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Striated muscle in the mammalian pineal organ.

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STRIATED MUSCLE I N THE MAMMALIAN
PINEAL ORGAN
W. B. QUAY
Department of Zoology, University of California, Berkeley
FIVE FIGURES
INTRODUCTION
Fibers of striated muscle were found in bovine pineals first
by Nicolas ('00) and then by Dimitrova ('01)' Calvet ( '34)
and Godina ( '39). I n human pineals such fibers have been
reported by Pappenheimer ( '10) and del Vecchio ( '34). All
of the reported occurrences pertain to bovine o r human material and the significance of these has remained obscure.
Recent investigators have apparently not observed striated
muscle in the pineal, perhaps due to the small size of the
series of specimens studied microscopically. A detailed review
of this subject has been provided by Bargmann ('43).
The purposes of this report are to record the occurrence
and microscopic organization of striated muscle fibers in the
rodent pineal organ and to discuss the significance of such
muscle within the mammalian pineal.
MATERIALS AND METHODS
Striated muscle fibers were discovered in the pineals of
three rats out of a series of about 1200 used in studies of
pineal phospholipid and blood content. Two of the animals
were normal adult males (242, 558 gm body weight) of the
Department of Psychology's mixed strains and one was a
three-month-old Long-Evans female (300 gm) ovariectomized
This investigation was supported by grants from the National Science Foundation (G-2910 and G-4036) and the National Institutes of Health, Public Health
Service (RG-5219).
57
58
TV.
B. QUAY
at one month of age. All pineals were prepared according to
Baker's ( '46) acid hematein procedure. Numerous frozen
sections, 10 p in thickness, were used from each pineal, but
serial sections were not saved.
RESULTS
The striated muscle fibers in the pineals are most readily
detected by their stained cross-banding with acid hematein
(plate 1)or with iron hematoxylin, frequently used by earlier
investigators. The fibers are usually 4 to 6 in diameter,
ranging up t o 12. The length of the fibers is difficult to determine due to oblique sectioning, but in one case a length of
over 95 p can be observed. Some of the fibers are isolated,
but the majority are arranged in small bundles containing
from several t o probably over 30 fibers. The nuclei of these
fibers usually appear to be peripheral. Their number and
exact distribution per fiber, however, remains obscure. While
myelinated n ~ r v efibers are frequently seen in the peripheral
zone of the pineals, juxtaposition or termination with respect
to muscle fibers is not observed. The isolated fibers are frequently found closely associated with or embedded in the
pineal parenchyma with minimal connective tissue investment
(figs. 4 and 5), while the larger bundles are covered by a
layer of connective tissue at least several microns in thickness. Association with, or parallel coursing with respect to,
pineal vessels is not seen. Although muscle fibers are frequently found deep within the pineal, to a distance of 90 p
from the capsule, they are not found in the central area
o r medulla nor in the distal mid-ventral area. I n all
specimens roported here, the muscle fibers are found in the
more dorsal and basal areas of the pineal, the area lying
closest to thp straight sinus distally and the great cerehral
r-pin (vein of Galcn) basally. These vascular relations of the
rat pineal have been diagrammed by Greene ('35) and Gardncr ( '53). The muscle fibers have two typical courses, both
more or less parallel to the pineal's surface, and both either
iinder or t o one side of the medial dorsal furrow formed by
PINEAL STRIATED MUSCLE
59
the above venous channels. Some fibers run roughly transversely beneath the dorsal furrow. The majority radiate out
from the basal area near the pineal stalk into the pineal
tissue on both sides and ventro-lateral to the dorsal furrow.
Contraction of these muscles would probably compress adjacent areas of pineal parenchyma and possibly the venous
channels lying more dorsally.
While the structural pattern of the fibers is generally the
same in the three specimens the number of fibers is quite
different. I n one, only three fibers are seen and these appear
in but one of the 15 available sections (figs. 2, 4 and 5). I n
each of the other two pineals, estimates of the total content
of muscle fibers is 60
and 40
and fibers appear respectively in 13/29 and 8/25 of the available sections. Since about
1200 pineals have been studied by this technique, it would
seem that less than 1%contain well differentiated striated
muscle fibers, even allowing for some undetected examples.
The pineals containing the muscle fibers are in all other
respects normal. The blood content, the parenchymal cells and
other features show no signs of pathology or abnormality.
+
+
DISCUSSION
From the standpoint of their rarity, size, structure, variable
covering with connective tissue, striated muscle fibers described in bovine and human pineals appear similar to those
described here in the rat pineal. The characteristic location
and orientation of the fibers in the rat, however, are difficult
to match with data from previous reports since the latter
do not provide sufficient detail for this purpose.
