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Biomedical subjects

A Roberts

Publications and source records attributed to A Roberts.

At least 271 records · Page 15Linked to original sources
PubMed1986

The left triangular ligament of the liver and the structures in its free edge (appendix fibrosa hepatis) in Chinese and Canadian cadavers.

The left triangular ligament of the liver was studied in 42 Chinese adult male cadavers and 50 Canadian adult cadavers. The free edge of the left triangular ligament was examined histologically in 37 of the Chinese and all 50 of the Canadian cadavers. The average length of the left triangular ligament in the 42 Chinese was 13.9 cm and 11.5 cm in the 50 Canadian. The Canadian sample was composed of 24 adult female cadavers with an average length of 10.7 cm and of 26 adult male cadavers with an average length of 12.3 cm. In a previous study (1980) of 58 Chinese adult male cadavers, the average length of the left triangular ligament was 12.7 cm. This resulted in an average length of 13.2 cm for the 100 Chinese cadavers. These findings greatly exceed the lengths given in the textbooks, and there is no significant difference between the male Chinese and Canadian cadavers. It was found that almost all the left triangular ligaments were attached to the superior surface of the left lobe of the liver. The left suprahepatic space was subdivided by this ligament into anterior and posterior spaces. Each of the left triangular ligaments had a long free edge which extended from the lateral extremity of the left lobe of the liver to the diaphragm. Histological examination of the free edges revealed the presence of blood vessels in all of the 37 Chinese suitable for study and the 50 Canadian cadavers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Growth cones and the formation of central and peripheral neurites by sensory neurones in amphibian embryos.

We have examined the primary growth of neurites by Rohon-Beard sensory neurones in embryos of Xenopus, Rana, and Ambystoma. Using transmission electron microscopy we have confirmed that some central longitudinal neurites first grow directly under the basal lamina which surrounds the spinal cord in Xenopus embryos. Using scanning electron microscopy of dissected embryos we have followed the growth of neurites from the spinal cord to their target tissue, the skin. Comparisons between the three genera are made and detailed observations on growth cones during fasciculation, on the somites and on the basal lamina of the skin are presented. The observations are discussed in relation to possible influences on the course of growth of the developing neurites.

Ambystoma mexicanum↗
PubMed1985

Dual-component amino-acid-mediated synaptic potentials: excitatory drive for swimming in Xenopus embryos.

The neuronal basis of the excitation received by motoneurones during swimming in curarized Xenopus embryos has been investigated further. Extracellular stimulation of axons in the fibre tracts of the spinal cord has been used to evoke unitary excitatory post-synaptic potentials (p.s.p.s) in motoneurones. The p.s.p.s. had a rise time of 3-5 ms and a long falling phase lasting up to 200 ms. These potentials consist of two components: a 'fast' p.s.p. which is insensitive to 50 microM-(+/-)-2-amino-5-phosphonovaleric acid (APV) but is blocked by 2 mM-cis-2,3-piperidine dicarboxylic acid (PDA) and is therefore probably mediated by kainate/quisqualate receptors, and a 'slow' p.s.p. which is blocked by both APV and PDA and is therefore probably mediated by N-methyl-D-aspartate (NMDA) receptors. Paired intracellular recordings from motoneurones and interneurones have revealed a class of spinal cord interneurone which makes descending excitatory amino-acid-dependent synapses onto motoneurones and commissural interneurones. The p.s.p.s evoked by intracellular stimulation of these excitatory interneurones consist of 'fast' and 'slow' components identical in shape and pharmacological properties to those of the extracellularly evoked potentials. One neurone may, therefore, be able to release a transmitter which activates both NMDA and non-NMDA receptors on the same post-synaptic neurone generating fast and slow post-synaptic potentials. The excitatory interneurones play an important role in the generation of the swimming pattern in the curarized Xenopus embryo. Like motoneurones, they fire once per swimming cycle in phase with the ipsilateral motoneurones and receive a background excitation during swimming that is excitatory amino acid mediated. They are therefore part of the swimming rhythm generator. The temporal summation of the extracellularly evoked p.s.p.s shows that these excitatory interneurones are sufficient to generate the excitatory drive received by motoneurones during swimming.

2-Amino-5-phosphonovalerate↗
PubMed1985

Synaptic potentials in motoneurons during fictive swimming in spinal Xenopus embryos.

