Observations on neurons and neuroglia from the area of the mesencephalic fifth nucleus of the cat in vitro

Summary Neurons from the mesencephalic root of the fifth nucleus from the kitten have been maintained in vitro for periods up to 70 days. During this time they retained their characteristic form and structure as seen in sectioned material. Axonic processes as long as 8 mm have been measured. The occurrence of recurrent axons intertwining with dendritic arborizations of the same neuron is discussed. Modulations are described for astrocytes in relation to their possible dependence on the scarcity of connective tissue elements and a lack of an outer mesenchymal tissue zone in cultures of mesencephalic explants.Grateful acknowledgment is made to Mrs. Walther Hild and Mrs. C. C. Morris for their generous contribution in the management of the tissue cultures and in executing staining procedures. Messrs G. Lefeber and E. Pitsinger offered indispensable aid with photographic work.This investigation was supported by a grant [PHS B-364 (C3)] from the National Institute of Neurological Diseases and Blindness, of the National Institutes of Health, Public Health Service, administered by C. M. Pomerat.     

Cytologic and metabolic parameters of pineal inhibition by continuous light in the rat (Rattus norvegicus)

Summary Adult rats (Rattus norvegicus) were subjected to continuous light or control conditions (14 hours light/day) for six weeks or longer, and quantitative cytological and metabolic studies were made of the pineal organs. After 11 weeks of continuous light, the pineal parenchymal cell's largest nucleolar eosinophilic mass is significantly reduced in diameter, especially in the medulla of the organ. Evidence of metabolic inhibition includes reduction of pineal glycogen content, succinic dehydrogenase activity, and respiration in the absence of exogenous substrates. Pineal ATP content, P³²-phosphate uptake and 5-hydroxy indole acetic acid content did not appear to be affected. Pineal serotonin content and melatonin-forming activity in the continuously lighted animals were measured but could not be interpreted metabolically, due to the diurnal fluctuations of these in control animals. Results provided here and elsewhere suggest that pineal inhibition by continuous light involves primarily the citric acid cycle, the accumulation of metabolites and lipid, and the synthesis of protein.This investigation was supported by grant GM-05219 from the National Institutes of Health, U.S. Public Health Service.I am grateful to Mrs. Virginia Green Bowers, Mrs. Ann Richards, Mr. Peter Charles Baker and Mr. Jorge Antonio Alvarado for laboratory assistance, and to Dr. Richard Strohman and Mr. David Epel, for advice on the determination of ATP.     

A cytochemical method for fixation and staining of lipids in frozen-dried mouse pancreas for study with light and electron microscopes

Summary A method is described for the cytochemical identification of lipids in acinar cells of the pancreas based chiefly on reactions of their carboxyl ester linkages and their double bonds. The method involves the reaction in vacuo of certain amine and hydrazine vapors with lipids in the solid state. The method is useful for studies with the light and electron microscopes.This research was supported in part by grants from the Public Health Service (GM 08328) and the Commonwealth Fund.I have been guided throughout by the perceptive advice of Professor Herbert S. Anker, Department of Biochemistry, University of Chicago. I am indebted also to the tireless work and support of Mrs. Faustina Manelis and Mrs. Elizabeth Vilkas.Dedicated to Professor Friedrich Wassermann with admiration and affection on the occasion of his eightieth birthday.     

Electron microscopical studies of the synapse in the developing chick spinal cord

Summary A search for synaptic strutures in the developing spinal cord of the chick has been made with the help of the electron microscope. We used as criteria of identification the presence of a) a thickening of neuronal membrane in contact with one another b) mitochondria and c) a type of vesicle usually associated with synapses. Structures fulfilling some of these requirements apear at the five day incubation stage and are clearly present at the ten day stage. Fully matured axosomatic and axo-dendritic synapses of both types appear at 16–18 days.Departmental technician for electronmicroscopy.We should like to acknowledge our gratitude to the Deutsche Forschungsgemeinschaft for their support, to Miss U. Wihlfahrt for technical assistance, Mrs. Bothe for the drawing of the diagramm, to the Welcome Trustees, London, for the loan of the Akashi microscope, and to the Volkswagenstiftung for the grant of the Siemens Elmiskop I.     

