Simultaneous determination of maltose and glucose using a screen-printed electrode system

A screen-printed sensor system consisting of a glucose oxidase (GOD) electrode and an amyloglucosidase/glucose oxidase (A/G) electrode was constructed to determine maltose and glucose simultaneously in a mixture. Sensor construction was optimised so that it contained 20 units of GOD/40 units of amyloglucosidase and 0.2 mM 1,1'-ferrocenedimethanol. These components were deposited onto a screen-printed carbon electrode and an outer membrane was printed from 3.5% hydroxyethyl cellulose (HEC) solution. The optimum pH was 4.8. The linear range of the system was up to 40 mM glucose or 20 mmol/L maltose with coefficients of variation (CVs) ranging from 3.5% to 5.29%. The results obtained by using the enzyme electrode system agreed well with those obtained by the Fehling titration method. When stored dry, especially at 4 degrees C, the enzyme electrodes showed good stability over four months.     

Intracellular recordings in response to monaural and binaural stimulation of neurons in the inferior colliculus of the cat

The inferior colliculus (IC) is a major auditory structure that integrates synaptic inputs from ascending, descending, and intrinsic sources. Intracellular recording in situ allows direct examination of synaptic inputs to the IC in response to acoustic stimulation. Using this technique and monaural or binaural stimulation, responses in the IC that reflect input from a lower center can be distinguished from responses that reflect synaptic integration within the IC. Our results indicate that many IC neurons receive synaptic inputs from multiple sources. Few, if any, IC neurons acted as simple relay cells. Responses often displayed complex interactions between excitatory and inhibitory sources, such that different synaptic mechanisms could underlie similar response patterns. Thus, it may be an oversimplification to classify the responses of IC neurons as simply excitatory or inhibitory, as is done in many studies. In addition, inhibition and intrinsic membrane properties appeared to play key roles in creating de novo temporal response patterns in the IC.     

Selective pathway choice of a single central axonal fascicle by a subset of peripheral neurons during leech development

In the CNS of leech, the central projections of peripheral sensory neurons segregate into three distinct axonal tracts during early development. We have previously shown that a subset of these neurons, recognized by the monoclonal antibody lan 4-2, projects axons into only one of these fascicles (Johansen et al., 1992, Neuron 8, 599). Here we report on a developmental and biochemical characterization of another fascicle-specific antigen labeled by the monoclonal antibody lan 3-6. By immunocytochemistry and double labelings we demonstrate that the lan 3-6 epitope is expressed only by a small subgroup of the peripheral neurons in Macrobdella embryos. The axons of these neurons selectively fasciculate in the CNS, but to only one of the three lan 3-2-positive tracts, which is different from the previously described lan 4-2-positive tract. These observations support the existence of a hierarchy of guidance cues mediating specific tract formation in this system. A biochemical analysis of the antigen suggests that it is likely to be a glycosylated protein with a molecular weight of approximately 200 kDa. Thus, the restricted expression of the lan 3-6 antigen and its biochemical properties are consistent with the hypothesis that this antigen may be playing a role in axonal guidance.     

Response of single Purkinje neurons in the flocculus of albino rabbits to caloric stimulation

The response of Purkinje neurons of the flocculus to caloric stimulation was investigated in the Urethane-chlorarose anesthetized rabbit. Twenty-five of 37 flocculus neurons which responded to ipsilateral caloric stimulation showed an increase in firing response, while 12 neurons showed a decrease. Fifteen of 28 flocculus neurons which responded to contralateral caloric stimulation showed an increase, while the firing of 13 neurons was decreased. Forty-one percent of flocculus neurons responded to ipsilateral caloric stimulation, and 41% responded to caloric stimulation of both sides. Eighteen percent of flocculus neurons responded only to contralateral stimulation. The ipsilateral flocculus may thus be responsible for the major control of the primary vestibular signal flow in the cerebellum.     

A study of diffusion isotropy in single neurons by using NMR microscopy

The apparent diffusion coefficient (ADC) of water was measured in single Aplysia californica neurons by using NMR microscopy encoded in each of two perpendicular gradient directions. Comparisons of the mean ADCs of the gross nuclear and cytoplasmic compartments in five cells, and 50 subregions within these cells, showed no significant difference between the diffusion measurements in the majority of cases. Since anisotropic diffusion would make the ADC dependent on the encoding direction, the results indicate that the ADC in these single neurons is isotropic at the spatial and temporal resolutions used in these studies. Consequently, a single scalar ADC measurement is sufficient for characterizing the ADC in these cells, hence reducing the acquisition time and measurement complexity that would have been required had the ADC been anisotropic.     

