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OJVRTM
Online Journal
of Veterinary Research©
Volume 25(2): 143-153, 2021.
Effect
of 23 hour light-dark cycles on pineal structure and serum melatonin
in young and adult rabbits (Oryctolagus cuniculus).
Ahmed
Ali Amer, Bahaa Fakhri Hussein
College of Veterinary Medicine, University of Baghdad, Iraq.
ABSTRACT
Amer AA, Hussein BF., Effect of 23 hour light-dark cycles on pineal
structure and serum melatonin in young and adult rabbits, Onl
J Vet Res., 25(2):
143-153, 2021. We describe effect of light-dark cycles on pineal histology and serum melatonin
at different ages in rabbits. Three groups of 5 rabbit pups, weaners and adults
each were exposed to 24h light, 23h dark/1h light and 12h light/12h dark
(controls) cycles for 14, 30 or 180 days. Compared with controls, light increased
(P < 0.05) melatonin ~40-52% in 14 and 30 day old rabbits but did not affect
melatonin in those kept dark at 14 days. In adults we found no difference
between controls and 24h light exposures but did note 42% higher levels in
rabbits kept dark. In 30 day weaners, however, melatonin was ~30% higher in
those kept dark compared with light exposure (P < 0.05). In pups darkness was
associated with ~0.19mm invagination of mesenchymal tissue from roof of
diencephalon pineal gland whereas in those kept in 24h light reached 0.25 mm.
We observed increased pineal mitotic activity in animals exposed to light. In
30 day old rabbits pineal length reached 3mm in darkness and 2.81mm in light
exposure. In adults we measured 7.15 mm in those kept in the dark, 5.40 mm in
light, and controls 6.10 mm.
KEY WORDS: Rabbit light/dark
cycles, melatonin, histology. pineal gland.
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