Publication: Circadian and seasonal changes of synaptic bodies in different parts of the rabbit pineal gland
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Date
1999
Authors
MartÃnez Soriano, F. ; Hernandez-Gil de Tejadal, T. ; Lopez Bigorra, M. ; Ballester Carmona, S. ; Vollrath, L.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
In the mammalian pineal gland, synaptic
bodies (SBs) are poorly understood organelles. Previous
studies in rabbits have shown that the organelles are
rather heterogeneous in shape, are few in number during
the day and increase in number at night. No studies are
currently available on seasonal changes in this species
and it is unknown whether the biological rhythms are
identical in the proximal, intermediate and distal parts of
the elongated pineal. To this end, a study was made of
84 rabbits kept under natural lighting conditions to
examine numerical variations of the different types of
SBs in the proximal, intermediate and distal regions of
pineal glands procured at different timepoints of a 24-
hour cycle and in each of the four annual seasons. In the
present study, rod-like, sphere-like, ovoid, rectangular
and triangular SB profiles were distinguished; the first
two types being the most abundant. In addition to the
well-known circadian changes, with low numbers of SB
profiles during the day and high numbers at night, we
found pronounced season-related differences as well as
differences related to pineal regions. In autumn and
winter, nighttime SR profile numbers were significantly
higher than in spring and summer. With respect to
regional differences it was found that the amplitude of
the circadian rhythm increased in a proximo-distal
direction in the gland. In autumn the strongly enhanced
nocturnal increase was restricted to the distal region of
the gland, whereas in winter it was seen in both the distal
and the intermediate regions. The regional differences
are probably related to the fact that the postganglionic
sympathetic fibres, which regulate pineal function, enter
the gland distally and proceed rostrally to the proximal
region. Taken together, the results show that day- and
nightlength are structurally coded in the pineal gland by
means of SB numbers. Provided the SBs of the
mammalian pineal gland are involved in synaptic
processes, the results suggest that synaptic processes are
enhanced at night as well as in autumn and winter.
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