Comparison of single-fiber and macro electrode recordings: relationship to motor unit action potential duration

The factors contributing to the duration of a motor unit action potential (MUAP) are believed to be well known, with both manual measurements and computer simulations agreeing with respect to MUAP durations approaching 10 ms. In this investigation, it is clearly demonstrated that use of a wide-open amplifier bandpass combined with signal-to-noise ratio enhancement results in MUAP durations approaching 30 ms recorded with either a macro or single-fiber electrode. Why the clinically recorded MUAP duration differs significantly from these physiologic durations is discussed. A hypothesis is presented whereby the major contributing factor toward MUAP duration is the total time of action potential transmembrane current flow along the muscle fiber from end-plate zone to musculotendinous junction.     

Simultaneous determination of planar chlorobiphenyls and polychlorinated dibenzo-p-dioxins and -furans in Dutch milk using isotope dilution and gas chromatography-high-resolution mass spectrometry

A method is described for the simultaneous determination of planar chlorobiphenyls and dioxins in milk using isotope dilution and gas chromatography-high-resolution mass spectrometry (GC-MS). The method is based on gel permeation chromatography, alumina clean-up and carbon chromatography and is highly automated, making a high sample throughput possible. Data on recovery, accuracy and reproducibility of results obtained with quality control samples are presented. Data for both dioxins and planar chlorobiphenyls from the analysis of samples of Dutch milk from several areas in the Netherlands are also presented. Possible interference of the chlorobiphenyls in the determination of the dioxins in the GC-MS method is discussed.     

Simultaneous induction of pathway-specific potentiation and depression in networks of cortical neurons

Activity-dependent modification of synaptic efficacy is widely recognized as a cellular basis of learning, memory, and developmental plasticity. Little is known, however, of the consequences of such modification on network activity. Using electrode arrays, we examined how a single, localized tetanic stimulus affects the firing of up to 72 neurons recorded simultaneously in cultured networks of cortical neurons, in response to activation through 64 different test stimulus pathways. The same tetanus produced potentiated transmission in some stimulus pathways and depressed transmission in others. Unexpectedly, responses were homogeneous: for any one stimulus pathway, neuronal responses were either all enhanced or all depressed. Cross-correlation of responses with the responses elicited through the tetanized site revealed that both enhanced and depressed responses followed a common principle: activity that was closely correlated before tetanus with spikes elicited through the tetanized pathway was enhanced, whereas activity outside a 40-ms time window of correlation to tetanic pathway spikes was depressed. Response homogeneity could result from pathway-specific recurrently excitatory circuits, whose gain is increased or decreased by the tetanus, according to its cross-correlation with the tetanized pathway response. The results show how spatial responses following localized tetanic stimuli, although complex, can be accounted for by a simple rule for activity-dependent modification.     

Design and clinical application of a double helix electrode for functional electrical stimulation

Disrupting bacterial biofilms is necessary for a wide application domains such as reusable medical devices, or systems of pipes for water or fluids in cosmetics, food and chemicals industry. Bacterial cells embedded in a biofilm are less susceptible to disinfectants than suspended cells. This property is referable to the structure of the biofilm itself. The gangue of exopolymers and the thickness of a 5-day-old biofilm of Escherichia coli (more than 200 layers of bacteria), contribute to this decrease of susceptibility. The present work deals with the release of an Escherichia coli biofilm by the sequential action of enzymes and a phenolic disinfectant on the one hand, and by the sequential or simultaneous action of surfactants and the previous disinfectant on the other hand. The decrease of bacteria count per mm2 and the Scanning Electron Microscope observations exhibited a synergic action in every case. Nevertheless, Escherichia coli biofilms quickly reconstructed even after exposition to the previous treatment.     

