Abstract
The neuropeptide PDF is released by sixteen clock neurons in Drosophila
and helps maintain circadian activity rhythms by coordinating a network
of approximately 150 neuronal clocks. Whether PDF acts directly on
elements of this neural network remains unknown. We address this
question by adapting Epac1-camps, a genetically encoded cAMP FRET
sensor, for use in the living brain. We find that a subset of the
PDF-expressing neurons respond to PDF with long-lasting cAMP increases
and confirm that such responses require the PDF receptor. In contrast,
an unrelated Drosophila neuropeptide, DH31, stimulates large cAMP
increases in all PDF-expressing clock neurons. Thus, the network
of approximately 150 clock neurons displays widespread, though not
uniform, PDF receptivity. This work introduces a sensitive means
of measuring cAMP changes in a living brain with subcellular resolution.
Specifically, it experimentally confirms the longstanding hypothesis
that PDF is a direct modulator of most neurons in the Drosophila
clock network.
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