Morphological characteristics of the deep layer of articularis genus muscle.

BACKGROUND: The articularis genus muscle pulls the suprapatellar pouch upwards when the knee joint is extended, preventing mechanical impingement of the joint capsule which theoretically could cause anterior knee pain. However, few anatomical studies have addressed this muscle. Here we present the precise morphology of articularis genus. MATERIALS AND METHODS: A total of 22 (13 male and 9 female) adult cadavers with no pathological conditions in the knee joints were examined during educational dissection at Nagoya City University Medical School in 2012. After exclusion of 4 joints due to their flexion contracture, 40 knee joints (18 right and 22 left) were analysed. We performed statistical analysis on anatomical laterality and the difference of sizes among lateral, medial and central branches and studied the correlation of the length and area of the articularis genus muscle to the lengthand cross-section area of the femur. RESULTS AND CONCLUSIONS: The average number of branches of the deep layer of the articularis genus muscle was 2.7 ± 0.5, the mean length of all brancheswas 5.4 ± 1.3 cm and the mean area of all branches was 5.5 ± 2.6 cm². There was no significant correlation between the length and area of the articularis genus muscle to the length and cross-section area of the femur. There was no significant laterality in central, medial and lateral branches; however we found that the medial branch was statistically longer and larger than the lateral branchon either knee. This could be contributing to prevention of lateral dislocation of the patella.

NADH-generating substrates reduce peroxyl radical toxicity in RL-34 cells.

There is general agreement that oxidative stress may induce apoptotic and necrotic cell death. Recently it has been shown that NADH can be considered an important antioxidant as it reacts with peroxyl and alkoxyl radicals under in vitro conditions. Therefore, in the present study we hypothesized that an increase in intracellular NADH using specific substrates will protect RL-34 cells against cytotoxicity of 2'-azobis (2-amidinopropane) dihydrochloride (AAPH), which is a peroxyl radical generating compound. Cells treated for 24 hours with 6.0 mM AAPH were severely damaged: mitochondria were vacuolated, and the level of free radicals significantly increased. Both apoptotic and necrotic cells were detected (11.1% and 11.4%, respectively) even after 5 hours of treatment. Pretreatment of the cells with substrates which increase the intracellular level of NADH, such as lactate, beta-hydroxybutyrate, and ethanol, distinctly inhibited AAPH-induced reactive oxygen species (ROS) formation and cell death. On the other hand, acetoacetate (AcA), which decrease the intracellular level of NADH, had opposite effects. Interestingly, NADH-generating substrates augment, while AcA reduced superoxide radical formation induced by AAPH. These results may suggest that although NADH generating substrates may exert some deleterious effects within a cell by inducing reductive stress, they diminish alkoxyl or peroxyl radical cytotoxicity. The protection is associated with a decrease in ROS formation measured by dichlorofluorescein, but with an increase in superoxide radical formation.

Induction of megamitochondria by some chemicals inducing oxidative stress in primary cultured rat hepatocytes.

Effects of hydrazine, hydrogen peroxide and bromobenzene, inducers of free radicals, and those of erythromycin and cycloheximide, inhibitors of protein synthesis on structural changes of mitochondria in primary monolayer culture of rat hepatocytes were examined using laser confocal microscope and electron microscope. After 22 h of incubation of hepatocytes with 0.2 mM hydrogen peroxide or 10 microg ml-1 of erythromycin, mitochondria became extremely enlarged. Mitochondria of hepatocytes isolated from control rats became slightly to moderately enlarged in the presence of 2 mM hydrazine, while those of hepatocytes isolated from phenobarbital-pretreated animals became extremely enlarged in the presence of 2 mM hydrazine. Cycloheximide (0.5-10.0 microg ml-1) and bromobenzene (0.1-1.0 mM) failed to induce structural changes of mitochondria. The level of cytochrome P-450 in freshly prepared hepatocytes from phenobarbital-treated rats was 2.5 times higher than that from the control rats, and remained about three times higher than the latter after 22 h of incubation with 2 mM hydrazine. The level of malondialdehyde was invariably elevated when megamitochondria were induced. These results may suggest that oxidative stress is intimately related to the mechanism of the formation of megamitochondria and that the inhibition of cytoplasmic protein synthesis seems not to contribute the phenomenon. However, the detailed mechanism by which free radicals may induce megamitochondria remains to be elucidated.

