The gonadotropic cells in the adenohypophysis of the blind mexican cave fish,Anoptichthys jordani

Summary The development and activity of the basophils in the meso-adenohypophysis of Anopthichthys jordani were studied in relation to the maturation of the gonads. In addition, pituitaries and ovaries of post-spawning females were studied during a period 0–11 days subsequent to spawning. The large and mainly PAS-positive basophilic cells in the meso-adenohypophysis were the only cell type that showed a correlation with the development and maturation of the ovaries and testes. These cells were subjected to a partial or complete degranulation in females following oviposition, when yolk formation in the ovary was at a maximum. It is concluded that the large PAS-positive basophils in the mesoadenohypophysis have a gonadotropic function and that only one gonadotropic cell type is present in the adenohypophysis of Anoptichthys jordani.This study was partly supported by a grant from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.).I wish to express my gratitude to Prof. Dr. P. G. W. J. van Oordt for his active interest and constructive suggestions. Mr. R. van den Hurk and Miss Tjitske van Soelen provided valuable assistence in the course of the experiments. Mr. H. van Kooten made the photographs. Special thanks are due also to Mr. M. J. van Oosterum and Mr. J. Rowaan; without their capable and constant help it would have been hardly possible to obtain such satisfactory spawning results.     

The cell types in the adenohypophysis of the Blind Mexican Cave Fish,Anoptichthys jordani (Hubbs and Innes)

Summary Staining sagittal sections of the pituitary of the Blind Mexican Cave Fish, Anoptichthys jordani, with a number of methods including Herlant's tetrachrome, Herlant's Alcian Blue (AB)-periodic acid Schiff (PAS)-orange G, Gabe's aldehyde fuchsin and lead hematoxylin according to Mac Conaill, made it possible to distinguish seven tinctorial cell types in the adenohypophysis: in the pro-adenohypophysis erythrosin-positive acidophils, and lead hematoxylin-positive amphiphils, lining branches of the neural lobe; in the meso-adenohypophysis orange G-positive acidophils, large, weakly AB- and AF-positive, strongly PAS- positive basophils, and smaller strongly AB- and AF-positive basophils; in the metaadenohypophysis lead hematoxylin-positive and -negative cells. These cell types are compared with those in other teleosts.This work was supported by a grant from the Netherlands Organization for the Advancement of Pure Research (Z. W. O.).The author gratefully acknowledges the constant interest and helpful suggestions of Prof. Dr. P. G. W. J. van Oordt. Thanks are also due to Mr. H. van Kooten for making the photographs.     

The identification of the thyrotropic cells in the adenohypophysis of the cichlid fish Cichlasoma biocellatum and the role of these cells and of the thyroid in osmoregulation

Summary In order to identify the thyrotropic cells in the pituitary gland of Cichlasoma biocellatum, adult animals were treated with thyroxine. Periodic acid Schiff (PAS)- and aldehyde fuchsin (AF)-positive, and Alcian blue (AB)-negative basophils in the meso-adenohypophysis as well as the thyroid were strongly inactivated by such treatment. Since other cell types in the adenohypophysis were not affected, it is concluded that the PAS-positive and AB-negative basophils in the meso-adenohypophysis are the thyrotrops. In normal animals the thyrotrops and the thyroid are very active. Propylthiouracil did not cause a further activation of TSH cells. Keeping the animals in 25% sea-water caused a strong inactivation of the prolactin cells, the thyrotrops and the thyroid. In deionized water the prolactin cells were stimulated, but the thyroid was less active than in controls. Injections of ovine prolactin did not enhance the activity of the thyroid in salt water animals. It is suggested that in Cichlasoma biocellatum prolactin does not have a direct stimulatory effect on the thyroid.Thanks are due to Prof. Dr. P. G. W. J. van Oordt for his continual interest and valuable suggestions, and to Dr. L. Boomgaart for correcting the english. We are indebted also to Messrs. H. van Kooten and E. van der Vlist for making the photographs. The National Institutes of Health, Bethesda, Maryland (U.S.A.) kindly presented the ovine prolactin.     

