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Biomedical subjects

H P Robinson

Publications and source records attributed to H P Robinson.

At least 19 recordsLinked to original sources
PubMed1996

Intracellular inositol 1,3,4,5-tetrakisphosphate enhances the calcium current in hippocampal CA1 neurones of the gerbil after ischaemia.

1. To examine the role of the phosphoinositide cascade triggered by disturbed Ca2+ homeostasis in ischaemic neurones, inositol 1,3,4,5-tetrakisphosphate (InsP4) was applied to the cytoplasmic face of membrane patches isolated from CA1 pyramidal neurones in the gerbil hippocampus. 2. In outside-out recordings, InsP4 induced an inward current which was increased by raising the extracellular [Ca2+]. In contrast, no clear channel openings could be observed in patches from neurones of sham-operated gerbils. 3. Open probabilities of InsP4-activated channels were significantly decreased upon application of omega-conotoxin but were not affected by omega-agatoxin or nifedipine. 4. In inside-out patches using high concentrations of Ca2+, Ba2+ or Sr2+ in the pipette solution, InsP4 enhanced inward currents. 5. Application of the isomers of InsP4 slightly enhanced the currents, but inositol 1,4,5-trisphosphate (InsP3) had no effect. 6. In the absence of InsP4 there was a single main Ba2+ current peak of 4.0 pA in amplitude, whereas upon its application two main peaks of 3.0 and 7.2 pA were present. 7. The open probabilities of these channels were apparently increased by InsP4. 8. These findings support the view that a disturbed phosphoinositide cascade occurs in the hippocampal pyramidal neurones after ischaemia and the InsP4 thus formed plays an important role in promoting the Ca2+ accumulation which results in neuronal death.

Animals↗
PubMed1996

Correlation between nuchal thickness and abnormal karyotype in first trimester fetuses.

OBJECTIVE: To evaluate the accuracy of ultrasound measurement of nuchal thickness in first trimester fetuses for predicting fetal karyotype. DESIGN: A prospective study of the nuchal thickness of fetuses measured during an ultrasound examination in all women undergoing first trimester chorionic villus sampling (CVS). SETTING: Two major public hospitals and two associated private practices between 7 September 1993 and 6 September 1994. PARTICIPANTS: Pregnant women with various indications for CVS (in 82% because of maternal age). RESULTS: 1306 women underwent CVS, including 11 with twin pregnancies: 1317 fetuses were tested. Karyotype results were obtained for 1312 fetuses: 41 (3.1%) had an abnormal karyotype, and 20 of these (49%) had a nuchal thickness measurement of 3 mm or more, compared with 44 (3.5%) of the 1271 fetuses with a normal karyotype. Of the 21 fetuses shown to have trisomy 21, 12 would have been detected if a nuchal thickness of 3 mm or more had been used as an indicator, giving a sensitivity of 57%. Nuchal thickness measurements of 1 or 2 mm excluded trisomy 21 with a negative predictive value of 99.3%. Fetuses with moderate nuchal thickening, normal karyotype and no other problems noted on the initial ultrasound scan had neonatal outcomes similar to those in the general obstetric population. CONCLUSION: Nuchal thickening in the first trimester (10 weeks on) of pregnancy in a high risk population is a powerful indicator of increased risk of aneuploidy.

Adult↗
PubMed1996

Spontaneous periodic synchronized bursting during formation of mature patterns of connections in cortical cultures.

Long-term recording of spontaneous activity in cultured cortical neuronal networks was carried out using substrates containing multi-electrode arrays. Spontaneous uncorrelated firing appeared within the first 3 days and transformed progressively into synchronized bursting within a week. By 30 days from the establishment of the culture, the network exhibited a complicated non-periodic, synchronized activity pattern which showed no changes for more than 2 months and thus represented the mature state of the network. Pharmacological inhibition of activity only during the period when regular synchronized bursting was observed was capable of producing a different mature activity pattern from the control. These results suggest that periodic synchronized bursting plays a critical role in the development of synaptic connections.

2-Amino-5-phosphonovalerate↗
PubMed1995

Single glutamate channels in CA1 pyramidal neurones after transient ischaemia.

Patch clamp recordings were made from CA1 pyramidal neurones to study changes in the glutamate receptor subtypes in the gerbil hippocampus after transient ischaemia. In whole-cell recordings, the maximum chord conductances of AMPA currents in ischaemic neurones were increased over those of control neurones but NMDA-induced currents in the ischaemic neurones were smaller than the control. In AMPA-activated single channel currents, an open time histogram of the control neurones was well fitted by a single exponential function whereas in the ischaemic patches it was fitted by a double exponential function, indicating that currents consisted of at least two kinetically different types. These functional changes of the glutamate receptor channels may contribute to the abnormalities of the excitatory synaptic currents recorded in post-ischaemic CA1 neurones.

