Analysis of PDF-dependent microcircuits in the circadian clock of the Madeira cockroach

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The neuropeptide pigment-dispersing factor (PDF) is an obligatory circadian coupling signal in insects which synchronizes circadian clocks distributed throughout the insect body. It shares astounding similarities in signaling on the molecular and cellular level with vasoactive intestinal polypeptide (VIP) the most important circadian coupling factor in mammals. Both, PDF and VIP signal via cAMP rises and are essential for the expression of large amplitude circadian rhythms in physiology and behavior in synchrony with external light-dark cycles. Nevertheless, our knowledge about the PDF/VIP-dependent neuronal circuits and their control via light is still limited.Our renewal proposal focuses further on cellular analysis of PDF-dependent circadian circuits in the clock of the night-active, long-lived Madeira cockroach, an established cellular model of circadian rhythm research. With intracellular and patch clamp electrophysiological analysis combined with Ca2+ imaging, multiple-label immunocytochemistry, and single-cell MALDI-TOF we examine the light input pathways to PDF neurons. Previous PDF-injections phase delayed locomotor activity rhythms during dusk and phase advanced during dawn comparably to cAMP- and light-stimuli. Furthermore, peaks in cAMP concentrations were measured in the cockroach circadian clock one at dusk and one at dawn. Thus, we propose and search for two PDF-dependent neuronal circuits in the cockroach clock locking either onto dusk or dawn to restrict locomotor activity rhythms to the night while photoperiod is changing during the course of the year.