Biomedical subjects
Publications and source records attributed to T Kosaka.
In thin sections of the rat dentate gyrus, neuronal gap junctions were observed in the polymorph layer. Gap junctions were seen on dendritic stems, on smooth and/or varicose dendrites, on spine-like appendages, and in one case on a soma. Somata of gap junction-bearing neurons showed indented nuclei with intranuclear inclusions, and received many asymmetrical and a few symmetrical synapses.
In Golgi and electron microscopic studies, dentate granule cell axon initial segments were revealed to be fasciculated in the granule cell layer and to receive many synapses. Combined Golgi-EM studies indicated that the presynaptic elements of these synapses might be beaded string-like axon collaterals of some type of basket cell.
In thin sections of the rat hippocampus, gap junctions were observed between dendrites of non-pyramidal cells in the stratum radiatum and the stratum oriens in CA1 and CA3 regions. Gap junctions were seen on dendritic shafts, sessile and/or pedunculated spine-like appendages, and on varicose parts of dendrites.
The temperature-sensitive Drosophila mutant, shibirets1 (shi), has been shown to exhibit a reversible block in synaptic transmission at 30 degrees C. Various synaptic terminals (neuromuscular, sensory, central) of this mutant were observed by electron microscopy. At 19 degrees C, all terminals of shi showed essentially the same structural features as those of wild-type (Oregon-R) flies, while at 30 degrees C (5 or 10 min of exposure) shi terminals exhibited various structural changes not seen in the wild type. The major structural change observed in all of the various types of terminals was the accumulation of many pitlike structures on the plasma membrane near presynaptic sites. These structures consisted of a spherical head portion, about 50-100 nm in diameter, and a cylindrical neck portion, about 20 nm long and 20-25 nm in diameter. The neck portion was surrounded by a kind of cytoplasmic dense material, about 10 nm thick, reminiscent of a "collar." Thus, these pits are referred to as "collared pits." Similar kinds of pits were observed, although very rarely, in wild-type flies at 19 and 30 degrees C and in shi flies at 19 degrees C. In addition, various degrees of vesicle depletion, and an increase in membranous structures (infoldings and cisternalike or tubulelike structures) often accompanied pit formation. The possibility that these pits are the result of a blocked step in the endocytotic process, which in turn causes vesicle depletion as exocytosis proceeds, is discussed.
Anecdotal reports of complement component deficiencies in patients with immune complex disease led to a systematic study of the levels of seven complement components in serum specimens from 178 patients with glomerulonephritis and 163 normal subjects. Deficiencies were found with significantly higher frequency (22.7%) among 44 patients with membranoproliferative glomerulonephritis (MPGN) types I and III, than among the normal subjects (6.7%, P less than 0.002) or among 134 patients with other glomerulonephritides (5.2%, P less than 0.001). The component deficiencies in MPGN were partial in nine patients and subtotal in one. They could not be ascribed to acquired hypocomplementemia or to a nephrotic syndrome. They were present over long periods, were found in family members, and involved C2, C3, factor B, C6, C7, and C8. Six were presumably the result of null structural genes, two were associated with a structurally abnormal component, and two were of unknown cause. The results give evidence that partial deficiency of one or more complement components is a factor predisposing to MPGN.
Temperature-induced structural changes in the cortical region of the garland cell, which is considered to be active in endocytosis, were investigated in a temperature-sensitive, single gene mutant of Drosophila melanogaster, shibirets1 (shi) and wild-type (Oregon-R). At 19 degrees C, both shi and wild type showed similar structural features: an irregularly extended network of labyrinthine channels, coated pits and vesicles, tubular elements and alpha vacuoles. Tannic acid (TA) impregnation showed that coated pits comprised approximately 20-25% of the total coated profiles at 19 degrees C in both shi and wild-type. When flies were incubated in a horseradish peroxidase (HRP) solution for 5 min, organelles such as coated profiles, tubular elements, and alpha vacuoles were labeled. In wild-type at 30 degrees C, minor changes were observed--mainly a decrease in the distribution of the labyrinthine channels and an increase in HRP uptake. On the other hand, in shi at 30 degrees C, the labyrinthine channels were much elongated and their network became far more complex, indicating the expansion of the surface area of the cell. Also, the coated profiles were increased in number while the number of tubular elements was decreased considerably. The TA method showed that almost all of the coated profiles were coated pits, coated vesicles being almost completely absent at 30 degrees C in shi. Furthermore, HRP uptake activity was considerably decreased at 30 degrees C. These structural changes, as well as the reduced HRP uptake activity, were reversible when the temperature was lowered to 19 degrees C. The observations suggest that in the garland cell of shi the conversion of coated pits to coated vesicles, that is, membrane pinch-off, is blocked at high temperature.