Role of thalamic and cortical neurons in augmenting responses and self-sustained activity: dual intracellular recordings in vivo

Progressively increasing (augmenting) responses are elicited in thalamocortical systems by repetitive stimuli at approximately 10 Hz. Repeated pulse trains at this frequency lead to a form of short-term plasticity consisting of a persistent increase in depolarizing synaptic responses as well as a prolonged decrease in inhibitory responses. In this study, we have investigated the role of thalamocortical (TC) and neocortical neurons in the initiation of thalamically and cortically evoked augmenting responses. Dual intracellular recordings in anesthetized cats show that thalamically evoked augmenting responses of neocortical neurons stem from a secondary depolarization (mean onset latency of 11 msec) that develops in association with a diminution of the early EPSP. Two nonexclusive mechanisms may underlie the increased secondary depolarization during augmentation: the rebound spike bursts initiated in simultaneously recorded TC cells, which precede by approximately 3 msec the onset of augmenting responses in cortical neurons; and low-threshold responses, uncovered by hyperpolarization in cortical neurons, which may follow EPSPs triggered by TC volleys. Thalamic stimulation proved to be more efficient than cortical stimulation at producing augmenting responses. Stronger augmenting responses in neocortical neurons were found in deeply located (<0.8 mm, layers V-VI) regular-spiking and fast rhythmic-bursting neurons than in superficial neurons. Although cortical augmenting responses are preceded by rebound spike bursts in TC cells, the duration of the self-sustained postaugmenting oscillatory activity in cortical neurons exceeds that observed in TC neurons. These results emphasize the role of interconnected TC and cortical neurons in the production of augmenting responses leading to short-term plasticity processes.     

Retinal pigment epithelial cells: autocrine and paracrine stimulation of extracellular matrix contraction

BACKGROUND: This study was carried out to examine the biological activity of contraction promoters produced by dedifferentiating retinal pigment epithelial cells (RPE) and to evaluate the importance of autocrine and paracrine effects within a semi-closed environment like the vitreal cavity. METHODS: RPE at different stages of dedifferentiation in culture were examined for their ability (a) to generate tractional forces in vitro, with and without serum stimulation, and (b) to produce and release contraction-stimulating proteins. Autocrine versus paracrine effects of cell-secreted promoters were tested by using RPE or human dermal fibroblasts (HDF) as target cells. The contraction-stimulating activity of the cell-secreted promoters was partially characterized and compared to the activity of defined promoters. RESULTS: Our study confirmed that RPE can synthesize and secrete cell-contraction-promoting factor(s) active in stimulating the development of tractional forces by RPE as well as HDF. The quantity of biological activity secreted per cell decreases with progressive dedifferentiation, yet the responsiveness of the cell to contraction promoters increases. The contraction promoter(s) synthesized by RPE is partially distinct from the promoters in serum, TGF-beta 1 and beta 2, IGF-1, ET-1 and PDGF. The contraction-promoting effects of the RPE product(s) can be completely blocked by staurosporine. CONCLUSION: De-differentiation of RPE is characterized by increasing capacity to generate tractional forces and decreasing synthetic capacity. RPE within a semi-closed system like the vitreal cavity can, theoretically, act both as promoting and active component of traction-related events (tractional retinal detachment).     

Effects of somatosensory and parallel-fiber stimulation on neurons in dorsal cochlear nucleus