Cycloheximide and 4-OH-TEMPO suppress chloramphenicol-induced apoptosis in RL-34 cells via the suppression of the formation of megamitochondria.

Toxic effects of chloramphenicol, an antibiotic inhibitor of mitochondrial protein synthesis, on rat liver derived RL-34 cell line were completely blocked by a combined treatment with substances endowed with direct or indirect antioxidant properties. A stable, nitroxide free radical scavenger, 4-hydroxy-2,2,6, 6-tetramethylpiperidine-1-oxyl, and a protein synthesis inhibitor, cycloheximide, suppressed in a similar manner the following manifestations of the chloramphenicol cytotoxicity: (1) Oxidative stress state as evidenced by FACS analysis of cells loaded with carboxy-dichlorodihydrofluorescein diacetate and Mito Tracker CMTH2MRos; (2) megamitochondria formation detected by staining of mitochondria with MitoTracker CMXRos under a laser confocal microscopy and electron microscopy; (3) apoptotic changes of the cell detected by the phase contrast microscopy, DNA laddering analysis and cell cycle analysis. Since increases of ROS generation in chloramphenicol-treated cells were the first sign of the chloramphenicol toxicity, we assume that oxidative stress state is a mediator of above described alternations of RL-34 cells including MG formation. Pretreatment of cells with cycloheximide or 4-hydroxy-2,2, 6,6-tetramethylpiperidine-1-oxyl, which is known to be localized into mitochondria, inhibited the megamitochondria formation and succeeding apoptotic changes of the cell. Protective effects of cycloheximide, which enhances the expression of Bcl-2 protein, may further confirm our hypothesis that the megamitochondria formation is a cellular response to an increased ROS generation and raise a possibility that antiapoptotic action of the drug is exerted via the protection of the mitochondria functions.

The co-existence of an aberrant origin of the right subclavian artery and a coronary myocardial bridge.

We encountered the co-existence of an aberrant origin of the right subclavian artery and a myocardial bridge on the left anterior descending coronary artery in the cadaver of an 80-year-old Japanese woman during the course of educational dissection at Nagoya City University Medical School. We document the precise gross anatomical findings with some morphometric measurements. Neither an aberrant origin of the right subclavian artery nor the cardial myocardial bridge is a very rare anomaly, but a case of both anomalies being found in the same body is very rare. We believe this is the first report of the simultaneous occurrence of these two anomalies.

Free radical-induced megamitochondria formation and apoptosis.

Pathophysiological meaning and the mechanism of the formation of megamitochondria (MG) induced under physiological and pathological conditions remain obscure. We now provide evidence suggesting that the MG formation may be a prerequisite for free radical-mediated apoptosis. MG were detected in primary cultured rat hepatocytes, rat liver cell lines RL-34 and IAR-20 and kidney cell line Cos-1 treated for 22 h with various chemicals known to generate free radicals: hydrazine, chloramphenicol, methyl-glyoxal-bis-guanylhydrazone, indomethacin, H2O2, and erythromycin using a fluorescent dye Mito Tracker Red CMXRos (CMXRos) for confocal laser microscopy and also by electron microscopy. Remarkable elevations of the intracellular level of reactive oxygen species (ROS), monitored by staining of cells with a fluorescent dye carboxy-H2-DCFDA, were detected before MG were formed. Prolongation of the incubation time with various chemicals, specified above, for 36 h or longer has induced distinct structural changes of the cell, which characterize apoptosis: condensation of nuclei, the formation of apoptotic bodies, and the ladder formation. Cells treated with the chemicals for 22 h were arrested in G1 phase, and apoptotic sub-G1 populations then became gradually increased. The membrane potential of MG induced by chloramphenicol detected by CMXRos for flow cytometry was found to be decreased compared to that of mitochondria in control cells. Rates of the generation of H2O2 and O2- from MG isolated from the liver of rats treated with chloramphenicol or hydrazine were found to be lower than those of mitochondria of the liver of control animals. We suggest, based on the present results together with our previous findings, that the formation of MG may be an adaptive process at a subcellular level to unfavorable environments: when cells are exposed to excess amounts of free radicals mitochondria become enlarged decreasing the rate of oxygen consumption. Decreases in the oxygen consumption of MG may result in decreases in the rate of ROS production as shown in the present study. This will at the same time result in decreases in ATP production from MG. If cells are exposed to a large amount of free radicals beyond a certain period of time, lowered intracellular levels of ATP may result in apoptotic changes of the cell.

