Seasonal Changes in Hypothalamic Gonadotropin-Releasing Hormone-I Immunoreactivity in Relation With Testicular Volume in Adult Male Free-Living European Starlings (Sturnus Vulgaris)


Birds from the temperate and cold zones show annual sexual activity accompanied by gonadal changes and fuctuation in their brain gonadotropin-releasing hormone (GnRH) levels. However, most of the studies were done on captive birds where the constant environment can profoundly modify periodical changes. Therefore our aim was to reveal annual variations of hypothalamic and gonadal changes in male, free-living European starlings (Sturnus vulgaris) captured directly from their natural environment. We analyzed hypothalamic GnRH-I immunoreactivity and testes volume. Four key time points of the active reproductive cycle and the photorefractory phase were studied. GnRH-I immunoreactivity was analyzed in the preoptic area (POA) and the median eminence (ME). Photorefractory birds (August) with regressed gonads had the lowest level of GnRH-I immunoreactivity compared to other birds from the active reproductive phases. These results suggest that parallel with the gonadal volume GnRH-I undergoes seasonal changes in adult male free-living European starlings.



avidin-biotin complex


follicle-stimulating hormone


gonadotropin-releasing hormone


GnRH immunoreactivity


potassium-phosphate buffer


light/dark hours per day


luteinizing hormone


median eminence


preoptic area


tractus septomesenchephalicus


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Pintér, O., Péczel, P. Seasonal Changes in Hypothalamic Gonadotropin-Releasing Hormone-I Immunoreactivity in Relation With Testicular Volume in Adult Male Free-Living European Starlings (Sturnus Vulgaris). BIOLOGIA FUTURA 61, 237–249 (2010).

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  • European starling
  • seasonal reproduction
  • GnRH-I
  • testes
  • immunohistochemistry