Dark pulse suppression of P‐ERK and c‐Fos in the hamster suprachiasmatic nuclei

Jul 21, 2005The European journal of neuroscience

Dark pulses reduce activity signals in the hamster's internal clock center

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Abstract

A 6-hour dark pulse at circadian time 8 reduced levels of phosphorylated ERK and c-Fos in the Syrian hamster suprachiasmatic nuclei.

Phosphorylated ERK (P-ERK) levels showed significant circadian variation in the SCN under constant light.
Dark pulses can down-regulate the expression of P-ERK and c-Fos in the SCN, but not phosphorylated Elk-1.
After a dark pulse, c-Fos levels increased beyond time-matched control values, while P-ERK levels remained unchanged.
A dark pulse at the beginning of the subjective night did not phase-shift behavioral rhythms or alter expression of c-Fos, P-ERK, or P-Elk-1.
In the visual thalamus, c-Fos expression was higher during the subjective night compared to the subjective day, but dark pulses did not significantly affect it.

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It is well-established that light pulses regulate components of the extracellular signal-regulated kinases I/II (ERK) cascade in the suprachiasmatic nuclei (SCN) circadian clock. These events are important for photic-resetting of the circadian clock. The SCN circadian clock is also reset by pulses of dark, but it is unknown if this stimulus alters the activity of ERK, the transcription factor Elk-1 or expression of the immediate early gene c-fos in the SCN. Using Syrian hamsters free-running in constant light, we determined the effects of dark pulses on these factors in the SCN. In constant light, levels of phosphorylated ERK (P-ERK) showed significant circadian variation in the Syrian hamster SCN, while levels of c-Fos or phosphorylated Elk-1 (P-Elk-1) did not. A 6-h dark pulse beginning at circadian time (CT) 8 down-regulated expression of P-ERK and c-Fos, but not P-Elk-1, in the SCN. Following termination of the pulse, levels of c-Fos increased above time-matched control values, while P-ERK expression did not. When given at the beginning of the subjective night (CT13), a 6-h dark pulse did not phase-shift behavioural rhythms and failed to alter the expression of c-Fos, P-ERK, or P-Elk-1 in the SCN. At the level of the visual thalamus, expression of c-Fos in the intergeniculate leaflet was higher during the subjective night as compared to the subjective day, although dark pulses had no robust effects on expression of c-Fos or P-ELK-1 in this structure. We conclude that dark-pulse resetting of the circadian clock is complex and involves both non-photic and photic components.

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Dark pulse suppression of P‐ERK and c‐Fos in the hamster suprachiasmatic nuclei

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