Hormonal control of neurons in the male zebra finch

Susanne Seltmann, Andries ter Maat, Lisa Trost

Melatonin is a key hormone in the regulation of circadian rhythms of vertebrates, including songbirds. Understanding diurnal melatonin fluctuations, and being able to reverse or simulate natural melatonin levels, is critical to investigating the influence of melatonin on various behaviors, such as singing in birds. Confirming that ‘lights off’ initiates melatonin production at night in a natural situation, we found that melatonin levels in zebra finches return to daytime levels as early as 30 min before ‘lights on’, suggesting that the presence of light in the morning is not essential for cessation of melatonin production in zebra finches. Thus, the duration of melatonin production seems not to be specified by the length of the night. Additionally, we show that natural melatonin levels in zebra finches can be successfully simulated through the application of melatonin containing skin-cream. Moreover, natural melatonin levels and their fluctuation on the transition from day to night can be imitated, enabling the decoupling of melatonin effects from neuronal activity, sleep and circadian rhythmicity (Seltmann et al., 2016).