Endotoxin-induced upregulation of type I interleukin-1 receptor mRNA expression in hepatocytes of mice: role of cytokines.

Interleukin-1 (IL-1) signal is transduced through the type I IL-1 receptor (IL-1RI). Although regulation of IL-1R expression has been extensively studied in vitro, little is known about it in vivo. By using RT-PCR analysis, we investigated the regulation of the IL-1RI mRNA expression level in various organs of mice at 2, 6, and 24 h following lipopolysaccharide (LPS) administration. IL-1RI mRNA expression in response to LPS appeared to be different in various organs. As a marked and sustained increase of IL-1RI mRNA expression in the liver was observed, we investigated the mechanism of the upregulation. IL-1, IL-6, and tumor necrosis factor (TNF) all increased the mRNA expression in the liver when administrated in vivo. In situ hybridization revealed that upregulation of IL-1R mRNA was observed in parenchymal liver cells (hepatocytes) in response to LPS administration. When primary cultured hepatocytes were treated in vitro, IL-1, IL-6, conditioned medium from LPS-treated mouse macrophages, and serum from LPS-treated mouse upregulated IL-1RI mRNA expression, but LPS, TNF, and prostaglandin E2 failed to do so. Therefore, these results suggest that the upregulation of IL-1RI mRNA in the hepatocytes by LPS administration is mediated by cytokines, especially by IL-1 and IL-6. The results also indicate that the regulation is different in different organs, and microenvironmental factors may be important.

Biogenesis and function of lipolysosomes in developing chick hepatocytes.

Proliferation of lipolysosomes is one of the characteristic aspects of embryonic chick hepatocytes. Formation of lipolysosomes is observed in the well-developed trans-Golgi network, with the highest frequency occurring from 11 to 14 days of incubation. The lipolysosomes usually contain a small and electron-dense lipid inclusion; however, during development, they gradually enlarge with an accompanying reduction in the electron density of the inclusion. Lipolysosomes isolated from neonatal chick liver homogenates were mainly composed of esterified cholesterol and showed considerably high activity of lysosomal enzymes. Moreover, the lipolysosome fraction is clearly shown to be a function of intralysosomal lipolysis via acid lipase. This accumulation of esterified cholesterol within lipolysosomes might be attributed to an excessive uptake and conversion of plasma lipoproteins to lipolysosomes. This concept is supported by the appearance of an abundance of coated pits and both "early" and "late" endosomes. The major components of plasma lipoprotein are low density lipoprotein (LDL) and high density lipoprotein (HDL), the cholesterol-rich lipoproteins, whose cholesterol content increases during the last week of incubation when the lipolysosomes quickly enlarge. Plasma lipoprotein particles are produced in the yolk sac epithelium from yolk very low density lipoprotein (VLDL) and transferred via the vitelline circulation to the chick liver. After hatching, when the supply of nutrients from the yolk sac is terminated, lipolysosomes immediately decrease in size and number. The cholesterol and fatty acids released are useful as an energy source and lipid metabolism in general, especially after hatching. Food intake induces the use of and accelerates the disappearance of lipolysosomes. Instead of lipolysosomes, lipid droplets appear and increase in number and size with concomitant increases of triglyceride concentrations in the liver homogenates, suggesting that lipogenesis has begun in the chick hepatocyte.

