The fine structure of sensory receptor processes in the auricular epithelium of the planarian,Dugesia tigrina

Summary The marginal epithelium of the lateral auricles of the planarian, Dugesia tigrina, includes a cell type with surface cilia and microvilli, a basal nucleus, and dense cytoplasm containing secretory vacuoles, Golgi elements, mitochondria and ribosomes. Through channels within the epithelial cytoplasm, cellular processes, interpreted as extensions of neurosensory receptor cells located in the subepidermis, project to the surface. The receptor processes, containing microtubules, mitochondria, vesicles and an agranular tubular reticulum, project beyond the epithelial cell surface; one or two cilia each emerge from a basal body in the apex of the projection. Close to the point of emergence to the epithelial surface, each cylindrical receptor process is surrounded by a collar-like septate junction between adjacent plasma membranes. The cilia of the projections differ from those of the epithelial cells in diameter, density of matrix and in the banding patterns of the rootlets. A few projections appear with the apex and basal body retracted below the epithelial surface. The possible function of these ciliated processes in sensory reception is discussed.This work was supported by Grant No. SO 1 FR 5369 from the U.S. Public Health Service to the University of Illinois at the Medical Center.I thank Dr. J. P. Marbarger, Director of the Research Resources Laboratory, for use of the electron microscope facilities, Miss Irena Kairys for technical help, Miss Marie Jaeger for assistance with photography, and Mr. Robert Parshall for the drawing.To Professor Arthur Wagg Pollister, I respectfully dedicate this article on the occasion of his retirement from Columbia University.     

Fine structure of cilia in rat cerebral cortex

Summary Cilia have been demonstrated on granular neurons and astroglial cells in the fascia dentata, a part of the hippocampal region, in the rat. Every granular cell seems to possess one cilium, which shows an 8+1 pattern in the greater part of its length. This 8+1 pattern is shown to result from the displacement of one peripheral doublet of a 9+0 cilium into the middle of the cilium. The neuronal cilia have a two-centriole basal organization, and fine rootlets radiate from the basal body proper into the cytoplasm. The possible function and significance of these cilia are discussed on the basis of earlier literature.This study was supported in part by Grant NB 02215 of The National Institute of Neurological Diseases and Blindness, U.S. Public Health Service, in part by The Norwegian Research Council for Science and the Humanities. This aid is gratefully acknowledged. I am greatly indebted to Dr. Th. Blackstad for encouragement and advice during this study, to Mrs. J. L. Vaaland, Mr. B. V. Johansen and Mr. E. Risnes for technical assistance, and to Dr. B. Afzelius for valuable discussions.     

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.     

The fine structure of the eye of the mollusc Pecten maximus

Summary The retina of Pecten maximus is divided into two light sensitive layers forming the distal and proximal retinae. The cells from these layers have different electrophysiological responses, the distal cells giving primary off responses, and the proximal cells giving on responses. The receptor surfaces of the distal retinal cells are formed from lamellae produced by the outer membranes of flattened cilia. These cilia have a basal body, basal foot, no root system and a 9 + 0 internal filament content. Each cell gives rise to an axon from its distal side, and this process goes up to the basement membrane, which is present below the cellular lens, passes along beneath it, and joins the distal optic nerve. The receptor part of the proximal retinal cells is formed from a vast array of microvilli. Each of these cells also bears one or two cilia with a probable 9 + 0 internal filament complement and no roots. The proximal cells give rise to axons, forming the proximal optic nerve. Below the proximal retina is a reflecting layer, the argentea, and below this is a pigment cell layer.We would like to acknowledge the advice and encouragement of Professor A. F. Huxley, Professor J. Z. Young and Dr. E. G. Gray. — We would like to thank Mrs. J. I. Astafiev for drawing Fig. 1, Mr. S. Waterman for photographic help and Miss C. Martin for clerical 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.     

Electron microscopic observations of lung alveolar epithelial cells of normal young mice,with special reference to formation and secretion of osmiophilic lamellar bodies

Summary Using the electron microscopy and electron microscopic histochemistry the authors studied the lung alveolar epithelial cell of normal young mice.Type II cell of the alveolar epithelium has characteristically numerous osmiophilic lamellar bodies. The lamellar boies are formed in the cytoplasmic vesicle, and never originate from the mitochondrion. These bodies have abundant acid phosphatase activity in their limiting membrane therefore it is considered to be lysosomal origin, but the mitochondria have no such enzyme activity.The body which is newly formed in the cytoplasmic vesicle grows up to the large lamellar body as a result of an accumulation of the fibrous dense substance, migrates to the free margin of the type II cell of alveolar epithelium, and then is discharged into the alveolar lumen as a merocrine type secretion.Acknowledgement is given to Professor Dr. Y. Sano and Professor Dr. H. Fujita, Department of Anatomy, and Assistant Professor Dr. S. Fujita, Department of Pathology, for their kind advice and criticism.     