Ultrastructural changes of the neurohypophysis of the rat after castration

Summary The infundibular processes of the neurohypophysis of male and female rats were studied after different periods of castration. After seven days an increase in neurosecretory granules was observed. Two types of neurosecretory nerve endings were identified: dark ones, with dense neurosecretory elementary granules of 1600 A, and clear ones, with lighter neurosecretory granules of 1800 A. Protoplasmatic pituicytes showed a large increase in lipid granules together with a general hypertrophy. After one week of castration but with hormonal therapy the protoplasmatic pituicytes appeared normal or even showed less lipid granules than in the controls.With one month of castration the changes already mentioned in the nerve endings and pituicytes were more pronounced and after six months even more accentuated. Two types of neurosecretory nerve endings were clearly identified and the protoplasmatic pituicytes were loaded with lipid granules.The probable significance of the two different neurosecretory axons was discussed in relation to recent studies on the isolation of neurosecretory terminals from the neurohypophysis. The changes in the protoplasmatic pituicytes were considered in relation to the possible significance of the lipid granules.Supported by grants from the Consejo Nacional de Investigaciones Cientificas y Técnicas and by the Air Force Office of Scientific Research (AF-AFOSR 963-67).We are deeply indebted to Mrs. Defilippi-Novoa and Mr. Alberto Saenz for their skillful assistence.Associated Investigator, Consejo Nacional de Investigaliones Científicas y Técnicas, Argentina.     

Accumulation of organelles at the ends of interrupted axons

Summary Proximal and distal stumps of the sciatic nerve of rats were examined with the light and electron microscope in the course of 48 hours following nerve crush. On both sides of the lesion organelles accumulate in axons beyond regions disorganized by injury. A stretch of clear axoplasm filled with fine granules usually separates the cone of accumulating particles from the damaged part of the fibre. From two hours onwards closely packed vesicles, tubules, mitochondria and other organelles form dense pellets which fill up the whole lumen of the fibre. Further away from the fibre tip organelles are stranded at the circumference only, whereas the central core is occupied by neurofilaments. In a number of fibres no pellets are observed and only a moderately increased network of axoplasmic reticulum is seen at the fibre ends.Measurements on isolated fibres have shown that the length of the pellet increases with time on both sides of the lesion up to 18 hours after crush; thereafter the elongation is arrested in the distal stump, while in the proximal stump it continues further at a slower rate.The authors wish to acknowledge gratefully the technical assistance of Mrs. M. Sobotková, Mr. M. Doubek, Mrs. J. Waryszewska and Mrs. B. Lwowska.     

Ultrastructural study of the regressing prothoracic glands of blattarian insects

Summary The prothoracic glands, source of the molting hormone ecdysone, regress within a few days after the final molt, a process which was analyzed with electron microscopic methods in the cockroaches Leucophaea and Blaberus. This strictly timed event is accompanied by drastic alterations in cellular fine structure. Early signs of breakdown appear in groups of nuclei whose substance becomes segregated into patches of contrasting electron density characteristic of pyknosis.The most conspicuous change in the cytoplasm of parenchymal cells concerns the appearance of large, heterogeneous inclusion bodies in which various cellular elements become segregated. These compartments seem to represent autophagic vacuoles within which the gradual degradation of much of their contents takes place, presumably under the influence of lysosomal enzymes. Undigested swirls of membranous character may remain sequestered within these packets for some time.At advanced stages of cellular atrophy, plasma membranes and nuclear envelopes have gradually disappeared, and masses of protoplasm undergoing autolysis become invaded by a greater number of hemocytes than are present in nymphal glands. These phagocytic elements appear to engulf debris of parenchymal cells as well as some degenerating connective tissue elements. After the completion of the regressive process, the axial band of musculature characteristic of the nymphal gland persists on its own. Whether or not some parenchymal cells (or possibly their precursors) capable of reactivation persist in the proximity of this muscle is unknown.The resorption of the prothoracic gland in the newly emerged insect is the result of physiological autolysis and seems to be aided by the activity of phagocytic hemocytes.Dedicated to Professor W. Bargmann on his 60th birthday in friendship and admiration.This study was supported by Research Grants AM-03984, NB-02145 and NB-05219 from the U.S.P.H.S.I wish to express my thanks to Mrs. S. Wurzelmann, Mrs. C. Jones, Mrs. C. Grubman, and Mr. S. Brown for their excellent technical assistance.     