Hypothalamic neurosecretion and metamorphosis inXenopus laevis

Summary The frontal brain was removed from premetamorphic larvae ofXenopus laevis. Part of the animals was kept in a 0.01% propylthiouracil (PTU) solution for 21, 30 or 90 days, together with unoperated controls. Others were reared in tap water for the same length of time. The hypothalamus, the pituitary and the thyroids were studied in sagittal sections stained with aldehyde fuchsin or pseudoisocyanine (PIC).Operated tadpoles lacking the telencephalon only, could not be distinguished from unoperated controls. Extirpation of the preoptic region of the hypothalamus lowered the activity of the thyrotropic (TSH) cells and of the thyroids, and blocked metamorphosis. In animals with intact PIC-positive cells in the dorsal preoptic region, PTU induced a degranulation of these cells, stimulated the TSH cells and caused a strong hypertrophy of the thyroids. It is concluded that these neurosecretory cells in the dorsal preoptic region produce a thyrotropin-releasing factor (TRF), indispensable for the endocrine regulation of metamorphosis, and that the thyroid hormones have a negative feed-back influence upon the TRF cells.In part of the animals lacking the rostral hypothalamus, new PIC-positive cells were observed to develop immediately behind the preoptic region. In these animals PTU was somewhat less effective than in the animals with an intact dorsal preoptic region. This means either that the newly differentiated PIC-positive cells have a TRF function or that the thyroids can exert a direct negative feed-back upon the TSH cells. The latter possibility is supported by the fact that even in the absence of any neurosecretory cell PTU stimulated the thyroids.Blocking of thyroid hormone production by PTU inhibited the differentiation of the hypothalamus, of the median eminence and of the portal vessels. It may be deducted that during metamorphosis the general morphogenetic effect of the thyroid hormones stimulates the differentiation of the structures necessary for the augmentation of the TSH activity.The author thanks Prof. Dr.P.G.W.J. van Oordt for his active interest and helpful advices, MissTineke Aafjes for technical assistance and Mr.H. van Kooten for making the diagrams and photographs.     

The effect of metopirone and aldactone on the interrenal tissue of intact and pars distalis-ectomized common frogs Rana temporaria

Summary The effects of metopirone (SU-4885) and aldactone (SC-9420) on the histology and histochemistry of the interrenal tissue of male common frogs, Rana temporaria, have been studied. From the changes in nuclear and cellular size, mitotic rate, and lipid and cholesterol content it has been concluded that in intact animals the administration of metopirone as well as of aldactone resulted in an increase of the interrenal secretory activity. The effects were very similar to that of ACTH. Ablation of the pars distalis prevented the interrenal activation by metopirone. The effect of aldactone was markedly reduced in operated frogs, but some stimulation remained. It is suggested that both substances act by way of enhancing pituitary ACTH ouput. The dependence of the secretion of corticosteroids on pituitary ACTH is discussed.I wish to thank Dr. W. J. van Dongen for his cooperation and criticism and for enabling me to do this work in his laboratory. I am endebted to Prof. Dr. P. G. W. J. van Oordt for his valuable and constructive suggestions. Thanks are also due to Miss Mieke Roelofsen and Miss Ineke Wienen for their conscientious technical assistance.     

