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Issue 7, 2018
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Photoperiodic control of GnRH-I expression in seasonal reproduction of the Eurasian tree sparrow

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Abstract

Day length has been shown to be a major source of temporal information regulating seasonal reproduction in the Eurasian tree sparrow (Passer montanus). The present study aims to investigate the photoperiodic expression of gonadotropin-releasing hormone-I (GnRH-I), and how it mediates seasonal reproduction in male tree sparrows. In different experiments, we studied photoperiod-induced changes in GnRH-I expressing neurons in the hypothalamic preoptic area (POA), together with changes in testicular size under both natural and artificial photoperiodic conditions. Experiment 1, which involved studying changes in GnRH-I expression and testicular volume during different phases of the annual reproductive cycle under natural day length (NDL), revealed that sparrows possess a definite seasonal cycle of GnRH-I peptide expression that runs parallel to testicular size. Birds showed significantly higher levels of GnRH-I expression in the breeding phase when compared to the non-breeding phase. In experiment 2, photosensitive birds were exposed to artificial short (SD: 9L/15D) and long (LD: 14L/10D) day lengths for 240 days to investigate the photoperiodic regulation of GnRH-I expression. They exhibited a significant increase followed by a decrease in GnRH-I expression and testicular size under LD but not SD, suggesting photoperiodic regulation. In experiment 3, when photosensitive birds were exposed to increasing photoperiods (9L/15D, 10L/14D, 10.5L/13.5D, 11L/13D, 12L/12D) for 30 days to find out the critical photoperiod for GnRH-I expression, they responded only when the daily photoperiod was 11 h or more. These results clearly indicate that tree sparrows are capable of fine discrimination of photoperiodic information and use day length for GnRH-I expression to control their seasonal reproduction.

Graphical abstract: Photoperiodic control of GnRH-I expression in seasonal reproduction of the Eurasian tree sparrow

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Publication details

The article was received on 10 Apr 2018, accepted on 23 May 2018 and first published on 18 Jun 2018


Article type: Paper
DOI: 10.1039/C8PP00153G
Citation: Photochem. Photobiol. Sci., 2018,17, 934-945
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    Photoperiodic control of GnRH-I expression in seasonal reproduction of the Eurasian tree sparrow

    A. S. Dixit and S. Byrsat, Photochem. Photobiol. Sci., 2018, 17, 934
    DOI: 10.1039/C8PP00153G

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