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Biomedical subjects

D Edgar

Publications and source records attributed to D Edgar.

At least 73 records · Page 4Linked to original sources
PubMed1983

Presence of nerve growth factor receptors and catecholamine uptake in subpopulations of chick sympathetic neurons: correlation with survival factor requirements in culture.

The presence of nerve growth factor receptors and the imipramine-sensitive uptake of catecholamines in sympathetic neurons of chick embryos were investigated by autoradiography. Neurons were dissociated from paravertebral ganglia of different embryonic ages and receptors and catecholamine uptake were then determined both at the beginning of culture and after 2 days in culture, at which time the number of surviving neurons is determined by the survival factors present. It was found that while essentially all the neurons specifically bound 125I-NGF both after dissociation and at the end of the culture period, only 60% of the neurons take up [3H]norepinephrine after dissociation, and this proportion remained constant through the culture period under conditions where all the neurons survived. All of the neurons maintained by NGF in culture (35% of the total) displayed this uptake, and in contrast, only one-quarter of those maintained by heart cell-conditioned medium alone (60% of the total) took up catecholamines. The uptake was shown to be neither induced by NGF nor suppressed by heart cell-conditioned medium. These results support the hypothesis that chick sympathetic ganglia contain discrete subpopulations of neurons which may be selected in culture by virtue of their different requirements for survival factors.

Animals↗
PubMed1983

The development of substance P, somatostatin and vasoactive intestinal polypeptide in sympathetic and spinal sensory ganglia of the chick embryo.

Antisera to substance P, somatostatin and vasoactive intestinal polypeptide were produced in rabbits and used to establish radioimmunoassays. The specificities and sensitivities of the assays were characterised before using them to measure the levels of these peptides in the paravertebral sympathetic ganglia and spinal sensory ganglia of embryonic chicks. The immunoreactive materials in the developing ganglia were shown to be identical with the peptides by the criterion of co-elution on reverse-phase high performance liquid chromatography. The levels of the peptides varied independently during the developmental period studied between day 8 and hatching at day 20 of incubation. Vasoactive intestinal polypeptide was first detectable on day 12 in the sympathetic ganglia and the levels increased through to hatching, at which time it first became detectable in the sensory ganglia. In contrast, substance P and somatostatin were detectable in both sensory and sympathetic ganglia throughout the period studied: the content of substance P increased up to day 18 after which time it declined, and somatostatin was present initially (day 8) at high levels before rapidly declining to a minimum at day 10 and then slowly increasing again, in parallel with the general growth of the ganglia, reflected by their protein contents. The differential changes in levels of substance P, somatostatin and vasoactive intestinal polypeptide during development indicates that different regulatory mechanisms are responsible for the ontogenesis of individual peptide phenotypes in the peripheral nervous system.

Animals↗
PubMed1982

Purification of a new neurotrophic factor from mammalian brain.

We report the purification from pig brain of a factor supporting the survival of, and fibre outgrowth from, cultured embryonic chick sensory neurons. The purified factor migrates as one single band, mol. wt. 12 300, on gel electrophoresis in the presence of sodium dodecylsulphate (SDS) and is a basic molecule (pI greater than or equal to 10.1). Approximately 1 microgram factor was isolated from 1.5 kg brain. The final degree of purification was estimated to be 1.4 X 10(6)-fold, and the specific activity 0.4 ng/ml/unit, which is similar to that of nerve growth factor (NGF) using the same assay system. This factor is the first neurotrophic factor to be purified since NGF, from which it is clearly distinguished because it has different antigenic and functional properties.

Animals↗
PubMed1981

Subpopulations of cultured chick sympathetic neurones differ in their requirements for survival factors.

Peripheral autonomic and sensory neurones derived from the neural crest will survive in vitro only if the culture medium is supplemented with specific factors (for review see ref. 1). For example, the nerve growth factor (NGF), although supporting the survival of sympathetic and spinal sensory neurons, is ineffective on parasympathetic neurones, whereas medium conditioned by chick heart cells (HCM) supports the survival of all three neuronal types. We showed previously that the requirements of cultured spinal sensory ganglion neurones for survival factors changed during development, and so provided a basis for the classification of such factors. We now demonstrate that cultured post-mitotic neurones from chick paravertebral sympathetic ganglia respond differentially to NGF, HCM and medium conditioned by C6 glioma cells (GCM). Thus, there three survival factors are functionally distinct in that they support the survival in culture of discrete subpopulations of sympathetic neurones. Those subpopulations responding to HCM and NGF are shown to differ not only in their requirements for survival factors but also in their contents of the cholinergic and adrenergic marker enzymes choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH).

Animals↗
PubMed1980

Sensory neurons in culture: changing requirements for survival factors during embryonic development.

The effect of nerve growth factor (NGF) and medium conditioned by glioma cells (GCM) on the survival of chicken sensory neurons in culture was investigated. Neurons were isolated from embryos 8 days (E8) to 16 days (E16) old and the proportion of surviving neurons was determined after 2 days in culture. In the absence of NGF or GCM, essentially no neurons survived at any age. In the presence of NGF, survival increased from 25% of the neurons at E8 to 40% between E10 and E12 and then decreased to background level (5%) at E16. In contrast, in the presence of GCM, survival increased continuously from 10% of the neurons at E8 to 75% at E16. At early developmental stages, the effect of NGF and GCM together was greater than the sum of their individual effects: at E8, about 80% of the neurons survived, double the number expected for a simple additive effect. Thus, a significant proportion of chicken neurons from dorsal root ganglia require both NGF and GCM for survival, and this may well include neurons from the ventro-lateral population, which do not respond to NGF alone. As neurons matured, the double requirement progressively decreased and, by E16, NGF no longer increased the number of neurons over that surviving in response to GCM alone. The facts that rat brain extracts mimicked the effect of GCM and that the potency of the brain extracts of rat in the postnatal period increased in parallel with the development of the glial cells suggest that glial cells produce a factor(s) both immunologically and functionally different from NGF which supports the survival of sensory neurons.

Age Factors↗
PubMed1978

Glucocorticoid induction of tyrosine hydroxylase in a continous cell line of rat pheochromocytoma.

We have established a continous cell line (G1) in which the tyrosine hydroxylase specific activity is increased as much as 50-100-fold in response to dexamethasone. This response is specific for the glucocorticoid class of steroid hormones; it is elicited by dexamethasone, corticosterone, and triamcinolone, but not by estradiol, testosterone, progesterone, or deoxycorticosterone acetate. The increase in tyrosine hydroxylase specific activity is likely to be due to the increased synthesis of new enzyme protein rather than an activation of existing protein molecules, inasmuch as this increase is completely blocked by cycloheximide.

Adrenal Gland Neoplasms↗