Electron microscope observations on synaptic vesicles in synapses of the retinal rods and cones

The submicroscopic organization of the rod and cone synapses of the albino rabbit has been investigated with the use of the electron microscope. The most common rod synapse consists of an enlarged expansion of the rod fiber (the so called spherule) into which the dendritic postsynaptic fiber of the bipolar cell penetrates and digitates. The membrane surrounding the terminal consists of a double layer, the external of which is interpreted as belonging to the intervening glial cells. The synaptic membrane has a pre- and a postsynaptic layer with a total thickness of 180 to 300 A. The presynaptic layer is frequently denser and is intimately associated with the adjacent synaptic vesicles. The synaptic membrane shows processes constituted by foldings of the presynaptic layer. The entire spherule is filled with synaptic vesicles varying in diameter between 200 and 650 A with a mean of 386 A. In addition, the spherule contains a few large vacuoles near the rod fiber, interpreted as endoplasmic reticulum, and a matrix in which with high resolution a fine filamentous material can be observed. The postsynaptic fiber is homogeneous and usually does not show synaptic vesicles. In animals maintained in complete darkness for 24 hours vesicles appear to accumulate near the synaptic membrane and its processes. After 9 days there is a sharp decrease in size of the synaptic vesicles. A special rod synapse in which the dendritic postsynaptic expansion penetrates directly into the rod cell body has been identified. In line with Cajal's classification this type of synapse could be considered as a somatodendritic one. The cone synapse has a much larger terminal with a more complex relationship with the postsynaptic fiber. However, the same components recognized in the rod synapse can be observed. In animals maintained for 9 days in complete darkness there is also a considerable diminution in size of the synaptic vesicles.     

Electron microscope observations on the early development of the rat

Summary The early development of the rat, from the mature oocyte through fertilization until the 8-cell stage, has been studied with the electron microscope. The fine structure is described and discussed, with particular reference to the following topics. The middle piece of the spermatozoon is found in every stage studied, within the ovum cytoplasm; it is not significantly altered by this situation. The nucleoli are numerous during the 1-cell stage and often present in positions that suggest their extrusion into the cytoplasm; in subsequent stages a branching structure develops around them. The dividing cell presents the mitotic apparatus with its centrioles, hollow looking fibers, chromosomes, but without centromeres; in the cytoplasm the small granules align in rows. Mitochondria are evenly distributed during the 1-cell stage and can be found in the 8-cell stage constricted as if dividing. The multivesicular bodies constitute an abundant population of cytoplasmic elements that may be related to the endoplasmic reticulum or the Golgi complex, neither of which is clearly recognizable. In the 8-cell stage the cytoplasm segregates into two zones, one of which contains all the multivesicular bodies, while the mitochondria are found in both of them; this distinction provides some basis to adscribe to the multivesicular bodies the properties of the so called metachromatic particles.The support of the Gildemeister Foundation is gratefully acknowledged.     

Electron microscope observations of the melanocyte of the human epidermis

Proteins and colloidal materials, administered orally to suckling rats and mice, were ingested by columnar absorptive cells of the jejunum and ileum, but not of the duodenum. Bovine gamma globulin and ovalbumin were identified in the apical cytoplasm by staining with fluorescent antibody; trypan blue, Evans blue, saccharated iron oxide, and colloidal gold were detected intracellularly by their color, specific staining, and appearance in the electron microscope. Each substance was segregated in membrane-enclosed vacuoles, apparently part of a system of potentially interconnecting vacuoles and tubules in the apical cytoplasm which is continuous in places with the apical cell membrane. We postulate that ingestion of foreign materials was accomplished by pinocytosis, that is, by invagination of the apical cell membrane to form vacuoles containing material from the intestinal lumen. Approximately 18 days after birth columnar absorptive cells lost the ability to ingest proteins and colloids, and no longer contained large vacuoles and numerous tubules. At this age rats and mice lose the ability to absorb antibodies from the intestine in an immunologically intact form, and we conclude that cellular ingestion is part of the mechanism of absorption of intact proteins in suckling animals. Particulate fat apparently is absorbed in both newborn and adult animals by micropinocytosis. Thus adult animals may not have lost the capacity for pinocytosis, but rather have become selective as to what substances provoke it. Cortisone acetate, administered subcutaneously to rats 8 to 10 days old alters the columnar absorptive cells within 72 hours so that they resemble the cells in adult animals and no longer ingest proteins.     

