Fine structure of the median eminence and the pars nervosa of the bullfrog,Rana catesbeiana

Summary The hypothalamic neurosecretory system of the bullfrog, Rana catesbeiana, was studied with light- and electron microscopy. The median eminence is roughly divided into two portions. The upper portion mostly consists of ependymal cells, glial cells and preoptico-hypophysial nerve tract, whereas in the lower portion, neurosecretory axons, glial cells, processes of glial and ependymal cells, and fine blood vessels of the hypothalamic portal vein are located. A part of the neurosecretory axons of the preoptico-hypophysial tract proceeds to the lower portion of the median eminence. These axons are arranged perpendicularly to the capillaries of the hypothalamic portal vein. The glial cells are densely located in the area of the median eminence where neurosecretory material is abundant. The neurosecretory material in the neurosecretory cells, their axons, the median eminence and the pars nervosa of the bullfrog shows a positive reaction to PAS treatment.The neurohemal area of the median eminence is occupied by many neurosecretory and non-neurosecretory axons, containing neurosecretory granules and/or synaptic vesicles. The axonal portions with the synaptic vesicles which are considered to be the nerve endings abut on the capillaries of the portal system. The size of synaptic vesicles in the axon terminals containing few neurosecretory granules is larger than those in the endings with many neurosecretory granules. Infrequently glial and ependymal processes are interposed between the nerve endings and the capillary wall.In the hilar region of the infundibulum, synapses are frequently observed between the thin fibers with or without neurosecretory granules and dendrites of non-neurosecretory neurons. The probable functions of these synapses are briefly discussed on the basis of our findings. Both in the hilar region of the infundibulum and in the pars nervosa, electron-dense neurosecretory granules of two different sizes were observed. The median eminence contains only one type of granules.The fine structure of the pars nervosa shows similar structures to those of the median eminence. Both in the median eminence and the pars nervosa, the fenestrated endothelium of the capillaries was frequently observed. The thick perivascular connective tissue space containing fibroblasts and collagen fibrils was observed both in the median eminence and the pars nervosa. Vesicles in the cytoplasm of the endothelial cells which appear to take a part in the transendothelial transport were observed.This investigation was supported in part by United States Public Health Service Research Grant, No. A-3678, to Hideshi Kobayashi from the National Institute of Arthritis and Metabolic Diseases and partly by a grant for Fundamental Scientific Research from the Ministry of Education of Japan. The authors wish to express their thanks to Prof. K. Takewaki for his kind encouragement.     

The primate median eminence II

Summary The ultrastructure of the normal median eminence of the male rhesus monkey (Macaca mulatta) is described using high-voltage electron microscopy. Surface specializations of ependymal cells lining the infundibular recess included cilia, apical extrusions, and microvilli. Supraependymal cells were predominantly macrophage-like, but examples of lymphocytic types were also seen. Tanycytes had long, branching, basal processes filled with numerous microtubules, some lipid droplets, and granules. The zona interna was composed of large unmyelinated neurosecretory fibers. A few myelinated fibers were also seen, but their character as neurosecretory fibers could not be established. The zona externa was composed of densely-packed profiles of neurosecretory fibers of small diameter, was well-vascularized and contained the terminations of tanycytes. Perivascular glial cells, vesiculated elements, pituicytes, and cellular elements common to connective tissue were observed. The intricate relationships between both the cellular and fibrous elements of the median eminence can be appreciated with the capability of high-voltage electron microscopy to discern ultrastructure in sections 10 times thicker than those used for low-voltage electron microscopy. The median eminence of this primate species has an ultrastructural organization similar to that described for most other species.Supported by USPHS Program Project Grant NS-11642 and USPHS HD-08867. The authors appreciate the excellent technical advice and assistance of Mr. George Wray in operation of the HVEMCareer Development Awardee K04-GM-70001     

In vitro peptidergic neurons from the adult locust pars intercerebralis: Morphological and immunocytological studies