The ultimobranchial body in Rana pipiens

Summary Autoplastic transplants of ultimobranchial glands of male Rana pipiens were bilaterally or unilaterally placed in a homeotopic or heterotopic site. Serum calcium levels were maintained at normal values in bilateral autotransplants, while total ultimobranchialectomy resulted in hypercalcemia. Electron microscopy verified the viability and functional state of transplanted, denervated glands. During the periods of denervation, ergastoplasm and Golgi membranes exhibited hypertrophy which was reversed when unmyelinated nerves reappeared in the pericapillary space. Autotransplants under hypercalcemic conditions indicated that the process of secretion is primarily an intrinsic cellular activity and independant of innervation. The present evidence suggests that the sympathetic axons which innervate the parenchyma probably are inhibitory in nature and may allow depression of glandular functions during periods of hypercalcemia.The technical assistance of Mrs. Lilly Weeks is gratefully acknowledged. This project was supported by N. I. H. Grant No. AM-11795; The National Institutes of Arthritic and Metabolic Diseases.     

Rhythmic cortisol secretion in the equine: Analysis and physiological mechanisms

Abstract

Four Thoroughbred mares (no. 1–4) were maintained under constant temperature (24°C) and controlled light (L/D:12/12 with lights on at 06.00 hr) conditions. They were fed and watered ad libitum with fresh feed and water given at 09.00 hr. After a 45‐day pre‐conditioning period, blood samples were obtained by veinipuncture at 4‐hr intervals for 14 days to determine circadian and day‐to‐day variation. The horses exhibited a circadian rhythm with maximum values attained at about 12.00 hr, however, there are periods of days in which no rhythm is distinguishable. Ultradian rhythms with mean periods of 105 to 128 and 24 to 31 min are superimposed upon the circadian rhythm. The individual rhythms are quite variable from horse to horse and within the same horse. During periods of decline in plasma cortisol with metabolic half‐lives of approximately 70 min, secretion of cortisol was very low or had ceased. During periods of increasing plasma concentration, secretion was occurring at a faster rate than degradation. Rapid decreases in plasma concentration (metabolic half‐life of approximately 30 min) was accompanied by a rise in specific activity indicating cortisol with a high specific activity was entering the plasma pool from other storage pools.     

Some aspects of the fine structure of the statocysts of the molluscsPecten andPterotrachea

Summary The statocyst ofPecten is composed of hair cells and supporting cells. The hair cells bear kinocilia and microvilli at their distal ends and the supporting cells bear microvilli. The cilia have a 9+2 internal filament content, and arise from basal bodies that have roots, basal feet and microtubular connections. Two different ciliary arrangements are described, one with a small number of cilia arranged in a ring, and another with many more cilia arranged in rows. Below the hair cells are probable synapses. A ciliated duct connects to the lumen of the static sac and passes through the centre of the static nerve. The hair cells in the statocyst ofPterotrachea bear kinocilia and microvilli. The possible importance of cilia and microvilli in the transduction process is discussed.We would like to thank ProfessorJ. Z. Young for bringing specimens ofPterotrachea from Naples and also the staff of the Stazione Zoologica for the provision of specimens, Dr.M. Land for providing specimens ofPecten, the Science Research Council (U.K.) for providing the electron microscope used in much of the study and also for a grant to one of us (V.C.B.), and Mrs.J. Parkers and Mr.R. Moss and Mrs.J. Hamilton for much photographic and technical assistance.     

Photoperiodic and osmotic influences on the ultrastructure of the hypothalamic neurosecretory system of the White-crowned sparrow,Zonotrichia leucophrys gambelii

Summary An attempt was made to correlate functional changes in the neurohypophysis of the White-crowned Sparrow, Zonotrichia leucophrys gambelii, with morphologic features on the light- and electron-microscope levels. The aldehyde-fuchsin-staining anterior median eminence possesses essentially the same ultrastructural features as the non-staining posterior median eminence. The axon terminals are characterized by the presence of a large number of small vesicles (approximately 400 Å in diameter) and occasional electron-dense granules. The more-or-less depleted anterior median eminence occasionally evident in the photosensitive bird showing testicular development is indistinguishable ultrastructurally from the more intensely staining median eminence generally characteristic of the photorefractory bird. In the median eminence, stainability and functional state do not seem to be correlated with changes in the type, size or number of vesicles. A slight increase in the number of granules was noted in the photorefractory bird but this was considered insufficient basis to account for differences in stainability.The pars nervosa, on the other hand, responded to osmotic stimuli (saline drinking water) by loss of stainability and decrease in numbers of elementary neurosecretory granules. Small vesicles are also present in the pars nervosa axon terminals, but are intermingled with neurosecretory granules in normal birds. Acute-osmotic birds, however, had axon terminals almost entirely occupied by small vesicles.It is to be emphasized that the pars nervosa and the median eminence are two structurally very different regions of the neurohypophysis. The basis for aldehyde-fuchsin staining in the median eminence appears to differ from that in the pars nervosa. The implications of these findings are considered in regard to hypothalamic control over gonadotropic activity in the White-crowned Sparrow.Dedicated to Professor Dr. W. Bargmann in honor of his 60th birthday.This investigation was supported by grant GB-2484 from the National Science Foundation to Professor Bern, grant GB-2819 from the National Science Foundation to Professor Mewaldt, and grant NB-01353 from the National Institutes of Health to Professor Farner. The authors wish to express their appreciation of the technical assistance of Mrs. Irene Brown, Mr. John Butchart, Sally S. Kibby, Mrs. Carol Nicoll, and Mr. John Striffler. Mrs. Emily Reid kindly prepared the histograms.     

