Circadian clock components in the rat neocortex: daily dynamics, localization and regulation

Area of Science:

• Neuroscience
• Chronobiology
• Molecular Biology

Background:

• The suprachiasmatic nucleus (SCN) in the hypothalamus acts as the mammalian brain's master circadian clock.
• Peripheral clocks exist in extra-hypothalamic brain regions, but their molecular mechanisms in the cerebral cortex are not well understood.

Purpose of the Study:

• To investigate the expression and rhythmicity of core clock genes in the rat neocortex.
• To determine the SCN's influence on neocortical clock gene expression.

Main Methods:

• Quantitative real-time PCR to assess clock gene expression.
• Lesion studies targeting the SCN.
• In situ hybridization and immunohistochemistry to localize clock gene products.

Main Results:

• Core clock genes (Per1, Per2, Per3, Cry1, Cry2, Bmal1, Clock, Nr1d1, Dbp) are expressed in the rat neocortex.
• Several neocortical clock genes (Per1, Per2, Per3, Cry1, Bmal1, Nr1d1, Dbp) exhibit daily rhythms, albeit with damped amplitude and delayed peaks compared to the SCN.
• SCN lesions abolish these neocortical rhythms, indicating SCN dependence.
• Per2 protein is found in neurons throughout all neocortical areas.

Conclusions:

• The rat neocortex harbors local circadian oscillators within its neurons.
• These neocortical oscillators are driven by the SCN master clock.
• This study elucidates the molecular basis of circadian rhythmicity in the cerebral cortex.