Primary cell cultures were prepared from a major neurosecretory center of the adult locust brain, the pars intercerebralis, in order to characterize neurosecretory cells growingin vitro. Individual pars intercerebralis could be removed free of surrounding tissue and dissociated by mechanical treatment. Mature neurosecretory neurons of different sizes regenerate new neurites during the initial three daysin vitro in serum-free medium. They show a tendency to sprout one primary neurite from which fine processes develop. By means of electron microscopy, we observed the integrity of the cellular organelles, indicating that cultured neurons are healthy, and we were able to distinguish three types of neurosecretory neurons on the basis of the ultrastructural aspects of the neurosecretory material. These three types have the same ultrastructural characteristics asin situ neuroparsin, ovary maturing parsin and locust insulin related peptide neurons. Immunogold labelling at the electron microscopic level, using the two available specific antibodies, anti-neuroparsin and anti-ovary maturing parsin, confirms the morphological characterization of neuroparsin and ovary maturing parsin cells. These results show for the first time that cultured locust neurosecretory neurons behave like thosein vivo, in terms of their ultrastructure and immunocytochemistry. Moreover, the presence of recently-formed neurosecretory material both in the Golgi zone of the perikaryon and in the neuronal processes indicates that cultured neurons have functional capacity since they are able to synthesizede novo and to transport the neurosecretory material along the neurite. Thus our well-characterized culture system provides a suitable invitro model to investigate the secretory mechanism of locust neurosecretory neurons.     

The fine structure of ependymal cells part II: An electron microscopic study of the soft-shelled turtle paraventricular organ,with special reference to the fine structure of ependymal cells and so-called albuminous substance

Summary The present study deals with the electron microscopic observations on the softshelled turtle paraventricular organ, with special reference to the relationship of the ependymal cells and the so-called albuminous substances. It is shown that the so-called albuminous substances consist of the tips of neuronal processes extending into the ventricular lumen. They probably arise from the nerve cells lying within the hypendymal or the underlying tissue. The ependymal cells of the PVO themselves are basically similar in structure to those of any other animal.The processes observed contain two types of vesicles, namely: the clear vesicle, 500 to 1600 Å in diameter, and the cored vesicle, measuring 600 to 1500 Å in diameter, which has a distinct membrane enclosing an extremely dense core of variable sizes. The functional significance of these vesicles is discussed in relation to that of inclusions in the neurosecretory and the autonomic nerve fibers in the hypothalamus.The findings indicate that in the terminal endings of the processes a production or formation of vesicles might occur and that these vesicles might be discharged into the cerebrospinal fluid by microapocrine secretion.The author's grateful thanks are due to Prof. E. Yamada for his continuously kind guidances and due to Prof. T. Sakurai for his constant encouragement.     

Histology and ultrastructure of the neural lobe of the lizard,Klauberina riversiana

Summary The pars nervosa of Klauberina riversiana belongs to a primitive tetrapod type which is characterized by the deep penetration of the infundibular recess, a thin-walled structure, and the virtual absence of pituicytes. The differential response of this gland to aldehyde fuchsin and periodic acid Schiff suggests the presence of two types of neurosecretory nerve endings. Ultrastructurally four kinds of nerve endings are distinguishable. Type I, probably a cholinergic nerve ending, contains only small clear vesicles ca. 400 Å in diameter. The relative abundance of cholinergic nerve endings in this pars nervosa may be related to the necessity of transporting hormone through the ependymal cell. Type II, containing granulated vesicles about 1,000 Å in diameter and probably aminergic, is very rare. The two remaining types apparently secrete neurohypophysial hormones. They are Type III, containing dense granules ca. 1,500 Å in diameter and Type IV containing pale granules ca. 1,500 Å in diameter. Evidence is reviewed which suggests that Type III nerve endings may secrete arginine vasotocin while Type IV endings may secrete (an)other hormone(s).All these axons end only on the ependymal cells, the vascular processes of which form a continuous cuff over the basement membranes of the blood vessels. Hence the ependymal cells link the cerebrospinal fluid, the nerve endings and the blood vessels. Particles resolvable with the electron microscope are traced through a possible transport pathway from the granules, through the ependymal cells to the basement membrane. It is suggested that pituicytes replace ependymal cells and assume their transport functions in animals with massive neural lobes containing large numbers of nerve endings and blood vessels.Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.This investigation was supported in part by a Public Health Service fellowship 1 FZ HD 32,949-01 REP from the national Institute of Child Health and Human Development.The authors wish to thank Professor H. Heller for his constant interest and constructive criticism.     

