Regulation of melatonin-sensitivity and firing-rate rhythms of hamster suprachiasmatic nucleus neurons: constant light effects

Guang Di Yu, Benjamin Rusak, Hugh D. Piggins

    Research output: Contribution to journalArticlepeer-review


    Rhythms of spontaneous firing rate and of responsiveness to pressure ejection of melatonin were recorded from neurons in the Syrian hamster suprachiasmatic nuclei (SCN) in a slice preparation. In animals taken from light-dark cycles (LD 14:10), SCN cells had high firing rates during the projected day and lower rates during the projected night. The proportion of melatonin-suppressed cells (35% overall) was also high during the day and fell during the night, while melatonin activated ∼23% of cells at all phases. To assess the source of the melatonin-responsiveness rhythm, hamsters were exposed for ∼48 h to constant illumination (LL) to suppress melatonin secretion. LL exposure before slice preparation altered both firing-rate and melatonin-responsiveness rhythms. Firing rates failed to show a morning peak and remained at low levels, with no indication of daily rhythmicity. Melatonin responsiveness also failed to show the usual rhythm and even tended to rise at night. Overall melatonin responsiveness rose after LL exposure so that 50% of cells were suppressed and 21% activated. LL exposure also increased the proportions of cells which showed regular baseline firing rates. Control studies indicated that pressure artifacts did not account for either suppression or activation by melatonin, while the composition of the saline vehicle appeared to be responsible for the activations recorded. The results indicate that brief LL exposure alters SCN sensitivity to melatonin and SCN rhythmicity in Syrian hamsters, perhaps as a result of the loss of the daily melatonin secretion rhythm. Physiological melatonin patterns may have important effects on the rodent circadian pacemaker. © 1993.
    Original languageEnglish
    Pages (from-to)191-199
    Number of pages8
    JournalBrain research
    Issue number2
    Publication statusPublished - 5 Feb 1993


    • Circadian rhythm
    • Constant light
    • Light-dark cycle
    • Melatonin
    • Neurophysiology
    • Pineal gland
    • Suprachiasmatic nucleus


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