Folliculo-stellate cells and intercellular communication within the rat anterior pituitary gland.

Folliculo-stellate (FS) cell are agranular and arranged around a follicle. They contain the S-100 protein and beta-adrenergic receptors. It has been suggested that they can act as stem cells, since they show mitotic figures, and could transform into granular or chromophilic cells according to the concept of a "cell renewal system." Cell-to-cell interactions among pituitary cells have been described, and recent progress with freeze-fracture electron microscopy has provided novel observations of the cell surface and gap junctions within the rat or teleost fish pituitary gland, or in cultured rat pituitary cells. In adult rats, the anterior pituitary was composed of lobules incompletely separated by a basement membrane. Follicles consisted exclusively of FS cells. Gap junctions were observed only between adjacent FS cells, in rare cases on the tips of their cytoplasmic processes. Thus, the FS cells, connected by gap junctions, made up a dense cellular network throughout the pituitary. Gap and tight junctions were absent on granular cells. Elongated follicles with columnar FS cells were observed in 10-day-old rats and were separated into smaller units. The number of gap junctions rapidly increased with age until 40-45 days of age. Few S-100 protein positive cells were observed on day 10, along the marginal cell layer and near the so-called postero-lateral wing. The frequency of positive cells increased with age and by day 40; numerous cells were observed throughout the anterior lobe. Gap junction number also varied with the stage of the estrous cycle, and frequency; during diestrus, they were half of that during proestrus or estrus. The number of gap junctions increased in late pregnancy and in lactating rats, probably due to changes in estrogen and progesterone. Hormone (LH-RH and testosterone) treated groups of rats showed accelerated development by almost 10 days, compared with controls. In castrated male rats, the ultrastructure of the pituitary remained immature even at 40 days of age, when the number of gap junctions was a quarter or less than the number in intact rats. Testosterone treatment restored the frequency of gap junctions to a normal level. We conclude that the appearance of gap junctions in the pituitary cells and maturation of the gland are dependent to a large degree upon gonadal steroids.

Participation of endodermal epithelial cells on the synthesis of plasma LDL and HDL in the chick yolk sac.

We ultrastructually examined the chick yolk sac endodermal epithelium and evaluated our findings in combination with the biochemical analysis of serum and yolk lipoproteins. Twenty-five to 30 nm-sized particles were demonstrated to be a principal element of the extracellular yolk mass and these were determined to be yolk very low density lipoprotein (VLDL). The particles were shown to be taken up by the epithelial cells via coated pits and engulfed by plasma membrane invaginations together with yolk subdroplets, another element of the yolk mass. Through apical vacuoles, the two yolk elements were incorporated into yolk drops, which were identified to be one of the lysosomal structures by a cytochemical procedure using acid phosphatase (AcP)ase activity. During the last week of incubation, which is the final third of the incubation period, the digestion seemed to progress rapidly in the yolk drops, which came to resemble lipolysosomes; lipoprotein production became active as expressed by an enlarged Golgi apparatus. The newly produced lipoprotein particles were electron-lucent and irregular in size (50-120 nm). They were sequestered in secretory vacuoles and secreted from the vascular surface of the epithelial cells. Finally, the particles were thought to be taken into the vitelline circulation as plasma lipoproteins. The major component of lipoprotein in serum was determined to be low density lipoprotein (LDL) and high density lipoprotein (HDL), while cholesterol content was found to increase during incubation. We concluded that endodermal epithelial cells participate the synthesis of plasma LDL and HDL. For this synthesis the cells probably apply lipids and apo-protein generated from yolk VLDL degradation.

