Neurobiology and Genetics

FO 207/16-1

FO 207/16-1: Characterisation of the dorsal clock neurons in the circadian system of Drosophila: the neuronal circuits for multi-modal integration.

The circadian clock enables animals to be prepared in advance for the regular changes between day and night. Furthermore, some animals use their circadian clock for the memory of time, the measurement of day length (to anticipate seasonal changes) and for time-compensated sky compass orientation. The circadian clock network in the brain of the fruit fly belongs to the best-investigated. It consists of interconnected lateral and dorsal clock neurons, which generate circadian molecular oscillations and mediate these to downstream interneurons and neurosecretory centres in the dorsal protocerebrum. During the last years the fruit fly became a model in
sleep research; the first connections from the circadian clock to metabolism have been established, it was demonstrated that fruit flies have a time memory and that the clock is involved in diapause induction. Even the first hints exist that fruit flies are able to perform time-compensated sky compass orientation. The dorsal clock neurons appear to be involved in all these clock functions. While the lateral neurons represent “master oscillators”, the dorsal neurons are multimodal integrators that are essential for transferring the circadian rhythms to downstream interneurons and neurosecretory cells. Nevertheless, recent studies are controversial concerning the exact role of the dorsal neurons. Some authors claim that a special group of dorsal neurons (the DN1p) is responsible for sleep, whereas others postulate a role of the same neurons in arousal and elevated metabolism. The reason for these contradicting views lies most probably in the diverse neuronal projections of individual DN1p neurons. We could show that the dorsal neurons represent extremely heterogeneous groups of cells, but that their neuronal projections are still insufficiently characterized.