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=The Histological Appearances of the Mammalian Pituitary Body=
 
By P. T. Herring.
 
From the Physiology Department, University of Edinburgh.
 
Received for publication 11th February 1908.
 
==Introduction==
The structure and significance of the pituitary body have long been objects
of much speculation. Erroneous conceptions of its structure are responsible
for some of the many theories which have been advanced with regard to
its functions. The pituitary, indeed, derives its name from the old idea
that it was a gland which discharges a secretion—pituita—into the
nostrils.
 
 
Rathke (32) discovered the double origin of the pituitary, and on developmental grounds classed it among glands. Other observers looked
upon it as part of the brain. Luschka (23) called it a “nerve-gland” in which the two parts are separated from one another by pia mater.
Ecker (8), on the other hand, held the view that both portions of the pituitary combine to form a unit of the nature of a “ blood-vessel gland.”
 
 
Burdach (4.-), Luschka (23), and Virchow (46) regarded the posterior lobe as the anterior terminal end of the cerebro-spinal canal, a “filum
terminale anterius,” resembling in structure the filum terminale of the spinal cord. Virchow also compared the anterior lobe to the thyroid
gland, and described in it vesicles containing colloid material which show a striking resemblance to the follicles of the thyroid. Rogowitsch (34), H. Stieda (43), Schonemann (39), and others have attached great importance to this resemblance, and ascribe similar functions to the two glands. Removal of the thyroid is, according to their observations, followed by a compensatory hypertrophy of certain parts of the glandular lobe of the pituitary.
 
 
In 1886 Marie drew attention to a relationship between changes in the pituitary and the disease acromegaly or gigantism. Clinical and
pathological experiences have led to the theory which assigns to the pituitary the role of regulating the normal development of the body, more especially of the extremities and bones. The nature of the change that the pituitary undergoes in acromegaly is uncertain, and before any light can be thrown upon its pathology it is necessary that the significance of the various histological elements that constitute the normal pituitary should be understood. Moreover, it appears that acromegaly may occur without
any apparent change in the pituitary, and that tumours of the pituitary
are not always attended by acromegaly. A feature as constant as acromegaly in affections of the pituitary is the occurrence of polyuria with
or without sugar in the urine (Hansemann (16), Sternberg (41)).
 
 
Oliver and Schafer (28) in 1895 described the presence of a substance
in saline extracts of the pituitary, which, when injected intravenously,
produces a rise of blood-pressure. Howell (18) showed that this substance is only present in the posterior lobe. Magnus and Schafer (24)
in 1901 noticed that intravenous injection of saline extract of the
posterior lobe is followed by a marked increase of urine flow. Schafer
and Herring (37) confirmed this observation, and showed the striking
parallelism which exists between the suprarenal capsules and the pituitary
in development, structure, and functions. In each there are two parts, one
of which, a highly vascular epithelium, yields no active extract, while the
other, of neuro—ectodermic origin, gives an extract which has a remarkable
physiological effect upon the heart and arteries. The view was conjectured
that in the epithelial part of each organ the material which is to furnish
the active agent of the secretion passes through certain stages of formation,
and that its production is merely completed in the neuro—ectodermic part,
in which part alone the full activity of the secretion is acquired. That
the posterior lobe of the pituitary should furnish an active secretion is
difficult to reconcile with the usual views held on its structure. The older
anatomists, W. Muller (27), Schwalbe (40), and Toldt (45), looked upon
it as a mass of connective tissue cells and fibres which during development
have destroyed all trace of the original nerve tissue. Berkley (2), on the
other hand, describes in it a complex arrangement of nerve cells and nerve
fibres, besides neuroglia and ependyma cells. Kolliker (19) takes up an
intermediate position, and believes that there are no true nerve cells, but
neuroglia and ependyma, a view similar to the one held by Virchow.
Peremeschko (30) first recognised that the posterior lobe has an epithelial
investment. Osborne and Swale Vincent (29) state that extracts of
the central part of the posterior lobe are more active than extracts of
the margin of the lobe, and believe that the epithelial investment would
be found to be inactive if it could be properly isolated.
 
