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Biomedical subjects

G Somjen

Publications and source records attributed to G Somjen.

At least 19 recordsLinked to original sources
PubMed1996

Combined semiclosed iliac endarterectomy and distal arterial reconstruction for multilevel arterial disease.

Semiclosed iliac endarterectomy in combination with an infrainguinal vascular reconstruction has been used over the past decade in the treatment of lower-limb ischaemia. Although the early results of this combination of operations were known, the durability of the external iliac endarterectomy had not been assessed and so an effort was made to review all surviving patients by duplex scanning. Between 1985 and 1993, 48 patients (51 limbs) underwent combined semiclosed iliac endarterectomy and infrainguinal vascular reconstruction for iliac and femoropopliteal occlusive disease. Some 49% of operations were performed for limb salvage. An iliofemoral bypass graft was required twice because of failure of the endarterectomy. A variety of distal arterial reconstructions was employed. One patient required a major amputation and there were two deaths. Mean (s.d.) ankle/brachial indices (ABI) rose from 0.54 (0.14) to 0.85 (0.25) after surgery. Some 85% of the patients who underwent operation for claudication became symptom free; 83% of patients who underwent operation for limb-threatening ischaemia became symptom free or improved to mild claudication during an average of 29 months follow-up. During the follow-up period five patients underwent a further procedure because of restenoses of the external iliac artery. A duplex scanning study was performed in 22 of the 51 limbs an average of 36 months after surgery. External iliac artery stenotic lesions were found in the area of the endarterectomy in three patients. Endarterectomy of the external iliac artery from the groin is an alternative for some patients with iliac arterial disease. In a patient scheduled for an infrainguinal bypass, when an unexpectedly greater degree of athermoma is found at operation in the common femoral and external iliac arteries, this operation may be performed. The durability of the operation as assessed by follow-up duplex scan is quite acceptable.

Aged↗
PubMed1994

Percutaneous transluminal angioplasty: follow-up with treadmill exercise testing.

Between 1986 and 1992, 308 percutaneous transluminal angioplasties in 252 patients were reviewed in the vascular laboratory of the Austin Hospital. The follow-up period ranged from 1 month to 6 years. Treadmill exercise testing was used as an additional mode of assessment to resting ankle/brachial pressure indices in monitoring outcome. Early haemodynamic improvement rate was 86.7%. In 267 successful cases, 199 had increased the mean(s.d.) resting ankle/brachial pressure index from 0.68(0.15) to 0.96(0.14) (P < 0.05) and another 68 with normal or unchanged resting ankle/brachial pressure indices after the procedure increased the mean(s.d.) post-exercise pressure index from 0.45(0.24) to 0.82(0.23) (P < 0.05). The primary haemodynamic improvement rate of initially successful percutaneous transluminal angioplasties was 80.1% at 1 year and was maintained in 46.1% of cases 5 years after. Treadmill exercise testing revealed reduction of the ankle/brachial pressure index in 69 patients during follow-up, indicating restenosis of the dilated lesion or development of a new arterial stenosis. Fifty-two of the 69 patients exhibited a significant drop in the resting pressure index. However, in the 17 remaining patients, only the post-exercise index decrease indicated haemodynamic deterioration. Treadmill exercise testing proved to be valuable adjunct in detecting haemodynamic changes after percutaneous transluminal angioplasty.

Adult↗
PubMed1988

Vesicular cholesterol in bile. Relationship to protein concentration and nucleation time.

A study was done to determine whether the nucleation time was related to the amount of cholesterol carried in vesicles. Bile was obtained from cholesterol gallstone patients and controls. Gel-exclusion chromatography was used to separate vesicles and micelles in the native bile using an eluting buffer containing 10 mM sodium cholate. The percent of total cholesterol carried in vesicles in gallbladder bile of stone patients was significantly greater than that in control patients. Total cholesterol concentration in gallbladder bile of stone patients was significantly greater than in controls. This difference was due to the fact that vesicular cholesterol concentration was significantly greater in the gallbladder bile of stone patients compared to controls. Micellar cholesterol concentrations were similar in the two groups. Nucleation time was related significantly to vesicular cholesterol concentration in correlation analysis and, as previously shown, so was total protein concentration. This study supports the importance of vesicular cholesterol in solid crystal formation and demonstrates for the first time that the rate of cholesterol monohydrate crystal formation is directly related to the amount of cholesterol transported in vesicles.