Egress route of emulsified 20 centistokes silicone oil from anterior chamber of rabbit.

Silicone oil is used in recent clinical practice, however, it may cause adverse reactions in the eyes. When the high viscosity silicone oil is contaminated with low molecular weight silicone oil, the contamination may cause ocular toxicity or elevation of the intraocular pressure. To obtain information on the distribution of this preparation, emulsified 20 centistokes silicone oil was injected into the anterior chamber of rabbit eyes. The silicone oil droplets were visualized by light and electron microscopy by using oil soluble phthalocyanine blue. This copper containing dye remains in the tissue after removal of the silicone oil by organic solvents. Two and 4 weeks after an injection, the silicone emulsion was observed as numerous small vacuoles with blue precipitate at the margin of vacuoles within elongated trabecular endothelial cells, fibroblasts along the route of uveoscleral outflow and cells of the iris. Three hours after the injection, only a few vacuoles were present in these cells. These results demonstrated that the emulsified silicone oil leaves the anterior chamber through the conventional and unconventional routes. Phagocytosis by the trabecular endothelial cells and fibroblasts along the uveoscleral route caused an accumulation of the emulsified silicone oil in these cells. With chronic exposure to emulsified silicone oil, changes in the trabecular meshwork may lead to a reduction in the outflow of aqueous humor and cause glaucoma.

Granulated 'marginal cell layer' in the rat anterior pituitary gland.

A granulated 'marginal layer cell' was observed in the lining of Rathke's residual pouch of 5 and 10 day-old rat anterior pituitary glands. Immunohistochemistry was not employed to identify the precise function of these cells. However, the cytological characteristics of nearly all of the cells indicated that they resembled GH-secreting cells, with a few displaying morphological features of corticotrophs. In pituitary glands of 5-20 day-old rats, both ends of Rathke's residual pouch extended into the pars distalis at the site of transitional zone of this lobe and of the pars intermedia. The cells within the 'invading' residual pouch contained numerous microvilli. In the middle portion of the residual pouch, cavities lined by 'marginal layer cells' had numerous microvilli and were adjoined by junctional complexes. In the adult rat pituitary gland, there were no granulated cells in the 'marginal cell layer' and no invasion of the residual pouch into the anterior lobe. From these data the possible source of the follicle and of the folliculo-stellate cells in the anterior pituitary of the rat is proposed.

Immunohistochemical study of the post-natal development of the folliculo-stellate cells in the rat anterior pituitary gland.

We investigated the post-natal development of cell-to-cell communication within the rat anterior pituitary gland cells using immunohistochemistry of the S-100 protein. Tissues of animals from 10 to 60 days of age were analyzed. At 10 days of age, S-100 protein-containing cells were rarely observed. With age, the population of S-100 immunostained cells increased until day 40 when they were found to be quite numerous. No further changes were noted from day 40 through day 60. From our previous studies, we conclude that the cells which reacted with the S-100 antiserum were folliculo-stellate cells and their developmental pattern parallels that of the hypophyseal-gonadal axis.

Cytochemistry of Ca(++)-dependent adenosine triphosphatase (Ca-ATPase) in rat anterior pituitary cells.

In the present study, we demonstrate the localization of Ca(++)-ATPase in the anterior pituitary of the male rat. Ca(++)-ATPase was mainly distributed on the membrane system of the granular cells, which included the plasma membrane, the outer mitochondrial membrane, the enveloping membrane of secretory granules, the smooth endoplasmic reticulum and some components of the Golgi complex. No reaction product was detected on the membrane of the rough endoplasmic reticulum or that surrounding the lysosomes. A positive reaction was clearly observed on the membranes surrounding 'large' secretory granules, while that present on the membranes of the 'small' granules was comparatively weak. The cells which contained the 'large' granules were interpreted as growth hormone-secreting cells and those in which the 'small' granules were located as gonadotrophs. There were either no reaction or one that was barely detectable on the plasma membrane of the folliculo-stellate cells. These data along with our previous findings (Soji, 1982, 1984) suggest that the membranous enzymes are not uniformly distributed over all pituitary cells but rather are specific for a given cell population(s).