1. Single units and evoked potentials were recorded in the dorsal cochlear nucleus (DCN) of paralyzed decerebrate cats in response to electrical stimulation at two sites: 1) in the somatosensory dorsal column nuclei (together called MSN below for medullary somatosensory nuclei), which activates mossy-fiber inputs to granule cells in superficial DCN, and 2) on the free surface of the DCN, which activates granule cell axons (parallel fibers) directly. The goal was to evaluate hypotheses about synaptic interactions in the cerebellum-like circuitry of the superficial DCN. A four-pulse facilitation paradigm was used (50-ms interpulse interval); this allows identification of three components of the responses of DCN principal cells (type IV units) to these stimuli. The latencies of the response components were compared with the latency of the evoked potential in DCN, which signals the arrival of the parallel fiber volley at the recording site. 2. The first component is a short-latency inhibitory response; this component is seen only with MSN stimulation and is seen almost exclusively in units also showing the second component, the transient excitatory response. The short-latency inhibitory component precedes the evoked potential. No satisfactory explanation for the short-latency component can be given at present; it most likely reflects a fast-conducting inhibitory input that arrives at the type IV unit before the slowly conducting parallel fibers. 3. The second component is a transient excitatory response; this component is seen with both MSN and parallel fiber stimulation; it is weak and appears to be masked easily by the inhibitory response components. The excitatory component occurs at the same latency as the evoked potential and probably reflects direct excitation of principal cells by granule cell axons. The excitatory component is seen in about half the type IV units for both stimulating sites. With MSN stimulation, the lack of excitation in some units suggests a heterogeneity of cochlear granule cells, with some carrying somatosensory information and some not carrying this information; with parallel fiber stimulation, excitation probably requires the stimulating and recording electrodes to be lined up on the same "beam" of parallel fibers. 4. The third component is a long-lasting inhibitory response that is observed in virtually all type IV units with both MSN and parallel-fiber stimulation; its latency is longer than the evoked potential. Evidence suggests that it is produced by inhibitory input from cartwheel cells. The appearance of this inhibitory component in almost all type IV units can be accounted for by the considerable spread of cartwheel-cell axons in the direction perpendicular to the parallel fibers. 5. The evoked potential and all three components of the unit response vary systematically in size over the four pulses of the electrical stimulus. These results can be accounted for by two phenomena: 1) a facilitation of the granule cell synapses on all cell types that produces a steadily growing response through the four pulses, resembles presynaptic facilitation, and is seen with both MSN and parallel-fiber stimulation; and 2) a strong reduction in the granule cell response between the first and second pulse for MSN stimulation only. This reduction probably occurs presynaptically in the glomerulus or in the granule cell itself and could reflect inhibitory inputs. 6. The response components described above are seen in type IV units recorded in both the fusiform-cell and deep layers of the DCN; this suggests that both pyramidal and giant cells are activated similarly. The simplest interpretation is that both principal cell types are activated by the cerebellum-like circuitry in superficial DCN. Alternatively, because giant cells appear to make limited contact with the granule-cell circuits of superficial DCN, this finding may suggest the existence of currently undescribed granule cell circuits in deep DCN that are si     

Effects of electrode geometry and combination on nerve fibre selectivity in spinal cord stimulation

The differential effects of the geometry of a rostrocaudal array of electrode contacts on dorsal column fibre and dorsal root fibre activation in spinal cord stimulation are analysed theoretically. 3-D models of the mid-cervical and mid-thoracic vertebral areas are used for the computation of stimulation induced field potentials, whereas a cable model of myelinated nerve fibre is used for the calculation of the excitation thresholds of large dorsal column and dorsal root fibres. The size and spacing of 2-D rectangular electrode contacts are varied while mono-, bi- and tripolar stimulation are applied. The model predicts that the highest preferential stimulation of dorsal root fibres is obtained in monopolar stimulation with a large cathode, whereas dorsal column fibre preference is highest in tripolar stimulation with small contacts and small contact spacings. Fibre type preference is most sensitive to variations of rostrocaudal contact size and least sensitive to variations of lateral contact size. Dorsal root fibre preference is increased and sensitivity to lead geometry is reduced as the distance from contacts to spinal cord is increased.     

Simultaneous microdialysis in brain and blood of the mouse: extracellular and intracellular brain colchicine disposition

A simultaneous brain and blood microdialysis system was developed to study the passage of colchicine through the blood-brain barrier in the mouse. Colchicine was administered as a bolus in the jugular vein (1.5 mg kg-1) and its hippocampal extracellular fluid (ECF) and blood kinetics were determined over a 4 h period using two microdialysis probes, one in the dorsal hippocampus, the other in the inferior vena cava. Colchicine rapidly diffused into the hippocampus (maximum concentration in the first dialysate sample) and brain and blood concentrations declined in parallel, suggesting rapid equilibration between these two compartments. However, only 6. 7% of total blood colchicine, 14% of unbound colchicine was present in the hippocampus suggesting that the P-glycoprotein efflux pump limits colchicine uptake by the brain. We also found, using conventional tissue homogenate analysis in parallel, that the concentration of colchicine in the hippocampal ECF was 10 times less than that in the intracellular space and that the hippocampus colchicine concentration was 2.8 times higher than that of the rest of the brain. This study shows that the simultaneous brain and blood microdialysis can be used to measure the passage of colchicine through the blood-brain barrier and to estimate the brain extra- and intracellular distribution of colchicine.     

