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The relationships of the epithelial components of the pituitary gland of the rabbit and cat.

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T H E RELATIONSHIPS O F T H E EPITHELIAL COMPONENTS O F THE PITUITARY GLAND OF
T H E RABBIT AND CAT
ALDEN B. DAWSON
Biological Laboratories, Harvard University
TWO PLATES (SEVENTEEN FIGURES)
During the course of the examination of a large number of
differentially stained, serial sections of the rabbit and cat
(Friedgood and Dawson, '37) the indefiniteness of certain of
the relationships between the pars anterior proper, pars intermedia and pars tuberalis became evident. I n the rabbit
neither the pars intermedia nor the pars tuberalis are completely and sharply segregated from the anterior lobe, proper
but each may invade it to a greater or less extent. I n the cat
the pars intermedia is for the most part rather clearly limited
from the pars anterior except in a restricted zone near the
stalk. On the other hand the pars tuberalis invades the anterior lobe to a much greater extent. This encroachment of
one part on the other is of little significance from the standpoint of the general organization of the pituitary gland but
is of great importance in studies dealing with the quantitative
relationships of the three classes of cells commonly recognized
in the pars anterior. The cells of the pars tuberalis proper
are chiefly chromophobes with relatively little infiltration of
basophiles and acidophiles while the pars intermedia is made
up primarily of basophiles. I n many studies in which differential cell counts on the pars anterior have been made
either no mention is made of the lack of clear limitations of
the three epithelial components or the condition is dismissed
as of little quantitative significance. The validity of the procedure is questionable.
471
THE ANATOMICAL RECORD, VOL. 69, N O . 4
472
ALDEN B. DAWSON
The present observations are based on pituitaries which
have been sectioned either frontally or sagittally, and differentially stained by a slight modification of Heidenhain’s
‘azan’ modification of Mallory’s triple connective tissue stain,
following fixation in a saturated solution of corrosive sublimate in physiological saline, 9 parts, and formalin, 1 part
(Dawson and Friedgood, ’37). I n the pars anterior proper
the acidophiles are either a deep red or bright orange, the
basophiles deep blue or light blue, and the chromophobes are
colorless or a light pink. The specific cells of the intermedia
are deep blue and light blue with scattered chromophobes,
and in the rabbit the epithelium of the irregular, cyst-like
spaces, sometimes ciliated, representing vestiges of the
residual lumen, stains similarly to the chromophobes. In the
tuberalis proper the cells react as chromophobes and colloid,
when present, stains a deep blue. However, in the region
more closely associated with the pars anterior proper the
reaction becomes variable, some times chromophobes predominate, a t other times basophiles are almost exclusively present
or there may be a mixture of chromophobes and basophiles.
T H E TUBERALIS O F T H E RABBIT
I n the rabbit, Wolfe, Phelps and Cleveland (’34) recognized
the peculiar concentration of basophiles (cells of type 111)
of the anterior pituitary in a small area on the periphery of
the gland, on the antero-ventral surface directly opposite the
posterior lobe. According t o their description basophiles
were found in this area almost to the exclusion of acidophiles
(cells of type I), although a large number of chromophobes
(cells of type IV) were present. They also noted that this
area was well indicated on the antero-ventral surface of the
fresh unfixed gland near the upper pole, where it appeared to
be much redder in color than the remaining portion of the
gland. I n the region closer to the lower pole of the gland this
isolated area gradually blended into the more general area
of the anterior lobe where all three types of cells were found
freely mixed. However, they felt that the cells of this special
T H E PITUITARY O F T H E RABBIT AND CAT
473
area made up only a very small percentage of the total number
of basophilic cells in the pars anterior.
Their observations were based on frontal sections. When
serial sagittal sections are studied it is seen that this anteroventral zone is of considerable extent and is morphologically
continuous with the pars tuberalis and that the organization
of the epithelial elements of the region gradually changes
until the typical structure of the tuberalis is attained (fig. 1).
In the area which is incorporated in the pars anterior the
epithelial cords are more closely packed, being invested by
very delicate connective tissue septa, but they gradually become more widely separated and eventually acquire lumina
which may contain colloid, giving a vesicular appearance to
the tissue, and characteristic of the pars tuberalis.
