Search PubMed⌕ Search

Biomedical subjects

B B Garber

Publications and source records attributed to B B Garber.

28 records · Page 2Linked to original sources

Separation and characterization of neuronal and glial cell populations from embryonic chick cerebra in culture.

A new procedure of separation of glial and neuronal cell population from embryonic chick cerebra has been described and their morphology in vitro was examined by SEM. This technique used the differential adhesive properties of the glial and neuronal cells to obtain an initial separation in primary monolayer culture. The neuronal fraction was then further purified by treatment with cytosine arabinoside. The homogeneity of the glial and neuronal cultures produced by this technique was examined by phase contrast and scanning electron microscopy, liquid scintillation counting of incorporation of radioactive precursors into the cultured cells and autoradiographic study of the cultures. The purity of the neuronal culture was estimated to be better than 97 and 98% based on LSC and autoradiography respectively. The purity of glial culture was assessed by phase contrast and SEM and was estimated to have a purity of over 99%. The viability of the both cultures was good following initial separation. The glial cells were typically epitheloid and formed confluent monolayer 7--10 days after initial separation. These cells have a smooth upper surface and are typically hexagonal in shape. The neuronal cultures formed small aggregates interconnected with compound neuronal processes. It was noted that the neuronal differentiation was closely related to the glial cells. In the presence of a glial carpet, the aggregates became flattened and well differentiated neuronal cells were found. On the contrary, round neuronal aggregates were found. In the case of mixed cultures of glial and neuronal cells neurites were seen grown mainly on the surface of glial carpet. Only in rare occasions, neurites were seen bridging over the bare glass surface.

Animals↗

Self-assembly of cortical plate cells in vitro within embryonic mouse cerebral aggregates. Golgi and electron microscopic analysis.

Mouse isocortical cells were dissociated at 18 days of embryonic development and were reaggregated in vitro by rotation in gyratory incubator shaker. The internal organization of the resulting aggregates was studied by conventional light microscopy, Golgi impregnation, and electron microscopy, establishing the following pattern of reassembly: (1) the predominant cell type in the aggregates was the pyramidal neuron; (2) each of these pyramidal neurons tended to orient its apical dendrite toward the surface of the aggregate; and (3) in larger aggregates (diameter > 600 microns) there was prominent parallel alignment of pyramidal cell apical dendrites. These characteristics resulted in an in vitro reconstruction of the major features of isocortex observed in situ, including formation of a superficial, rather acellular plexiform layer. Reconstruction of isocortical architecture appeared to take place independently of either a germinal epithelium, a radial glial framework, or an outer mesenchymal scaffold. Analysis of the events occurring during aggregate formation suggests that intrinsic cellular information accounts for the expression of basic pyramidal cell morphology. However, dendritic orientation and alignment are most likely determined by cell-cell interactions dependent upon specific cell surface recognition properties, as well as by geometric restraints imposed by the spherical or cylindrical shape of the aggregates.

Animals↗

Glutamine and related analogs regulate guanosine monophosphate reductase in Salmonella typhimurium.

The addition of a glutamine analog, 6-diazo-5-oxo-L-norleucine, or an inhibitor of glutamine synthetase, L-methionine-dl-sulfoximine, to the growth media of most Salmonella typhimurium strains resulted in a marked elevation of guanosine monophosphate reductase levels. The elevation caused by either compound required protein synthesis and could be antagonized by exogenous glutamine. In addition, when glutamine auxotrophs were grown in suboptimal concentrations of glutamine, the guanosine monophosphate reductase levels were increased. It is postulated that glutamine or a product of its metabolism may function under normal conditions as a negative regulatory element in the control of guanosine monophosphate reductase and that decreased effective intracellular levels of glutamine result in an increase in the level of the enzyme.

Azo Compounds↗

Utilization of 2,6-diaminopurine by Salmonella typhimurium.