Electron microscope observations of radiation-induced Hela giant cells

Summary An electron microscope study of X-ray produced giant Hela cells is described. The results extend earlier light microscope observations to the sub-microscopic region where clear differences from normal structures are apparent. Of particular interest are intra nuclear inclusions, nucleolar fragments, membrane abnormalities and possible mitochondrial changes.This investigation was supported in part by the U. S. Atomic Energy Commission and in part by a predoctoral fellowship CF 8984 from the National Cancer Institute, Public Health Service.     

Electron microscope observations on chemo- and mechano-receptor cells of fishes

Summary This paper reports on the fine structure of chemo and mechano-receptor cells found in three species of fishes (Corydoras paleatus, Cnesterodon decemmaculatus, Fitzroyia lineata).Taste cells were studied in the food-finding barbels of adult species belonging to the Genus Corydoras. They are characterized by the presence of a great amount of vesicular material concentrated at the level of the apical and medial region. Most of these cells terminate at the barbel surface by means of a cylindrical or tapered extremity devoid of sensory hairs. It was possible to observe, in some cases, the existence of short and ill defined microvilli. The basal pole of each sensory cell contacts with several sensory nerve fibers. These fibers contain mitochondria and a few vesicles.The fine structure of the olfactory neurons was studied in full-developed embryos of Cnesterodon and Fitzroyia. The olfactory sensory hairs consist of long cilia which project into the lumen of the olfactory pit. Cilia arise from the olfactory knob which is merely an apical swelling of the dendrite. The dendrite of the olfactory neuron shows profiles of small tubules, aligned parallel to its length. Near the basement membrane of the epithelium groups of axons are seen encased in the surface of the sustentacular cells.The mechano-receptor cells studied were: 1.) The sensory cells existing in the neuromasts of the lateral line system of Cnesterodon and Fitzroyia, and 2.) the receptor cells of the ampullar crests of the same species.Neuromast receptor-cells have well developed sensory hairs which consist of cilia and microvilli. It is highly probable that each receptor cell, like those of the vestibular epithelium, bears only one cilium asymmetrically located in relation to the units of the sensory process. One of the most striking characteristics of this type of cell is the existence of a high amount of vesicular material accumulated in the cytoplasm of the basal region; it is at this level that the nerve fibers take contact with the receptor cell membrane.Three main types of neuroepithelial junction are described in the neuromasts (nerve fiber deeply recessed in the cytoplasm, calyx type and knob-like ending). In these junctions the vesicular material is almost exclusively concentrated in the cytoplasm of the receptor cell, while only few vesicles are seen within the neuroplasm of the sensory fibers.The receptor cells occuring in the ampullar crests of Cnesterodon and Fitzroyia show many structural characteristics similar to those present in neuromasts' receptor cells. Like these, they bear sensory hairs consisting of several microvilli and only one cilium which is always asymmetrically located within the group of hairs. The basal region of the cell is filled with a large amount of small vesicles. Nerve endings also show vesicles but they are less in number than inside the cytoplasm of the receptor cell.Comments are made on the apparent significance of the sensory hairs. These structures are considered (in chemo-receptor cells) as devices serving to enlarge the active surface of the cell and increasing by this way the effectiveness of the whole receptive system. In mechano-receptor cells cilia and microvilli may act as levers of different mechanical characteristics which convey stimuli to the receptor-cell cytoplasm.In this paper three main types of neuroepithelial junctions connecting receptor cells with the central nervous system are described.