Animals↗
PubMed1995

The mechanisms of generation and propagation of synchronized bursting in developing networks of cortical neurons.

The characteristics and mechanisms of synchronized firing in developing networks of cultured cortical neurons were studied using multisite recording through planar electrode arrays (PEAs). With maturation of the network (from 3 to 40 d after plating), the frequency and propagation velocity of bursts increased markedly (approximately from 0.01 to 0.5 Hz and from 5 to 100 mm/sec, respectively), and the sensitivity to extracellular magnesium concentration (0-10 mM) decreased. The source of spontaneous bursts, estimated from the relative delay of onset of activity between electrodes, varied randomly with each burst. Physical separation of synchronously bursting networks into several parts using an ultraviolet laser, divided synchronous bursting into different frequencies and phases in each part. Focal stimulation through the PEA was effective at multiple sites in eliciting bursts, which propagated over the network from the site of stimulation. Stimulated bursts exhibited both an absolute refractory period and a relative refractory period, in which partially propagating bursts could be elicited. Periodic electrical stimulation (at 1 to 30 sec intervals) produced slower propagation velocities and smaller numbers of spikes per burst at shorter stimulation intervals. These results suggest that the generation and propagation of spontaneous synchronous bursts in cultured cortical neurons is governed by the level of spontaneous presynaptic firing, by the degree of connectivity of the network, and by a distributed balance between excitation and recovery processes.

Animals↗
PubMed1994

Inositol 1,3,4,5-tetrakisphosphate as a mediator of neuronal death in ischemic hippocampus.

Selective death of CA1 pyramidal neurons after transient forebrain ischemia has attracted interest for its possible relation to the pathogenesis of memory deficits and dementia. Using whole cell patch-clamp recording from CA1 pyramidal neurons in hippocampal slices of gerbils after ischemia we studied the intracellular signaling mechanisms related to the phosphoinositide cycle. Intracellular application of an antibody against phosphatidylinositol 4,5-bisphosphate rescued ischemic neurons from stimulus-induced irreversible depolarization. Furthermore, application of inositol 1,3,4,5-tetrakisphosphate in normal cells caused an irreversible depolarization in response to synaptic input, which mimicked the deterioration of ischemic neurons. Depolarization of both ischemic and normal neurons in the presence of inositol 1,3,4,5-tetrakisphosphate was prevented by the addition of the Ca2+ chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetate. Application of antibody against inositol 1,4,5-triphosphate 3-kinase, which blocks formation of inositol 1,3,4,5-tetrakisphosphate, also protected against cell deterioration. Our results suggest that the vulnerability of hippocampal pyramidal neurons following ischemia is caused by a disturbed phosphoinositide cascade, with one metabolite, inositol 1,3,4,5-tetrakisphosphate, playing a key role in the induction of Ca2+ accumulation, which leads to neuronal death.

Animals↗
PubMed1993

The 18 to 20 week obstetrical scan. A joint statement from the Australasian Society for Ultrasound in Medicine, the Royal Australian College of Obstetricians and Gynaecologists and the Royal Australasian College of Radiologists.

The Australasian Society for Ultrasound in Medicine, The Royal Australian College of Obstetricians and Gynaecologists and the Royal Australasian College of Radiologists have produced jointly the accompanying document on the 18-20 week obstetrical scan. It is an important document not only for the sonologists and sonographers but also for clinicians who request ultrasound examinations for pregnant women, so that they may have a better idea of what the examination should cover and its limitations.

Female↗
PubMed1993

Single channel properties at the synaptic site.

The properties of single channels activated during spontaneous postsynaptic currents in small cultured rat hippocampal neurons were investigated in low-noise whole cell recordings. The technique of nonstationary fluctuation analysis, which has previously been applied to sodium currents, was modified so that fluctuations were measured around the least-squares scaled fit of the ensemble average to individual synaptic currents. This had the effect of separating channel gating fluctuations from the quantal fluctuations of scale from event to event. Single channel amplitude was estimated from the variance--current distribution, and the kinetics of channel gating fluctuations were studied. Channels involved in the non-N-methyl-D-aspartate (non-NMDA) phase of the excitatory glutamatergic postsynaptic current showed a single channel amplitude of 1.5 pS, while those in the NMDA phase had a conductance of 42 pS. The single channel conductance estimated for the inhibitory chloride synaptic current was 14 pS. In addition, NMDA phase channel openings could be resolved directly in the whole cell current against the low noise level afforded by the small cells. Single channel lifetime and amplitude distributions of the channels activated during the postsynaptic current were measured, and confirmed the accuracy of the fluctuation method.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1993

Injection of digitally synthesized synaptic conductance transients to measure the integrative properties of neurons.