Autoradiographic study of the proliferative activity of the preoptic recess ependyma in yearling and juvenile common frogs

Proliferative activity of the ependyma, lining the recessus praeopticus in juvenile frogs was studied with 3H-thymidine radioautography. Usually much more pronounced proliferation of ependymal cells occurred in the preoptic region in one year old frogs as compared with two year old ones. It can be concluded that in the former animals the migration of postmitotic labeled cells into the subependymal zone of the recessus preoptic area is significantly more intense. By the 30th day after multiple isotope injections some newly formed neurosecretory cells with labeled nuclei were found in the 1-5 cellular position of the recessus praeopticus subependymal zone. It is postulated that in juvenile frogs the ependyma of lateral wall of recessus praeopticus is probably a source ("cambium"), from which some young neurosecretory cells may originate.     

The annual cycle of activity of the subfornical organ in the green frog Rana esculenta

Abstract

The nuclear volume in cells of the subfornical organ of Rana esculenta shows a cyclic annual size change. It is pronounced both in the so‐called Gomori‐positive cells and the ependymal covering of the organ. There appears a maximum in April in the epen‐dyma and in May in the Gomori‐positive cells. The amount of neurosecretory material present in the subependymal layer also shows a maximum in April.     

A micromorphological and histoenzymological study on the third ventricular ependyma of the teleost Clarias batrachus (L.).

The circum ventricular region of C. batrachus is highly vascular and the ependymal cells appear differently when stained with haematoxylin, silver impregnation and Golgi-Cox techniques. The ventricule has PAS and AF positive material and some ependymal cells themselves are PAS positive. Few AF positive peptidergic and several AF negative small neurons have liquor contacting terminals. Golgi-Cox preparations reveal a variety of forms among the tanycytes. Their basal processes which are barbed or studded with varicosities, usually end on blood vessels and other neuronal elements. These basal processes themselves are often seen in direct morphological contact. Smaller silver positive cells without basal processes are also evident. Some tanycytes have apical processes resembling broadened endfeet. Few neurosecretory tracts are Golgi-Cox positive and can be differentiated from the tanycytic processes by their smooth surface. Varying degrees of ascorbic acid activity are noticed inside the ventricle, among the tanycytes and in the neurons of the NLT. Some of the latter neurons have liquor contacting terminals as well. The ChE activity noticed in some parts of the ependyma and in some NLT cells suggest their probable differential cholinergic control. Presence of SDH, NADPH and NADH diaphorases and cytochrome oxidase in varying quantities in the ependymal cells suggests that they are metabolically active. Presence of MAO positive tracts bridging the subependyma and ventricle suggests the degradation of monoamines at these sites. The presence of various enzymes and the morphological relationship of the tanycytes described in this species are comparable to those of the mammals. It is significant as this species is reported to have a median eminence morphologically resembling the tetrapods.     

Adrenergic neurons in the spinal cord of the pike (Esox lucius) and their relation to the caudal neurosecretory system