Simultaneous Removal of Naphthalene and Sulfur Dioxide using Surfactant

Anionic surfactant was added during absorption to investigate the solubility of vapor phase naphthalene and SO2 in water. Anionic surfactant employed was sodium dodecyl sulfate. Lower than critical micelle concentration (CMC), the apparent solubility and absorption rates of SO2 or naphthalene with or without SO2 were practically identical to those of pure water. However, higher than CMC, equilibrium SO2 or naphthalene apparent solubility increased linearly in proportion to the surfactant concentrations. The solubilization effect of micelles resulted in the increase. Because the micelle solubilization effect was greater than that of the decrease of the mass transfer coefficient, the gas absorption rate increased. When surfactant concentration was 0.1 M, the enrichment factor (EF) value of naphthalene with SO2 was 4.54, which was only half of its value without SO2. When surfactant concentration was 0.2 M, the SO2 EF values increased to 2.24. These empirical findings confirm that to increase the removal efficiency of simultaneous absorption of hydrophobic organic compounds and SO2 via a spray or packed tower, an anionic surfactant can be employed.     

Effect of a single element subcutaneous array electrode added to a transvenous electrode configuration on the defibrillation field and the defibrillation threshold

Even with the use of biphasic shocks, up to 5% of patients need an additional subcutaneous lead to obtain a defibrillation safety margin of at least 10 J. The number of patients requiring additional subcutaneous leads may even increase, because recent generation devices have a < 34 J maximum output in order to decrease their size. In 20 consecutive patients, a single element subcutaneous array lead was implanted in addition to a transvenous lead system consisting of a right ventricular (RV) and a vena cava superior lead using a single infraclavicular incision. The RV lead acted as the cathode; the subcutaneous lead and the lead in the subclavian vein acted as the anode. The biphasic defibrillation threshold was determined using a binary search protocol. Patients were randomized as to whether to start them with the transvenous lead configuration or the combination of the transvenous lead and the subcutaneous lead. In addition, a simplified assessment of the defibrillation field was performed by determining the interelectrode area for the transvenous lead only and the transvenous lead in combination with the subcutaneous lead from a biplane chest X ray. The intraoperative defibrillation threshold was reconfirmed after 1 week, after 3 months, and after 12 months. The mean defibrillation threshold with the additional subcutaneous lead was significantly (P = 0.0001) lower (5.7 +/- 2.9 J) than for the transvenous lead system (9.5 +/- 4.6 J). With the subcutaneous lead, the impedance of the high voltage circuit decreased from 48.9 +/- 7.4 omega to 39.2 +/- 5.0 omega. In the frontal plane, the interelectrode area increased by 11.3% +/- 5.5% (P < 0.0001) and in the lateral plane by 29.5% +/- 12.4% (P < 0.0001). The defibrillation threshold did not increase during follow-up. Complications with the subcutaneous electrode were not observed during a follow-up of 15.8 +/- 2 months. The single finger array lead is useful in order to lower the defibrillation threshold and can be used in order to lower the defibrillation threshold.     

Excitatory synaptic transmission in the inner retina: paired recordings of bipolar cells and neurons of the ganglion cell layer

Properties of glutamatergic synaptic transmission were investigated by simultaneously voltage-clamping a pair of connected bipolar cells and cells in the ganglion cell layer (GLCs) in the newt retinal slice preparation. Activation of the Ca2+ current in a single bipolar cell was essential for evoking the glutamatergic postsynaptic current in the GLC. Depolarization for as short as 15 msec activated both NMDA and non-NMDA receptors. On the other hand, analysis of the spontaneous glutamatergic synaptic currents of GLCs revealed that these currents consisted of mainly non-NMDA receptor activation with little contribution from NMDA receptors. This suggests that non-NMDA receptors of GLCs are clustered in postsynaptic membrane regions immediately beneath the release sites of bipolar cells and that NMDA receptors have lower accessibility to the released transmitter than non-NMDA receptors. Glutamate that is spilled over from the release sites may activate the NMDA receptors. When a prolonged depolarizing pulse was applied to a bipolar cell, the response induced by non-NMDA receptors was limited greatly by their fast desensitization, whereas NMDA receptors were able to produce a maintained response. The relationship between the pulse duration applied to the bipolar cell and the integrated charge of the response evoked in the GLC was almost linear. Therefore, we propose that both non-NMDA and NMDA receptors cooperate to transfer the graded photoresponses of bipolar cells proportionally to GLCs.