Hypothalamic neurosecretion and metamorphosis in Xenopus laevis

Summary Normal and propylthiouracil (PTU) treated Xenopus laevis tadpoles were fixed during all stages of metamorphosis and sagittal sections were stained with aldehyde fuchsin (AF) or pseudoisocyanine (PIC). Whereas AF positive neurosecretory material could only be demonstrated in the preoptic nucleus from late prometamorphosis, increasing amounts of PIC positive material were found in cells of the dorsal part of the preoptic region from early premetamorphosis. The development of these cells correlated with that of the thyrotropic cells and the thyroids. Likewise, signs of hyperactivity in thyroids and thyrotropic cells of PTU treated larvae were accompanied by a depletion of the dorsal PIC positive cells. In the ventral preoptic region PIC positive cells developed from late prometamorphosis in control larvae, but failed to do so in PTU treated animals. It is argued that the differentiation of the PIC positive cells is largely dependent on thyroid hormones; that the dorsal PIC positive cells may produce a thyrotropin releasing factor; and that the function of these dorsal cells is inhibited by thyroid hormones.The authors thank Dr. P. G. W. J. van Oordt for his active interest and helpful advices, Miss Tineke Aafjes for technical assistance and Mr. H. van Kooten for making the photographs.     

Effects of thyroxine and cold exposure on hypothalamic TRH levels in rats with various pituitary-thyroid states.

The hypothalamic content and concentration of thyrotropin-releasing hormone (TRH) were determined by radioimmunoassay in normal, thyroidectomized, hypophysectomized and cold-exposed rats with or without thyroxine. In normal animals, the single administration of thyroxine (1,5 and 20 microgram/100 g B.W.) altered neither the content nor the concentration of TRH in the hypothalamus. However, seven days' administration of this hormone resulted in the dose-dependent increase in the hypothalamic TRH levels. In thyroidectomized rats the hypothalamic TRH levels were slightly reduced in spite of the marked increase of plasma TSH levels and decrease of pituitary TSH levels. In the animals given thyroxine (10 microgram/100 g B.W.) for 7 days in addition to thyroidectomy, however, the TRH levels exceeded that in the animals which underwent throidectomy alone. The hypothalamic TRH levels were markedly reduced in hypophysectomized rats. Conversely, in hypophysectomized rats given 7 days' thyroxine (1 and 5 microgram/100 g B.W.), the levels were increased dose-dependently. In cold-exposed rats, the plasma TSH levels roughly doubled, but the TRH levels remained unchanged. These findings strongly suggest that the feedback site of thyroxine extends not only to the pituitary gland but also to the hypothalamus, and that thyroxine has an increasing effect of the hypothalamic TRH level, though the mechanism(s) remain to be clarified.     

Localization of thyrotropin (TSH) in the dog pituitary gland

Summary Using the immunoperoxidase technique and antisera to the specific beta () subunits of bovine and rat TSH¹, selective immunocytochemical staining was localized in a specific cell population in the pars distalis of the dog pituitary gland. These TSH cells were found to be positive to aldehyde fuchsin, alcian blue, periodic acid-Schiff (PAS) and aniline blue. With the performic acidalcian blue (pH 0.2) -PAS-orange G procedure these cells stained blue-purple, demonstrating FSH/LH cells (blue or turquoise), ACTH/MSH cells (redpurple) and PRL cells (orange-red). The TSH cells were further differentiated from other functional cell types of the pars distalis on the basis of their typical cytological features, intraglandular distribution and by immunocytochemical double staining. In the pars distalis of adult male dogs the TSH cells were mostly shown to be smaller in size and less numerous than in bitches in the anestrous phase of the sexual cycle. Moreover, cytological alterations in the immunoreactive thyrotrophs in the pituitary of male and female dogs generally paralleled the spontaneous changes in thyroid function associated with thyroid atrophy and/or pituitary insufficiency, and thyroid hyperplasia or goiter. In conclusion, because of their specificity and high potency, the antisera to the -subunits of bovine and rat TSH represent an effective tool for the selective immunocytochemical localization of TSH in the dog pituitary. This allows the study of the morphology and function of TSH cells under different physiological, pathological and experimental conditions.Abbreviations for Hormones cited in this Paper ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin - TRH TSH Releasing Hormone - CG Chorionic Gonadotropin The authors are grateful to Mrs. B. Schilk and Miss U. Tüshaus for their excellent technical assistance     

The effect of propylthiouracil and temperature on avian thyroid activity.