Evidence that Müller cells can phagocytize egg-lecithin-coated silicone particles.

This study is designed to better understand the function of the Müller cells of the retina through the use of silicon particles that had been injected into the vitreous body of the eye and via an analysis of the number of gap junctions associated with these cells. Following intraocular injection of a silicone oil mixture into the rabbit retina, numerous small silicone particles less than 1 micron in diameter were found attached to the basement membrane of the inner limiting membrane, subjacent to the Müller cells. On the sites to which the silicone particles attached, the basement membrane was reduced in thickness or completely disappeared. The 'end-feet' of the cell membrane facing the silicone particles became concave appearing as if they were in the process of incorporating the particles into the cell. Similarly, the Müller cells occasionally extended cytoplasmic processes through the basement membrane and towards the silicone particles, as if to engulf them. Gap junctions were observed but only in association with the Müller cells. They were often found between the 'end-feet' of adjacent Müller cells or the 'end-feet' of one cell and very thin cytoplasmic process of a neighboring cell. On rare occasions, they were located between 'end-feet' of the same Müller cell. The percentage of 'end-feet' displaying gap junctions was 38 +/- 8% (mean +/- SE). These data suggest that the Müller cells are important in the maintenance of normal retinal function by their ability to phagocytize foreign substances and by their ability to transmit information to various parts of the retina through cell-to-cell connections established by gap junctions.

Septate-like junctions in the normal male rat pituitary gland.

Septate-like junctions were observed in the rat anterior pituitary gland of the adult male solely between adjacent folliculo-stellate cells. Considering their location, it is presumed that their function is cellular adhesion and mechanical support for the hypophyseal follicles.

Effects of ruthenium red on the cellular functions and ultrastructure in intact ferret ventricular muscles.

The effects of ruthenium red (RR) on the cellular functions (intracellular Ca2+ handling and contraction) and permeation of the dye through the cell membrane were investigated in intact ferret papillary muscles. The intracellular Ca2+ concentration ([Ca2+]i), measured using aequorin, was simultaneously recorded with tension. The permeation of the dye through the cell membrane was studied with electronmicroscopy. The preparation was continuously stimulated at 0.2 Hz and treated with 50 microM RR at 30 degrees C. [Ca2+]i was increased by electrical stimulation (0.07 and 2 Hz) and rapid cooling (from 30 to 4 degrees C) (RC). In electrical stimulation, RR time-dependently decreased the peak light of aequorin without a significant change in the time course at 30 degrees C. However, in RC, treatment with RR for about 100 min significantly prolonged the decay time of the light signal and increased the peak light. The peak tension in RC was decreased after treatment with RR for a longer time. The pCa-tension relation of skinned preparations was significantly shifted to the right by 50 microM RR. In the RR (50 microM)-treated specimens, mitochondrial outer membranes were darkly stained if OsO4 was used for fixation. Even though the specimen treated with 500 microM RR was fixed without OsO4 and electron staining, the matrices of mitochondria became electron dense. We concluded that RR could penetrate into intact mammalian cardiac myocytes, and that RR inhibits the release of Ca2+ from the sarcoplasmic reticulum in electrical stimulation, inhibits mitochondrial Ca2+ uptake, and decreases the Ca2+ sensitivity of the myofilaments.

Postnatal development of synovial capillaries of rats with special reference to permeability.