Fine structure and absorption patterns of intestinal epithelial cells in rainbow trout alevins

Summary The intestinal epithelium in the rainbow alevins at the period of initial feeding is composed of typical columnar cells with a striated border and goblet cells with mucigen droplets. The columnar epithelial cells are provided with well organized cell organelles which are found in the intestinal absorptive cells of vertebrates in general. Remarkable differences are seen in some morphological aspects of columnar epithelial cells between the antero-mid intestine and the posterior intestine. Those in the antero-mid intestine are loaded with considerable quantities of fat droplets, whereas those in the posterior intestine are characterized by containing vacuoles with less dense materials which resemble engulfed protein in general feature. No pinocytotic process is found in the former, but vigorous pinocytosis occurs in the latter. The membranous lamellar structures are developed in the mid-basal portion of the columnar epithelial cells. Those in the basal portion of the cells in the mid intestine are arranged in parallel to the longitudinal cell axis with associated groups of mitochondria.The cellular morphology of the intestinal epithelium suggests the possibility that absorption of nutrients derived from external foods occurs in the rainbow alevins still having a small yolk sac.I am grateful to Dr. Kiyomatsu Matsubara of our laboratory, Dr. Reuben Lasker of the U.S. Bureau of Commercial Fisheries, La Jolla, and Dr. Carl L. Hubbs of the Scripps Institution of Oceanography, La Jolla, for much valuable criticisms and encouragement. Thanks are due to Mr. Tomomi Watabe of the Japan Electron Optics Laboratory for his generous help.     

Scanning electron microscopic studies of cilia

Summary A simple method for the preparation of ciliated epithelia for study with the scanning electron microscope is described. Ciliary groups are well preserved and it is possible to discern individual cilia and work out their numbers and orientation. Following scanning electron microscopical study some of the material was prepared for transmission electron microscopy and the ultrastructure of the tissue was found to be surprisingly well preserved. The tracheal epithelium of the rabbit, the olfactory epithelia of the goldfish and the rabbit, and the sensory epithelia in the statocyst of a cephalopod mollusc were examined with the scanning electron microscope to demonstrate the possibilities of the method. Acknowledgements. We would like to thank Professor J. Z. Young for his continued interest and support. The scanning electron microscope was purchased with a grant provided by the Science Research Council to Dr. Boyde, Mr. R. Willis helped in the initial stages of the study, Mr. G. Savage provided help with the goldfish material, Mr. S. Waterman provided much photographic assistance, and Mrs. N. Finney the secretarial assistance.     

Detection of numerous CC and Cc membranes in the femoral condyle

The authors (1,2) discovered a two-membrane system in the head of the femur and its distal condyles (Copf et al. ^1,2,3). The one membrane serves the hydrodynamic principle. It was termed the CC membrane. According to the provisional opinion of the authors, the second membrane, which is designated as Cc membrane, serves for exchange of fluid supply of energy and information flow in view of its original perforations. In contrast to the head of the femur, CC membranes are more numerous. The Cc membranes are also more numerous here, but in some cases differ in terms of their elongate form. The first impression indicates a very much more pronounced component of the hydrodynamic system in the region of the femoral condyle.     

Electron microscopic observations of synaptic endings in cultures of mammalian central nervous tissue

Summary Synapses were found in rat cerebellar and brainstem cultures with the electron microscope. Three distinct types of synaptic terminals were described. The similarity between synapses found in vitro and in vivo was emphasized.Supported by USPHS Grants 5 Tl 459-04 and NB 03114-03S1 from the National Institutes of Health, Bethesda, Maryland.The authors wish to express their sincere appreciation to Mrs. Eleanor Morris for her assistance in preparing the cultures and Mr. Earl Pitsinger for his photographic assistance.     

