PDF receptor-expressing neurons in the ellipsoid body: a link between the locomotor and sleep circuits?

PÍREZ, NICOLÁS; GRIFFITH, LESLIE C.

Destin, Florida

Conferencia; Society for Research on Biological Rhythms Meeting; 2012

Society for Research on Biological Rhythms

The neuropeptide PDF is an important regulator of the circadian clock in insects. Other targets of this peptide have not been identified. pdfR-GAL4 drives expression in cells of the ellipsoid body (EB), a component of the central complex. This suggests that the EB may provide an important link between the clock and sleep/activity circuits. How the circadian clock and sleep deprivation might affect the activity of this group of neurons was unknown. To approach this issue, we performed whole brain optical imaging experiments using flies that express the FRET-based cAMP sensor Epac1-camps under the control of the pdfR promoter. Basal cAMP levels were insensitive to time of day and to 1 µM TTX, which blocks action potential generation and eliminates synaptic inputs to EB, but were reduced by mutation of the pdfR gene. Bath application of PDF (10 M) caused a significant change in the cAMP level of EB cells measured as the ratio of YFP/CFP which was blocked by mutation of the pdfR gene. When TTX was included in the bath, we found that the response elicited by PDF was increased in the early morning, but not affected in the middle of the night, implying the existence of a temporally-regulated, PDF-stimulated input that blocks increases in cAMP. Several other neurotransmitters were also tested. ACh was found to cause a significant increase in cAMP levels, which had both direct (TTX-insensitive) and indirect (TTX-sensitive) components during the day, but was totally TTX-insensitive at night. This implies that ACh is able to stimulate inputs to EB during the day that increases cAMP, but that these inputs are not active at night. In order to test the effect of sleep deprivation on the physiology of these cells, we performed behavioral experiments in which flies were sleep deprived for 12 h prior to imaging. The imaging session was done either immediately after the end of deprivation or following a 4 h recovery. Although the effect of sleep deprivation is clear at the behavioral level, the cAMP responses of these cells to either PDF or ACh remained similar to non-sleep deprived controls, suggesting that cyclase coupling is not modulated by sleep deprivation.