Practical use of the central venous access port for contrast-enhanced CT: comparison with peripheral intravenous access regarding enhancement and safety.

AIM: To evaluate the efficacy of using the central venous (CV) port compared with peripheral intravenous access for contrast-material injection for contrast enhancement during the portal venous phase. MATERIALS AND METHODS: Patients were divided into three groups: CV delay, CV routine, and peripheral access (PA) groups. Patients in the CV delay group underwent injection in the arm-down position with an additional delay, while those in the CV routine and PA groups underwent injections with the routine injection protocol for portal venous phase imaging. Contrast enhancement was evaluated by measuring the mean radiodensity (Hounsfield units) values for the aortic arch, abdominal aorta, inferior vena cava, portal vein, and spleen. The peak injection pressure was recorded and compared among the three groups. RESULTS: No complications related to power injection were observed during 119 contrast-material injections performed using the CV port device. The CV delay group showed significantly lower radiodensity values than the PA group (165.7 ± 20.1 versus 181 ± 19 HU [p<0.01] for the portal vein); however, no significant differences in mean radiodensity values were observed between the CV routine and PA groups (p>0.05). The median peak injection pressure was 73.5, 67, and 47 psi in the CV delay, CV routine, and PA groups, respectively (p<0.01). CONCLUSION: The CV port can be used for safe contrast-material injection while maintaining contrast enhancement on portal venous phase comparable to that achieved with peripheral intravenous access.

Effect of a saline flush technique for head and neck imaging in dual-energy CT: improvement of image quality and perivenous artefact reduction using virtual monochromatic imaging.

AIM: To evaluate the effect of the saline flush (SF) technique on the depiction of lesions and the reduction of perivenous artefacts in the head and neck region using dual-energy computed tomography (CT) with virtual monochromatic imaging (VMI). MATERIALS AND METHODS: Fifty patients with head and neck cancer were divided into two groups: group A, without a SF and group B, with a 30-ml SF. All images were acquired using fast kilovolt-switching CT (Revolution HD, GE Healthcare, Milwaukee, WI, USA). Contrast-to-noise ratios (CNRs) of the lesions were calculated at VMI energy levels ranging from 40 to 80 keV. Subjective analysis of overall image quality, delineation of lesions, and perivenous artefacts was conducted by two reviewers at both VMI energy level 40 keV and the optimal energy level (which showed optimal CNR by objective analysis). RESULTS: Optimal energy level was 63 keV for group A and 61 keV for group B. At VMI energy levels ranging from 40 to 80 keV, the CNR was higher for group B. The highest subjective overall image quality was shown for group B at the optimal energy level (subjective image quality mean value, 3.40). Subjective delineation of lesions was comparable. The perivenous artefact score was significantly higher for group B (2.44 versus 2.74 [p<0.05] at 40 keV, 3.20 versus 3.46 [p<0.05] at the optimal energy level). CONCLUSION: The SF technique results in an improvement of lesion CNR and a reduction of perivenous artefacts in VMI using duel-energy CT, especially at 40 keV.

Early postnatal development of substantia nigra neurons in rat midbrain slices: hyperpolarization-activated inward current and dopamine-activated current.

Whole-cell voltage-clamp recordings in rat midbrain slices were used to determine the characteristics and postnatal development of a hyperpolarization-activated inward current (Ih) and a dopamine receptor-activated current of neurons in the substantia nigra pars compacta (SNC). Ih was activated by membrane hyperpolarization beyond the resting membrane potentials, and displayed strong inward rectification. No sign of time- and voltage-dependent inactivation was apparent. The reversal potential of Ih in mature (P12-P13) SNC neurons was -39.2 +/- 4.3 mV, and the activation curve of Ih was well fitted by a sigmoidal function with half-maximal activation at -114.0 +/- 5.6 mV. Those values are essentially the same in immature (P3-P5) neurons. The rate of Ih activation was best approximated by a single exponential function. The time constants were voltage dependent, ranging from 692.3 ms at -110 mV to 342.8 ms at -150 mV at P12 neurons, and 1142.5 ms at -110 mV to 593.2 ms at -150 mV at P3 neurons. There was a marked increase in the amplitude of Ih during postnatal development of SNC neurons, while the membrane capacitance did not alter after P5. The increase in Ih after P5 thus appears to result from an increase in Ih current density. Application of dopamine produced a hyperpolarization of mature SNC neurons, leading to suppression of action potentials. Dopamine-activated outward current was negligible during the first postnatal week, and increased rapidly after the second week. Our results indicate that the SNC neuron of the rat midbrain is not fully mature at the time of birth in terms of voltage-gated ion channels and neurotransmitter receptors, but develops over the first two postnatal weeks.