A simple method for following the fate of alanine-containing components in murein synthesis inEscherichia coli

The fate of the alanine-containing components in murein synthesis was followed by incorporation of¹⁴C-l-alanine inE. coli under conditions allowing cell-wall synthesis while preventing protein synthesis. The components were separated by chromatography and detected by autoradiography.Spots containing murein, cell-wall precursors, alanine andd-alanyl-d-alanine were identified. A further component was probably identical to pyruvic acid. Two unidentified spots were found in the region where lipid-intermediates in cell-wall synthesis are usually found. However, the absence of turnover of these two components was at variance with the proposed properties of the lipidintermediates. d-Alanyl-d-alanine and the component which is probably identical to pyruvic acid were excreted into the medium, whereas murein and cell-wall precursors were found in the cellular fraction.The influence of the concentration of alanine, and of the number of cells per ml, on the acid-precipitable activity were studied. The latter increased during, at least, the first two hours and represented mainly lysozyme-degradable material.Significant turnover of murein could be detected neither in the presence nor in the absence of protein synthesis.A time course of the activity of the radioactive components is provided. The influence of a number of antibiotics inhibiting cell-wall synthesis on the acid-precipitable activity and on the activity of the main intermediates in murein synthesis was studied.We thank Mrs. Arna van Schijndel-van Dam and Mr. A. A. G. Verweij for excellent assistance. We thank Dr. P. E. Reynolds (University of Cambridge) for teaching one of us (E J. J. L.) several techniques in the field of bacterial cell walls, and Dr. H. J. W. Wijsman for stimulating discussions.     

Cells with microvillous borders in the cerebral ganglion of Leptodora kindtii focke (Crustacea)

Summary Groups of large cells in the cerebral ganglion of Leptodora kindtii join in intricate patterns to enclose lacunar spaces. The cell surfaces bordering on these lacunae are covered by long, densely packed microvilli that all but fill the spaces. Near their brush borders the cells are joined by adhesion plates; for the rest they are separated from each other by glial septa. The possible significance of these structures is discussed.Dedicated to an inspiring teacher and loyal friend, Prof. F. Wassermann on the occasion of his 80th birthday, August 13, 1964.Supported by Grant No. NB-02145 from the United States Public Health Service. The expert assistance of Mrs. Cynthia Jones, Mrs. Sarah Wurzelmann, and Mr. Stanley Brown is gratefully acknowledged.     

An electron microscopic study of the development of rat testis in the first 10 postnatal days

Summary The ultrastructure of testis of immature rats from birth to ten postnatal days was studied in order to describe the development of germ cells into definitive spermatogonia. The primordial germ cells showed no structural changes from birth to 4 days after birth. At the 5th postnatal day the gonocytes were transformed into darker cells and began to migrate towards the basement membrane. As they reached the periphery of the seminiferous cords they resumed mitoses and gave rise to smaller gonocytes, which were progressively transformed in definitive spermatogonia. A lighter kind of supporting cell was also detected.We wish to thank Mrs. L. Giaccardo, A. Pozzolini and E. Taccini for skilled technical assistance.From the Department of Medical Pathology, Pisa University, Pisa, Italia.     