Summary The lower spinal cord including the caudal neurosecretory system of the pike (Esox lucius) was investigated by means of light and electron microscopy and also with the fluorescence histochemical method of Falck and Hillarp for the visualization of monoamines. A system of perikarya displaying a specific green fluorescence of remarkably high intensity is disclosed in the basal part of the ventrolateral and lateral ependymal lining of the central canal. The area corresponding to the upper half of the urophysis has most cells; their number decreases caudally and cranially. A considerable number of their beaded neurites reach the neurosecretory neurons by different routes but are only occasionally present in the actual neurohemal region. An intensely fluorescent dendritic process is sometimes observed terminating with a bulbous enlargement at the ependymal surface in the central canal. Besides small, electron lucid vesicles in the terminal parts of the axons, the neurons contain numerous large dense-core vesicles which can apparently take up and store 5-hydroxydopa (5-OH-dopa) and 5-hydroxydopamine (5-OH-DA). These neurons are thought to be adrenergic and to contain a primary catecholamine, possibly noradrenaline.The varicosities of the adrenergic terminals are repeatedly observed contiguous to some of the neurosecretory axons, the membrane distance at places of contacts generally ranging from 150–200 Å. Another type of nerve terminals that contain only small empty vesicles, also after pretreatment with 5-OH-dopa or 5-OH-DA, are frequent among the neurosecretory neurons. These axons establish synaptic contacts with membrane thickenings on most of the neurosecretory neurons. Thus it seems that the neurosecretory neurons are innervated by neurons morphologically similar to cholinergic neurons and that part of them receive an adrenergic innervation, which supports the view hat the caudal neurosecretory cells do not constitute a functionally homogeneous population.Supported by the Deutsche Forschungsgemeinschaft and the Joachim-Jungius Gesellschaft zur Förderung der Wissenschaften, Hamburg.Supported by the Swedish Natural Research Council (No. 99-35). This work was in part carried out within a research organization sponsored by the Swedish Medical Research Council (Projects No. B70-14X-56-06 and B70-14X-712-05).Supported by the Deutsche Forschungsgemeinschaft and USPHS Research Grant TW 00295-02.     

The filum terminale of the frog spinal cord

Summary The filum terminale, or terminal portion of the spinal cord, was studied in normal adult frogs (Rana pipiens) by means of light and electron microscopy. Astroglial cells are the predominant elements in this region. The rostral portion of the filum terminale consists mainly of (1) a peripheral dense ring of myelinated and some unmyelinated nerve fibers, and processes of astrocytes terminating at the subpial space; (2) an intermediate zone, in which astrocytes are the main cellular elements in addition to a few degenerated neurons; and (3) a central region where the central canal is lined by dark and light ependymal cells. In the caudal portion of the filum terminale, the amount of neuropil is greatly reduced. This region is formed mainly by astrocytic glial cells and very few neuronal elements. The central canal in the caudal portion is located ventrally and contains a lining consisting almost exclusively of dark ependymal cells.     

Identification of adenohypophysiotropic neurohormone producing neurosecretory cells in Rana temporaria

Summary By means of electron microscopy, in the median eminence of Rana temporaria, the terminal arborizations of axons of six different types of neurosecretory cells, located in the pars ventralis of the tuber cinereum, were identified. In addition, phenomena connected with the release of neurosecretory material from the axon terminals of these neurosecretory cells into the blood capillaries of the median eminence are described.Preliminary results suggested the existence, in the median eminence, of additional different neurosecretory axon types which could also belong to corresponding neurosecretory cell types probably located in the apical part of the pars ventralis of the tuber cinereum. Moreover, in the external region of the normal median eminence, separate monoaminergic nerve fibres were tentatively identified. Arguments are adduced which plead (1) against the assumption that the ependyma or the pituicytes of the median eminence could produce adenohypophysiotropic hormones; (2) against the inference that the ependymal cells of the median eminence might be involved in the transport of adenohypophysiotropic hormones from the cerebrospinal fluid into the blood capillaries of the median eminence.     

Ultrastructural changes in the median eminence of the rat following deafferentation of the basal hypothalamus

Summary This report concerns a light and electron microscopic investigation of the median eminence and dorsal infundibular stem of the rat following surgical isolation (deafferentation). Using a modification of the Halász technique, the basal hypothalamus, including the arcuate nucleus and median eminence were surgically isolated from surrounding structures. Special attention was directed to the contact (external) zone of the median eminence and rostral infundibulum where tuberohypophyseal axons as well as ependymal cell processes abut upon the abluminal basement membrane of the portal perivascular space. The results of this study to date suggest that 9, 20, and 40 days following surgical isolation, there is a distinct increase in the population of tuberohypophyseal dense core vesicles. It is suggested that deafferentation abolishes inhibitory and excitatory input that serves to modify the cellular dynamics of tuberohypophyseal neurosecretory elements. Comments are also made on the presence of cistern-like structures in the lateral median eminence; the presence of vesicle-like inclusions in terminal ependymal processes is discussed in relationship to the role that ependyma may play in linking the third ventricle with the adenohypophysis.This research was supported by USPHS Grants NB 08171 and AM 10002. The authors are indebted to the excellent technical assistance provided by G. Krobisch Dudley. Further, the authors wish to express their thanks to Dr. Adolph Weindl for his valuable advice and criticism, and to Matilde Holzwarth for her helpful assistance.     