Adult↗
PubMed1988

Effect of vaso-active intestinal polypeptide on systemic and splanchnic haemodynamics: role in vasodilation following mesenteric ischaemia.

Vaso-active intestinal polypeptide (VIP) and the related peptide, peptide histidine isoleucine, were infused intravenously in anaesthetized sheep. The VIP doses were designed to reproduce plasma concentrations seen after mesenteric ischaemia. The vasodilator action of VIP varied between different segments of the circulation and these differences in sensitivity were observed for both the degree and duration of the vaso-active action. A sustained vasodilation was detected in the coeliac artery and portal vein vascular beds during a 30-min VIP infusion. VIP is likely to be a contributory factor involved in the development of circulatory collapse during reperfusion after experimental mesenteric ischaemia.

Animals↗
PubMed1987

Nucleation of cholesterol from vesicles isolated from bile of patients with and without cholesterol gallstones.

Bile was obtained from patients with and without cholesterol gallstones at surgery. Biliary vesicles were separated from micelles by gel filtration. The cholesterol/phospholipid ratio in vesicles was much higher than in micelles. Cholesterol crystals nucleated from vesicular fractions, but nucleation from the micellar fractions was slow or did not occur at all. Cholesterol nucleated from vesicles obtained from bile of control patients as rapidly (2.4 days +/- 0.7) as from patients with stones (2.4 days +/- 0.9) and there was no difference in the vesicular cholesterol/phospholipid ratio. The effect of alteration of the bile salt environment was studied by changing the concentration of sodium cholate in the eluting buffer. At low concentrations (5 mM) only vesicles were eluted from the column. These vesicles had a relatively low cholesterol/phospholipid ratio and cholesterol nucleated slowly from these vesicles. At higher concentrations the proportion of micelles increased. The proportion of vesicles decreased progressively but their cholesterol/phospholipid ratio increased and the nucleation time fell. These studies demonstrate that cholesterol nucleates from vesicles in the absence of micelles, that control vesicles are not protected by tightly bound antinucleating substances and that exposure of vesicles to micelles strips relatively more phospholipid than cholesterol from the vesicular fraction, resulting in vesicles with higher cholesterol/phospholipid ratios and shorter nucleation times.

Bile↗
PubMed1987

Direct and relayed projection of periodontal receptor afferents to the cerebellum in the ferret.

Field potentials in the cerebellar cortex of the ferret have been studied in response to stimulation of alveolar, muscular and cutaneous branches of the trigeminal nerve. Responses from the alveolar nerves are unusual in their very short latency. Evidence based on latency analysis, frequency following and comparison with other well-known inputs supports the view that the earliest field potentials are due to direct, unrelayed afferents, which terminate as mossy fibres. There is, in addition, a monosynaptically relayed afferent path via mossy fibres. The alveolar nerve afferents concerned with the direct projection are shown to come from periodontal mechanoreceptors and not from cutaneous receptors. No such connections are found from jaw-muscle spindle afferents. The direct and relayed periodontal pathways are both ipsilateral and crossed. They terminate in the cerebellar cortex in the parvermal region of lobules IV, V and VI. The functional significance of the direct periodontal afferent projection is considered particularly in the light of parallels with the vestibular system, which also has direct and relayed cerebellar projections.

Afferent Pathways↗
PubMed1987

Focal synaptic potentials due to discrete mossy-fibre arrival volleys in the cerebellar cortex.

