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

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.

Hypothalamic expression of GnRH-I and GnIH in the Eurasian tree sparrow over a single long day

“…4). The above observations support our earlier findings wherein the tree sparrows exposed to long (14L: 10 D) and short (9L: 15D) day lengths for 8 months and to the resonance light dark cycles exhibited an anti-phasic pattern of expression of GnRH-I and GnIH genes [19,31]. Similar observations were also reported in the Japanese quail that shows opposite pattern for hypothalamic expression of GnRH-I and GnIH.…”

“…However, the specificity of the immunoreactions was tested through control procedures that involved the removal of the primary antisera from the reaction and also its replacement by buffer or BSA. There was total loss of immunoreactivity in both the above procedures [15,19,31].…”

“…The detailed nature of above antibody is described in Urbanski et al [41] and Urbanski [42]. The specificity of both the above antibodies has already been tested in our earlier studies on tree sparrow [15,19,31]. However, the specificity of the immunoreactions was tested through control procedures that involved the removal of the primary antisera from the reaction and also its replacement by buffer or BSA.…”

“…A minimum of 6-week exposure of sparrows to short day lengths terminates photorefractoriness [2,9,30]. Recent studies in our laboratory have revealed photoperiodic expression of hypothalamic neuropeptides, i.e., GnRH-I and GnIH in control of reproduction in the tree sparrows [15,19,31].…”

Bright artificial light at night is associated with increased body mass, poor reproductive success and compromised disease tolerance in Australian budgerigars (Melopsittacus undulatus)

“…Like all mammals, many avian species use the natural photoperiod to predict environmental changes and to regulate various adaptive physiological and behavioral functions, such as reproduction, growth, energy intake, metabolism, immunity and migration (Wang et al 2016;Schultz et al 2017;Dixit & Byrsat 2018;Robart et al 2018). The effects of ALAN on variant physiological, behavioral and ecological functions in birds have been reviewed (Navara & Nelson 2007).…”