The complete extent of this zone within the pars anterior
and its relationship with typical tuberalis tissue is best seen
in sagittal sections (figs. 1, 2, 3 ) ; its lateral extent is more
readily determined in frontal sections (figs. 8, 9 ) . Its general
form is that of a relatively broad tongue of tissue which extends ventrally and caudally from the tuberalis toward the
lower end of the pars intermedia, becoming less and less distinctly separated from typical anterior tissue and lying deeper
in the gland toward its termination. The typical tuberalis
forms an epithelial collar investing the infundibular stalk
(figs. 4, 5) and more ventrally assumes the form of a solid
cylinder lying anterior to the main body of the gland and
sharply separated from the anterior proper by a dense band
of connective tissue which frequently contains small bands of
smooth muscle running transversely to the sagittal plane
(figs. 6, 7 ) . More ventrally it is fused with the anterior lobe
(fig. 8) and gradually becomes merged into the special zone
of this portion of the gland (fig. 9). This sheet of connective
tissue extends deep into the anterior lobe along the dorsal
surface of the tongue-like epithelial extension from the
tuberalis proper and is accompanied by relatively wide blood
vessels which appear to become continuous with the dilated
capillaries in the central area of the pars anterior, adjoining
474
ALDEN B. DAWSON
the region of the residual cleft (Wolfe, Phelps and Cleveland,
'34).
Warbritton and McKenzie ('37) describe the pars anterior
of the ewe as differentiated into a central core and a peripheral zone but do not indicate the relative proportions of the
two regions. They also point out that the histological structure of the core is very similar to that of the tuberalis region
and that in fresh tissue a medial sagittal section shows a
vascular area radiating from the anterior tuberal part
through the central part of the pars anterior.
The morphological relationships of the tuberalis proper
and the antero-ventral area of the pars anterior proper
strongly suggest that this special zone might be regarded as
an integral part of the tuberalis complex (derivatives of the
lateral lobes) and this view is supported by the relationships
clearly described by Atwell ('18, figs. 28, 31, 3 5 ) in the developing gland of the rabbit. Dorsally, in the developing
gland, the pars tuberalis is separated from the main body of
the gland by a wide fossa which is filled with connective tissue.
Later the fossa becomes greatly reduced and the connective
tissue it contains is compressed. As Atwell ('18) points
out this imprisoned connective tissue is a landmark of greatest
importance since it serves to demark sharply the pars
tuberalis from the anterior end of the pars intermedia.
Furthermore as shown in his illustrations the connective
tissue of the fossa extends ventro-caudally beyond the intermedia, into the main glandular mass. The tissue so separated
and continuous anteriorly with the pars tuberalis is apparently derived from the lateral lobes which also give rise
to the pars tuberalis proper. The portion of each lateral
lobe, between the brain wall and the oral epithelial stalk, is
deeply constricted off from the remainder of the gland and
eventually forms a temporary cortex limited to the nasal end
of the anterior lobe proper. Atwell ( '18), however, believes
that in the rabbit the lateral lobes do not form a cortex for
the entire anterior lobe and that the localized cortex as seen
in a 17- and 18-day embryo does not persist long in this position and eventually disappears. Later in development, the
THE PITUITARY OF T H E RABBIT AND CAT
475
point of attachment of the epithelial stalk shifts from the
ventral side t o the nasal end of the anterior lobe and comes
very close to the attachment of the pars tuberalis. This is
due t o the bending of the gland to form the fossa, to the approximation of the lateral lobes t o the brain wall in the formation of the pars tuberalis and to a rapid growth of the glandular anterior lobe proper. I n the differential growth which
carries the stalk anteriorly it appears possible that the cortical area of the nasal end of the gland does not disappear as
Atwell suggests but is overgrown to a considerable extent
by the anterior lobe proper and becomes partially embedded
in it. Accordingly the special zone on the antero-ventral
surface of the gland, sharply delimited dorso-caudally by the
persisting connective tissue of the embryonic fossa and merging gradually into the pars tuberalis proper, should possibly
be regarded as a persisting cortex derived from the lateral
lobes, even though it does not occupy a true cortical position
throughout its entire extent.
Since the embryonic history of this special zone, lying on
the median antero-ventral surface of the anterior lobe, is
not d e a r it seems unwise to refer to it as a cortex and it is
proposed, on the basis of its morphological relation to the
pars tuberalis, to designate it as the zona tuberalis.