The previously described direct and relayed projections of periodontal afferents to the cerebellar cortex have been examined in detail by extracellular field-potential analysis. Advantage is taken of the very small temporal dispersion of the afferent volleys to permit identification of the presynaptic spike potential of mossy fibres, the subsequent synaptic potential and the firing of granule cells. Changes in form of the presynaptic potential with depth are compared with published descriptions of presynaptic potentials elsewhere. The negative synaptic potential in the granular layer is shown to have a positive aspect in the molecular layer. Granule-cell firing can, under some conditions, yield a population spike interrupting the synaptic potential wave. Records are presented showing all-or-none complex waves, which appear to be single glomerular potentials, not previously described in the mammalian cerebellum. Their distinction from cellular spike potentials is emphasized.

Afferent Pathways↗
PubMed1981

Calcium dependence of synaptic transmission in the hippocampal slice.

'Population' afferent spike and 'population' EPSP were recorded with extracellular microelectrodes in slices of hippocampal tissue maintained in vitro. Calcium concentration was changed in the bathing solution, and calcium activity ([Ca2+]0) was measured in interstitial fluid of the slice with ion-selective microelectrodes. Synaptic transfer was a non-linear continuous function of [Ca2+]0. Deviation of [Ca2+]0 by 0.1 mM from the 1.2 mM control level caused a change of approximately 15% in the slope of the input-output function.

Animals↗
PubMed1980

The effects of convulsant doses of penicillin on primary afferents, dorsal root ganglion cells, and on 'presynaptic' inhibition in the spinal cord.

Intracellular recordings were made from neurons in dorsal root ganglia (DRG) of rats, isolated in vitro. The depolarization of DRG cells caused by the application of gamma-aminobutyric acid (GABA) diminished reversibly when penicillin (0.08--2.0 mM) was added to the bathing fluid. The decrease of the input resistance of DRG cells measured during GABA perfusion was also depressed in the presence of penicillin, but no evidence of a shift of the reversal potential of the GABA-induced depolarization was found. Nor did penicillin (up to 10 mM) cause a change in the voltage-current function, in electrical excitability, in the inclination to repetitive firing, bursting discharge, or after discharge. In decapitate cat preparation the amplitude of the negative dorsal root potential (DRP or DR V) diminished by 0--50% after the i.v. administration of 0.5--1.0 X 10(6) I.U./kg (the convulsant dose) of penicillin. Post-tetanic depression of the DRP was aggravated by penicillin. The degree of depression of the DRP bore no relationship to the promptness of the eruption, and to the intensity, of the seizure activity induced by penicillin. The rates of rise and fall of the negative DRP (DR V) were consistently slowed, the positive DRP (DR VI) reduced, and the dorsal root reflex (DRR) blocked by penicillin. Inhibitory reflex effects presumed to be presynaptic were either enhanced or unchanged, never depressed by penicillin. This was seen when inhibitory function was gauged by monosynaptic reflex amplitude, and also from the inhibition of ventral root electrotonic excitatory postsynaptic potentials (VP EPSPs). Possible explanations of these seemingly paradoxical findings are discussed, with arguments in favor and against each.

Afferent Pathways↗
PubMed1979

Oxidative metabolism, extracellular potassium and sustained potential shifts in cat spinal cord in situ.

Changes in the ratio of reduced/oxidized cytochrome a,a3 were measured by reflection spectrophotometry in decerebrate cat spinal cord during microelectrode monitoring of extracellular K+ and extracellular potential. In 'resting' cord, cytochrome a,a3 was approximately 60% reduced, compared to 30% in cerebral cortex and 1% in isolated mitochondria. Stimulation of a dorsal root or afferent nerve caused linearly correlated responses, consisting of oxidation of cytochrome a,a3, elevation of K+0 and a negative shift of potential. In spinal cord, unlike cerebral cortex, the local volume of blood increased upon stimulation. The rate of recovery of the oxidation response of cytochrome a,a3 was consistently faster in cord than in cortex. Pentobarbital (i.v.) in anesthetic dosage reduced the amplitude and slowed the rate of recovery of all 4 parameters, indicating that the optical signals originate from gray matter. It is speculated that the spinal cord, even more than cortex, may depend for its viability on the maintenance of PO2 above a certain level, and that much of the metabolic activity following stimulation is associated with the restoration of ionic gradients.

