PTTH (Prothoracicotropic hormone)

Definition

A neurohormone produced by neurosecretory cells in the brain of insects that stimulates the prothoracic glands to synthesize and release ecdysteroids, thereby initiating the molting process. PTTH serves as the critical upstream signal that translates environmental and physiological cues—such as photoperiod, nutrition, and body size—into the hormonal cascade governing ecdysis, metamorphosis, and reproduction.

Etymology

From prothoracic (referring to the prothoracic glands, its target tissue) + -tropic (attracting or influencing) + hormone.

Example

In the tobacco hornworm Manduca sexta, a surge of PTTH release into the hemolymph triggers a sharp rise in ecdysteroid titer, committing the larva to pupal metamorphosis within hours.

Synonyms

• ecdysiotropin
• brain hormone

Related Terms

• ecdysteroid
• Ecdysone
• prothoracic gland
• corpus allatum
• Juvenile hormone
• molting
• Metamorphosis
• neurosecretory cell
• Hemolymph

Usage Notes

PTTH is sometimes called 'brain hormone' in older literature, though this term is ambiguous and also applied to other cerebral factors. In Lepidoptera, PTTH is a large peptide (~30 kDa) produced by lateral neurosecretory cells; in other insects, homologous peptides may differ in structure but serve the same functional role. The hormone's release is gated by multiple inhibitory and stimulatory inputs, making it a key integration point for developmental timing.