Electron microscopy of the esophageal ganglion complex of the gastropod pulmonate Triodopsis divesta. I. Ultrastructure of the epineurium

The epineurium of the esophageal complex of the gastropod pulmonate Triodopsis divesta was examined by electron microscopy. The epineurium consists of two main regions: an inner dense fibrous region adjacent to the avascular neural tissue of the ganglion and an outer cellular region comprised of a variety of cell types embedded in a connective tissue matrix. The dense fibrous region contains smooth muscle cells and associated nerve processes and is invested on the neural side by thin processes of glial cells. The outer highly cellular region contains smooth muscle cells, nerve processes, wandering cells (amebocytes), globular cells, and myoepithelial cells comprising the walls of the vascular system. In addition, a cell type not previously identified in other gastropod epineuria is present. These cells resemble neurosecretory cells. The morphology and structural interrelationships of these various constituents are presented and the possible functions of individual cell types and the epineurium in general are discussed in relation to information available on other molluscs.     

The projections of neurosecretory cells in the brain of the North-American medicinal leech,Macrobdella decora,using intracellular injection of horseradish peroxidase

The projections of four anatomically distinct groups of putative neurosecretory cells found within the supra-oesophageal ganglion of the leech Macrobdella decora were studied by intracellular injection of horseradish peroxidase. All four groups have their own characteristic branching pattern while sharing the common feature of possessing primary branches that project into the dorsal commissure. Numerous secondary processes extend from these primary branches to terminate within the neural lamella, as well as within the neuropile. Electron microscopy of the regions into which these secondary processes project reveals numerous neurosecretory terminals. The data suggests that the midregion of the dorsal commissure constitues a neurohemal complex. These observations strengthen the argument that the four groups of identified cells are indeed neurosecretory.     

Structure of the neurohypophysis and the hypothalamo-hypophysial vascularization in the teleost Channa punctatus Bloch.

In C. punctatus the median eminence includes the subterminal region of the hypothalamus and the anterior neurohypophysis. It is formed of ependymal, fibrous and reticular layers as in the tetrapods. Primary capillary plexus extends from the subterminal region to the extremity of the anterior neurohypophysis. Only few portal vessels from the hypothalamus enter in the pars distalis. All the components of pituitary including the pars intermedia are irrigated by the secondary plexus formed from the portal vessels emerging out of the anterior neurohypophysis. The neurosecretory axons and the ependymal cells are in close morphological contact with the primary plexus. Several axons have perivascular endings at the median eminence. Some axons were found to be only silver or aldehyde fuchsin positive whereas some others take up both. The silver positive axons were abundant in the pars distalis and the AF positive ones were more concentrated in the pars intermedia with greater accumulation of neurosecretory material.     

Histology and ultrastructure of the neurohypophysis of the south american lungfish,Lepidosiren paradoxa

