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In many organs, part of the over-all protein synthesis serves the growth of cells by completing the new members of the cell population which arise after mitosis. In the adult brain, the neurons appear to undergo mitosis only to a very limited extent, while glial cells do divide under special circumstances.' Thus, cell renewal and growth cannot account for the main part of the extensive protein synthesis occurring in the brain.In an effort to explain the role of protein turnover in brain function, extensive efforts are under way in a number of laboratories to isolate proteins specific to the brain and to determine their cellular localization, metabolic half life, and function. Moore and co-workers2 3 have recently isolated and characterized an acidic protein (named S100 protein) specific to nervous tissue which makes up 0.5 per cent of the brain's soluble proteins. Antiserum to this protein, isolated from beef brain, showed cross reaction to protein from all vertebrate species examined. 4 The suggestion has been made that the S100 protein is located in glial cells,5 while another proposal has been made that it is a neuronal protein.3 In this paper, evidence will be presented that the S100 protein is mainly localized in the glial system of the Deiters' nucleus of the rabbit brain stem. The S100 protein is also found in the cell nuclei of the large neurons, while it is distinctly absent from the nuclei of the glial cells.Material and Methods.-Microanalysis: The large neurons and surrounding glia from the lateral vestibular (Deiters') nucleus of the rabbit brain stem were used. After rapid removal of the brain stem, a section was placed at the rostral boundary of the tubercula acustica. The sections of both sides, 3-4 mm thick, were placed in cold 0.25 M sucrose solution. The neurons or the glia were separated and cleaned by freehand dissection as previously described.6 The reason for using these types of neurons is that many data on their biochemical characteristics have been collected during the last 10 years. Also, the relationship between the Deiters' neuron and its surrounding glia has been elucidated in measurements of enzymatic activity and RNA studies.7 -10 Each Deiters' nerve cell has a dry weight of 2 X 10-8 gm. The dry weight per .s3 for both the nerve cell body and the surrounding glia is 0.20 juug. Therefore, biochemical data obtained on the same volume of neurons or glia can be compared.Twenty to thirty nerve cells or glial samples are transferred by freehand manipulation to a drop of homogenizing solution on top of a Teflon homogenizer pestle, 2 mm in diameter. The cells are homogenized in 20 Al of distilled water containing 0.5% w/v Triton X-100. After homogenization, centrifugation took place in 0.5-mm capillary tubes at 12,000 rpm.Single diffusion agar precipitation using antiserum against the S100 protein was performed in glass capillaries, 300 IA or 500 A in diameter (Microcaps: Drummond Scientific Co., Broomall, Pennsylvania), according to a micromodification of Oudin's technique."1 Agar in a ...

Abstract— The Thy‐1 antigen of rat brain is a membrane glycoprotein of molecular weight 17,500. It was localized in sections of brain and spinal cord by indirect immunofluorescence using rabbit antisera raised against purified Thy‐1 and fluorescein conjugated purified sheep F(ab')2, anti‐(rabbit IgG) antibody fragments. The specificity of the anti‐(Thy‐1) sera was tested by a quantitative indirect radioactive binding assay which is particularly useful for ascertaining the specificity of reagents used in immunohistochemical studies. Purified Thy‐1 was used to absorb the anti‐(Thy‐1) sera for controls in the immunofluorescence experiments. Strong specific fluorescence was found throughout the gray matter of brain and spinal cord with lesser amounts in white matter. The nuclei of all neural cells and also myelin lacked fluorescence. Some of the large neurons contained weak cytoplasmic fluorescence, but the majority of the immunofluorescence was located in the neuropil of the brain and spinal cord. There was an indication that Thy‐1 was associated with synaptic knobs due to its presence in synaptic glomeruli and its granular appearance around some neurons. An additional association with glial membranes could not be excluded.

57 58 HOLGER H Y D~N and ANURZEJ PIGONContacts between oligodendrocytes and astrocytes, and the nerve cell including its processes can be seen in silver-stained sections. The same axon has contact both with the post-synaptic neuron and with its oligodendrocytes (SCHEIBEL and SCHEIBEL. 1955, 1958). In electronmicrographs the oligodendrocytes contain more particles and mitochondria than do the astrocytes (LUSE, FARQUHAR and HARTMANN, 1957; DEVPSEY and Luss, 1958; andothers). SCHULTZ et a/. (1957) and DE ROBERTIS (1960) also stress the empty appearance of the astrocytes after fixation and embedding. The so-called neuropil is filled with the delicate, membrane-like processes from both the neurons and the neuroglia. The astrocytes ensheath the capillary walls and establish complicated contacts with the neurons and with the oligodendrocytes. The nerve cells are clearly isolated from the immediate blood supply by the glia. The only 'extra-cellular' space seems to be the 100-200 8, which separate the protoplasmic membranes.In 1954, DE ROBERTIS and BENNETT described the existence of vesicles, 35S650 A in diameter, in the endothelial cells of brain capillaries and in oligodendrocytes. They suggested that the vesicles were fluid globules, indicating a fluid transport by pinocytosis across the capillary wall. They also suggested that glial cells, Qhwann cells and oligodendrocytes mediate the exchange between the nerve cell and the intercellular space.WYCKOFF and YOUNG (1956, 1958), FARQUHAR and HARTMANN (1957) and SCHULTZ et a / . (1957) have pointed out that morphological findings suggest that astrocytes may serve as the principal transport system to the nerve cells. DE ROBERTIS (1960) presents arguments for assuming that the astrocytes are the main centres for the salt exchanges in the brian, thus adding to the subject of the relationship between neuroglia and the blood-brain barrier. The narrow, 100-200 A-wide clefts between the osmium-stained cell membranes offers another possible transport system. According to the present authors (see also HYD~N, 1958, 1959) a cautious view ought to be taken as their dimensions in uiuo may well be 300 A instead of 10CL200 A. The fixation and embedding introduces, as a net result, a three-dimensional shrinkage, which is unlikely to affect all nervous structures in the same degree. Furthermore, the cytological procedure removes up to 80 per cent of the glial substance. S C H~ (1959) has discussed the effect of the ionic strength, osmotic pressure and of the presence of metabolites on the equilibrium separation between membranes in a 100-200 A channel. As SCHMITT * Stainless steel threads are supplied by A. B. Kanthal, Hallstahammar, Sweden.