Circadian rhythms in olfactory responses of Drosophila melanogaster

The core mechanism of circadian timekeeping in arthropods and vertebrates c onsists of feedback loops involving several clock genes, including period ( per) and timeless (tim)(1,2). In the fruitfly Drosophila, circadian oscilla tions in per expression occur in chemosensory cells of the antennae, even w hen the antennae are excised and maintained in isolated organ culture(3). H ere we demonstrate a robust circadian rhythm in Drosophila in electrophysio logical responses to two classes of olfactory stimuli. These rhythms are ob served in wild-type flies during light-dark cycles and in constant darkness , but are abolished in per or tim null-mutant flies (per(01) and tim(01)) w hich lack rhythms in adult emergence and locomotor behaviour. Olfactory rhy thms are also abolished in the per 7.2:2 transgenic line in which per expre ssion is restricted to the lateral neurons of the optic lobe(4). Because pe r 7.2:2 flies do not express per in peripheral oscillators, our results pro vide evidence that peripheral circadian oscillators are necessary for circa dian rhythms in olfactory responses. As olfaction is essential for food acq uisition, social interactions and predator avoidance in many animals, circa dian regulation of olfactory systems could have profound effects on the beh aviour of organisms that rely on this sensory modality.