The opinions of previous authors as well as the new data
presented here suggest that striated muscle in the mammalian
pineal as presently known, is a rare anomaly. While it is
tempting to imagine some functionally significant precursor
in an ancestral lower vertebrate, living forms in so far as information is available do not provide us with any likely homologues. Likewise, paleontological evidence f o r muscular acces-
60
W. B. QUAY
sories to the pineal and parietal eye structures in reptiles is
lacking (Edinger, ’55).
SUMMARY
Striated muscle fibers are described from three rat pineals
from a series of about 1200 stained with acid hematein. While
this is the first report of striated muscle in the rodent pineal,
there are several records in the older literature of such occurrences in bovine and human pineals. I n the rat pineal the
fibers are dorsal and basal in location and either run roughly
transversely beneath the dorsal furrow, or more commonly,
radiate from the basal area near the pineal stalk posterolaterally into the pineal tissue to a depth of 90 p and generally
parallel to the surface of the organ. The pineals of these
animals appear to be otherwise normal. At this time, striated
muscle in the mammalian pineal appears to be a rare anomaly
without known homologues in lower vertebrates.
ACKNOWLEDGMENTS
I wish to thank Jean Grant, Charlotte Holton and Tom
Fashinell for technical aid and the Department of Psychology,
University of California, for some of the animals used in
this study.
LITERATURE CITED
BAKER,J. R. 1946 The histochemical recognition of lipine. Quart. J. Micros.
Sci., 8 7 : 441-472.
BARGM-~NN,
W. 1943 Die Epiphysis cerebri. I n : Handbuch der Mikroskopischen
Anatomie des Menschen. Ed. by W. v. Mollendorff, Springer, Berlin,
6 ( 4 ) : 309-535.
CALVET, J. 1934 L ’6piphgse (glande pin6ale). Etude embryologique, histophysiologique et anatomo-clinique. J. B. Baillhre et Fils, Paris, 149 pp.
DEL VECCHIO,G. 1934 Sul reperto di fibre muscolari striate nell’ “Epiphisis
cerebri” umana. Ospedale psichiatrico (Naples), 8: 1-11.
DIMITROVA,
Z. 1901 Recherches sur la structure de la glande pinbale ehez
quelques mammifhres. Nevraxe, 8 : 259-321.
EDINGER,T. 1955 The size of the parietal foramen and organ in reptiles. A
rectification. Bull. Mus. Comp. Zool. Harvard Coll., 114(1) : 1-34.
GARDNER,J. H. 1953 Innervation of pineal gland in hooded rat. J. Comp.
New., 99: 319-329.
GODINA, G. 1939 Sulla presenza di fibre muscolari striate nell’ “epiphysis
cerebri” dei bovini. Monit. Zool. Ital., 50: 39-44.
P I N E A L STRIATED M U S C L E
61
GREENE,E. C. 1935 Anatomy of the rat. Trans. Amer. Philos. SOC., n.s. 2 7 :
xii 370 pp.
NICOLAS,
M. A. 1900 Note sur la presence de fibres musculaires stribes dans
la glande pineale de quelques mammif6res. C. R. SOC. de Biol., Paris,
+
.5Z: 876-877.
PAPPENHEIMER,
A. M. 1910 Uber Geschwulste des Corpus pineale. Virchow 's
Arch. f u r path. anat. u. physiol. u. klin. nicd., 600: 122-141.
PLATE 1
EXPLANATION OF FIGURES
Photomicrographs of rat pineals in frozen sections, 10 p in thickness and stained
with acid hematein.
Horizontal section of entire pineal of an old 8 (558 gm), showing bundles
of striated muscle extending from the area of the pineal stalk (bottom of
figure) to deep within the dorsolateral pineal parenchyma (arrows). The
most posterior or distal portion of the pineal is a t the top of the figure. X 50.
IIorizontal section of entire pineal of a n adult 8 (242 gm), showing three
striated muscle fibers (arrows) in the dorsolateral parenchyma. Orientation
as in figure 1. X 50.
Bundle of fibers enlarged from figure 1. X 500.
Two oblique fibers near point of attachment in pineal parenchyma; enlarged from figure 2. Pineal parenchymal cell nucleus with dark nucleolus
appears a t the right of the fibers. X 1050.
Longitudinally sectioned fiber enlarged from figure
to muscle fiber of pineal parenchpmal nuclei (pale
cytoplasmic processes (irregular and broken black
erythrocytes in n capillary show a t lower right. X
62
2. Note close proximity
with dark nucleoli) and
lines a t arrows). Black
1050.
P I K E A J J STRIATED MUSCLE
W . 13. QUAY
ELATE 1
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