The pathway for the utilization of 2,6-diaminopurine (DAP) as an exogenous purine source in Salmonella typhimurium was examined. In strains able to use DAP as a purine source, mutant derivatives lacking either purine nucleoside phosphorylase or adenosine deaminase activity lost the ability to do so. The implied pathway of DAP utilization was via its conversion to DAP ribonucleoside by purine nucleoside phosphorylase, followed by deamination to guanosine by adenosine deaminase. Guanosine can then enter the established purine salvage pathways. In the course of defining this pathway, purine auxotrophs able to utilize DAP as sole purine source were isolated and partially characterized. These mutants fell into several classes, including (i) strains that only required an exogenous source of guanine nucleotides (e.g., guaA and guaB strains); (ii) strains that had a purF genetic lesion (i.e., were defective in alpha-5-phosphoribosyl 1-pyrophosphate amidotransferase activity); and (iii) strains that had constitutive levels of purine nucleoside phosphorylase. Selection among purine auxotrophs blocked in the de novo synthesis of inosine 5'-monophosphate, for efficient growth on DAP as sole source of purine nucleotides, readily yielded mutants which were defective in the regulation of their deoxyribonucleoside-catabolizing enzymes (e.g., deoR mutants).

2-Aminopurine↗

Fibronectin associated with the glial component of embryonic brain cell cultures.

In the basic approach to investigations of neuronal--glial interactions during both normal brain development and its pathogenesis, embryonic brain cell populations were fractionated into purified neuronal and glial components. Using separation procedures based on differential adhesion and cytotoxicity, the isolated neuronal and glial phenotypes could be identified by distinct morphological and biochemical characteristics, including the visualization of glial fibrillary acid protein (GFA) within glial cells in immunohistochemical assays with monospecific anti-GFA serum. When unfractionated cerebrum cells dissociated from 10-day chick or 14-day mouse embryos were plated as monolayers and cultured for 1--14 days, monospecific antiserum against fibronectin (LETS glycoprotein) was found to react with many, but not all, of the cells as revealed by indirect immunofluorescence microscopy. The isolated neuronal and glial components of these populations were used to determine whether the appearance of membrane-associated fibronectin was characteristic of one cell type or the other, or both, and if neuronal--glial cell interaction was required for its expression. It was found that the surfaces of glial cells, completely isolated from neurons, showed an intense fluorescent reaction to the anti-fibronectin serum. In contrast, the purified neuronal cultures showed no fluorescence with either the anti-GFA or anti-fibronectin sera. These results demonstrate fibronectin as a cell surface protein associated primarily with glial cells and independent of neuronal--glial cell interaction for its expression. Furthermore, the results indicate that the fibronectin observed on glial cell surfaces in these cultures is produced endogenously and is not due to the preferential binding of fibronectin present in the culture medium. The role of fibronectin as an adhesive molecule in neuronal--glial interactions is discussed.

Animals↗

Selective cell association of catecholamine neurons in brain aggregates in vitro.

Brain tissues (aggregates) were reconstructed in vitro from dissociated single cell suspensions derived from 12- to 18-day embryonic mouse midbrain containing the substantia nigra. The application of the Falck-Hillarp histofluorescence method to these cell systems allows the visualization and identification of this specific population of developing catecholamine (CA) neurons during their reassembly, differentiation and histogenetic patterning in vitro. CA neurons are unselectively distributed in the initial dissociated cell suspension and in the reaggregating tissue up to 24 h. By 48 h the CA neurons have selectively associated into small clusters which further coalesce into a thick and elongated band along one margin of the aggregate by 96 h. This structure is similar in organization to the morphology exhibited by substantia nigra neurons in situ during their migratory phase in normal development. In addition, the differentiated neurons observed in the later aggregates appear to produce normal processes. Catecholamine analyses show a significant increase in dopamine and noradrenaline levels during the process of differentiation and histogenetic organization in vitro.

Animals↗

Control of epithelial development.

Interactions between epidermal and dermal cells of integumental systems exert finely regulated controls over epithelial development. Experimental reconstruction of skin tissues, in vitro and in vivo, from selected populations of dissociated embryonic chick and mouse cells provides a unique opportunity for analyzing the morphogenetic information intrinsic to individual cells. Dermal cells are shown not only to induce and specify particular epithelial structures; they also exercise the power to suppress potential developmental programs. Epidermal cells not only recognize and respond to dermal directives; they are also critical agents in the communication of cues for histogenetic patterning to both neighboring epithelial cells and subadjacent dermal elements. The role of the cell surface as a site for developmental control is discussed in the context of current evidence.

Animals↗