Embryos spinalized at the 3rd to 6th postotic myotome and immobilized in 10(-4) M tubocurarine can respond to a brief skin stimulus with motor root activity suitable for swimming. Embryos spinalized at the more caudal levels give shorter episodes of fictive swimming. We have previously described the synaptic inputs to motoneurons during fictive swimming in intact embryos (23). In the present paper we look to see if similar synaptic inputs are present in spinal embryos and are therefore spinal in origin. All motoneuron firing during fictive swimming is associated with a tonic depolarization that falls away slowly once firing stops, is increased by hyperpolarizing current, and is reduced by depolarizing current. A slow depolarizing potential evoked by lower levels of skin stimulation has similar properties and rate of fall. In 1-2 mM PDA, an excitatory amino acid antagonist, only a small remnant of the depolarization remains, and motoneuron firing stops. The NMDA antagonist 50 microM APV reduces the depolarization less but also blocks firing. Motoneurons fire one spike per swimming cycle, in phase with nearby motor root discharge. Spikes are preceded by a depolarizing prepotential. This increases with hyperpolarizing current, which can block the spike to reveal an underlying depolarizing potential. In phase with motor root discharge on the opposite side of the body, motoneurons receive a midcycle inhibitory postsynaptic potential, which increases with depolarizing current, decreases with hyperpolarizing current, and is blocked by 10(-6) M strychnine. Strychnine, 5 X 10(-7) M, leads first to broadening of motor root bursts then to loss of the alternating swimming pattern of activity, which is replaced by synchronous bursts on both sides of the body. We conclude that the synaptic inputs to motoneurons during fictive swimming in spinal embryos are very similar in properties and pharmacology to those in intact embryos. These inputs, including the tonic depolarization always associated with motoneuron firing during swimming, must be at least partly spinal in origin.

Amino Acids↗
PubMed1985

Neuromuscular transmission in the jellyfish Aglantha digitale.

In the jellyfish Aglantha digitale escape swimming is mediated by the nearly synchronous activity of eight giant motor axons which make direct synaptic contact with contractile myoepithelial cells on the under-surface of the body wall. The delay in transmission at these synapses was 0.7 +/- 0.1 ms (+/- S.D.;N = 6) at 12 degrees C as measured from intracellular records. Transmission depended on the presence of Ca2+ in the bathing medium. It was not blocked by increasing the level of Mg2+ to 127 mmol l-1. The myoepithelium is a thin sheet of electrically coupled cells and injection of current at one point was found to depolarize the surrounding cells. The potential change declined with distance from the current source as expected for two-dimensional current spread. The two-dimensional space constant (lambda) was 770 micron for current flow in the circular direction and 177 micron for radial flow. The internal resistance of the epithelium (178-201 omega cm) and the membrane time constant (5-10 ms) were direction independent. No propagated epithelial action potentials were observed. Spontaneous miniature synaptic potentials of similar amplitude and rise-time were recorded intracellularly at distances of up to 1 mm from the motor giant axon. Ultrastructural evidence confirms that neuro-myoepithelial synapses also occur away from the giant axons. It is likely that synaptic sites are widespread in the myoepithelium, probably associated with the lateral motor neurones as well as the giant axons. Local stimulation of lateral motor neurones generally produced contraction in distinct fields. We suppose that stimulation of a single motor giant axon excites a whole population of lateral motor neurones and hence a broad area of the myoepithelium.

Action Potentials↗
PubMed1985

The metabolism of 14C-cyclohexylamine in mice and two strains of rat.

After administration of 14C-cyclohexylamine (35-500 mg/kg) to male mice and rats, 80% of the dose of 14C was excreted in the urine, mostly within the first 24 h after dosing. In Wistar rats, 7-9% of the 14C in the 0-24 h urine was present as cis-4-aminocyclohexanol, with a similar amount as the corresponding 3-isomers. In the DA rat, only 1-2% of the 14C, and in mouse less than 1% of the 14C was present in the urine as aminocyclohexanols; unchanged cyclohexylamine accounted for about 95% of the activity. The extent of metabolism was not affected by either dose or route of administration. The species differences in metabolism may be implicated in the differences in toxicity during chronic high-dose administration.

Animals↗
PubMed1985

Peripheral blood erythroid progenitors from patients with sickle cell anemia: HPLC separation of hemoglobins and the effect of a HbF switching factor.