The effects of adenohypophysectomy on the hypothalamic-hypophysial neurosecretory system and the adrenal gland of the toad Bufo arenarum Hensel

Summary The effects of adenohypophysectomy were studied on the hypothalamichypophysial neurosecretory system and the adrenal glands of Bufo arenarum Hensel. An increase in vascularization of the pars intermedia was found and the neurosecretory material (NSM) in the glandular region of the median eminence disappeared. Its reappearance later was accompanied by hypertrophy of the pars intermedia; differentiated chromophil cells appeared in the pars intermedia around the vessels and, at the same time, the adrenal reverted to normal. These findings are interpreted as hypertrophy and differentiation of the pars intermedia with replacement, at least partly, of the functions of the pars distalis. The probable mechanism of differentiation and the functions of chromophil cells of the pars intermedia are discussed.This paper was presented at the VI Reunión de la Asociación Latinoamericana de Ciencias Fisiológicas (A.L.A.C.F.), Viña del Mar, Chile, 1964. It was carried out under the auspices of the Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina) and the Rockefeller Foundation (School grant RF-58028).Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.The authors wish to thank Prof. M. H. Burgos for his constant interest, Prof. B. A. Houssay, Prof. H. Heller and Dr. J. H. Tramezzani for their criticisms, Miss B. Rodriguez and Mr. L. Castro for their technical assistance.     

Ultrastructure of the peptidergic and monoaminergic neurons in the hypothalamic neurosecretory system of Anuran Batracians

Summary In the toad Bufo arenarum Hensel the following regions of the hypothalamic — neurohypophyseal system were studied under the electronmicroscope: preoptic and paraventricular nuclei, median eminence and infundibular process of the neurohypophysis.Neuronal perikarya of the preoptic nucleus are loaded with typical neurosecretory granules of peptidergic nature having a mean diameter of 1660 Å. While most neurons of the winter toad are in a storage stage a few show signs of a more active synthetic activity. A distinctive feature of preoptic neurons is the presence of large lipid droplets. The paraventricular nucleus contains small neurons containing granulated vesicles with a mean diameter of 800-1000 Å. In the region extending between these two nuclei and the median eminence axons containing either neurosecretory elementary granules or granulated vesicles are observed.The inner zone of the median eminence is occupied by axons of the preoptic neurohypophyseal tract; two types of axons, according to the size and density of the neurosecretory granules, may be recognized. The outer zone of the median eminence contains mainly axons and nerve terminals containing granulated vesicles of probable monoaminergic nature and only a few with granules of peptidergic type.The neurohypophysis contains two kinds of axons: one with more dense granules of 1800 Å and the other with granules of lesser electron density and 2100 Å. At the ending proper small clear vesicles of synaptic type are found.A progressive increase in volume of the peptidergic granules along the axon is demonstrated. This is of the order of 218% from the preoptic perikarya down to the infundibular process. The physiological significance of the two neurosecretory systems — i.e. the monoaminergic and the peptidergic — and the probable nature of the two types of peptidergic axons is discussed.Supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas and by the Air Force Office of Scientific Research (AF-AFOSR 963-67).The authors want to express their gratitude to Mrs. Defilippi-Novoa and Mr. Alberto Sáenz for their skillful assistance.     

On the cilium cell relationship in the adenohypophysis of the mouse

Summary The 8+1 cilia previously reported in the adenohypophysis have been reinvestigated with special emphasis on their relation to the parent cell. In contrast to the fibril pattern which is remarkably constant, this relation shows great variation, supporting the hypothesis that the cilia are rudimentary.This study was supported in part by Grant NB 02215 of The National Institute of Neurological Diseases and Blindness, U. S. Public Health Service. This aid is gratefully acknowledged. The author wishes to thank Dr. Th. Blackstad for valuable advices and Mrs. J. L. Vaaland for skillful technical assistance.     

