[In vitro malignant transformation of fetal hamster brain cells by methylnitrosourea]

Using primary cultures originating from 14 day old fetal Hamster brain, we have obtained a cell line with glial morphology. These cell remain non transplantable during the first year of in vitro culture, but undergo spontaneous transformation during the second year. Following prolonged contact of the glial-like cells with 25 to 50 microgram/ml of methylnitrosourea (MNU), a malignant transformation is observed 5 months after the treatment. The lowest concentrations of (MNU) do not cause malignant transformation, but seem to inhibit (or postpone) the spontaneous transformation. After MNU treatment, cells retain their glial nature.

Molecular forms of acetylcholinesterase: their de novo synthesis in mouse neuroblastoma cells

Rat mouse AChE molecular forms are indistinguishable with respect to their sedimentation coefficients and their evolutive proportions during brain maturation. Among rat or mouse erythrocytes, rat C6 glial cells, and mouse 2A and NS 20 neuroblastoma cells, only neuroblastoma cells showed both the ES and HS molecular forms with a 1:1 proportion for NS 20 cells. All these cells lack a third molecular form (16S), which is present in rat and mouse superior cervical ganglia. After irreversible inhibition of pre-existing NS 20 neuroblastoma AchE, the ES form is first synthesized (de novo synthesis). The HS form begins to appear after a lag time of several hours and represents, 24 h after inhibition, only 15% of the total recovered activity, which is near the initial level. The initial relative proportions return by 2 to 3 days after inhibition. The recovery of the HS form is, for the most part, blocked by actinomycin D, which does not block the recovery of activity itself, which remains as an ES form. It seems that integration of the ES form into the HS form more probably depends on the synthesis of a new messenger RNA, which is required for the synthesis of either new AChE polypeptide chain, polymerization initiating protein or activating enzyme.

Torpedo marmorata acetylcholinesterase; a comparison with the Electrophorus electricus enzyme. Molecular forms, subunits, electron microscopy, immunological relationship

Electron microscopy, sequential degradation by hydrolytic enzymes and the physical-chemical properties of the molecular forms of Torpedo acetylcholinesterase indicate that these molecules are structurally related to each other in the same way as the molecular forms of Electrophorus acetylcholinesterase: all are derived from a complex structure in which three tetrameric groups of subunits are associated with a rod-like 'tail'. In aged preparations the catalytic subunits are split into fragments in a manner similar to those of Electrophorus acetylcholinesterase. Immunological cross-reaction between both enzymes demonstrates the occurrence of common antigenic sites. The enzymes from the two sources, however, are different in their molecular weights and susceptibility to hydrolytic enzymes. Also, Torpedo acetylcholinesterase does not precipitate with either isologous or heterologous antibodies.

[In vitro malignant transformation of fetal hamster brain cells by benzo (a) pyrene]

Hamster embryo brain cells exposed in vitro for 24 hrs. to benzo (a) pyrene and then subcultivated. undergo a morphological transformation. After several passages, transformed cells are capable in most cases of inducing tumors of a special type through intraocular or intracerebral grafting. Histological characterisation of these tumors suggests that they are of glial type. Untreated control brain cells subcultivated for one year, keep their normal characteristics and do not induce tumors when grafted in Hamster.

[Influence of chloride ions on the kinetic parameters of rat brain choline acetyltransferase]

Kinetic properties of Rat brain choline acetyltransferase were studied. Chloride ions promoted the increase of the Km values for the two substrates. Vmax was increased sixty times when chloride ions concentration was elevated from 4.6 to 291 mM.

Dissociated cell cultures from fetal mouse hypothalamus. Patterns of organization and ultrastructural features

Dissociated fetal hypothalamic cells mainly taken from 14 day-old mouse fetuses were grown in vitro for increasing time (9 to 60 days). Soon after inoculation the cells partly reaggregated and attached. The small reaggregates were then interconnected by fibers bundles. After the first week the cultures were composed of a continuous basal monolayer of flat and transparent cells, over which various types of refractile cells were lying in discontinuous areas. The ultrastructural study enabled us to identify these cell types, to describe their spatial relationships, and to follow their evolution with time in culture. The basal cell formed several superimposed layers. With increasing age, they displayed typical features of astrocytes and of ependymal cells. The latter exhibited rhythmic ciliary movements in culture. The overlying cells corresponded to three types which were associated in small clumps: primitive neuro-epithelial cells, maturing as well as mature neurons and typical neurosecretory cells. The latter cells were found as early as 9 days of culture of 14 day-old fetal hypothalamic cells and retained their typical features up to two months. Neuronal processes formed very dense networks at the surface of the cultures and terminated within the basal layers. Axon and dendrites were precociously found and were still present after two months. Within axon terminals dense-core vesicles appeared at the same time as neurosecretory cells. Synaptic vesicles and synaptic junctions were found later on.

[3H] norepinephrine binding by rat glial cells in culture. Lack of correlation between binding and adenylate cyclase activation

Subcellular fractions prepared from rat glial cells in culture (clonal line c6) were used in an attempt to characterize the adrenergic receptor involved in adenylate cyclase activation. Both [3H] norepinephrine binding and enzyme activation were measured under identical experimental conditions. Binding sites for norepinephrine could be detected; their main characteristics were: apparant Km: 4 - 10-6 M, macimal capacity: 20 pmol/mg protein. Their stereospecificity towards structually related drugs was found to be different from the stereospecificity of the receptor involved in adenylate cyclase activation. Thus, 3-methoxydopamine (a competitive inhibitor of norepinephrine for adenylate cyclase activation), phenylephrine (a partial adrennergic agonist) and the blocking agent propranolol were unable to compete with [3H] norepinephrine for binding. On the other hand, several molecules like dopa bearing a catechol group and which are unable to interact with the adenylate cyclase as agonists or competitive inhibitors strongly inhibited [3H] norepinephrine binding. As in several other systems so far studied, the presence on the glial cell's membrane of a large number of "catechol-binding sites" makes it difficult to characterize the beta-adrenergic receptor.

Establishment of a clone of mouse hypothalamic neurosecretory cells synthesizing neurophysin and vasopressin

Hypothalamic cells taken from 14-day-old mouse embryos were cultured for 6 days and transformed with simian virus 40. After cloning, a homogeneous cell population was obtained. Its morphological, Ultrastructural, biochemical, and immunochemical properties were studied. These cells possess ultrastructural features of primitive neurosecretory cells. They synthesize (35)S-labeled protein components that have the molecular weight and isoelectric focusing behavior of, and display the same immunoreactivity as, neurophysin. In addition, a (35)S-labeled peptidic fraction with a molecular weight close to 1000 is synthesized and is radioimmunologically indistinguishable from vasopressin. Immunochemical staining shows that both neurophysin and vasopressin are localized in the cytoplasm. These observations strongly suggest that a clone of mouse hypothalamic neurosecretory cells has been obtained with the synthesizing capacities of secretory neurons of the magnocellular hypothalamic nuclei.