Temporal expression of genes coding for aryl-alkamine-N-acetyltransferase and melatonin receptors in circadian clock tissues: Circadian rhythm dependent role of melatonin in seasonal responses

Publication date: Available online 10 May 2019Source: Physiology & BehaviorAuthor(s): Amit Kumar Trivedi, Ila Mishra, Vinod KumarAbstractWe investigated at the transcriptional level the role of daily rhythm in melatonin secretion in seasonal responses in the migratory blackheaded bunting (Emberiza melanocephala), which when exposed to short (SP) and long (LP) photoperiods exhibits distinct seasonal life-history states (LHSs). We reproduced the seasonal LHS by subjecting buntings to SP (8 h light: 16 h darkness, 8 L:16D), which maintained the nonmigratory/ nonbreeding phenotype, and to LP (16 L:8D), which induced the premigratory/ prebreeding, migratory/ breeding and nonmigratory/ postbreeding phenotypes. Plasma melatonin measured at 4 h intervals showed loss of the daily rhythm in the LP-induced premigratory/ prebreeding and migratory/ breeding LHSs. Subsequently, mRNA expression of genes coding for the aryl-alkamine-N-acetyltransferase (AANAT; the rate-liming enzyme of melatonin biosynthesis) and for the receptors for melatonin (Mel1A, Mel1B and Mel1C) was examined in the retina, pineal and hypothalamus; the interacting independent circadian clocks comprising the songbird circadian timing system. Except AANAT that was not amplified in the hypothalamus, we found significant alterations in both, the level and persistence of 24 h rhythm in mRNA expression of all genes, albeit with photoperiod and seasonal differences between three circadian clock tissues. Particular...
Source: Physiology and Behavior - Category: Physiology Source Type: research