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Biomedical subjects

I G Morgan

Publications and source records attributed to I G Morgan.

At least 73 records · Page 4Linked to original sources
PubMed1980

Kainic acid destroys displaced amacrine cells in post-hatch chicken retina.

Laser-induced axotomy of chicken retinal ganglion cells leads to the death of the cells. This leaves intact a population of small neurons in the retinal ganglion cell layer which accounts for 30-35% of the total cells in that layer. The cells which are resistant to axotomy are destroyed by intraocular injection of kainic acid, whereas ganglion cells are not killed. We suggest that the population of small, axotomy-resistant, kainic acid-sensitive neurons corresponds to the displaced amacrine cells reported by other workers.

Animals↗
PubMed1980

Retinal benzodiazepine receptors are destroyed by kainic acid lesions.

[3H]Diazepam binds to preparations of membranes from chicken retina. Two binding sites were detected; a high affinity site (KD, 1.8 nM and Bmax, 0.17 pmol/mg retina protein) and a low affinity site (KD, 132 nM and Bmax, 1.46 pmol/mg retinal protein). GABA stimulated [3H]diazepam binding to these retinal membranes. One week after injection of kainic acid into the eye, which destroys the horizontal and amacrine cells of the retina, the low affinity site disappeared, while the level of the high affinity site was hardly affected. These results establish that chicken retina contains benzodiazepine receptors, which are closely associated with GABA receptors. The benzodiazepine receptors are probably associated with horizontal and/or amacrine cell synapses which use GABA as a transmitter.

Animals↗
PubMed1979

Biochemical effects of cycloheximide in developing chick brain.

The timecourses of inhibition of protein synthesis in forebrain roof 15 min to 24 hr after either intracerebral or peripheral injection of 40 microgram of cycloheximide (CXM), show maximum inhibition (68--85%) 1 hr after injection in 12 hr, 2-day- and 16-day-old chicks. In 2-day-old chicks, the level of free lysine was elevated by around 250% 1 hr after intracerebral injection of CXM. The total radioactivity in the forebrain roof/mg protein following peripheral injection of labelled lysine increased by around 80% compared to saline controls. Following unilateral injection of 20 microgram in 25 microliter CXM into a forebrain hemisphere, the inhibition of protein synthesis spread to the opposite forebrain hemisphere and both optic lobes within 5 min. Smaller volumes did not seem to give a clear unilateral inhibition capable of explaining the unilateral behavioural differences which have been reported. Central injection of CXM in 2- and 16-day-old chicks, resulted in an inhibition of liver protein synthesis of 55% and 40%, respectively. There were also gross signs of pathological effects in the liver and gall bladder. The implications of these effects of CXM are discussed in terms of the use of the drug in behavioural experiments.

Animals↗
PubMed1977

A possible role of the phosphorylation of synaptic membrane proteins in the control of calcium ion permeability.

Incubation of synaptosomes under conditions which result in complete phosphorylation of membrane bound accepter proteins does not affect the permeability to Na+ or K+ as measured by a spectrophotometric method. This technique was not, however, sensitive enough to determine permeability to Ca2+ which was thus estimated, using 45Ca2+. It was found that although phosphorylation did not affect the equilibrium binding of 45Ca it did lower the rate of both Ca2+ uptake and efflux. The most likely interpretation of these results is that phosphorylation of proteins in the synaptic membrane lowers the permeability of the membrane to Ca2+. This could have a role in the regulation of synaptic transmission.

Animals↗
PubMed1976

Localization in the synaptic junction of the cyclic AMP stimulated intrinsic protein kinase activity of synaptosomal plasma membranes.

Synaptosomal plasma membrane fragments contain a tightly bound protein kinase which can catalyse the phosphorylation of endogenous protein the reaction bein stimulated by cyclic AMP. A fraction enriched in synaptic junctions, which can be isolated from Triton X-100-treated synaptosomal plasma membranes, is also enriched in the cyclic AMP stimulated intrinsic protein kinase. The location of the enzyme in the synaptic junction suggests that cyclic AMP-stimulated phosphorylation may have some role in synaptic transmission.

Animals↗
PubMed1976

Biochemical evidence on the role of gangliosides in nerve-endings.

From the biochemical and developmental data in the literature, there appears to be some specific relationship of gangliosides to synapses. Whether the concentration of polysialo-gangliosides is located in the immediately pre-synaptic part of the neuronal plasma membrane is not known. There are many unanswered questions about the gangliosides, which we have attempted to pose in this article. There are as many hypotheses about roles for gangliosides, and virtually no data to back them up. In fact there are not even real indications of possible functions. We believe that it will be very difficult to define the functions of gangliosides until more of the basic questions are answered-even if their synaptic localization is a constant temptation to speculate.

Cell Aggregation↗
PubMed1975

Synaptosomal plasma membrane glycoproteins: fractionation by affinity chromatography on concanavalin A.

Synaptosomal plasma membrane glycoproteins were solubilized in 0.08% sodium dodecyl sulfate (SDS) and separated by affinity chromatography on concanavalin A-Sepharose. Three fractions were obtained. Fraction CO (unadsorbed) contained 63% of the protein, but only 23% of the sugar and was rich in fucose, galactose and N-acetyl-neuraminic acid (NANA) relative to the other sugars. Many proteins were detected in this fraction by polyacrylamide gel electrophoresis, but only on band stained well for carbohydrate. Fraction CR (retarded) contained glycoproteins which reacted weakly with concanavalin A and stained poorly with periodic acid-Schiff reagent (PAS). There was no enrichment in total sugar/mg protein relative to the original fraction, but there was a marked enrichment in N-acetyl-glucosamine and NANA relative to the other sugars. The protein profile of this faction was complex, but only one major PAS-positive band was detected. However, most, if not all, the proteins seemed to be weakly PAS-positive. Fraction C1 (adsorbed) was markedly enriched (5-fold) in sugar/mg protein, particularly in mannose and N-acetyl-glucosamine. It had a relatively simple protein profile, and most of the protwin bands stained well with the PAS reaction. Glucose was detected in the initial fraction, and in all the subfractions, but it could not be shown definitely to be either a contaminant or an intrinsic constituent of synaptosomal plasma membrane (SPM) glycoproteins. Minor sugars, if present, could, at most, account for less than 0.25% of the carbohydrate.

Animals↗