 
The pituitary body is found in all vertebrates, and, although differing
widely in structure and in the arrangement of its component parts, possesses
many features common to all. In fishes, the posterior lobe has a complex
vascular structure of a glandular nature, which was called the “saccus
vasculosus” by Gottsche (12). L. Stieda (44) proved that the saccns
vasculosus communicates with the brain cavity, and Rabl-Riickhard (31)
named it an infundibular gland. Their researches have been confirmed
by Kupffer (21). The function of the saccus vasculosus is unknown, but
its secretion, if it is a secretory gland, apparently mixes with the fluid
contents of the ventricles of the brain. According to Kupffer, the posterior lobe of the mammalian pituitary in its early development
retains for a time a glandular structure. In the adult mammal the
epithelial investment of the posterior lobe is regarded by Ktilliker as
the representative of an infundibular gland. B. Haller (14«) states that
in mammals—as a type of which he takes the mouse——and in all other
classes of vertebrates the anterior lobe of the pituitary and epithelial
investment of the posterior lobe form a gland, the tubules of which open
by a small median and ventral mouth into the space between the pia and
dura mater. Haller believes that the pituitary in all vertebrates secretes
directly into the subdural space. Edinger (9) denies that this is true
of the human pituitary, Salzer (36) could find no opening in the pituitary
of the rat and mouse, and Sterzi (42) found none in the pituitary of
Petromyzon.
 
There are other views on the structure and functions of the pituitary
body. Boeke (3) and Gemelli (11) describe appearances in the posterior
lobe of fishes which they regard as indicative of sense organs. Cyon (6)
looks upon it as an organ which regulates the amount of blood passing
to the brain. Guerrini (13) and others believe that the pituitary
produces a secretion which has a vague antitoxic action.
 
Our knowledge of the structure of the pituitary body is, therefore,
far from exact, and is inadequate to account for the physiological effects
which follow intravenous injection of extracts, especially of the posterior
lobe. Even the important question as to whether the glandular portion
secretes directly into the subdural space is still unsettled. The work, the
results of which are given in this paper, was begun with the intention of
investigating the physiological histology of the posterior lobe, but the two
portions of the pituitary were found to be so closely associated that no
part would be complete without careful consideration of the other. The
development and comparative anatomy of the pituitary body have been
examined, but are only touched upon in this paper where reference to them
throws light upon the particular point considered.
 
==Material and Methods Employed==
 
The cat furnishes some of the best material for the study of the pituitary
body, for in this animal the posterior lobe retains throughout life its
original cavity in free communication with the third ventricle of the brain.
The structure of the posterior lobe in the cat is thus rendered simpler
because the arrangement of the cells which line the cavity persists in the
adult in much the same manner as obtains in the developing organ. The
parts which are derived from the buccal mucous membrane form an almost
complete investment for the nervous portion, and the original lumen of
the epithelial pouch also persists throughout life in the form of a well
marked cleft. The so-called colloid cysts are also prominent features in
the pituitary of the cat.
 
 
The pituitary of the monkey more closely resembles that of man, and
is a type in which greater fusion of the original elements from which
it is developed has taken place. The posterior lobe is solid throughout.
Its investment by the epithelial portion is not so complete as it is in the
cat, and only a small cleft remains as the representative of the original
buccal pouch.
 
 
The pituitary of the dog offers in some respects a type which‘ is intermediate between that of the cat and that of the monkey. The posterior
lobe is solid, but the cavity of the third ventricle of the brain is continued downwards and backwards towards the neck of the posterior lobe. The epithelial investment is very complete, and the cleft in it well developed
as in the cat. The colloid cysts are more numerous than in the pituitary
of the monkey, and their arrangement and structure present features
which distinguish them from those of the cat’s pituitary. The morphology
of the pituitary bodies of the cat, dog, and monkey will be described briefly,
and the structure of the various parts more minutely detailed in the cat.
 
 
For the investigation of the finer structure of the pituitary body
Flemming’s fixative gives the best results; a 10 per cent. solution of
formol and saturated corrosive sublimate have also been employed.
Sections have been cut serially in a vertical antero-posterior plane; these
show the relations of the Various parts of the pituitary to one another
better than do sections cut in other directions. Most of the material has
been cut in paraflin, but the freezing microtome has also been used, and
the Golgi preparations cut by hand.
 
 
The structure of the anterior lobe is shown to the best advantage by
staining with eosin and methylene blue, or by the employment of some
of the many methods devised for the staining of blood films. Many
preparations were made by Ca_jal’s silver reduction method, which is
especially valuable for showing the fibrils of the neuroglia, and the
ependyma cells of the posterior lobe. Cox’s modification of Golgi’s
method was also adopted for the investigation of the nervous elements.
Fresh tissues have been teased out and examined in salt solution and
in osmic acid, and chromic acid fixed preparations have been cut by the
freezing microtome. The blood-vessels were also injected from the common
carotids with carmine gelatine, and the vascular supply of the pituitary body studied in thick sections.
 
