Circadian Structural Plasticity Drives Remodeling of E Cell Output

Area of Science:

• Neuroscience
• Chronobiology
• Animal Behavior

Background:

• The Drosophila circadian network, comprising 150 neurons, regulates daily locomotor activity patterns.
• Small ventral lateral neurons (sLNv) expressing pigment-dispersing factor (PDF) are known as
• M cells
• linked to morning activity.
• Dorsal lateral neurons (LNds) and PDF-negative sLNv, termed
• E cells
• , are crucial for evening activity peaks.

Purpose of the Study:

• To investigate the synaptic connections between evening (E) and morning (M) clock neurons in the Drosophila circadian network.
• To determine if E-to-M cell connectivity is dynamic and changes across the day.
• To identify the neurotransmitters involved in E-to-M cell communication and their role in circadian output.

Main Methods:

• Utilized both structural and functional approaches to analyze neuronal connectivity.
• Investigated changes in E-to-M cell synaptic input throughout the daily cycle.
• Identified neurotransmitters released by E cells and assessed the responsiveness of M cells.

Main Results:

• Demonstrated the existence of synaptic input from E cells onto M cells.
• Revealed that E-to-M cell connectivity is plastic and changes diurnally, with increased excitatory input before dusk.
• Identified acetylcholine as the neurotransmitter responsible for excitatory E-to-M cell input, with M cells showing heightened responsiveness to acetylcholine in the evening.

Conclusions:

• Established evidence for an excitatory feedback loop between circadian neuron clusters in Drosophila.
• Uncovered significant daily remodeling of synaptic connections within the E cells, highlighting neural plasticity in circadian regulation.
• Revealed the specific roles of acetylcholine and glutamate in mediating circadian rhythmicity and robust behavioral output.