Tannic acid modulates the activity of bombyxin- and PTTH-producing neurons in Lymantria dispar L. (Insecta: Lepidoptera) caterpillars

Abstract Lymantria dispar caterpillars were exposed for 3 days to tannic acid, added to the artificial diet in the following concentrations: 1, 2.5 and 5%. Changes in the morphometric parameters of medial A2 bombyxin immunopositive and dorsolateral L2` prothoracicotropic (PTTH) immunopositive neurosecretory neurons (nsn; sizes of six nsn, the size of their nuclei, and quantification of cytoplasm density) were analysed upon caterpillars’ exposure to this allelochemical. Protein band density, obtained by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) electrophoresis, from regions of bombyxin and PTTH molecular mass (Mr) were estimated. A2 nsn decreased in size, while the size of their nuclei did not change significantly. Relative cytoplasm density and relative band density from the bombyxin Mr region (Mr 4–5 kD) were decreased upon exposure to 1% and 2.5% tannic acid, while the addition of 5% tannic acid to artificial diet increased all of these parameters. Results suggested that lower concentrations of tannic acid stimulate the release of neurosecretory material from A2 nsn, most probably bombyxin-like protein. High tannic acid concentration (5%) probably allocates resources towards induction of other stress protective components instead of bombyxin-mediated metabolic stress response mechanisms. In L2` nsn, the size of nsn, nuclei and the relative cytoplasm density were increased, and relative band density from the region of big PTTH form (Mr 11–15 kD) was higher in all treatments in comparison to control. Results indicate that PTTH is synthesised and stored in the cytoplasm of L2` nsn.