The subcellular fractionation of the electric organ of Torpedo

Summary The acetylcholine-rich electric organ of Torpedo has been submitted to subcellular fractionation in an attempt to isolate nerve endings and synaptic vesicles derived from cholinergic neurones. Fractions containing small vesicles and granules as their only morphologically identifiable components also contained appreciable amounts of bound acetylcholine; however, it was not possible to demonstrate a specific enrichment of any one fraction with respect to bound acetylcholine as has been possible in brain. The tissue proved difficult to homogenize and few detached nerve endings (synaptosomes) were formed. A low-speed fraction rich in Na, K- activated adenosine triphosphatase contained numerous membrane fragments with tubular appendages derived from the non-innervated surface of electroplaques. Homogenization in media isotonic with elasmobranch plasma (e.g. 0.5 M sucrose + 0.33 M urea) was essential to preserve the structure of osmotically sensitive organelles (e.g. mitochondria).We wish to express our gratitude to Dr. R. D. Keynes who arranged the supply of Torpedos and to Mr G. H. C. Dowe and Miss L. Swales for skilled technical assistance. The electron microscopic facilities were provided by a grant from the Wellcome Trust and the work was supported by a grant no. NB-03928-02 (to V.P.W.) from the National Institute of Neurological Diseases and Blindness, U.S. Public Health Service. During the period of this work Dr. Sheridan held a Postdoctoral Fellowship of the U.S. Public Health Service and Dr. Israël was an Exchange Scholar of the Medical Research Council.We are also most grateful to Professor Sir Bryan Matthews, C.B.E., Sc. D., F.R.S., for providing aquarium facilities in the Physiological Laboratory of Cambridge University.     

Nerve supply and distribution of cholinesterase activity in the external nose of the mole

Summary Nerve supply and the distribution of cholinesterase activity were studied in the skin of the external nose of seven moles using a simplified Bielschowsky-Gross silver method and Koelle's histochemical technique.The sensory units of the mole's nose or the organs of Eimer are surrounded by blood sinuses which facilitate their movements during mechanical stimulation. All nerve fibres of the plexus deep to the basal cell layer of Eimer's organ ultimately become intra-epidermal endings. Contrary to the findings of earlier investigators, Merkel's discs, Pacinian corpuscles and Ruffini corpuscles have not been observed at the base of Eimer's organ. In the superficial layer of the plexus, the Schwann sheath cells increase in number, undergo modification and give a positive cholinesterase reaction.It is suggested that the organ of Eimer, the specialised nerve plexus deep to it and the surrounding blood sinus together constitute the touch receptor on a similar principle of transmission by leverage as in the tactile hair or the intermediate ridge of the papillary ridge.The role of the intra-epidermal nerve endings of the mole's nose as tactile receptors is disputed. A suggestion is made that tnese nerves may constitute pain and temperature receptors and that several modalities of sensation may be carried to the brain along one and the same medullated axon.We gratefully acknowledge the technical assistance of Miss Jill Hocknell. Our thanks are also due to Mr. C. J. Duncan and the staff of the Photography Department for their aid with the photographic work. We are particularly grateful to Mr. D. Burgess of the Ministry of Agriculture and Fisheries for kindly supplying us with live moles. One of the authors (N.C.) acknowledges an equipment grant from the Royal Society.     

Organization of actin microfilaments in the apical border of oviduct ciliated cells

Actin microfilaments were localized in quail oviduct ciliated cells using decoration with myosin subfragment S1 and immunogold labeling. These polarized epithelial cells show a well developed cytoskeleton due to the presence of numerous cilia and microvilli at their apical pole. Most S1-decorated microfilaments extend from the microvilli downward towards the upper part of the ciliary striated rootlets with which they are connected. From the microvillous roots, a few microfilaments connect the proximal part of the basal body or the basal foot associated with the basal body. Microfilament polarity is shown by S1 arrowheads pointing away from the microvillous tip to the cell body. Furthermore, short microfilaments are attached to the plasma membrane at the anchoring sites of basal bodies and run along the basal body. The polarity of these short microfilaments is directed from the basal body anchoring fibers downward to the cytoplasm. At the cell periphery, microfilaments from microvillous roots and ciliary apparatus are connected with those of the circumferential actin belt which is associated with the apical zonula adhaerens. Together with the other cytoskeletal elements, the microfilaments increase ciliary anchorage and could be involved in the coordination of ciliary beating. Moreover, microvilli surrounding the cilia probably modify ciliary beating by offering resistance to cilium bending. The presence of microvilli could explain the fact that mainly the upper part of the cilia appanars to be involved in the axonemal bending in metazoan ciliated cells.     

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.     

