Abstract
This study determined the effect of norepinephrine and light exposure on melatonin secretion in goose pineal explants. Additionally, it investigated changes in the content of norepinephrine, dopamine, and their metabolites [3,4-dihydroxyphenylacetic acid; vanillylmandelic acid (VMA); homovanillic acid] in goose pineal glands in vivo under 12 h of light and 12 h of darkness (LD), a reversed cycle (DL), constant light (LL), and constant darkness (DD). In vitro content of melatonin was measured by radioimmunoassay; contents of catecholamines and their metabolites were measured by high-performance liquid chromatography. Exposure of pineal explants to LD or DL established rhythmic melatonin secretion; this rhythm was much better entrained with norepinephrine exposure during photophase than without it. When the explants were kept in LL or DD, the rhythm was abolished, unless NE was administered during natural scotophase of a daily cycle. In vivo, norepinephrine and dopamine levels did not display rhythmic changes, but their respective metabolites, HMV and VMA, displayed well-entrained diurnal rhythms. These results indicate that norepinephrine and sympathetic innervation play key roles in regulation of pineal secretory activity in geese, and that pineal levels of VMA and HMV provide precise information about the activity of sympathetic nerve fibers in goose pineal glands.
Highlights
The pineal gland produces melatonin (MLT), which regulates many physiological processes cued by the environmental light-dark cycle
The profiles of MLT secretion were irregular: secretion from individual explants varied substantially from day to day, and there was substantial variation between explants (Supplementary Figures 1, 2A). These results indicate that alternating light and dark phases might not be enough to establish a wellentrained rhythm of MLT secretion by goose pineal glands
The question arises as to whether the goose pineal gland is photosensitive or whether day/night differences reflect the activity of an endogenous oscillator
Summary
The pineal gland produces melatonin (MLT), which regulates many physiological processes cued by the environmental light-dark cycle. Most studies on mechanisms regulating MLT secretion have been performed with chickens (Robertson and Takahashi, 1988a,b, Nakahara et al, 1997; Csernus et al, 1998, 1999; Zawilska et al, 2000; Turkowska et al, 2014). In this species, environmental light entrains a diurnal rhythm of MLT secretion in both in vivo and in vitro conditions; light acts as both a synchronizing factor in MLT production and an inhibitor of its production
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