Circadian mPer1 gene expression in mesencephalic trigeminal nucleus cultures

May 13, 2008Brain research

Daily patterns of mPer1 gene activity in nerve cell cultures from the midbrain facial nerve area

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Abstract

Elevated transgene expression was discovered throughout the mesencephalic trigeminal nucleus (Me5) of the brain stem.

The circadian timing system includes the suprachiasmatic nucleus (SCN) and other less characterized pacemakers in the body.
Circadian rhythms in the Me5 correspond with the dark portion of the light cycle.
Large sensory neurons in the Me5 receive signals from periodontal ligaments and muscle spindles.
The Me5 may play a role in regulating daily feeding behavior due to its interactions with other brain regions.
This discovery of a circadian pacemaker in the Me5 could facilitate single-cell analyses of circadian gene expression.

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The circadian timing system includes the major circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus and less well characterized circadian pacemakers in the brain and peripheral tissues throughout the body. The coupling between these discrete circadian clocks is not well understood, although individual neurons of the SCN are considered competent circadian pacemakers that interact to produce rhythms in the SCN and in its afferents. Because the SCN is a complex assemblage of small neurons of several phenotypes, we sought a simpler circadian brain nucleus with larger neurons that might provide insight into circadian timing not easily obtained from the SCN. Using bioluminescence imaging of brain tissue explants from transgenic mice containing the firefly luciferase gene luc controlled by the mPer1 promoter, we discovered elevated transgene expression throughout the mesencephalic trigeminal nucleus (Me5) of the brain stem. Large sensory neurons of the Me5 receive proprioceptive signals from periodontal ligaments and masseter muscle spindles. The Me5 cells displayed circadian rhythms with elevated expression in culture corresponding with the dark portion of the prior light cycle. Because of known interactions between the Me5 and the tuberomammillary nucleus and because of the role of both nuclei in satiety, it is possible that a circadian clock in the Me5 serves in regulating daily feeding behavior. This newly identified circadian pacemaker in the Me5 may prove useful for single-cell analyses of circadian gene expression in clock cells and for comparison with the SCN.

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Circadian mPer1 gene expression in mesencephalic trigeminal nucleus cultures

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