Abstract
The embryonic ontogeny of pineal secretory activity in birds has been investigated almost exclusively in chickens. This study aimed to characterize this process in domestic geese. The pineal organs of embryos aged 18–28 days were incubated in superfusion culture under different light conditions for 4–5 days and treated with norepinephrine (NE). Melatonin (MLT) was measured by radioimmunoassay and other indoles by HPLC with fluorescence detection. Additionally, pineal organs were collected from embryos at 14–28 days of age and used to measure catecholamines by HPLC with electrochemical detection. MLT secretion increased with embryo age, most intensively between the 22nd and 24th days of life. The daily changes in MLT secretion under the 12 L:12D cycle occurred on the first day of culture, starting from an embryonic age of 24 days. MLT secretion was controlled by the light-dark cycle in all age groups studied. However, exposure to light during the scotophase did not alter the secretion of MLT. The endogenous oscillator expressed its activity in regulating MLT secretion in the pineal organs of embryos aged 24 days and older but could not generate a rhythm after one cycle. The rhythm of 5-hydroxytryptophan release during the first day of culture was found in the pineal organs of all embryos, while the rhythmic release of N-acetylserotonin and 5-methoxyindole acetic acid started at the age of 24 days. The proportion of released indoles changed with embryo age. NE caused a decrease in MLT secretion and provoked an increase in serotonin release. Incubation of the pineal organs induced the development of MLT secretory machinery and its diurnal rhythmicity. The pineal content of catecholamines increased prominently at the end of embryonic development.
Highlights
The embryonic development of pineal secretory activity in birds has been investigated almost exclusively in chickens [1,2,3,4,5,6,7,8,9,10]
Our results showed that the secretory activity of the embryonic pineal organs changed significantly during the course of superfusion culture performed under the 12 L:12D cycle
It could be concluded that the isolation of the embryonic pineal organs from their niche induced the development of the MLT secretory machinery and its daily rhythmicity
Summary
The embryonic development of pineal secretory activity in birds has been investigated almost exclusively in chickens [1,2,3,4,5,6,7,8,9,10]. In our previous study [11], the contents of 5-hydroxyindoles and 5-methoxyindoles were measured in the pineal organs of goose embryos aged 14–28 days (ED 14–ED 28). The domestic goose was chosen as the object of the study largely because of the characteristic metabolic profile of indoles with a high 5-HT level [12], opposite to that in the chicken [13], but it seems to be much more common in birds [14,15]. The pineal contents of 5-HT, 5-hydroxytryptophan (5-HTRP), and 5-hydroxyindole acetic acid (5-HIAA) show daily variations from ED 14, when eggs are incubated under a 12L:12D cycle. Melatonin (MLT) and 5-methoxyindole acetic acid (5-MIAA) are detectable in the pineal organs from ED 18 and show significant daily variations in their contents from ED 20
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