The size of a substance is a major factor determining whether it can permeate the wall of synovial capillaries. The maximum diameter of particles that can move across the synovial capillary wall has generally been thought to be 50 nm. We studied the permeability of the synovial capillaries of the rat between day 20 and 30 after birth using a polystyrene particle whose diameter was 240 nm. In addition using lecithin-coated polystyrene particles, we studied the maturation of the barrier function supported by endothelial and peripheral cells against foreign bodies. Lecithin-coated particles were found within the fibroblast-like synovial cells near the capillary in the 20 day-old rats, while non-coated particles remained in the endothelial wall and in the peripheral cells of capillaries. In the 30 day-old rats, lecithin-coated particles were present in the peripheral cells and the neighboring synovial cells; however, the non-coated particles were never found in the synovial or perisynovial cells. The present study shows that the size of the transportable substance by transcytosis may be larger than previously thought. Furthermore, the synovial capillaries functionally changed between day 20 and 30 suggesting that active movement of the joint led to the functional maturation of the synovial capillaries.

Gap junctional communication between the satellite cells of rat dorsal root ganglia.

Many studies have described the ultrastructure of the dorsal root ganglia in various embryonic and adult animals, but in spite of the efforts of many investigators the functional role of the satellite cells in this tissue is not clearly understood. In this study, we discuss the function of this cell type based on the concept of cell-to-cell interaction through gap junctions. Five male 60 day-old Wistar strain rats were used. All animals were anesthetized with pentobarbital and perfused with glutaraldehyde fixative, then the dorsal root ganglia in levels L4, L5 and L6 were taken from each rat. After postosmication, the specimens were prepared for observation by transmission electron microscopy. All nerve cells were completely surrounded by satellite cell cytoplasmic expansions. The boundaries between adjacent nerve cells and satellite cells were complicated due to the presence of perikaryal projections of nerve cells. Gap junctions which showed the typical trilamellar structure of plasma membranes were found mainly between satellite cell processes belonging to the same nerve cell. On the other hand, some gap junctions were found between the satellite cell projections belonging to different nerve cells. The size of the gap junctions ranged from 300 to 400 nm. No gap junctions were associated with the plasma membrane of any nerve cell. In conclusion, only satellite cells can share free transcellular exchange of cytoplasmic molecules such as ions, amino acids, sugars and several second messengers including cAMP and inositol 1,4,5-triphosphate by way of gap junctions in dorsal root ganglia.

Cytological changes of the pituitary basophils in rats slowly infused with thyrotropin-releasing hormone (TRH).

Young male rats were slowly infused with synthetic TRH, 1 microgram/hr, for 1, 3, 24, 48 and 72 hr, respectively. In the control rats, the basophils of the pituitaries can be divided, in their cytological properties, into the II- (classical thyrotrophs), II/III-,III, (classical LH-cell), and III/IV-type cell. The typical IV-type cells (classical FSH-cell), however, are scarcely found in the young rats. Following 1-hr infusion of TRH, the II-type cells decrease in number with the advancement of granular release, but morphological changes are not yet concrete on the other types of basophils. The II-type cells are quickly invisible following a 3-hr infusion, while the III- and III/IV-type cells remain without any significant changes. The III- and III/IV-type cells are progressively degranulated after a 24-hr infusion. The diameter of secretory granules is reduced to 100--150 nm. The smallest ones below 50 nm in diameter, are disintegrated to disperse into the ground matrix. After degranutlaion, the III/IV-type cells appear to revert to the polygonal or stellate cells with the identical fine structure with the II-type cells. There is evidence that the thyroidectomy cells may develop from the III/IV-type cells only after a 48-hr infusion. After 72 hr, most basophils are provided with the uniform structure of "reversionary II-type cells". In reference to the high serum TSH concentration and no significant change of pituitary TSH concentration under the same experimental condition (Soji, 1978), the present author conclusively postulates that the degranulation of the III/IV-type cells may mainly reflect the conspicuous elevation of serum TSH concentration. The above morphological results are contradictory a plausible view that TRH acts only upon the thyrotrophs to release TSH. The fact that all the basophils ultimately take an appearance of "reversionary II-type cells" in the gland by the prolonged infusion of TRH may not only suggest the share of responsiveness of all the basophils to TRH, but also support the hypothesis of secretory cycle of the basophils.