Prothoracicotropic hormone
Encyclopedia
Prothoracicotropic hormone (PTTH) was the first insect hormone
that was 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.
Later it was established that the insect brain produces a number of hormones, but the hormone which was the cause of the observations made by Kopeć and Wigglesworth was prothoracicotropic hormone. PTTH is secreted by a neurohemal organ, the corpus cardiacum (in some insects the corpus allatum
secretes PTTH) which is actually a discrete structure posterior to the brain. PTTH is released in response to environmental stimuli and as its name implies PTTH acts on the prothoracic glands, which respond by releasing molting hormone (an ecdysteroid
) into the haemolymph. Molting hormone stimulates the molting process.
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
that was discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć
Stefan Kopec
Stefan Kopeć was a Polish biologist and pioneer of insect endocrinology, who studied at the Jagiellonian University in Kraków. He received his PhD. there in 1912, and worked at Puławy Agricultural Research Station in Poland between 1915 and 1920...
(1922) and Vincent Wigglesworth
Vincent Wigglesworth
Sir Vincent Brian Wigglesworth FRS was a British entomologist who made significant contributions to the field of insect physiology.In particular, he studied metamorphosis...
(1934), who realized that ligation
Ligation
Ligation may refer to:* In molecular biology, the covalent linking of two ends of DNA molecules using DNA ligase* In medicine, the making of a ligature * Chemical ligation, the production of peptides from amino acids...
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
Sessility (zoology)
In zoology, sessility is a characteristic of animals which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a part of a plant or dead tree trunk, a rock, or the hull of a ship in the case of barnacles. Corals lay down their own...
ligated abdomen or an abdomen under diapause
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...
would induce molting or pupation. Thus, the brain was originally thought to be the source of the hormone that induces molting in insects.
Later it was established that the insect brain produces a number of hormones, but the hormone which was the cause of the observations made by Kopeć and Wigglesworth was prothoracicotropic hormone. PTTH is secreted by a neurohemal organ, the corpus cardiacum (in some insects the corpus allatum
Corpus allatum
The corpus allatum , in insect physiology, is an endocrine gland which generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata can cause an immature larva to pupate at its next molt, resulting in a miniature adult...
secretes PTTH) which is actually a discrete structure posterior to the brain. PTTH is released in response to environmental stimuli and as its name implies PTTH acts on the prothoracic glands, which respond by releasing molting hormone (an ecdysteroid
Ecdysteroid
Ecdysteroids are insect moulting and sex hormones which include ecdysone and its homologues such as 20-hydroxyecdysone. Ecdysteroids also occur in other invertebrates where they can play a different role. They also appear in many plants mostly as a protection agents against herbivore insects...
) into the haemolymph. Molting hormone stimulates the molting process.