Publication: Day-night changes in plasma melatonin levels,
synaptophysin expression and ultrastructural
properties of pinealocytes in developing female
sheep under natural long and short photoperiods
Authors
Redondo, E. ; Regodón, S. ; Franco, A. ; Masot, A.J. ; Gázquez, A. ; Cardinali, D.P.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The aim of the present study was to analyze
the 24-h rhythm in plasma melatonin concentration and
the day-night differences in synaptophysin expresion and
ultrastructural characteristics of the pinealocytes in
developing female sheep. Ewes of three different ages
were examined: infantile (1-6 months old), pubertal and
early fertile age (9-24 months old) and adult (36-60
months old). Experiments were conducted under natural
non-stimulatory (long) and stimulatory (short)
photoperiods. The obtained results were similar for both
analyzed photoperiods. Plasma melatonin concentration,
measured in samples obtained every 4 h, showed a
similar pattern in the three age groups, with peak values
at 02:00 h and troughs at 14:00 h. Mean value of plasma
melatonin levels in 9-24 month-old sheep was
significantly greater than that in younger or older sheep.
The weight of pineal glands obtained at night (02:00 h)
was significantly higher than in daylight (14:00 h).
Pubertal and early fertile sheep had the largest pineal
glands. The pineal volume, and the total number of
pinealocytes per gland of 9-24 months-old sheep differed
significantly from that of younger or older sheep. The
pineal volume, and the mean volume of pinealocytes
was significantly greater in animals killed at night.
Number of pinealocytes did not vary between animals
killed during daylight or at night. The mean volumen of
pinealocytes did not show statistical differences between
the age groups. In quantitative ultrastructural analysis of
pinealocyte cells, the relative volume of mitochondria,
rough endoplasmic reticulum and Golgi complexes was
significantly greater in 9-24 month-old sheep and in
animals killed at night. The relative volume of lipid
droplets was highest in older sheep. Collectively, the data support the existence of developmental changes in
pinealocyte morphology and quantity, partially in
coincidence with a higher melatonin secretion rate.
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