ELECTRON MICROSCOPIC OBSERVATIONS OF THE OLFACTORY MUCOSA AND OLFACTORY NERVE

The olfactory receptor cell is characterized by a distal process (the dendrite) which terminates in the olfactory passage as the olfactory rod. The olfactory rod is provided with numerous cilia which are similar in structure to those seen in other tissues. The central processes of the bipolar cell constitute the fila olfactoria. The cytoplasmic organelles of the sustentacular cell are concentrated at the apical and basal ends of the cell with a paucity of cytoplasmic elements in the region of the nucleus. The plasma membrane of the supporting cell forms a mesaxon for both the dendrite and axon of the bipolar cell. Terminal bars are present in the epithelial cells. The axons constituting the fila olfactoria form fascicles which are ensheathed by mesaxons of adjacent Schwann cells. Thus the olfactory neurons are ensheathed throughout their course by the membranes of sustentacular and Schwann cells. Observations of the olfactory mucosa with the electron microscope are discussed with respect to recent electrophysiological studies.     

The ultrastructure of the test of the tadpole larva ofCiona intestinalis

Summary The test of the tadpole larva ofCiona intestinalis consists of an amorphous background substance in which are long 4–7 nm fibrils. There is a narrow outer dense region of the test where both the background material and the test fibrils are more concentrated and orientated. Fibrils of similar dimensions are found in the epithelial cells below the test, and also in cells associated with the outside surface of the test. No such fibrils are found in the cells located within the test substance. There are some regions where the external cell membrane of the epithelial cells is indistinct and in these regions the fibrils of the test are continuous with the fibrils within the epithelial cells. No large or small vesicles opening from the epithelial cells into the test have been seen.This evidence has been interpreted as support for the tunicization theory of test formation. It is suggested that the cells within the test are the source of the polyphenols that are necessary for quinone tanning that gives rigidity to the test.The fibril-containing cells outside the test probably add fibres to the cuticular region of the test.I wish to thank ProfessorJ. Z. Young, F.R.S. for much advice and encouragment, also Dr.R. Bellairs for the use of electron microscope facilities and Mr.R. Moss and Mrs.J. Hamilton for skillful technical assistance.     

Endothelial microvilli in the vessels of the rat gasserian ganglion and testis

Summary In the Gasserian ganglion and testis of the rat the endothelium of the small blood vessels has a singular appearance due to the presence of a high number of microvillous processes. These arise from the luminal surface, either individually, or in small groups. The significance of this structure is not known. It is pointed out that these vessels are particularly sensitive to cadmium intoxication.This investigation was performed during a tenure by Dr. Gabbiani of a fellowship of the Medical Research Council of Canada and was supported by the National Institutes of Health (Grant No. 5R01 HE-08794-04) and the Ministère de la Santé du Québec (projet 604-7-635).The authors wish to thank Dr. S. M. Shea for his advice in the measurement of the villi. The technical assistance of Miss Virginia Gilmore and of Mr. Eduardo Garriga is gratefully acknowledged.     

Fine structure of the Paraventricular organ of Xenopus laevis tadpoles

Summary The ultrastructure of the Paraventricular organ in the hypothalamus of Xenopus laevis tadpoles is described. It appeares that the Paraventricular organ of this anuran species is homologous with the Organon vasculosum hypothalami or the Paraventricular organ of other vertebrates.The Paraventricular organ of Xenopus laevis is characterized by an ependymal lining with only few cilia and by two types of nerve cells. Both types of nerve cells have ventricular processes, protruding into the lumen of the third ventricle and forming a network. The protrusions bear cilia of the 8+1 pattern. It has been possible to distinguish both types of nerve cells on account of their dense-core vesicles. A secretory function of both cell types is suggested.In a region close to the Paraventricular organ, another granulated type of nerve cell has been observed. A relationship between these cells and the preoptic nucleus is discussed.The author thanks Prof. Dr. P. G. W. J. van Oordt for his helpful comments and criticism, Mr. H. van Kooten for photographic assistance and Mr. F. Dijk for technical assistance.     

Studies on the receptors in Ciona intestinalis

Summary A photoreceptor type structure not previously described has been found in the dorsal wall of the cerebral vesicle of the tadpole larva of Ciona intestinalis. The membranes of this receptor are organised as tubules some 60–100 nm in diameter and up to 1.5 m long. The tubules are confined in bundles about 1.5 m in diameter, which extend from the cell surface into the cavity of the cerebral vesicle. These tubules are similar to those in the rhabdomeric type of photoreceptor. However, in the cells from which the tubule processes arise are structures typical of the bases of cilia, and found in ciliary type photoreceptors.I should like to thank Professor J. Z. Young, F. R. S. for his continuing encouragement and help, and Dr. R. Bellairs for the use of electron microscope facilities. Mr. R. Moss and Mrs. J. Hamilton gave excellent technical assistance.     

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.