Paper - The histological appearances of the mammalian pituitary body
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Herring PT. The histological appearances of the mammalian pituitary body. (1908) Quar. Jour. Ex. Physiol., 1: 121-159.
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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.
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.
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
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