Abstract: Physiological reactions to a suddenly changing environment or responses to attacking by predators would be beneficial to the animals; otherwise it could lose the battle with the critical conditions or could even be eaten by its predators. Stress physiology has been intensively investigated in vertebrates. As a result, we already have several knowledge windows to see how chemicals affect the human brain. However, we almost know nothing about the stress physiology of insects, the most successfully evolved group of animal on earth. How is their tiny brain affected by chemicals of which the synthesis or release is induced by an outside critical condition, e.g. when a predator is approaching, is a challenging field to study. Insects can serve as very good experimental animal model systems for both behavioral and physiological studies, and many basic physiological systems are very well conserved in evolution. Hence, our experiments will not only contribute to a better insight in stress physiology of insects themselves, but they are likely to provide important information for other fields, such as neuroethology and evolution.
During our previous and ongoing behavioral study on honeybee workers, we found that the worker bees postponed their return to experimental food sources by more than 30 minutes if they had been anesthetized before by chilling or CO2, as compared to their normal returning that was less than 3 minutes. Without anesthetizing the worker bees, stress induced by vertical spinning also delays the workers’ returning behavior. The stressed bees did not directly go towards their hive but they seemed to loose their way to the hive. Such stressed bees also delayed their return to the feeders. Previous studies on bee memory had shown that the established pathway between bee workers’ hive and food sources is stored as a function of long-term memory. Our behavioral results suggest that the stressed bees could not find the way to their hive and back to the feeders again because they suffered from some temporal dysfunction in their long-term memory.
Further investigations with HPLC to analyze the content of octopamine, the so-called stress hormone of insects, and other biogenic amines such as dopamine and serotonin, which are considered to be stress-related neurohormones in the vertebrate brain, did reveal significant changes in the stressed bee brains. However, some as yet unknown biogenic amines and peptides (or proteins) were induced dramatically in the brains by the stress treatments. What are the stress-induced compounds, and what do they do in a stressed bee brain? Do these novel compounds play similar roles as some peptides found in a stressed human brain do? Is temporally losing memory induced by stress causally related to the appearance and action of stress-induced compounds in the brain? These are the questions for which we would like to provide answers in this proposed project.