High ambient temperatures cause a reduction in thyroid gland size of chickens but propylthiouracil (PTU) treatment produces an increase in gland size regardless of temperature. This increase in size after PTU treatment during high temperature is evident after 7 days of PTU treatment but not after 14 days of treatment. Cyclic AMP-dependent protein kinase is activated in the thyroid gland with PTU treatment during high temperatures with no alteration in activity in the pituitary. These results suggest that the pituitary is not activated by TRH during periods of high ambient temperature and the thyrotrophs may release TSH in direct response to lowered serum thyroid levels produced by PTU treatment.     

Histological changes in the pituitary-thyroid axis during spontaneous and artificially-induced metamorphosis of larvae of the flounder Paralichthys olivaceus

Summary Histological changes in the pituitary TSH cells and in the thyroid gland of flounder (Paralichthys olivaceus) larvae during spontaneous or artificially induced metamorphosis were studied. Activity of the immunoreactive TSH cells (IrTSH cells) gradually increased during premetamorphosis, reaching the highest level in prometamorphic larvae, and the cells were degranulated in metamorphic climax. The IrTSH cells were most inactive at the post-climax stage. The thyroid gland was morphologically the most active in metamorphic climax when the degranulation occurred in the pituitary IrTSH cells, and appeared inactive at post-climax. A few weeks after metamorphosis, both the IrTSH cells and the thyroid gland appeared to be activated again in the benthic, juvenile flounder. Administration of thyroxine or thiourea revealed negative feedback regulation of the pituitary-thyroid axis in flounder larvae. These results indicate that activation of the pituitary-thyroid axis induces metamorphosis in the flounder.     

Thyroid hormone action on ACTH secretion

Thyroid hormone effects on pituitary ACTH have not been well established. Adult male Sprague-Dawley rats were rendered hypo- and hyperthyroid while undergoing treatment with 6-Propylthiouracil (PTU) and L-Thyroxine (T4). At the time of decapitation, plasma values for T4 (micrograms/100 ml) were 3.9 +/- 0.4 in the control, 17.3 +/- 2.2 in the T4 and less than 2 in the PTU treated group; plasma T3 and TSH confirmed hyper- and hypothyroidism in the T4 and PTU treated groups respectively. Plasma immunoassayable ACTH and corticosterone were significantly increased in hyperthyroid and decreased in the PTU treated animals. Pituitaries were removed and incubated in DMEM. After 3 h incubation, ACTH content and secretion to the medium were significantly lower in the PTU group. As expected, pituitary TSH content and secretion were decreased in the T4 treated animals. These data indicate that thyroid hormones influence pituitary-adrenal function by increasing ACTH secretion and consequently corticosterone production.     

The influence of social rank on adenohypophysial cell activity in Salmo irideus

Summary In nine cell types of the adenohypophysis in untreated adult rainbow trout, histologically different activity phases, seasonal changes in activity, and the relation between certain cell types and the interrenal gland, thyroid or gonads were investigated by light and, occasionally, by electron microscopy. Special attention was given to the effect of social rank on the synthetic activity in adenohypophysial cells of trout kept in small groups in which a social hierarchy with one (light) dominant and several (dark) submissives is established.Cell types in the rostral pars distalis were azocarminophil (I) or amphiphil (II). Proximal pars distalis cell types were slightly basophil (IV), orangeophil (V), strongly basophil (VI) or chromophobe (VII). In the pars intermedia, cell types were amphiphil (VIII) or very slightly basophil (IX). Type III was a non-secretory supporting (?) cell.Histologically different activity phases abounded in type IV cells, which mainly occurred in the proximal pars distalis but were also found dispersed in the rostral pars distalis, the pars intermedia and the neurohypophysis.Influences of social rank were pronounced in type IV cells. Phases with a high synthetic activity were exclusively found in submissive animals, phases with a low synthetic activity occurred in dominants. As a positive relation existed between type IV cell activity and the social rank dependent activity of the interrenal gland, it was suggested that type IV cells produce ACTH.In (dominant) male trout treated with DOCG or ACTH, colloid-containing type IV cell phases, reflecting accumulation of the secretory product, were found. This supported the earlier suggestion that ACTH in the trout is produced in the basophil type IV cells and not, as reported in the literature, in cells comparable to type II.The author is greatly indebted to Miss M.C. Wentzel, Miss I. Stulen, Mr. J. Veening and Dr. J.G. van Rhijn for their help with histological techniques, interrenal cell measurements and statistical aspects     

