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The circadian nature of melatonin secretion in Japanese quail ( Coturnix coturnix japonica )
Author(s) -
Kumar V.,
Follett B.K.
Publication year - 1993
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1993.tb00502.x
Subject(s) - melatonin , quail , darkness , endocrinology , medicine , circadian rhythm , photoperiodism , biology , coturnix coturnix , rhythm , coturnix , zoology , botany
Plasma melatonin concentrations were measured in Japanese quail held under different photoperiods and constant darkness (<1 lux). When subjected to LD6:18 (6 hr light: 18 hr darkness), levels rose ∼2 hr after lights‐off, attained a peak level 8 hr after lights off, and subsequently declined to low daytime levels before the next lights‐on signal. This generated a distinct daily rhythm in melatonin secretion with a duration of ∼13 h. On exposing quail to a range of photoperiods, containing 6, 9, 11, 12, 13, 15, 18, or 20 hr of light per day, the onset of melatonin secretion remained essentially similar with the rise occurring soon after lights‐off. However, the offset of melatonin secretion was suppressed by the light of the next day and thus a much truncated rhythm was produced under long (> 12 hr) photoperiods. Importantly, between night lengths of 4 to 18 hr (i.e., LD 20:4 to LD 6:18) a linear relationship existed between the duration of night‐length and secretion of melatonin with the duration increasing by about 0.8 hr for each additional hour of darkness. If quail were released into darkness following a short (LD 6:18) or long (LD 20:4) day schedule, the rhythm persisted for at least two cycles with peaks occurring at about 24 hr intervals. In those quail coming into darkness from long days (LD 20:4), the rhythm of melatonin secretion decompressed rapidly on both sides of the peak, indicating that both the onset and offset of melatonin secretion were suppressed under long days. The endogenous nature of melatonin secretion was tested further by exposing birds to LD 6:30 for 4 cycles and then releasing into darkness. The rhythm in melatonin secretion persisted for at least three cycles before beginning to damp‐out. The circadian nature of the rhythm in melatonin secretion was also examined by subjecting quail to T‐cycles and then releasing into darkness. Both under the T‐cycles and darkness following T‐cycle treatments, the phase of the melatonin rhythm was advanced by > 3 hr under T = 27 hr cycles (LD 3:24) compared with T = 24 hr cycles (LD 3:21). This property is consistent with the melatonin oscillator being a circadian rhythm.