylcholine in synaptic transmission, and later proved by Austrian physiologist Otto Loewi, to be the neurotransmitter involved in the proximal synapses of the autonomic nervous system (initially named "Vagusstoff" by Loewi, and later identified as acetylcholine). The same happened to another autonomic neurotransmitter, noradrenaline ("Akzeleransstoff" by Loewi), which later proved to be chemically similar to a long used pharmacological agent, adrenaline, a hormone secreted by the adrenal glands. Both scientists were awarded the 1936 Nobel Prize for Physiology or Medicine for their pioneering and important contributions.