OSTROWSKI, E.; LI, S.; OUYANG, Y.C.; BORST, D.W.; Illinois State University, Normal; Chinese Academy of Sciences, Beijing, PRC: Characterization of allatotropin in the brain of the lubber grasshopper

The production of juvenile hormone (JH) by the corpora allata (CA) is regulated by allatotropin (AT) and allatostatin (AST), two brain neuropeptides that stimulate and inhibit the CA, respectively. We used a radiochemical assay to study these neuropeptides in the lubber grasshopper (Romalea microptera). One CA was incubated in medium alone and the contralateral CA in medium containing a brain extract. Their levels of JH synthesis were then compared. Extracts of adult brains from both females and males stimulated JH synthesis, suggesting the presence of AT. This activity appears to be a peptide since it was not affected by acid or heat and was destroyed by protease treatment. The effects of the brain extract were rapid and reversible. During the oviposition cycle (~ 35d long), the sensitivity of CAs to brain extract was highest at 16-18d (~3-fold greater than control CA) and then declined. Therefore, we used CAs from 16d females in a bioassay for AT. Brain extract (0.03 to 0.5 brain equivalents) produced a linear stimulatory response, though higher amounts (1 and 2 equivalents) decreased activity, possibly due to the presence of AST. AT activity in brain extracts of females increased steadily during the oviposition cycle, reached its maximum (~4 fold than the control) on 25d (when JH synthesis was highest), and then decreased rapidly. AT was partially purified from brains by reversed phase (C18) HPLC. Two peaks of AT activity eluted at ~28% and ~33% acetonitrile: water. Lepidopteran AT had no effect but two ASTs (YXFGL-NH2-AST and W2W9-AST) had some inhibitory activities in this bioassay. This is a step toward the molecular characterization of this neuropeptide in grasshoppers. (Supported by NSF grant DBI-9978810 to DWB)