PROTHORACICOTROPIC HORMONE IN RHODNIUS-PROLIXUS - IN-VITRO ANALYSIS AND CHANGES IN AMOUNTS IN THE BRAIN AND RETROCEREBRAL COMPLEX DURING LARVAL ADULT DEVELOPMENT

Prothoracicotropic hormone (PTTH) was extracted from the brain-retroce rebral complex of fifth instar larvae of Rhodnius prolixus and was ass ayed iii vitro by its ability to stimulate a statistically significant increase in ecdysteroid synthesis by prothoracic glands (PGs). PTTH s timulated synthesis in a dose-dependent manner with linear increase be tween 0.25-1.0 brain complex equivalent. Significant stimulation was o bserved with 0.4 eqt and maximum stimulation with 1.0 eqt, which stimu lated ecdysteroid synthesis 3.5-fold. The dose-response curves for PTT H extracted from unfed and day 4 fed animals were closely similar. PTT H activity was found in both brain and retrocerebral complex but not i n other ganglia. The activity was destroyed by pronase. PGs were maxim ally activated by exposure to PTTH for 20 min. Longer exposure did not increase the response. PGs of young fifth instar larvae are highly re sponsive to stimulation by PTTH, whereas PGs from animals later in the moult cycle were refractory to further stimulation. The content of PT TH in the brain and in the retrocerebral complex both exhibit large, s ystematic changes during larval-adult development. Complete loss of PT TH activity in both structures occurred at previously documented times of PTTH release. Large increases in PTTH content occurred at previous ly described times of active synthesis and transport in the medial neu rosecretory cells of the brain. PTTH lost by release was replenished i n the latter part of development such that the adult insect after ecdy sis contained an amount of PTTH comparable to that of the unfed larva.