The mitral cell in the olfactory bulb of the goldfish was examined by means of light microscopy, high-voltage electron microscopy, and conventional electron microscopy. Mitral cells are located rather diffusely throughout the glomerular and plexiform layers. They do not make their own discrete layer. The cell bodies are rounded or triangular, and are about 10-25 micrometers in diameter. In Golgi-impregnated material, thick cylindrical dendrites can be seen arising from the cell bodies and branching in the glomerular layer. Dendritic branches of some cells make two or more rather compact tufts, while the dendrites of other cells intermingle loosely with one another. In semithin and thin sections, darkly stained nodules appear to be scattered diffusely in the glomerular layer without clustering into discrete spheres, which are characteristic of the mammalian glomerulus. Hence, instead of the glomerulus, the "glomerular area" is defined as an area consisting of darkly stained nodules with rather pale granular regions surrounding them. Branches of mitral cell dendrites in the glomerular area consist of cylindrical shafts and irregular appendages arising from them. The shafts appear in the pale granular region and the appendages are found in the darkly stained nodules. Synapses can be found on all parts of the mitral cell: the soma, axon hillock, axon initial segment, thick dendritic stems, and dendritic branches. The abundance of synapses seems to vary considerably from part to part, and is highest on the dendritic branches in the glomerular area. The mitral cell is postsynaptic to olfactory nerve terminals and granule cell dendrites, and presynaptic to granule cell dendrites and some processes of unknown origin. Olfactory nerve terminals make asymmetrical synapses specifically on the appendages of the dendritic branches. Of the synapses on the shafts of the mitral cell dendritic branches in the glomerular area, 90% are with granule cell dendrites. Of the synapses between two different kinds of processes 30% are mitral-to-granule asymmetrical synapses, 20% are granule-to-mitral symmetrical synapses, and 50% are reciprocal pairs. Gap junctions and mixed synapses are also seen on branches of mitral cell dendrites. Features of the goldfish mitral cell are compared with those of the mammal. The differences in neuronal organization between the olfactory bulbs of teleosts and mammals are discussed.
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The three-dimensional structure of the ruffed cell dendrite in the olfactory bulb of the goldfish (Carassius auratus) was studied by means of light and high-voltage electron microscopy of Golgi-impregnated material, combined Golgi-electron microscopy, and electron microscopy of serial thin sections. Ruffed cell dendrites ramify in the glomerular area with tufted branching patterns. They give rise to many appendages of various shapes and sizes: sheetlike processes, fingerlike projections, or small tuftlike appendages. These appendages, singly or together, appear to entwine or cover other neuronal processes. In thin sections ruffed cell dendritic appendages frequently look like glial processes; that is, they appear to conform in shape to the contours of surrounding neuronal elements, such as mitral and granule cell dendrites. Ruffed cell dendrites display intimate relationships with mitral cell dendrites. The former appear to coil around and cover the latter. Nothwithstanding the intimate relationship between ruffed cell dendrites and mitral cell dendrites, there seem to be no synaptic connection between them. Ruffed cell dendrites bear a rather small number of presynaptic and postsynaptic sites, most of which area with granule cell dendrites. Ruffed cell dendrites seem to receive no synapses from olfactory nerve terminals.
When mature female rats having been showing at least 2 consecutive 4-day estrous cycles were raised in a room with continuous lighting (LL), their vaginal smear pattern became irregular by 7 to 9 days. and a persistent-estrus (P-E) appeared around 25 to 75 days of exposure. Ovaries from LL-exposed rats showing irregular cycles or P-E had signs of cystic follicles and anovulatory polycystic follicles, respectively. When P-E rats were placed again under the light-dark cycling condition (14L: 10D; Lights on 05: 00 h), the regular 4-day cycles were recovered soon and ovarian structures became normal after about 5 cycles. In P-E rats injected i.v. with 10 microgram LH/day at 4-day intervals under the LL condition, the regular estrous cycle reappeared and ovarian structures became normal after 5 administrations. These results suggest that the polycystic ovary of P-E rat induced by LL is reversible with cyclic stimulation by LH.
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The ruffed cell is present in the olfactory bulb of the catfish, Parasilurus asotus, and of the sea eel, Conger myriaster. Its morphological features have been studied by light microscopy, high-voltage electron microscopy, and conventional electron microscopy. The ruffed cell of the catfish is very similar to that of the goldfish in its location and in its structural features. It has a spheroidal or ovoid cell body about 15 to 30 micrometer in diameter. Several dendrites arise from the cell body to form a rounded dendritic field about 100 micrometer in diameter near the cell body. The initial unmyelinated portion of its axon (IP) consists of a shaft and many protrusions arising from it. The shaft, about 1 micrometers in diameter, located extends for about 100 to 200 micrometer, where it acquires a myelin sheath. The protrusions intermingle with one another in a complex manner to form a rather discrete spheroidal field about 20 to 50 micrometers in diameter, located in the vicinity of the cell body. In contrast, the ruffed cell of the sea eel differs rather significantly from that of the goldfish in its morphological features. The ruffed cell of the sea eel is of a bipolar type. One thick dendrite arises from the cell body and extends for about 50 to 100 micrometers, where it gives rise to many thread-like dendritic branches. The IP arises from the cell body as a smooth thin process. However, about 30 to 70 micrometers distant from its origin, many elaborate protrusions arise from the axonal shaft. These intermingle with one another to form a spheroidal or ovoid field about 20 to 40 micrometers in diameter. Distal to this protrusion-bearing part, the axon continues as a smooth, thin process. In spite of these differences in structural features, the ruffed cell of the catfish and that of the sea eel are very similar in their synaptic features in the nest (the special synaptic field around the ruffed cell IP, composed of its protrusions, of granule cell dendrites, and of other neuronal processes); that is, synapses between the ruffed cell IP (its shaft and protrusions) and granule cell dendrites and serial synapses made by the ruffed cell IP, granule cell dendrites, and perinest cell dendrites. These results suggest that the ruffed cell is generally present in the teleostean olfactory bulb, although its detailed structural features may vary from species to species. Moreover, the neuronal organization of the olfactory bulb seems to be fundamentally similar in various species of teleosts.