Aging and gender affect the response of thyrotropin (TSH) to gastrin releasing peptide (GRP) in rats

We had previously shown that GRP acts directly at the pituitary gland inhibiting basal and TRH-stimulated TSH secretion in adult male rats. In this study we showed a gender dimorphism in this response of old animals pituitaries to GRP. In both female and male young adult animals, GRP-incubated pituitaries showed approximately 50% less basal and TRH-stimulated TSH secretion to the medium, without affecting the pituitary content of TSH. However, GRP did not have any significant effect upon TSH secretion in old male rats, but the old female showed the same degree of response to GRP as the young adult female rat, regarding basal and TRH-stimulated TSH secretion, while the TSH pituitary content after GRP incubation was higher than that of the young female group. Our data suggest a loss of thyrotrope responsiveness to GRP in aged male rats that could contribute to the decrease in TSH pituitary stores leading to lower basal and TRH-stimulated TSH secretion. Meanwhile, the preservation of GRP responsiveness could help in the relative maintenance of these parameters in the old female rat.     

Histological,immuno- and enzyme-histochemical investigations on the adenohypophysis of the urodeles,Mertensiella caucasica and Triturus cristatus and the caecilian,Chthonerpeton indistinctum

Summary The pituitary glands of two urodelan species (Mertensiella caucasica, Triturus cristatus) and one caecilian species (Chthonerpeton indistinetum) were examined with histological (Alcian blue, Brookes' trichrome stain), enzyme histochemical (acid phosphatase, -naphthylacetate-esterase, acetylcholinesterase) and immunofluorescence techniques (anti-carp GTH, anti-ovine prolactin, anti-synthetic -MSH). In the pituitary gland of Mertensiella and Triturus six chromophilic cell types could be distinguished. A strong fluorescence was observed in the MSH-, GTH- and TSH-cells.In the pituitary gland of Chthonerpeton only five chromophilic cell types could be distinguished: in the rostral part of the pituitary gland the B₃-cell; in the basal region of the central area the B₂-cell; dorsocaudally the B₁-cell. The acidophilic cells were found in the central and caudal part of the pars distalis. The basophils of the pars intermedia could be observed in the dorsocaudal part of the pituitary gland surrounding the neurohypophysis. All acidophilic cells showed a strong immunofluorescence with anti-ovine prolactin (LTH).     

Therapeutic exploration of betulinic acid in chemically induced hypothyroidism

Hypothyroidism is a chronic condition characterized by abnormally low thyroid hormone production. The decreased serum level (>5.1 mIU/l) of thyroid-stimulating hormone (TSH) in blood indicates hypothyroidism. The study was an attempt to access the effect of betulinic acid on chemically induced hypothyroidism in female albino rats. Betulinic acid is a naturally occurring pentacyclic triterpenoid, which has antiretroviral, antimalarial, and anti-inflammatory properties, as well as anticancer potential, by inhibiting topoisomerase. Hypothyroidism was induced in female albino rats using propylthiouracil (PTU) at a dose of 60 μg/kg body weight orally for 1 month. Induction of hypothyroidism was confirmed by increased TSH level. At the end of second month, blood was collected, centrifuged and serum was analyzed for TSH, T3, and T4 level and protocol was terminated by killing of animals. The animals exposed to PTU were treated with pure standard drug thyroxine at a dose of 10 μg/kg of body weight by oral route and the test drug betulinic acid 20 mg/kg by oral route through force feeding in their respective groups. Treatment was carried out for a period of 2 months. Group with PTU-induced hypothyroidism showed an elevation in serum TSH and reduction level, which was restored by the betulinic acid in treated female albino rats. Betulinic acid also reduced the damage caused in the thyroid tissues by PTU, thus minimizing the symptoms of hypothyroidism. Histopathological examinations of the thyroid tissue showed changes in the thyrocytes of PTU-treated group while thyroxine group showed normal thyroid follicles cell architecture and the group treated with betulinic acid also showed marked improvement in the follicles integrity which shows that betulinic acid has some protective activity. This study shows that the betulinic acid has thyroid-enhancing potential by lowering down the TSH levels and reducing the damage caused in the thyroid tissues, thus minimizing the symptoms of hypothyroidism when used anaphylactically in rats.     

