A Subset of Circadian Neurons Expressing dTRPA1 Enables Appropriate Phasing of Activity Rhythms in Drosophila melanogaster Under Warm Temperatures.

Under conditions of prolonged durations of warmth, flies counter potential temperature stress by shifting their locomotor activity from day into night when the conditions are likely to be less harsh. Modulation of a rhythmic behavior such as this in response to the environment would require interaction between at least 2 neuronal systems: (1) a sensory system to receive input from the environment, and (2) the internal clock to correctly time rhythmic activity in response to this thermosensory input. Our previous studies found that a thermosensory mutant of the ion channel Drosophila Transient Receptor Potential-A1 ( dTRPA1 ) failed to shift activity into the dark like control flies do and also identified the role of a specific cluster of the dTRPA1 -expressing neurons, the dTRPA1 sh+ neurons necessary for this. In this study, we extended our previous findings and characterized the identity of these dTRPA1 sh+ neurons based on their overlap with circadian neurons. Utilizing various genetic manipulations, we asked whether the overlapping neurons could be potential points of intersection between the 2 circuits that modulate behavior under warm temperature, meaning whether they function as both-sensory and clock neurons. We found that the molecular clock within the dTRPA1 sh+ cluster was not necessary, but the expression of dTRPA1 in a subset of circadian neurons, the small ventrolateral neurons (sLNvs), was necessary in modulating phasing of behavior under warm temperature. Furthermore, attempting to identify the neuronal circuit, we were able to uncover the potential roles of serotonin and acetylcholine in modulating this temperature-dependent behavior. Finally, we also discuss possible parallel neuronal pathways that may exist to give rise to this modulation of behavior under warm temperature, thereby supporting and expanding the knowledge of the field about circuits that control temperature-mediated behavioral outcomes.