Summary The neurohypophysis of the South American lungfish Lepidosiren paradoxa has been studied with light and electron microscopy, including the Falck-Hillarp technique for catecholamines. The pars nervosa hypophyseos is a well-marked, dorsally located subdivision of the pituitary gland composed of lobes or follicles, each one constituted of a central core of ependymal cells, a subependymal hilar region made up of nerve fibers and a peripheric palisade zone of nerve endings which contact capillary vessels. Four types of neurosecretory axons can be distinguished under the electron microscope. Type I, the most common, contains spherical elementary granules of high electron density, 1500–1800 Å in diameter. The scarce type II axons contain irregularly-shaped elementary granules. Type III contains only small clear vesicles, 400–600 Å in diameter. Type IV, mostly present in regions of the gland contacting the pars intermedia, contain large granulated vesicles, 900–1000 Å in diameter. The Falck-Hillarp technique revealed axons with a positive reaction for catecholamines at sites corresponding approximately to the location of type IV of the electron microscope.Ependymal cells are of large size, linking the cerebrospinal fluid, the nerve endings and the blood vessels. A conspicuous membrane-bound, spherical dense material, 1400–2000 Å in diameter, is observed in both the apical and vascular processes of these cells. The ependymal processes which traverse the hilar and palisade regions contain structures resembling degenerated neurosecretory axons. These results are discussed in relation with the currently available information on the comparative anatomy of the pars nervosa. The possible functional significance of ependymal cells and of each type of axon are also discussed.This study was aided by the following grants: NIH NS 06953 to Prof. De Robertis, Consejo Nacional de Investigaciones Científicas y Técnicas to Prof. Zambrano, Comisión de Investigaciones Científicas de la Provincia de Buenos Aires and Comisión de Investigaciones Cientificas de la Universidad Nacional de la Plata: to Prof. Iturriza.The authors are indebted to Prof. De Robertis for his generosity in granting us his laboratory facilities, and to Dr. F. J. J. Risso and Mr. A. Fernández (Resistencia, Chaco) who provided the specimens used in this study. The able microtechnical assistance of Miss L. Riboldazzi and Mrs. R. Raña and the photographic work of Mr. A. Saenz are much appreciated.Members of the Scientific Career, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.     

Cellular organization of the lateral and postinfundibular regions of the median eminence in the rat

Summary The structural organization of the rostral, lateral and postinfundibular regions of the median eminence (ME) of 5-day cyclic diestrous rats was studied with light and electron microscopic methods. The ependymal cells lining (i) the floor of the infundibular recess (IR) at rostral levels, (ii) the lateral extensions of the IR, and (iii) the floor of the premammillary recess appear to represent the same type of tanycyte ependyma (1 tanycytes). In the entire width of the rostral and postinfundibular palisade regions, as well as in the lateral palisade region of the preinfundibular ME, the processes of the 1 tanycytes form a continuous cuff. This cuff separates the nerve endings from the blood vessels and the pars tuberalis. At this level, synaptoid contacts between neurosecretory axons and the ependymal cuff can be observed. The ultrastructural characteristics of the 1 tanycytes are described and their ependymal endings tentatively classified into three types. In the lateral regions of the ME, the Golgi study revealed the presence of two fiber systems: (i) one possessing a latero-medial trajectory and distributed in the subependymal region; (ii) the other formed by a loose longitudinal tract originating from neurons of the arcuate nucleus. Some functional implications of the cellular organization of the rat ME are discussed.Supported by Grants from PLAMIRH (92.171.2.77) and from the Dirección de Investigaciones, Universidad Austral (S-77-28)The authors wish to thank Miss Rosario Andrade, Mrs. Elizabeth Santibáñez and Mr. Armando Bilbao for their assistance     

The distribution of monoamine oxidase and acetylcholinesterase in the hypothalamus and its relation to the hypothalamo-hypophysial neurosecretory system in the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary The distribution of monoamine-oxidase and acetylcholinesterase activities in the hypothalamus of the White-crowned Sparrow has been studied in relation to the hypothalamohypophysial neurosecretory system. The enzyme activities, as revealed by the methods employed, are unaffected during photoperiodically induced testicular growth. Monoamine oxidase has a distribution distinctly different from that of the aldehyde-fuchsin positive neurosecretory material in that there is high activity in the peripheral palisade layers of both the anterior and posterior divisions of the median eminence. Intimate contact is made between these areas with the primary vessels of the hypophysial portal system. A second concentration of activity lies in a layer between the ependymal cells and the neurosecretory material of the fiber tract. In general, monoamine oxidase appears to be associated with glial elements and non-neurosecretory axons. The pars nervosa has little or no monoamine-oxidase activity. The distribution of acetylcholinesterase activity in the anterior division of the median eminence is very similar to that of the aldehyde-fuchsin positive neurosecretory neurons; however, acetylcholinesterase also occurs in the posterior division without associated neurosecretory fibers. These distribution of enzyme activities are considered in relation to possible adrenergic and cholinergic mechanisms in the median eminence.Dedicated to Professor Berta Scharrer in honor of her 60th birthday.Supported by grant NB-01353 from the National Institutes of Health to Professor Farner. This investigation was conducted while Doctor Kobayashi was a National Science Foundation Senior Foreign Scientist at Washington State University. We are indebted to Doctor Christian Da Lage, Laboratoire de Histologie, Falculté de Médecine de Paris, for the preliminary development of some of the techniques used in these investigations.     

