WHEN brain tissue is homogenized under carefully controlled conditions, a high proportion of the presynaptic nerve terminals are torn away from their attachments to form discrete particles for which the term 'synaptosomes' has recently been adopted (WHITTAKER, MICHAELSON and KIRKLAND, 1964). These particles may be separated from other subcellular brain particles by differential and density gradient centrifuging. They retain all the structural features of the nerve endings, together with their content of transmitter substances. On suspension in hypotonic media, a proportion of them swell and burst, discharging the contents of their cytoplasm. A simple density gradient procedure enables the various components of the synaptosome-soluble cytoplasmic constituents, synaptic vesicles, external membranes and intra-terminal mitochondriato be separated from the disrupted synaptosomes in relatively pure form, thus enabling the compartmentation of transmitter substances and other constituents of the nerve ending to be determined (WHITTAKER et al., 1963, 1964). Synaptosomes were first prepared by HEBB and WHITTAKER (1958) and first identified as such by GRAY and WHITTAKER (1960, 1962 see also WHITTAKER, 1960). The effect of hypotonic disruption was studied by WHITTAKER (1959, 1961), JOHNSTON and WHITTAKER (1963), DE ROBERTIS, RODRIGUEZ DE LORES ARNAIZ, SALGANICOFF, PELLEGRINO DE IRALDI and ZIEHER (1963) and WHITTAKER et al. (1964) (definitive papers only are quoted).The subject has been comprehensively reviewed by WHITTAKER (1964 a, b).This paper describes some further observations which have been made on the morphology and acetylcholine content of pure preparations of isolated synaptic vesicles. In a study of the properties of synaptosomes isolated from various areas of the central nervous system, regional differences in stability were observed during exposure to hypotonic conditions. Synaptosomes from the cerebral cortex were found to be more readily disrupted than those from some other areas and to give a higher yield of synaptic vesicles. Accordingly, cortical tissue was used as the source of synaptic vesicles in the present study. Methods have been devised for determining the average number of acetylcholine molecules/vesicle and the findings are discussed in relation to the problem of the quantized release of acetylcholine at cholinergic nerve endings. Preliminary accounts of this work have been given by SHERIDAN and WHITTAKER (1964) and WHITTAKER (1 964 c). METHODS Isolation ojsynuptic vesicles.Unless otherwise stated, synaptic vesicles were isolated from synaptosomes derived from the cerebral cortex of guinea pigs (domesticated varieties of Cuuia cutleri) and coypus (Myocusfer coypus) by a modification (method B of ElCHBERG, WHITTAKER and DAWSON, 1964) of the density gradient procedure of WHITTAKER ef at. (1964). NO morphological differences were observed between synaptosomes or synaptic vesicles of the two species. The animals were decapitated, the cranial cavity opened, the brain-stem sectioned at the level of the...
Electron microscopic observations of developing albino rat lung provide further evidence for the endodermal origin of the type I and I1 pulmonary epithelial cells, and for the mesodermal origin of the interstitial pulmonary cells.Cytoplasmic glycogen increased in the fetal endodermal cells from day 16 to the twentieth day of gestation. Further development revealed a decrease of this substance in the differentiating pulmonary epithelial cells, and a concurrent increase in the 1 Supported by research Fellowship grants 1-Fl-GM-33 009, 5-Fl-GM-33, 009, and grant-in-aid GRSG-FR-05203 from the National Institutes of Health. ZRevision of a thesis submitted in partial fulfillment of the requirements for the degree, Doctor aOther names applied to this cell type are: small alveolar cell, type A epithelial cell, pulmonary epithelium, membranous pneumonocyte and small alveolar epithelial cell. *Other names applied to this cell type are: large alveolar cell, type B epithelial cell, macrophage, granular pneumonocyte, large alveolar epithelial cell, septal cell, niche cell, epicyte. vacuolated alveolar cell, histiocyte and dust cell. 181 LITERATURE CITED Altman, P., and D. Dittmer (Eds.) 1964 Biological Handbook Series: Growth (Reproduction and Morphological Development). Fed. Amer. SOC. Exp. Biol., Washington, D. C. pp. 1964 The role of alveolar inclusion bodies in the developing lung. Lab. Invest., 13: 1215-1229. 1964 Granular pneumonocytes: Electron microscopic evidence of their exocrinic function. Science, 145: 1318-1319. Bensley, S. H., and M. B. Groff 1935 Changes in the alveolar epithelium of the rat at birth. Anat. Rec., 64: 27-39. Bertalanffy, F. D. 1961 The modem concept of respiratory tissue structure. Acta Cytol., 5: 1964 Respiratory tissue: structure, histophysiology, cytodynamics. Part 11. New approaches and interpretation. Int. Rev. Cytol., On the nomenclature of the cellular elements in respiratory tissue. Amer. Rev. Resp. Dis., 91: 605-609. Bloom, W., and D. W. Fawcett 1968 A Textbook of Histology, 9th ed., W. B. Saunders Co., Philadelphia, pp. 635-651. Brooks, R. E. 1966 Concerning the nomenclature of the cellular elements in respiratory tissue. h e r . Rev. Resp. as., 94: 112-113. Bullough. W. S. 1952 The energy relations of mitotic activity. Biol. Revs., Cambridge Phil, SOC., 27: 133-138. Campiche, M. 1960 LRs inclusions lamellaires des cellules alveolahes dans le poumon du 84-86. Balis, J.
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