PARS INTERMEDIA O F T H E RABBIT
I n the adult rabbit the residual lumen persists to varying
degrees. I n some pituitaries it is seen as a continuous slit
of considerable extent, in others it is represented by a varying number of closed vesicles which are frequently ciliated
and may contain a basophilic colloid. I n the more central
region of the gland the pars intermedia is usually sharply
limited from the pars anterior proper and there is little intermingling of cellular elements of these two components of the
gland even though they are in intimate contact with each
other, following the reduction or partial disappearance of
the residual lumen. However, more peripherally at the region
where the intermediate tissue, formed with the dorsal wall
476
ALDEN B. DAWSON
of the hypopliyseal sac, retains its original embryonic continuity with the portion giving rise to the pars anterior there
is a considerable intermingling of anterior and intermediate
tissue (figs. 1, 2, 9). This intermingling occurs in a narrowly
restricted zone in the ventral and ventro-lateral margins of
the intermedia but dorso-laterally it is quite extensive. Embryologically in this dorsal region processes of the pars intermedia grow up and almost, or completely surround the portion of the neural lobe with which they are in contact (Atwell,
'18) so that in the adult pituitary only the more caudal portion of the posterior lobe is fully exposed on the surface of
the gland.
Laterally the tissue of the pars anterior also accompanies
thew dorsal intermediate processes (figs. 5, 6, 7 ) so that the
narrower, more dorsal portion of the posterior lobe lies embedded in the pars intermedia which in turn lies in a depression of the pars anterior proper. I n this entire zone the
basophilic cells of intermedia are not sharply delimited but
extend as irregular clusters into the anterior tissue, the
basophilic infiltration being most extensive in the anteroventral regiori (figs. 1,2). Accordingly in the rabbit there is
a relatively large area of the pars anterior in which it is very
difficult to distinguish the basophiles infiltrated from the pars
intermedia from the true, deeply basophilic cells of the anterior proper as clustered basophiles, presumably of intermediate origin, become isolated and merge imperceptibly into
the characteristic mosaic of basophiles, chromophobes and
acidophiles of the anterior tissue.
Although the pars intermedia is very closely associated with
the posterior lobe it does not invade it t o a marked degree.
At the periphery of the gland there is a slight extension of
the basophilic cells at the edge of the intermedia into the
posterior tissue but more centrally this does not occur with
any regularity. However there are occasional areas where
apparently a true infiltration has occurred so that isolated
clusters of basophilic cells may be found deep in the neural
tissue. I n other instances, an appearance of infiltration is
T H E PITUITARY O F T H E RABBIT AND CAT
477
given in sections by the irregularities in the contours of the
two opposing tissues.
Atwell ('18) has noted localized areas of contact or connections between the tissues of these two parts but he regarded them as due to the active grow€h of processes of the
neural lobe into the intermediate part and does not interpret
them as evidences of invasions of the neural lobe by cell
masses from the intermedia (Herring, '08). It appears
possible that such connections as occur in the embryo may provide the means for a mutual invasion by elements of the
two parts.
PARS TUBERALIS OF THE CAT
The general morphological relations of pars tuberalis and
the pars anterior of the pituitary of the cat are strikingly
similar to those of the rabbit but there is no definite landmark
such as the connective tissue of the fossa to sharply demark
the pars tuberalis from the intermedia and to delimit dorsally
the extension of the so-called zona tuberalis into the pars
anterior.
The tissue of the tuberalis proper has a conspicuous
vesicular appearance due to the accumulation of colloid in the
lumina of the cords and the wide separation of the epithelial
units by loose connective tissue. It appears as relatively
thin sheets investing the infundibular stalk (fig. 10) but is
greatly thickened a t the regions where it joins the median
antero-dorsal margin of the pars anterior (fig. 11)i.e., in the
region of saccular eminence of the tuber cinereum (Tihey,
'13).
At this point the tissue is distinctly separated into a
peripheral, loose, vesicular zone and a central, compact zone.
In the compact zone the interstitial connective tissue is greatly
reduced and the epithelial cords rarely contain colloid. This
central area becomes continuous with the anterior lobe,
forming an irregular zone which occupies the median, anteroventral region of the pars anterior and extends centrally
to the pars intermedia (figs. 12 to 17). This central mass
478
ALDEN B. DAWSON
is accompanied by short ventral processes of typical tuberalis
tissue which lie on the surface of the anterior lobe just
lateral t o the compact tissue (figs. 14, 15).
This extension of the compact portion of the tuberalis area
into the anterior lobe seems to be homologous with the similar
region described in the rabbit which has been designated, zona
tuberalis. I n the cat the typical tuberalis tissue is sharply
delimited from the zona tuberalis while in the rabbit one
gradually merged into the other. On the other hand the
zona tuberalis is more localized in the anterior lobe of the
rabbit. I n the cat it is infiltrated by scattered acidophile
cells and is frequently broken into irregular cords and masses
by invasions of typical pars anterior tissue (figs. 15, 16, 17).
Histologically it is identical with the zona tuberalis of the
rabbit, being composed predominately of chromophobic and
basophilic cells.
