Corpus allatum is release site for insect prothoracicotropic hormone

The primary effector of insect postembryonic development is a peptide neurohormone, the prothoracicotropic hormone (PTTH) 1,2 . PTTH is the product of a single neurosecretory cell (NSC) in each hemisphere of the protocerebrum of the tobacco hornworm, Manduca sexta 3 . Its neurohaemal organ, however, has not previously been identified. Determination of the site of release would complete the identification of the neuroendocrine axis of PTTH and establish the boundaries of an intracellular system within which factors controlling the synthesis, transport, storage and release of an identified neurohormone could be investigated. The neurohaemal organ for PTTH has been assumed to be the corpus cardiacum (CC), a structure located between the brain and corpus allatum (CA) 1,2 , but alternative sites of release have been suggested, including the CA 4–7 and the brain itself 8,9 . In this study, a novel in vitro assay for PTTH 10,11 has been used to identify the CA as the neurohaemal organ for PTTH in Manduca .