A novel technique was developed for injecting a time-varying conductance into a neuron, to allow quantitative measurement of the processing of synaptic inputs. In current-clamp recording mode, the membrane potential was sampled continuously and used to calculate and update the level of injected current within 60 microseconds, using a real-time computer, so as to mimic the electrical effect of a given conductance transient. Cellular responses to synthetic conductance transients modelled on the fast (non-N-methyl-D-aspartate) phase of the glutamatergic postsynaptic potential were measured in cultured rat hippocampal neurons.

Animals↗
PubMed1993

Block of long-term potentiation by intracellular application of anti-phosphatidylinositol 4,5-bisphosphate antibody in hippocampal pyramidal neurons.

We examined the effects of black widow spider toxin and anti-phosphatidylinositol 4,5-bisphosphate antibody on the changes in excitatory postsynaptic currents and spontaneous excitatory postsynaptic currents accompanying long-term potentiation using whole-cell recording from hippocampal CA1 pyramidal neurons of rodents. In the presence of black widow spider toxin, tetanic stimulation of input fibers produced a short-lived potentiation followed by a gradual decline of the excitatory postsynaptic current amplitude. With an anti-phosphatidylinositol 4,5-bisphosphate antibody containing pipette, tetanus elicited only decremental potentiation of excitatory postsynaptic currents with a reduced frequency of spontaneous excitatory postsynaptic currents, suggesting inhibition of retrograde reinforcement from the antibody-injected neuron. With both black widow spider toxin and anti-phosphatidylinositol 4,5-bisphosphate antibody, neurons showed a rapid depression of excitatory postsynaptic currents after tetanus. The results indicate that time-dependent interactions between presynaptic terminals and the postsynaptic spikes take place during long-term potentiation.

Action Potentials↗
PubMed1993

Simultaneous measurement of intracellular calcium and electrical activity from patterned neural networks in culture.

Multisite extracellular electrical activity and intracellular calcium were recorded simultaneously. Electrical signals were measured using microelectrode array substrates. A novel cell positioning technique was combined with a method for controlling neurite outgrowth, which allowed cell-electrode contacts to be established easily, thus facilitating the electrical recording. Intracellular calcium was measured optically using the indicator fluo 3. Under low-magnesium conditions, cultured rat cortical neurons showed periodic transients of fluo-3 fluorescence, which were synchronized with the periodic bursting observed electrically. The intervals between bursts could be determined by electrical stimulation through the substrate electrodes. The results suggest that functional synaptic connections are formed in the culture system.

Animals↗
PubMed1993

Presynaptic glutamate receptors depress inhibitory postsynaptic transmission in lobster neuromuscular synapse.

1. We examined the functional role of GTP-coupled glutamate receptor (GluB-R) in the presynaptic membrane of lobster neuromuscular synapse. 2. Injection of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), a hydrolysis-resistant analogue of GTP, into the excitatory axon mimicked the presynaptic glutamate response and effectively suppressed excitatory postsynaptic potentials or excitatory postsynaptic currents (EPSCs). 3. Statistical analysis revealed that the coefficient of variation (standard deviation divided by the mean of EPSC amplitude) was increased after injection of GTP gamma S into the excitatory axon, indicating a presynaptic inhibition of transmitter release. 4. The effect of glutamate on inhibitory postsynaptic potentials (IPSPs) or inhibitory postsynaptic currents (IPSCs) was studied when the postsynaptic glutamate receptors were blocked by the Joro spider toxin (JSTX). Glutamate depressed IPSPs or IPSCs in the JSTX-treated preparation. Furthermore, repetitive stimulation of the excitatory nerve produced effective inhibition of IPSCs. 5. Quisqualate and kainate suppressed IPSCs in a similar way to glutamate. In contrast, N-methyl-D-aspartate, ibotenic acid, trans-D,L-1-amino-1,3-cyclopentanedicarboxyloc acid, and 2-amino-4-phosphonobutanate had no effect on GluB-R. 6. Our results indicate that GluB-R, which exists in both excitatory and inhibitory nerve terminals, regulates transmitter release by a presynaptic inhibitory mechanism.