Neurosecretion. XIII. The ultrastructure of the corpus cardiacum of the insect Leucophaea maderae

Summary The corpora cardiaca of Leucophaea maderae contain two classes of intrinsic elements, parenchymal and interstitial cells. The parenchymal cells produce a secretory material first visible in the Golgi zones of the perikarya in the form of distinct electron-opaque granules. These undergo changes (gradual loss of electron-density, emergence of internal structure) as they accumulate in cellular processes.The parenchymal cells are best classified as neuroglandular elements since, in addition to secretory inclusions, they possess characteristics of ganglion cells such as axonlike processes, neurotubules, and sheaths. These covers are provided by branches of the second type of intrinsic elements, the interstitial cells. They are non-glandular structures of considerable morphological complexity. In the manner of glial elements, they permeate the entire organ and encapsulate not only the perikarya of parenchymal cells but cellular processes as well.The cytoplasmic processes include a) relatively short ones belonging to parenchymal cells, and b) long axons whose cell bodies lie within the central nervous system. Many of the latter contain electron-opaque granules of the kind found in electron-micrographs of typical neurosecretory cells. These extrinsic granules represent the second category of secretory products stored within the corpora cardiaca. By comparison with the product of the intrinsic gland cells, the neurosecretory granules seem to be fairly stable. Neither type seems to pass through the connective tissue sheath of the corpus cardiacum in the form of discrete granular entities.This sheath, which sends branches into the interior of the corpora cardiaca, has the properties of a basement membrane. It represents a pathway for the exchange of substances between the cellular components of the corpus cardiacum and the surrounding hemocoele.The dual character of the corpus cardiacum, namely that of a storage and release center for extrinsic neurosecretory substances and of an endocrine organ in its own right, is herewith established beyond doubt. The number of secretory products discernible on the basis of their morphology and localization (two size categories of extrinsic and one intrinsic type of granules) does not match the variety of physiologically active principles known at present. The assignment of specific functions to discrete morphological elements must await further studies.Supported by Research Grants A-3984 and B-2145 from the U.S.P.H.S.     

Histochemical demonstration of monoamine oxidase in the hypothalamo-hypophysial system of the tree sparrow and the rat

Summary Localization of monoamine oxidase (MAO) was investigated essentially according to the method of Glenner et al. (1957) in the hypothalamo-hypophysial system of the tree sparrow and the rat. The hypothalamic neurosecretory cells of both species showed relatively weak MAO activity. A similar localization of MAO activity was observed in the median eminence of both species: (1) slight or no MAO activity was observed in the ependymal layer, (2) relatively strong activity was revealed in the tissue just beneath the ependymal layer, (3) strong activity was revealed in the outer layer, particularly in the tissues surrounding capillary loops of the primary plexus. It is suggested that an adrenergic mechanism functions in the median eminence. In the pars nervosa, strong reaction was observed in the rat, while a weak reaction occurred in the tree sparrow. However, the color and the size of formazan crystals deposited in the rat pars nervosa differed from those in the hypothalamus. As a whole, the distribution of the neurosecretory material differed from the localization of MAO activity in the hypothalamo-hypophysial system. It is discussed that the neurosecretory neuron is not adrenergic but cholinergic.Aided by Grant A-3678 from the United States Public Health Service. The authors are indebted to Dr. S. Kambara, Zoological Institute, and Dr. H. Hirano, Department of Anatomy, University of Tokyo, for their valuable advice, and also to Assoc. Prof. S. Yamamoto, Department of Hygiene, University of Tokyo, for making available some facilities. They also wish to thank Dr. L. M. Barbato, University of Illinois, and Mr. K. Asami, National Institute of Radiological Sciences, Chiba, and Mr. Suzuki, Research Laboratory, Chugai Pharmaceutical Company Ltd., Tokyo, for the kind supply of MAO inhibitors.