Survival of chick embryo sympathetic neurons in cell culture

Changes in neuronal numbers during the development of the chick embryo paravertebral sympathetic nervous system have been examined using cell culture techniques. Early sympathetic ganglia contain predominantly cells having neuronal phenotypes and these increase in number until embryonic day 9. Subsequently there is a large decrease in the number of neurons and an increase in the population of non-neuronal cells. This in vivo pattern is maintained when the neurons are grown in vitro, where Nerve Growth Factor more readily prevents the death of neurons cultured from 12-day or older embryos than those from earlier stages of development

A rapid assay for DNA repair synthesis using neutral and alkaline sodium iodide gradients

A modification to the method for estimation of repair DNA synthesis in cultured mammalian cells using density labeling which reduces the time and labor involved is described. Centrifugation times are reduced by using high-molecular-weight DNA which is loaded onto the top of a preformed sodium iodide gradient. Cerenkov counting is used to locate the region of the gradient containing light DNA for rebanding and likewise to identify appropriate fractions from alkaline gradients for acid precipitation for scintillation counting. The procedures give results indistinguishable from cesium chloride equilibrium gradients in a shorter time, with less effort, and at a lower cost

Control of DNA repair linked to neuroblastoma differentiation

Mouse neuroblastoma cells, which can be induced to undergo reversible differentiation in culture, were used as a model to investigate the effects of ultra violet (U.V.) radiation on terminally differentiated nerve cells. Differentiated neuroblastoma cells were found to be extremely sensitive to U.V. radiation when compared with proliferating cells from the same clone. However, normal resistance was regained if the differentiated cells were allowed to proceed to the next G1 phase of the cell cycle before irradiation. Neuroblastoma cells in the differentiated mode are capable of carrying out some excision repair of DNA damage, but they appear to lack a repair mechanism present in proliferating cells

Development of sensitivity to acetylcholine in cultured chick embryo sympathetic ganglion neurones

Dissociated sympathetic neurones from chick embryos of various ages were maintained in culture for several days and changes in sensitivity to iontophoretically applied acetylcholine (ACh) measured over 5 days in vitro. Neurones from 12-day embryos show a marked increase in ACh sensitivity, neurones from 14-day embryos a smaller change and those from 19-day embryos do not alter. These changes parallel those observed previously for binding of [Iα-bungarotoxin

Dependence on Cloning Method of Survival of Human Melanoma Cells after Ultraviolet and Ionizing Radiation

The resistance of a human melanoma cell line (MM96) to both ultraviolet and ionizing irradiation was compared by two different methods of cloning, on plates and in agar. A high level of resistance to both ultraviolet (D= 320 ergs/sq mm) and ionizing irradiation (D= 4300 rads) was observed when viability of cells was determined by cloning in agar. In contrast, melanoma cells were found to be as sensitive as were other cells when viability after irradiation was determined by cloning on plastic plates. The difference in sensitivity to radiation between the two methods of cloning can be explained in a model involving damage to membranes as well as to DNA. At least for ionizing radiation, this effect is not restricted to melanoma cells since a HeLa subline, HeLa-QB1, showed a similar response. In contrast, a human lymphoblastoid line (JHP) cloned in agar was sensitive under these conditions (D= 120 rads)