Kenneth E. Peck

Allatinhibin, a neurohormonal inhibitor of juvenile hormone biosynthesis in Manduca sexta

The corpora allata (CA) of Manduca sexta larvae become incapable of synthesizing juvenile hormone (JH) early in the wandering stage of the last larval stadium. They then switch to the synthesis and release of JH acids. This change in CA activity is induced by an inhibitory factor--allatinhibin (AI)--from the brain. AI activity is present in the fifth (Vth) instar hemolymph from about Day 4 (day of wandering) until Day 7 (early prepupa). CA of early fifth instar larvae (uninhibited) incubated in vitro with brain-corpora cardiaca-corpora allata (Br-CC-CA) complexes or brain alone from wandering larvae are inhibited as demonstrated by bioassay. On the basis of these observations, an in vitro-in vivo assay for AI was developed. Br-CC-CA or Br alone were first incubated in tissue culture medium overnight. Day 0 (0d) Vth instar CA incubated for 16 hr in such medium will lose the ability to induce a larval molt in allatectomized 0d IVth instar larvae if the medium contained AI activity. The highest AI activity was exhibited by the medium obtained from incubations of brain from wandering larvae whereas the medium from incubation of 0d Vth and 0d pupal brains showed no AI activity. Dose-response data show that AI is active at 0.03 brain equivalents/200 microliters medium. CA must be exposed to AI for 12-16 hr for manifestation of inhibition. AI causes a stable inhibition of CA. AI is heat-labile, protease sensitive, has a molecular size between 1.0 and 3.5 kDa, and is clearly distinct from the allatostatins described by others.

Corpus allatum activity (In vitro) in female Culex pipiens during adult life cycle

Abstract In vitro incubation followed by radiochemical assay of the incubation medium showed that corpora allata from female Culex pipiens produce juvenile hormone III. The rate of hormone synthesis was relatively constant for corpora allata from 1- to 8-day old sugar-fed females with a mean rate of synthesis of 27.1 fmol per h per pair of allata. Blood feeding by the mosquito suppressed the production of juvenile hormone by corpora allata. Corpora allata from blood-fed mosquitoes synthesized only 8.4 fmol per h at 4 h and 1.4 fmol per h at 12 h after the blood meal. As eggs matured after the blood meal, the corpora allata gradually synthesized more juvenile hormone. However, production was again suppressed if the mosquitoes were forced to retain their eggs.

Juvenile hormone acid synthesis and HMG-CoA reductase activity in corpora allata of Manduca sexta prepupae

Abstract Corpora allata (CA) of last instar larvae of Manduca sexta switch from juvenile hormone (JH) to JH acid secretion just before the onset of wandering behavior. JH acid secretion peaked during the prepupal period and ceased prior to pupal ecdysis. HMG-CoA reductase activity also peaked during the prepupal period and then declined. However, substantial enzyme activity was present in pupal and pharate adult glands. Removal of the brain at the wandering stage caused a reduction in JH acid secretion by prepupal CA. The profile of HMG-CoA activity in CA of debrained larvae resembled that of sham-operated larvae except that the prepupal peak was smaller than in control larvae. Addition of brain extracts to CA maintained in vitro neither stimulated not inhibited JH acid secretion and HMG-CoA reductase activity. It is suggested that the brain regulates CA activity in post-wandering stages via intact nerves.