 
A word must be said about the removal of the pituitary body for purposes of examination. In order to investigate the question raised by
B. Haller as to the presence of an opening on the median ventral aspect
connecting the epithelial cleft with the subdural space by means of a
lymph space, it is almost essential to remove the sella turcica and part of
the brain from below, to decalcify the bone and cut sections of the pituitary
in situ. This can be more readily done in the young animal. For most
purposes it is suflicient in the adult animal to dissect the bone piecemeal
from the dura mater, which forms an envelope to the pituitary, thickened at certain points, especially behind. Great care must be taken not to
rupture the thin layer of epithelium which in the cat is continued backwards from the anterior lobe, to be reflected at the place where the
blood-vessels enter the posterior lobe to form a closely fitting investment
over the ventral aspect of the latter. Removal of the pituitary from the
cranial cavity by raising the brain and dissecting from above is almost
invariably followed by rupture of the neck of the posterior lobe. The
dura mater should always be preserved intact without being pulled upon,
and the best way to do this is to dissect off the bone from below, disturbing the base of the brain as little as possible. A portion of the brain can then be cut out with the pituitary attached, and the piece trimmed after
hardening.
 
 
   
 
'''Fig. 1.''' Mesial sagittal section through pituitary body and sella turcica of new-born kitten. (Semi-diagrammatic.) a, optic chiasma; b, tongue-like process of pars intermedis; c, third ventricle; d, anterior lobe proper; e, epithelial cleft ; f, central cavity of posterior lobe ; g, nervous substance of posterior lobe ; h, posterior reflection of epithelium.
 
==Morphology==
 
The relations of the anterior and posterior lobes of the pituitary to one another, and to their immediate surroundings, can be most readily
appreciated by reference to the comparatively simple pituitary of the new-born kitten. Fig. 1 is a diagram of a mesial sagittal section through
the pituitary and sella turcica of a new-born kitten. The infundibulum cerebri is a continuation of the brain backwards and slightly downwards, and consists of a comparatively thin wall of brain substance enclosing a cavity which is a continuation of the third ventricle. The
infundibulum has a funnel-shaped origin from the base of the brain, narrowing as it passes backwards to a tubular neck, then expanding to form a hollow club-shaped body which makes up the larger portion of the posterior lobe. The central cavity also enlarges behind the neck of the infundibulum.
 
 
The anterior lobe, composed of epithelial cells, lies below, and its thickest portion is in front of the infundibulum. It extends for some distance anteriorly, forming a tongue-shaped projection which reaches to the under surface of the tuber cinereum. The anterior lobe also spreads further laterally, and enfolds the sides of the infundibulum, the neck of which is encircled completely, so that, as in the figure, a portion of the anterior lobe appears above it. In some kittens the wrapping of the epithelium round the posterior lobe is more complete, and the only part of the lobe which is never covered by epithelium is a small part behind where the blood-vessels make their entrance. A narrow and somewhat S-shaped space lies inside the epithelium close to and following in its outline the under surface of the nervous portion of the posterior lobe, but separated from it by several layers of epithelium. The space or cleft is, as Kolliker
(20) pointed out, the remnant of the cavity of the pouch of buccal
epithelium from which the anterior lobe is derived. The layer of epithelium which lies between the cleft and the part of the posterior lobe
developed from the brain is comparatively thin, and very closely applied
to the nervous substance, thus forming an investment to it which is more
or less complete according to the degree in which the anterior lobe has
grown round the posterior. The cleft extends laterally, and in some cases
almost surrounds the body of the posterior lobe. The posterior lobe as
separated from the anterior by the cleft is therefore a composite body
derived from the brain and from buccal epithelium, and it is to this
structure of elements derived from two sources that the name of posterior
lobe is usually applied, although strictly speaking the epithelial investment
belongs developmentally to the anterior lobe. The cleft is sometimes
more complicated, and branches of it may run into the substance of the
anterior lobe. Serial sections show no opening below such as has been
described by B. Haller (14), nor does there appear to be an opening at
any point; the cleft is a closed cavity in the kitten, but very great care
has to be taken in the removal and preparation of the pituitary to prevent
rupture of the thin layer of epithelium which is continued backwards
from the anterior lobe.
 
 
The greater portion of the anterior lobe is a solid structure made up of columns of cells and wide blood-channels. Granules are present in many of the cells of this part, but are not so marked a feature of the anterior
lobe in the new-bom kitten as they are in the adult cat. Colloid cysts are
not found in the pituitary of the new-bom kitten.
 
The relation of the pituitary body to the sella turcica is shown in fig. 1.
 
 
 
 
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[[Category:Pituitary]][[Category:1900's]][[Category:Cat]][[Category:Draft]]

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