@phdthesis{KayaZeeb2023,
  author    = {Kaya-Zeeb, Sinan David},
  title     = {Octopaminergic Signaling in the Honeybee Flight Muscles : A Requirement for Thermogenesis},
  doi       = {10.25972/OPUS-31408},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-314089},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {For all animals the cold represents a dreadful danger. In the event of severe heat loss, animals fall into a chill coma. If this state persists, it is inevitably followed by death. In poikilotherms (e.g. insects), the optimal temperature range is narrow compared to homeotherms (e.g. mammals), resulting in a critical core temperature being reached more quickly. As a consequence, poikilotherms either had to develop survival strategies, migrate or die. Unlike the majority of insects, the Western honeybee (Apis mellifera) is able to organize itself into a superorganism. In this process, worker bees warm and cool the colony by coordinated use of their flight muscles. This enables precise control of the core temperature in the hive, analogous to the core body temperature in homeothermic animals. However, to survive the harsh temperatures in the northern hemisphere, the thermogenic mechanism of honeybees must be in constant readiness. This mechanism is called shivering thermogenesis, in which honeybees generate heat using their flight muscles. My thesis presents the molecular and neurochemical background underlying shivering thermogenesis in worker honeybees. In this context, I investigated biogenic amine signaling. I found that the depletion of vesicular monoamines impairs thermogenesis, resulting in a decrease in thoracic temperature. Subsequent investigations involving various biogenic amines showed that octopamine can reverse this effect. This clearly indicates the involvement of the octopaminergic system. Proceeding from these results, the next step was to elucidate the honeybee thoracic octopaminergic system. This required a multidisciplinary approach to ultimately provide profound insights into the function and action of octopamine at the flight muscles. This led to the identification of octopaminergic flight muscle controlling neurons, which presumably transport octopamine to the flight muscle release sites. These neurons most likely innervate octopamine β receptors and their activation may stimulate intracellular glycolytic pathways, which ensure sufficient energy supply to the muscles. Next, I examined the response of the thoracic octopaminergic system to cold stress conditions. I found that the thoracic octopaminergic system tends towards an equilibrium, even though the initial stress response leads to fluctuations of octopamine signaling. My results indicate the importance of the neuro-muscular octopaminergic system and thus the need for its robustness. Moreover, cold sensitivity was observed for the expression of one transcript of the octopamine receptor gene AmOARβ2. Furthermore, I found that honeybees without colony context show a physiological disruption within the octopaminergic system. This disruption has profound effects on the honeybees protection against the cold. I could show how important the neuro-muscular octopaminergic system is for thermogenesis in honeybees. In this context, the previously unknown neurochemical modulation of the honeybee thorax has now been revealed. I also provide a broad basis to conduct further experiments regarding honeybee thermogenesis and muscle physiology.},
  subject      = {Octopamin},
  language  = {en}
}