Connexin and AMPA receptor expression changes over time in the rat olfactory bulb

Area of Science:

• Neuroscience
• Chronobiology
• Olfactory System Research

Background:

• Circadian rhythms influence olfaction through poorly understood molecular pathways.
• The mammalian olfactory bulb (OB) functions as an intrinsic circadian oscillator, independent of the suprachiasmatic nucleus.
• Electrical activity in the OB exhibits daily rhythmicity, with clock gene Period1 showing oscillatory expression.

Purpose of the Study:

• To investigate the molecular mechanisms synchronizing circadian electrical oscillations in the OB.
• To test the hypothesis that daily fluctuations in connexins and AMPA receptor (AMPAR) subunits synchronize OB electrical activity.
• To identify specific synaptic proteins involved in the circadian regulation of olfactory processing.

Main Methods:

• Utilized polymerase chain reaction (PCR) to detect clock genes in the OB.
• Employed quantitative PCR and SDS-PAGE/Western blot analysis to assess fluctuations in Period2, connexins, and AMPAR subunits across light/dark cycles.
• Analyzed messenger RNA (mRNA) and protein expression levels over 24-48 hour periods.

Main Results:

• Observed significant daily variations in the mRNA and protein expression of target clock genes, connexins, and AMPAR subunits.
• Identified rhythmic expression patterns for most targets across different measurement scales.
• Found that GluR1 mRNA and protein exhibited the most consistent rhythmic expression across all tested time scales and methods.

Conclusions:

• Differential expression of synaptic proteins, particularly GluR1, across the light/dark cycle likely underlies the circadian synchronization of action potential firing in the OB.
• These rhythmic changes in synaptic proteins may modulate synaptic interactions, affecting olfactory coding.
• Potential impacts include altered granule cell inhibition and modified glutamate binding/gap junction conductance in the OB.