Zum Verhalten blinder Fische

• 1 Das Verhalten bei der Nahrungsaufnahme wurde nach Augenexstirpation an Phoxinus phoxinus L., Gasterosteus aculeatus L. und Hemigrammus caudovittatus Ahl beobachtet, sowie zum Vergleich am Höhlenblindfisch Anoptichthys jordani Hubbs und Innes.
• 2 Bei Dressuren auf Saccharose zeigen die genannten Arten unterschiedliches Lernvermögen: Phoxinus benötigt ca. 37, Gasterosteus und Hemigrammus 21 und Anoptichthys lediglich 10 Dressuren (1 Dressur pro Tag), um die Aufgabe zu erlernen.
• 3 Bei Dressuren auf verschiedene Geschmacksstoffe lernt Phoxinus am schnellsten seine Aufgabe bei Saccharose, langsamer bei Essigsäure und Natriumchlorid, am langsamsten bei Chinin-hydrochlorid.
• 4 Ein Einfluß des Wetters auf das Verhalten der Fische während der Dressur konnte nicht festgestellt werden.
• 5 Das Verhalten geblendeter Fische im Schwarm sehender Artgenossen wurde beobachtet.
• 6 Ein geblendeter Hemigrammus kann sich in einem Schwarm des blinden Höhlenfisches Anoptichthys jordani behaupten.
• 7 Von den 3 geblendeten Arten konnte Phoxinus II 3 Jahre und 11 Monate, Hemigrammus XII 2 Jahre und Gasterosteus XVII 4 Monate am Leben erhalten werden.
• 8 Die Beobachtungen werden anhand der Schilderungen anderer Autoren diskutiert, u. a. auch im Hinblick auf die Existenzmöglichkeit geblendeter Fische in natürlichen Gewässern.

     

Effects of thyroidectomy, propylthiouracil, and thyroxine on pituitary content and immunocytochemical staining of thyrotropin (TSH) and thyrotropin releasing hormone (TRH)

Previous studies have demonstrated immunocytochemical staining for beta chains of thyroid stimulating hormone (TSH-beta) in rough endoplasmic reticulum of pituitary cells hypertrophied after thyroidectomy ("thyroidectomy cells") (Moriarty CG(1976): J Histochem Cytochem (24:846; Moriarty GC, Tobin RB (1976): J Histochem Cytochem 24:1140). Here we report the localization of thyrotropin releasing hormone (TRH) in serial sections of the same pituitaries to determine if it could be found at similar sites. No staining for TRH was found in hypertrophied TSH cells formed 42 days after the surgery, or after 14, 34, and 70 days of propylthiouracil (PTU) treatment. The loss in immunostaining in the PTU-treated rats was correlated with radioimmunoassay (RIA) measurements that showed a 65% reduction in anterior pituitary TRH content after 34, 70, and 98 days of PTU treatment (from 22.9--7.8 pg/mg wet wt) and a 50% reduction in TSH content after 34 days of treatment. When thyroxine was administered to hypothyroid rats for 3 days before death, our previous studies had demonstrated intense staining for TSH in granules inside the rough endoplasmic reticulum. In this study, the radioimmunoassay showed that TSH content rose dramatically in the hypothyroid animals treated with PTU for 77 days and thyroxine for 2 days before death (from 8.5--64.1 mU/mg wet wt); however, the rise in TRH content was minimal (5.8--9.8 pg/mg wet wt). The immunocytochemical stain for TRH correlated well with the RIA showing a weak reaction mainly on small granules in the cytoplasm. No reaction for TRH was found in rough endoplasmic reticulum. These results suggest that TRH and TSH storage sites are dissimilar in the hypothyroid rat. The presence of stain for TRH in granules in the cytoplasm suggests that it might play a role in the storage or packaging of TSH. Its absence in profiles of rough endoplasmic reticulum staining intensely for TSH suggests that it is not synthesized at this site. No definite conclusions about its origin can be drawn at this time.     

