Pigment-dispersing factor (PDF) has different effects on Drosophila's circadian clocks in the accessory medulla and in the dorsal brain

The neuropeptide pigment-dispersing factor (PDF) is a key transmitter in the circadian clock of Drosophila melanogaster. Here we studied the rhythmic behaviour of neural mutants with modified arborizations of the large PDF neurons. In sine oculis(1) (so(1)) mutants we found a higher density of PDF fibbers in the fly's pacemaker center, the accessory medulla. These flies exhibited a significantly longer period (24.6) than control flies. When PDF levels were elevated to very high levels in the dorsal brain as true for so(mda) mutants and small optic lobes;so(1) double mutants (sol(1);so(1)), a short-period component split off the long period in behavioral rhythmicity. The short period became shorter the higher the amount of PDF in this brain region and reached a value of similar to 21h. The period alterations were clearly dependent on PDF, because so(1);Pdf(01) and so(mda);Pdf(01) double mutants showed a single free-running component with a period similar to Pdf(0). mutants (similar to 22.5h) and significantly longer than the short period of so(mda) mutants. These observations indicate that PDF feeds back on the clock neurons and changes their period. Obviously, PDF lengthens the period of some clock neurons and shortens that of others.