The fine structure and synaptic features of the ruffed cell, especially those of the initial unmyelinated portion of its axon (IP), were investigated by means of electron microscopy. The round or oval cell body is 10 to 20 micrometers in diameter. Near the cell body, there is a specialized region of the IP, about 20 to 40 micromerters in diameter, which consists of branched protrusions from the IP. Many neuronal processes end on these protrusions, and the whole assembly reminds one of a bird's nest. The nest has a little higher electron density than the surrounding field. The nucleus of the cell itself is round or oval with irregular undulations, and measures 7 to 10 micrometers in diameter. The perikaryon contains the usual cell organelles; especially many clusters of free ribosomes. Two kinds of dendrites arise from the cell body: thick dendrites, about 4 micrometers thick, which appear to be extensions of the perikaryon; and thinner dendrites, about 1 to 2 micrometers in diameter. In addition to these two, processes resembling those of glia arise from the cell body or from the thick dendritic trunk. Some of the dendritic branches enter the glomerulus. The IP arises from the cell body as a protrusion-bearing process about 0.8 to 1.5 micrometer in diameter. The IP is divided into three parts: part 1, where many elaborate protrusions arise to constitute a nest; part 2, where several scattered protrusions arise; and part 3, which has no protrusions. Part 1 of the IP is further subdivided into three portions according to the fine structure of its shaft. The first portion, about 10 to 15 micrometers long, is rather straight and exhibits the two characteristics of the conventional initial segment, i.e., membrane undercoating and fascicles of microtubules. The second portion, about 10 to 20 micrometer long, shows the membrane undercoating, but no fascicles of microtubules. The third portion of part 1 as well as parts 2 and 3 exhibits neither of the two distinguishing characteristics of the initial segment. Synapses are encountered on the cell body, the dendrites, and the IP. Most of them are formed with granule cell dendrites. The ruffed cell is presynaptic in asymmetrical synapses whose postsynaptic elements are the granule cell dendrites and other kinds of neuronal processes of unknown origins. It is also postsynaptic in symmetrical synapses from the granule cell dendrites. Reciprocal pairs of these two types of synapses are also seen, both on the dendrite and the IP. The numbers of synapses on the dendrite and the cell body seem far less than on the IP. The number of synapses on one IP is roughly estimated to be 1,000 to 2,000. The ratios of the synaptic types are as follows: asymmetrical synapses from the IP, 63%; symmetrical synapses onto the IP, 12%; and reciprocal pairs of synapses, 25%. Gap junctions are also seen between protrusions of the ruffed cell IP and dendrites of the perinest cell, which is a small neuron located at the periphery of the nest...
The axon initial segments (ISs) of pyramidal cells in the rat hippocampus (CA3 region) were studied by means of light microscopy of Golgi-impregnated material and electron microscopy of random and serial thin sections. The ISs display three distinguishing characteristics; fascicles of microtubules, membrane undercoating and clusters of ribosomes. The ISs contain cisternal organelles which are often associated with synapses and are in continuity with smooth and rough endoplasmic reticulum. Small spines are recognized on the ISs both in the light and electron microscope. There are 10-25 on each IS and they are usually concentrated on the proximal 30 micrometers of the IS. Axonic spines contain spine apparatuses, clusters of ribosomes, multivesicular bodies and other organelles. Several collaterals are also recognized to originate from the axon proximal to the start of a myelin sheath. The IS receives many synapses both on its shaft and spines. Almost all of them are of the symmetrical type with flattened vesicles but a few asymmetrical synapses with spherical vesicles occur. Pyramidal cell ISs are very rarely presynaptic at asymmetrical synapses with spherical vesicles. Based on serial sectioning studies, the number of synapses on one IS is estimated at 100-200. These abundant synaptic contacts on the IS suggest that it is an important synaptic site. The possibility that there are two different inhibitory systems controlling the output of the pyramidal cell is discussed.
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