Synaptic targets of circadian clock neurons influence core clock parameters

Area of Science:

• Neuroscience
• Chronobiology
• Insect models

Background:

• The Drosophila circadian clock network relies on neuronal connections for timekeeping.
• Small ventral lateral neurons (sLNvs) are key pacemaker neurons in Drosophila.
• While neuropeptide signaling (PDF) from sLNs is known, their synaptic targets are less understood.

Purpose of the Study:

• To investigate the role of synaptic connections from sLNs to downstream neurons.
• To characterize the function of previously uncharacterized superior lateral protocerebrum 316 (SLP316) neurons.

Main Methods:

• Connectomic analysis to identify sLNv synaptic targets.
• Genetic manipulation (tetanus toxin, sodium channel) to alter SLP316 neuronal activity.
• Behavioral assays to measure circadian period and activity patterns.

Main Results:

• Connectomics identified SLP316 neurons as major postsynaptic partners of sLNs.
• Silencing SLP316 neurons shortened the circadian free-running period.
• Hyperexciting SLP316 neurons lengthened the free-running period.
• SLP316 neuron silencing altered daytime activity and sleep under light-dark cycles.

Conclusions:

• SLP316 neurons are critical for regulating circadian period and daily rhythms in Drosophila.
• These neurons represent a non-clock neuronal type influencing sleep-activity timing.
• Synaptic output from pacemaker neurons to SLP316 neurons is crucial for robust timekeeping.