We describe the use of HPLC for the separation and quantitation of hemoglobin and globin chains. Utilization of this sensitive technique allows the analysis of hemoglobin and globin chains in the total accumulated and newly synthesized hemoglobin. Using this methodology, we have studied the effect of a previously described HbF factor in fetal calf serum on peripheral blood BFUe-derived erythroblasts from patients with sickle cell anemia. As in previous studies of peripheral blood BFUe-derived erythroblasts from hematologically normal adults, this HbF factor promoted the increased synthesis of HbF in the BFUe-derived erythroblasts from the sickle cell anemia patients.

Anemia, Sickle Cell↗
PubMed1984

DNA and enzyme studies on chorionic villi for use in antenatal diagnosis.

A study has been undertaken to determine the efficiency of current methods in providing an adequate amount of chorionic villus DNA for antenatal diagnosis using recombinant DNA techniques or enzyme assay. Chorionic biopsies were obtained from 40 women undergoing elective first trimester termination of pregnancy (8-12 weeks) under general anaesthesia. The villus tissue was isolated from maternal tissue under a dissection microscope and the presence of any remaining contamination was ascertained by conventional histology and immuno-cytochemical examinations. A high level of success was achieved in obtaining a pure fetal sample. In the first 20 samples the DNA yield obtained using the method of Williamson et al [1] was found to be 0.5 +/- 0.5 micrograms/mg wet weight of villus tissue (mean +/- 1 SD). In the subsequent 20 biopsies using a modified procedure, the yield was significantly improved to 1.0 +/- 0.65 (p less than 0.002). A normal range for the enzyme iduronate sulphatase, which is deficient in Hunter's syndrome (mucopolysaccharidosis II), is also reported. It is suggested that as little as 20 mg of chorionic villi may be used to provide sufficient material for a reliable study using recombinant DNA or biochemical methods.

Amniotic Fluid↗
PubMed1984

Sensory physiology, anatomy and immunohistochemistry of Rohon-Beard neurones in embryos of Xenopus laevis.

Rohon-Beard neurones show substance P-like immunoactivity in their somas and in their centrally projecting axons. Peripherally, the morphology of their free nerve endings within the trunk skin has been shown using horseradish peroxidase staining. The excitation of Rohon-Beard neurones by natural and electrical stimulation of the skin has been examined using intracellular micro-electrodes in the late embryo of Xenopus laevis. Rohon-Beard cells are sensitive to transient, local indentation of the trunk skin, responding with one or a few impulses. They adapt rapidly to repeated stimulation. They can also be excited by a brief current pulse to the skin. They are not sensitive to slow indentation of the skin, nor are they excited by epithelial action potentials. The responses to skin stimulation are not abolished by a Ringer solution containing 12 mM-Mg2+ and only 0.5 mM-Ca2+. Intracellularly evoked action potentials in single Rohon-Beard cells are sometimes sufficient to evoke sustained episodes of fictive swimming. The results indicate that Rohon-Beard cells are responsible for detecting light touch stimuli to the embryo's body and for initiating swimming in response to this stimulus.

Animals↗
PubMed1984

Excitatory amino acid receptors in Xenopus embryo spinal cord and their role in the activation of swimming.

Bath application of N-methyl-D-aspartate (NMDA), kainate or quisqualate to Xenopus embryos depolarized spinal cord motoneurones and reduced their input resistance in both normal salines and salines containing 20 mM-Mn2+ and 0.5 mM-Ca2+, or 2 X 10(-6) M-tetrodotoxin. This suggests that motoneurones possess all three types of excitatory amino acid receptor. These receptors have similar specificities to excitatory amino acid antagonists as those occurring in adult frog and cat spinal cords. Application of 30-40 microM-NMDA or 5-6.5 microM-kainate to the medium bathing spinalized embryos can cause a sustained patterned motor output similar to that of swimming evoked by natural stimulation of intact animals. At these concentrations NMDA and kainate depolarized motoneurones by 19.0 +/- 1.80 (mean +/- S.E. of mean) and 18.0 +/- 2.00 mV respectively and decreased their input resistance by 23.0 +/- 2.82% and 24.0 +/- 3.46%. These changes are similar to those associated with the tonic excitation which motoneurones receive during naturally evoked swimming. Bath application of 5-8 microM-quisqualate to spinal embryos can also cause a sustained motor output. However, this was different to that evoked by NMDA and kainate and was inappropriate for swimming. When applied to intact animals during swimming both 2-3 mM-cis-2,3-piperidine dicarboxylic acid (PDA) and 0.5 mM-gamma-D-glutamylglycine (DGG) selectively blocked the tonic excitation of motoneurones and in doing so abolished the motor output of the spinal cord. 50-200 microM-2-amino-5-phosphonovaleric acid reduced the tonic excitation but to a lesser extent than either PDA or DGG. The tonic excitation of motoneurones which occurs during swimming therefore appears to be mediated via an endogenous excitatory amino acid transmitter which acts on NMDA and kainate receptors.