Afferent Pathways↗
PubMed1979

LSD's effect on neuron populations in visual cortex gauged by transient responses of extracellular potassium evoked by optical stimuli.

The effects of systemic LSD (10--25 micrograms/kg) on visually evoked [K+]o responses from the striate cortex have been investigated in cats. Elevation of [K+]o was dependent on the orientation, and direction of stimulus movement and showed ocular dominance. LSD most commonly produced a depression of [K+]o transients and a deterioration in their directional selectivity. These observations suggest that the effect of LSD is to produce a net depression in visually evoked neuronal firing.

Animals↗
PubMed1978

The projection of jaw elevator muscle spindle afferents to fifth nerve motoneurones in the cat.

1. By spike-triggered averaging of intracellular synaptic noise it has been shown in pentobarbitone anaesthetized cats that jaw elevator muscle spindle afferents with their cell bodies in the mid-brain have a relatively weak monosynaptic projection to masseter and temporalis motoneurones. 2. Extending the spike-triggered averaging method to recording extracellular excitatory field potentials it has been shown that virtually all the spindles do project monosynaptically to the motoneurone pool. It is concluded that the general weakness of the projection is due to its restriction to a small proportion of the motoneurones, possibly those concerned most with tonic postural functions. 3. The shape of individual intracellular e.p.s.p.s together with the spatial distribution of extracellular excitatory potential fields provide some evidence for a dentrically weighted distribution of the synapses. 4. Evidence is presented that both primary- and secondary-type spindle afferents project monosynaptically, the secondary effects being some 71% of the strength of the primary ones.

Action Potentials↗
PubMed1977

Phenytoin, electric, ionic, and metabolic responses in cortex and spinal cord.

Post-tetanic potentiation (PTP) of monosynaptic reflex was estimated in spinal cords in the drug-free state after the administration of a convulsant dose of penicillin and after the administration of phenytoin. There was no apparent correlation between the degree of depression of PTP and the efficacy of controlling seizure activity by phenytoin. Extracellular potassium levels were measured with ion-selective microelectrodes. The post-stimulation clearing of [K+]0 was not accelerated by phenytoin, and frequently it was slowed. Post-stimulus undershooting of [K+]0 was diminished. Oxidation of NADH in cortex and of cytochrome a, a3 in spinal cord were measured by optical methods. Stimulus-evoked transient oxidation responses evoked by electrical stimulation were depressed by phenytoin. It is concluded that systemic administration of phenytoin in therapeutic doses does not stimulate Na+-K+-activated membrane ATPase in cortex and spinal cord. Unlike other depressants, phenytoin did not cause a reduction of "resting" redox levels of respiratory enzymes. The local regulation of blood flow remained unaltered after phenytoin administration. Phenytoin caused a moderate but consistent depression of the stimulus-evoked responses of potassium activity, electric potential, and oxidative enzymes, consistent with diminished outflow of potassium from cells, owing either to lesser activation of cells or to a lesser exchange of ions.

Animals↗
PubMed1976

The transmission of reflexes in the spinal cord of cats during direct irradiation with microwaves.

The spinal of cats was directly exposed to 2450 CW microwave radiation in order to study the effect on reflex response and synaptic function. A small but statistically significant increase in the reflex response was detected in the first series of experiment, which indicates enhancement of the synaptic transmission. However, this effect was not observed in a second series of experiments in which the incident power density was increased from 10 mW/cm(2) to 20 mW/cm(2) and a more rigorous experimental design was employed. The slight changes that were observed in the second series could be attributed to small temperature variations during the experiment.

Animals↗
PubMed1976

Improved voiding in response to electrical stimulation of the spinal cord of paraplegic dogs.

Bipolar electrodes were inserted into the conus medullaris and attached to the proximal urethra of paraplegic dogs. Repeated stimulus trains were delivered to the spinal cord electrodes and the urethral electrodes in an attempt to improve voiding induced by cord stimulation. The results indicate that the increased outflow resistance which often accompanies electromicturition can be significantly overcome both by repeated spinal cord stimulation and by prestimulation of the proximal urethra.

Animals↗