Lactate dehydrogenase gene function in the blind cave fish,Anoptichthys jordani,and other characins

The functions of the genes encoded for lactate dehydrogenase (LDH) in six genera of characins (teleost) were examined by electrophoretic and immunochemical analyses of the LDH isozymes. The characins possess the LDH A and B loci present in all vertebrates. The eyeless Mexican cave fish (Anoptichthys jordani) and other characins possessing normal eyes, e.g., Mexican tetra (Astyanax mexicanus, which is able to hybridize with the cave fish), blue tetra (Mimagoniates microlepis), sailfin tetra (Crenuchus spilurus), head and tail light tetra (Hemigrammus ocellifer), and the piranha (Serrasalmus spilopleura), all lack the function of a third LDH locus (the E locus) present in many teleosts which codes for a distinctive isozyme synthesized in the nervous system, particularly in the neural retina.This research was supported by NSF grant GB 16425 to G.S.W. F.S.M. was a James Scholar at the University of Illinois during the course of this research.     

Correlation between microtubular number and transport activity of hypothalamo-neurohypophyseal secretory neurons

Summary The lower pituitary stalk has been studied in rats given hypertonic saline for four days and in rats with congenital diabetes insipidus (GDI), that is, in two groups of animals in which there is evidence of an increase in the transport of polypeptides down the axons of the tractus hypophyseus.A quantitative ultrastructural analysis of this tract, the first yet made, has demonstrated that in normal animals it is composed of unusually small axons, over half of which are less than 300 nm in diameter.In this tract there is a significant increase in axonal diameter and microtubular content in animals given hypertonic saline for four days. In adult rats with CDI, these changes are even more marked, a feature which is correlated with the fact that in these animals the transport of polypeptides has probably been abnormal since birth.An alteration in the microtubular content of neurons has not previously been observed either in physiologically stressed animals or in diseased animals; such alterations suggest the participation of microtubules in polypeptide transport. The narrow diameter of axons in the tractus hypophyseus of the normal animal raises the possibility of the extravesicular transport of such polypeptides.Abbreviations used ADH antidiuretic hormone - AF aldehyde fuchsin - CDI congenital diabetes insipidus - HNS hypothalamo-neurohypophysiel system - NSM neurosecretory material - NSV neurosecretory vesicle - PVN paraventricular nucleus - SON supraoptic nucleus This paper is dedicated to Professor W. Bargmann.We are grateful to Miss Pauline Chapman for technical assistance.This project is supported by the Medical Research Council.     

Changes in thyroid function caused by continuous treatment with thiouracil in rats

Serum concentration evolution of thyroxine and triiodothyronine, and thyrotropin (TSH), have been studied in rats while they were given 6-propylthiouracil (PTU) as antithyroid drug, and during the recovery period after suppression of treatment. In the same way thyroid hypertrophy and plasmatic levels of thyrotropin were correlated. Animals received orally a daily dose of 1 mg/100 g body weight during thirty-five days and had a two week recovery period. Thyroid hormone concentrations in plasma were determined by immunoenzymatic assay ELISA with peroxidase as labelled enzyme. From the results obtained, it can be stated that chronic administration of PTU implies a continuous decrease in thyroid hormone concentrations in plasma, reaching nearly zero values, while after treatment, levels recover their normal values in a week's time. A parallelism exists between thyroid hypertrophy and pituitary TSH hypersecretion, due to a decrease in thyroid hormone levels.