Inhibition of corpora allata by larval brain extract in the cockroach diploptera punctata.

Extract of brains from final-instar males inhibited juvenile hormone synthesis by corpora allata from adult females and larval males in vitro. The inhibition was dose-dependent; maximal response was 70% reduction in activity elicited by 0.5 protocerebrum. Inhibition occurred within 1 h as did recovery. The inhibitory factor is trypsin-sensitive. Inhibitory activity was found in extract of brains from males of the three larval instars and adults, and was not localized to a particular region of the brain. Larval corpora allata showed nerve endings containing neurosecretory granules; extracts of larval corpora allata inhibited juvenile hormone synthesis in vitro. The hypothesis that an inhibitory factor is released from these nerve endings was supported by the observation that corpora allata treated with high concentrations of potassium were inhibited, but not in the presence of magnesium.