Biogenic amines and aggressive behavior in the lobster cockroach Nauphoeta cinerea

In insects, biogenic amines such as dopamine (DA), octopamine (OA), and serotonin (5-HT) have been identified in a wide range of species. There are sometimes potent reciprocal relationships between biogenic amines and behavior. The lobster cockroach Nauphoeta cinerea is an insect species well known for its male intraspecific agonistic behavior and hierarchy. Therefore, we tested the relationships among aggressive behavior, hierarchy, and biogenic amines by measuring biogenic amines levels and applying drugs in this cockroach species. We use high performance liquid chromatography with electrochemical detection (HPLC-ECD) to measure changes in the levels of biogenic amines. Age is important in determining the rank of socially naïve males (SNMs). Older males (70 days after emergence) usually defeat younger males (20 days after emergence). However, all three biogenic amines of younger males in the brain are higher than older males. For SNMs, brain biogenic amines level was not differed by adopting aggressive posture or not. For 2 males interactions, octopamine levels of dominant males increased at 5-11 days, no change being observed in dopamine and serotonin. For 3 males interactions, octopamine level increased in both dominant and subordinate males, and the difference of octopamine level between dominant and subordinate males was less than that for 2 males interaction. After 10 days interaction, octopamine level of dominant males was decreased, and subordinate males began to display aggressive posture and rank switch occurred. Finally, brain microinjection of 1 ng octopamine enhanced ability to switch rank. However, octopamine had no effect on rank establishment. The results showed that the octopamine level in the brain of male N. cinerea may influence rank maintenance.