Ultrastructure of transitional epithelium of man

Summary Blocks of human normal renal pelvis and ureter obtained at the time of surgery were fixed in glutaraldehyde and osmium with or without ruthenium red, for electron microscopic observations. The transitional epithelium is arranged in three cell layers: basal, intermediate and superficial. All epithelial cells show numerous microvilli and contain the characteristic vesicles of transitional epithelium, bundles of cytoplasmic filaments, microtubules and numerous free ribosomes. The epithelial extracellular compartment is notably large and appears as an intricate, tridimensional network of canaliculi and cisternae which are wider in the intermediate and superficial layers and in which microvilli and cytoplasmic folds of vicinal cells are often attached or interdigitated. At these sites there are desmosomes.The surface of all transitional epithelial cells is covered by a fibrillar mucous coat which is more developed at the plasmalemma of the free border of luminal cells in which microvilli are also seen. Ruthenium red stains selectively the plasmalemma and the mucous coat of the free surface of the epithelium, indicating the presence of an acid polysaccharide. With this technic (Luft, 1965), it is observed, radiating from the plasmalemma, branching filaments which measure 100 Å in diameter forming a zone of varying density which is about 400 m wide and which corresponds, at the light microscopic level, to the luminal border of the transitional epithelial cells in which a sialomucin has been identified. The slender filaments have a beaded appearance. At the free border, superficial cells are attached by functional complexes in which tight junctions seal the epithelial intercellular space, which is opened at the level of the basement membrane where only desmosomes are observed.The ultrastructure of human transitional epithelium of urinary tract resembles the duct cells of the salt gland of certain marine birds (Fawcett, 1962) and the amphibian epidermis (Farquhar and Palade, 1965) in which there are active processes of transport. The mucous surface coat, selectively stained by the ruthenium red, contains a sialomucin (Monis and Dorfman, 1965, 1967).The ultrastructure and histochemistry of the mucous fluffy coat of man transitional epithelium and the observations of Porter and Tamm (1955), on the ultrastructure of preparations of the Tamm and Horsfall mucoprotein (1952) are bases for suggesting that transitional epithelium of urinary tract of man is the site of biosynthesis of certain urinary mucoids. Present investigations are directed to obtain evidence to substantiate this hypothesis.General Abbreviations B basal cell - E exfoliating cell - I intermediate cell - L lumen - S superficial cell - SC surface coat - bm basement membrane - ci cell infolding - d desmosome (macula adhaerens) - f fibroblast - fi cytoplasmic filaments - is intercellular space - jc junctional complex - ly lysosome - lym lymphocyte - mt microtubules - m mitochondria - mv microvilli - n nucleus - r ribosomes - rv round vesicle - zo zonula occludens - za zonula adherens Dr. Monis wishes to thank Dr. E. De Robertis for the use of the electron microscope facilities of the Instituto de Anatomía General y Embriologia, Facultad de Medicina, Universidad de Buenos Aires. — Prof. E. Trabucco and Dr. R. J. Borzone (Cátedra de Clinica Genitourinaria de la Facultad de Medicina, Universidad de Buenos Aires) generously supplied the specimens which were the bases of this study. — Thanks are due to Mrs. A. M. Novara and Mrs. Defilippi-Novoa for efficient technical help and to Miss Rosa Gentile for secretarial assistance. Photomicrography by Mr. M. A. Saenz.Dr. Zambrano is investigator (CNICT).     

Particles resembling microbodies in normal and neoplastic perianal glands of dogs

Summary By electron microscopy, the parenchymal cells of the perianal glands of dogs contain granules which have the morphological features of microbodies (peroxisomes) including marginal plates and, occasionally, dense nucleoids. Like microbodies, they are occasionally attached to the endoplasmic reticulum. Histochemical evidence is presented suggesting that they contain at least one of the peroxisomal enzymes, L--hydroxy acid oxidase. The granules of a perianal gland adenoma showed abnormal morphologic variations.Mrs. Murtie Still, Mrs. Bertha McClure and Mr. Bob White gave valuable technical assistance.     

Vascularization of the hypophysial region of the normal and adenohypophysectomized toad

Summary The study of standarized sections of the hypophysial regions, and in vivo observations showed the presence of communicating vessels between the capillary network of the median eminence and the large capillaries of the neurointermediate junction. Moreover, direct branches from the hypophysial artery are described which give off branches, at the level of the neural stalk, to the median eminence and to the large capillaries of the neurointermediate junction.A second portal system similar to the one described by Cruz has been observed. Its primary plexus originates in several encephalic regions, and its secondary plexus is distributed through the neural lobe and thence to the pars intermedia. The course of flow in this system is a descending one. The arterial contribution to this system appears to arise from branches from the basilar and retroinfundibular arteries. — There are small venous-type vessels between the large capillaries of the neurointermediate junction and the posterodorsal region of the pars distalis. — After adenohypophysectomy, the blood which normally goes towards the pars distalis, flows towards the pars intermedia, following the path of the communicating vessels between the median eminence and the pars intermedia.This paper was presented at the VII Reunion de la Asociación Latinoamericana de Ciencias Fisiológicas (A.L.A.C.F.), Mar del Plata, Argentina, 1966. It was carried out under the auspices of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Rockefeller Foundation (School grant RF-58028).Fellows of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina. — The authors wish to thank Prof. B. A. Houssay and Drs. J. H. Tramezzani and J. la Pointe for their criticism, to Prof. M. H. Burgos and Dr. F. Sacerdote for their help.