Animals↗
PubMed1993

Periodic synchronized bursting and intracellular calcium transients elicited by low magnesium in cultured cortical neurons.

1. In Mg(2+)-free external solution, rat cortical neurons in cultured networks entered a stable firing mode, consisting of regular bursts of action potentials superimposed on long-lasting depolarizations. The average separation between bursts varied from culture to culture, but was usually between 5 and 20 s. The distribution of burst intervals followed a Gaussian or normal distribution, with a standard deviation of typically 10% of the average burst period. 2. A gradually depolarizing pacemaker potential was never observed between bursts, but the threshold for action potentials during the quiescent phase was > or = 10 mV above the resting potential. No progressive change in conductance or excitability was observed during the quiescent period. Intracellular stimulation of action potentials did not reproduce the long-lasting depolarization. 3. Switching from current clamp to voltage clamp at the resting potential revealed large postsynaptic currents, mainly excitatory but with a small inhibitory component, at the same phase and frequency as the spike bursts, showing that periodic synaptic input is responsible for the burst-depolarizations. The current could be eliminated by local application of 2-amino-5-phosphonovaleric acid (APV) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the postsynaptic cell. In the presence of tetrodotoxin, irregular miniature excitatory postsynaptic currents were observed. 4. A fluorescent calcium indicator (fluo-3, 100 microM) was included in the whole-cell pipette solution, to allow simultaneous electrical and calcium measurements in the same cell. In current clamp, transient intracellular calcium increases were found, which were synchronized to the spike bursts. The Ca2+ rise lasted as long as the action potential burst, and was followed by an exponential decay considerably slower than that of the membrane potential. Calcium transients disappeared during voltage clamp at the resting potential, suggesting that calcium influx through voltage-dependent calcium channels greatly exceeds that through synaptic channels. 5. Multisite Ca2+ recording, after loading with fluo-3 acetoxymethyl (AM) ester, revealed that the onsets of burst-related calcium transients were synchronized in all active cells of each view-field, to within approximately 20 ms. Occasionally, secondary rhythms were observed in which only a subset of cells participated. The times to peak and the decay times of calcium transients varied among synchronized cells. 6. The pharmacology of the burst-related calcium transients was investigated by bath application of a variety of compounds.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1992

Importance of complete follow-up of spontaneous fetal loss after amniocentesis and chorion villus sampling.

Women who are the most difficult to trace after amniocentesis or chorion villus sampling are often those who have had an adverse pregnancy outcome. To calculate total fetal loss figures for use in prenatal counselling we have followed in a multicentre study 100% of women who had undergone these procedures. Early spontaneous loss (within three weeks of the procedure) and total spontaneous loss were much lower after amniocentesis (0.2% and 1.3%, respectively) than after chorion villus sampling (1.2% and 2.9%). Four spontaneous fetal losses among the 20 pregnancies that were the most difficult to follow-up increased the loss rate by 0.5% for chorion villus sampling. Risk of early fetal loss after chorion villus sampling was related to experience of the operator (relative risk [RR] 4.3, p = 0.003), and total fetal loss was lower in pregnancies tested at 10 weeks' or more gestational age compared with those tested before 10 weeks' (RR 0.4, p = 0.01). A table showing the frequency of each of the seven possible outcomes after amniocentesis and chorion villus sampling is useful in counselling those considering one or other test.

Abortion, Spontaneous↗
PubMed1992

Purification of AMPA type glutamate receptor by a spider toxin.

A glutamate receptor was purified from Triton X-100-solubilized bovine cerebellum membranes. The purification was carried out in two steps: affinity chromatography using a spider toxin (Joro spider toxin; JSTX) immobilized on a lysine-agarose column, and a Mono Q anion exchange column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the purified active fraction showed a single band with Coomassie Blue staining, which migrated with a M(r) = 130,000. The specific [3H]amino-3-hydroxy-5-methyl-isoxazole propionate ([3H]AMPA) binding activity of the affinity-purified fraction was 2095-fold higher than that of the crude soluble fraction. Lineweaver-Burk plot analysis showed a Kd of 12.7 nM [3H]AMPA in the purified fraction. The purified fraction was examined with patch-clamp recording methods in reconstituted liposomes. A glutamate-activated channel was observed and was inhibited with JSTX. The rank order of potency of agonists inducing channel currents was AMPA = glutamate greater than quisqualate much greater than kainate greater than NMDA. Thus, there is strong evidence that the 130 kDa protein is a purified component of the native AMPA type glutamate channel of bovine cerebellum.

Animals↗