Animals↗
PubMed1984

Interneurones in the Xenopus embryo spinal cord: sensory excitation and activity during swimming.

The dorsolateral spinal cord of embryonic Xenopus laevis has previously been shown to contain two anatomical classes of interneurones with dendrites in the dorsal tract where they could be contacted by the central axons of Rohon-Beard cells (Roberts & Clarke, 1982). The activity of these neurones within the dorsolateral spinal cord has been examined using intracellular micro-electrodes. Following electrical stimulation of Rohon-Beard neurites within the ipsilateral skin, dorsolateral neurones receive a short-latency, compound, excitatory post-synaptic potential (e.p.s.p.). The amplitude of the e.p.s.p. depends upon the number of Rohon-Beard cells stimulated. The e.p.s.p. consists of early and later components. The early components may result from monosynaptic connexions from Rohon-Beard cells, the later components from some unidentified interposed neurones. During episodes of fictive swimming the dorsolateral neurones are inhibited by rhythmic inhibitory post-synaptic potentials. Following Rohon-Beard neurite stimulation, neurones in the contralateral spinal cord receive e.p.s.p.s. These contralateral e.p.s.p.s are probably one of the post-synaptic effects of one of the dorsolateral neurone classes. The results suggest that the dorsolateral neurones are responsible for amplifying and distributing the primary afferent signals of Rohon-Beard cells, and may be involved in the initiation of swimming and reflex movements.

Animals↗
PubMed1984

Isolation of nontoxigenic Vibrio cholerae O group 1 from a patient with severe gastrointestinal disease.

A nontoxigenic strain of Vibrio cholerae O group 1 was isolated in Florida from the stool of a patient with severe diarrhea. The strain had the same hemolytic and unique phage-sensitivity pattern as all toxigenic isolates from recent cases of cholera in Texas and Louisiana. Identical strains were transiently isolated from sewerage systems in two other Florida communities, suggesting that multiple human infections had occurred. This is the first indication that V. cholerae O1 strains which do not produce cholera toxin may be able to cause gastrointestinal disease in humans. The identification of these strains also raises questions about the relationship between toxigenic and nontoxigenic strains of V. cholerae O1 along the Gulf Coast of the United States.

Antigens, Bacterial↗
PubMed1984

Activity of commissural interneurons in spinal cord of Xenopus embryos.

Horseradish peroxidase- (HRP) filled microelectrodes have been used to examine the anatomy and physiology of "commissural interneurons," a morphologically defined class of spinal cord interneuron in Xenopus laevis embryos. Commissural interneurons have unipolar cell bodies in the dorsal half of the spinal cord. Their dendrites lie in the mid to ventral parts of the lateral tracts and their axons cross the cord ventrally, T branch, and ascend and descend on the opposite side of the cord. Recordings were made from animals immobilized in tubocurarine and responding to natural stimulation with three patterns of fictive motor activity. During episodes of fictive swimming, commissural interneurons are phasically excited to fire 1 spike/cycle in phase with motor discharge on the same side and receive a midcycle inhibitory postsynaptic potential (IPSP) in phase with motor discharge on the opposite side. Rhythmic activity is superimposed on a background depolarization. During periods of synchrony, phasic excitatory input doubles in frequency so that cells fire with half the swimming cycle period. The background depolarization is generally stronger than during swimming. During periods of fictive struggling, evoked by electrical stimulation of the skin, commissural interneurons fire a burst of spikes per cycle, cells being relatively hyperpolarized when motoneurons on the opposite side are active. In response to ipsilateral skin stimulation, some cells receive an IPSP at a latency of 12-20 ms. This precedes the onset of fictive locomotion. We discuss how anatomy and activity of commissural interneurons is suitable for a reciprocal inhibitory role.

Animals↗