As in the rabbit this region, characterized by the marked
restriction of acidophiles, has not been recognized in studies
of the embryology of the gland in the cat (Brahms, '32) and
no additional information on its developmental history can
be gained from this species.
THE P A R S INTERMEDIA O F THE CAT
The pars intermedia of the cat completely invests the posterior lobe. It fuses with the pars tuberalis proper and the
zona tuberalis in the region of the irifundibular stalk without
any sharp line of demarcation (figs. 10,11,12). Brahms ( '32)
on the other hand, has described the pars tuberalis as distinctly separated from the pars intermedia by connective
tissue as in the rabbit. Our observations agree with the
earlier description of T h e y ('13). However the pars intermedia except for a restricted zone near the stalk is completely separated from the pars anterior proper by the persistence of a well-defined residual lumen. Accordingly there
is no problem of infiltration of basophilic cells of the intermedia into 'the anterior lobe proper such as occurs in the
rabbit.
THE PITUITARY O F THE RABBIT A N D CAT
479
DISCUSSION AND SUMMARY
Attention is called to the presence in the pituitary gland
of the rabbit and cat of a specialized zone of tissue which
occupies the median antero-ventral region of the pars anterior
proper and is continuous antero-dorsally with the thickened
portion of the pars tuberalis associated with the saccular
eminence of the tuber cinereum. Owing to its morphological
relation t o the pars tuberalis it has been designated as the
zona tuberalis of the pars anterior.
This region is characterized primarily by the marked restriction of acidophiles and the predominance of basophiles
and chromophobes. I n addition this zone exhibits great shifts
in cell population being at times almost exclusively occupied
by basophiles, and at others, by chromophobes. These
changes are correlated with certain phases of the reproductive
cycle and are also induced by certain experimental procedures. In the castrated female rabbit the area is almost
exclusively basophilic ( Smith, Severinghaus and Leonard,
'33) and in the adrenalectomized cat the basophiles may practically disappear leaving the tissue predominately chromophobic. These changes occur in all of the compact tissue of
the zona tuberalis but rarely invade the typical vesicular
tuberalis tissue to any extent. The extreme lability of the
tissue of this area so far as basophilic and chromophobic
cells are concerned stands in marked contrast with the behavior in the typical pars anterior where the changes in the
population of these cells are much less marked.
The functional significance of the cells of the zona tnberalis
is not clear but the distribution of the cells in this region cannot be ignored in making djfferential counts of the cellular
constituents of tlie anterior pituitary of either the rabbit or
cat. I n addition, the evaluation of the basophilic population
of the anterior lobe of the rabbit is further complicated by a
considerable intermingling of the cells of the pars intermedia with those of the pars anterior, especially in the anterodorsal region where the intermedia grows up to invest the
adjoining portion of the post,erior lobe.
480
ALDEN B. DAWSON
L I T E R A T U R E CITED
ATWELL,W. €1. 1918 The development of the hypophysis cerebri of the rabbit
(Lepus cuniculus L.). Am. J. Anat., vol. 24, pp. 271-337.
BRAHMS,S. 1932 The development of the hypophysis of the cat (Felis
domestica). Am. J. Anat., vol. 50, pp. 251-272.
1937 The differentiation of two classes
DAWSON,A. B., AND H. B. FRIEDGOOD
of acidophiles in the anterior pituitary of the female rabbit and cat.
Stain Technology. ( I n press.)
FRIEDGOOD,
H. B., AND A. B. DAWSON 1937 Cytological studies of the anterior
pituitary of the rabbit before and after its physiological stimulation.
ilnat. Rec., vol. 67 (Suppl. no. 3 ) , p. 18.
HERRING,
P. T. 1908 The histological appearances of the mammalian pituitary
body. Quart. J. E,xp. Physiol., vol. 1, pp. 121-159.
SMITH, P. E., A. E. SEVERINGHAUS
AND S. L. LEONARD1933 The effect of
castration upon the sex-stimulating potency and the structure of the
anterior pituitary in rabbits. Anat. Rec., vol. 57, pp. 177-196.
TILNEY, F. 1913 A n analysis of the juxta-neural epithelial portion of the
hypophysis cerebri with a n embryological and histological account of
a hitherto undescribed part of the organ. Internat. Monatsch. f .
Anat. Physiol., Bd. 30, S. 258-293.
WARBRITTON,
E., AND F. F. MCKENZIE 1937 The pituitary glands of ewes in
various phases of reproduction. Mo. Agr. Exp. Sta., Res. Bull., no. 257,
59 PP.
WOLFE,J. M., D. PHELPS
AND R. CLEVELAND1934 The anterior hypophysis of
the rabbit during oestrus and pseudo-pregnancy. Am. J. Anat., vol.
