Role of the Brain in Juvenile Hormone Synthesis and 06cyte Development: Effects of Dietary Protein in the Cockroach

We demonstrate links between the protein content of diets, food intake, the resultant body mass, juvenile hormone synthesis by the corpora allata, and o6cyte maturation in Blattella germanica. Oiicyte development and oviposition were suppressed in starved females as well as in females fed deficient artificial diets (low- or high-protein contetits). On all diets, as well as in starved females, oiicyte growth was significantly potentiated by hydirene, indicating that the suppressed oiicyte growth on deficient diets was largely due to juvenile hormone deficiency. Also, under all dietary treatments, including in starved females, transection of the nervi corporis cardiaci (NCC)-I and II significantly potentiated juvenile hormone biosynthesis, o6cyte development and oviposition compared with the respective sham-operated females. These results clearly show that intact nerves are a major route of allatostatic signals from the brain which in turn are regulated by food quality. However, a partial suppression of juvenile hormone synthesis and smaller o6cytes in females with denervated corpora allata that were fed protein-deficient diets (starved, 0%, 5%) or high-protein diets (78%) compared with females that were fed normal diets (25%, dog and rat foods) highlights the importance of humoral signals in allata activity. OScyte size and juvenile hormone biosynthetic rates were also significantly lower in adult females that were fed a 7.5%~protein diet as nymphs compared with females fed a 25%-protein diet. Denervation of the corpora aUata resulted in potentiation of their activity, but to significantly lower rates in females that were raised on the low-protein diet as nymphs, further supporting the importance of the nutritional milieu in corpus allatmn activation. Both food intake and body mass varied directly with the protein content of the diet, confounding the conclusion that corpus allaturn activity was affected by signals related to the dietary protein content. To dissociate food consumption and body mass from corpora allata activity and oiicyte growth, 2% trypsin synthesis inhibitor was added to a 7.5%-protein diet. Neither body mass nor total food consumption were changed relative to control females, but o6cytes were significantly small on this diet. Together with data showing that o6cyte maturation can be induced with hydroprene in protein-deprived or even in starved females, these data argue that signals associated with the protein content of the diet partially lift brain inhibition of the corpora aUata.