Light-Modulated Circadian Synaptic Plasticity in the Somatosensory Cortex: Link to Locomotor Activity

Area of Science:

• Neuroscience
• Chronobiology
• Synaptic Plasticity

Background:

• The circadian clock regulates essential physiological processes, including synaptic function and neuronal activity.
• Light is a critical external cue for synchronizing the internal biological clock with the environment.
• Understanding the interplay between the circadian clock, light, and synaptic plasticity is vital for comprehending brain function.

Purpose of the Study:

• To investigate the effects of the circadian clock and light on synaptic plasticity in the mouse somatosensory cortex.
• To explore the role of locomotor activity in mediating circadian and light-induced changes in synaptic function.
• To analyze circadian and light-dependent regulation of key synaptic proteins and excitatory synapse density.

Main Methods:

• Mice were exposed to four lighting conditions: 12:12 light-dark, constant darkness, 16:8 light-dark, and constant light.
• Synaptic protein expression was analyzed using double-immunofluorescence labeling and confocal microscopy.
• Excitatory synapse density was quantified by co-labeling presynaptic and postsynaptic markers.
• Locomotor activity was monitored using individual wheel-running systems.

Main Results:

• Circadian regulation of synaptic proteins (Synaptophysin 1/PSD95, Piccolo/Homer 1, Neurexins/PICK1) was observed, modulated by light conditions.
• Constant light exposure disrupted rhythmicity for most proteins, except for Piccolo and Homer 1.
• Locomotor activity correlated with circadian changes in postsynaptic proteins and showed an inverse relationship with excitatory synapse density.
• Constant light elevated excitatory synapse density, disrupting its normal daily fluctuations.

Conclusions:

• Light and the circadian clock are critical regulators of synaptic protein expression and excitatory synapse density.
• Locomotor activity plays a significant role in modulating synaptic plasticity in response to circadian and light cues.
• Disruption of light-dark cycles, such as under constant light, alters synaptic plasticity and excitatory synapse density, highlighting the importance of environmental light cues for brain function.