55, pp. 363-406.
PLATES
481
EXPLANATION O F PLATES
All figures, both of the rabbit and cat, were outlined at the same magnification
and the distribution of the various parts indicated as follows: pars anterior
proper, fine stipple; pars intermedia, solid black; pars tuberalis proper, large
open circles; zona tuberalis, large solid dots ; pars posterior, irregular lines.
All sections were cut 4 p thick and differentially stained, following fixation
i n corrosive sublimate-formalin by a slight modification of Heidenhain’s ‘azan’
stain.
Plate 1 illustrates the relationships in the pituitary of the rabbit, plate 2 in
the cat.
PLATE 1
EXPLANATION OF FIGURES
1 Sagittal section of the rabbit pituitary. The region of the’stalk has been
reconstructed t o a slight extent a s this is usually distorted i n the removal of the
gland and is seldom cut in a sagittal plane. F indicates the connective tissue
of the embryonic fossa which separates the pars tuberalis from the pars intermedia and estends into the pars anterior along the dorsal surface of the zona
tuberalis. Note the diffusion ventrally of intermedia tissue of the antero-lateral
region into the pars anterior. The numbered lilies (4 t o 9) show the approximate levels from which the frontal sections (figs. 4 t o 9) were drawn. The
meningeal relationships a r e not shown.
2 Parasagittal section slightly lateral to the infundibular stalk and passing
through the more lateral portion of the antero-dorsal extension of the pars
intermedia.
3 A similar section lateral t o the antero-dorsal extension of the pars intermedia and passing through the lateral margin of the zona tuberalis.
4 A frontal section through the stalk cutting the dorsal extension of the
thickened pars tuberalis in the region of the saccular eminence and passing through
the recessus tuberalis.
5 A frontal section showing the relationships of the several parts as the
stalk joins t h e body of the gland. I n this and the succeeding four sections the
indefiniteness of the boundary zone between pars intermedia and pars anterior
is shown.
6 A frontal section showing the cylindrical portion of the tuberalis, medial
and antcrior t o the body of the gland.
7 A frontal section showing the gradual transition from the pars tuberalis
proper t o zona tuberalis and t h e separation from the body of the gland by the
connective tissue of the fossa (F).
8 A frontal section showing the zona tuberalis embodied in the pars anterior
and passing through the ventro-caudal extension of the fossa.
9 A frontal section showing the extent of the zona tuberalis a t this level
and t h e infiltration into it of typical pars anterior tissue.
482
THE PITUITARY OF THE RABBIT AND CAT
ALDEN
PLATE 1
B. DAWWN
6
I
2
7
3
a
9
483
PLATE 2
EXPLANATION OF FIGURES
I n these figures the pars anterior is shown embracing the posterior lobe but
not completely surrounding it as it sometimes does. I n the adult cat the posterior margin of the typical anterior lobe frequently ends abruptly and is continued as a thin layer of connective tissue, with scattered epithelial cells. It
extends caudally to join the intermedia lying on the posterior surface of the
infundibulum and thereby encloses the residual lumen. This thin laxer was removed along the the capsule of the gland.
10 Frontal section passing through the stalk and showing the absence of
any sharp demarcation of pars tuberalis, intermedia and anterior.
11 Frontal section (184p ventral to the level of fig. 10) passing through the
tuberalis in the thickened region associated with the saccular eminence of the
tuber cinereum and showing the sharp segregation of the tissue into a loose
vesicular, peripheral and a compact, central zone.
12 Frontal section ( 9 2 p ventral t o the level of fig. 11) showing a more intimate association of the compact tissue (zona tuberalis) with the pars anterior.
13 Frontal section ( 1 2 0 p ventral to the level of fig. 12) showing the zona
tuberalis incorporated into the median anterior region of the pars anterior with
ventral extensions of typical pars tuberalis tissue lying laterally. These ventral
extensions may also be seen in figures 14 and 15.
14 Frontal section (160 p ventral to the level of fig. 13).
15 Frontal section (260 p ventral t o the level of fig. 14).
16 Frontal section (228 p ventral t o the level of fig. 15).
17 Frontal section (240 L./ ventral t o the level of fig. 16).
I n these four figures the extent of the tissue of the zona tuberalis and the
degree of infiltration by the tissue of the typical pars anterior are illustrated.
484
THE PITUITARY OF THE RABBIT AND CAT
ALDEN B. DAWSON
PLATE 2
14
15
12
16
17
485
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