Principles of synaptic encoding of brainstem circadian rhythms

Area of Science:

• Neuroscience
• Autonomic Nervous System Regulation
• Circadian Biology

Background:

• Physiological processes are synchronized with the daily light cycle via circadian regulation of autonomic tone and reflex pathways.
• The brainstem, particularly the nucleus of the solitary tract (NTS), is crucial for rhythmic control of the autonomic nervous system.
• Understanding the mechanisms of circadian control over autonomic neurocircuitry is an emerging area of research.

Purpose of the Study:

• To review the neurophysiological principles governing synaptic transmission in the NTS.
• To explore how circadian rhythms impact NTS synaptic transmission throughout the day.
• To highlight the role of the NTS in integrating circadian cues and non-photic entraining stimuli.

Main Methods:

• Review of existing literature on circadian rhythms and brainstem neurophysiology.
• Analysis of transcriptional, synaptic, and circuit-level changes in the NTS.
• Focus on pre- and postsynaptic mechanisms influencing synaptic efficacy.

Main Results:

• Rhythmic clock gene expression and action potential firing in vagal afferent neurons and the NTS.
• Demonstrated rhythmic spontaneous glutamate release in the NTS.
• Observed daily variations in postsynaptic conductances affecting synaptic efficacy.

Conclusions:

• Coordinated pre- and postsynaptic changes in the NTS provide nuanced control of synaptic transmission across the day.
• Circadian rhythms tune the sensitivity of primary afferent input and govern reflex output.
• The brainstem NTS may be an underappreciated center for mediating circadian effects, including those from non-photic cues.