Seasonal Changes in Hypothalamic Gonadotropin-Releasing Hormone-I Immunoreactivity in Relation With Testicular Volume in Adult Male Free-Living European Starlings (Sturnus Vulgaris)
Abstract
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.
Keywords
European starling seasonal reproduction GnRH-I testes immunohistochemistryAbbrevations
- ABC
avidin-biotin complex
- FSH
follicle-stimulating hormone
- GnRH
gonadotropin-releasing hormone
- GnRH-ir
GnRH immunoreactivity
- KPBS
potassium-phosphate buffer
- L:D
light/dark hours per day
- LH
luteinizing hormone
- ME
median eminence
- POA
preoptic area
- TrSM
tractus septomesenchephalicus
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References
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