Time course of miniature currents in regenerating neuromuscular junctions of the cockroach Periplaneta americana.

Miniature excitatory junctional currents in regenerating neuromuscular junctions have been recorded from the denervated leg muscle fibers of the cockroach, Periplaneta americana with an external focal electrode. Miniature currents first reappeared after 21 days after denervation at 26 degrees C. These currents occurred at a lower frequency and had a slower time course than miniature currents at normal junctions. The decay time constant of the falling phase of the earliest current was more than twice the control and the mean amplitude was less than half of the control. The decay time constant of the currents became shorter and their amplitude increased with increasing time after regeneration and approached control values at about 60 days after crushing the nerve. During regeneration of neuromuscular junctions, the falling phase of the miniature currents was always along a single exponential just as in the control. The observed change in the decay time constant of the currents suggests that the open time of the overall population of synaptic receptor-channels increases after denervation and returns to the control with time.

Ca ions and potassium contracture in the retractor unguis muscle of the cockroach.

Potassium contracture consists of a phasic and a sustained component. Extracellular Ca ions are essential for both components. In the phasic component the Ca-induced Ca release mechanism is activated by the entry of the Ca ions.

Choline acetyltransferase and acetylcholinesterase activities in muscles of aged mice.

The activities of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were assayed in intact diaphragm, extensor digitorum longus (EDL), and soleus muscles or their homogenates of young (2-6 months) and aged (24-34 months) mice. CAT activity (per mg of protein) was significantly higher in diaphragm and soleus of old mice in comparison with the young but the age change in EDL was negligible. On the other hand, AChE activity (per mg of protein) was significantly higher in EDL of old mice but in diaphragm and soleus muscles the enzyme activity did not show any significant change statistically. The diaphragm muscle was divided into two fractions, one being neuromuscular (NM) fraction and the other the remainder of the muscle (M fraction). No appreciable change in the ratio of the enzyme activities of NM fraction to the one of M fraction was obtained between the young and aged preparations. Thus, it seems likely that there is an age-related change in CAT and AChE activities which might be affected by the degree to which muscle activity is maintained.

L-glutamate and potassium-induced contractures in denervated cockroach muscles.

1. The effects of denervation on the mechanical responses to various concentrations of L-glutamate in retractor unguis muscle of cockroach (Perilpaneta americana) was examined, comparing them with contractures induced by high potassium saline. 2. The dose-response curve was shifted to the lower concentrations of L-glutamate after 9 days of denervation. 3. Following a transient increase in the maximum contracture tension, it decreased with days after denervation and reached a constant level by several days. However, from 16 to 20 days after denervation, the tension ratios of the maximum glutamate to potassium contractures were significantly higher than that of the innervated muscles. 4. A sustained contracture was observed on and after treatment of L-glutamate in the denervated muscle. Pretreatment of the muscle by concanavalin A facilitated to induce L-glutamate contracture. 5. It was suggested that the sensitivity of the muscle membrane to L-glutamate was increased in the denervated muscle.

Histochemical study on end-plate cholinesterase in aged mice.

The cholinesterase activity at the motor end-plate of aged mice was investigated histochemically. A relative quantitative method was applied for studying the reaction at end-plates by utilizing varying concentrations of eserine. The number of end-plates reacting at a concentration of more than 5 X 10(-6) M eserine was reduced in aged diaphragm but increased in aged soleus muscle at 10(-5) M eserine in comparison with those in the young. It seems likely that there is an age-related change in cholinesterase activities in relation to muscle fiber types.

Postsynaptic effects of nickel ions at the insect neuromuscular junction.

The effect of extracellular nickel on the excitatory postsynaptic response at the insect neuromuscular junction was studied in the segmental muscle of the larval mealworm Tenebrio molitor. The response to L-glutamate applied iontophoretically (glutamate potential, GP) was potentiated in the presence of Ni2+ though the excitatory postsynaptic potential (EPSP) was reduced. It seems unlikely that Ni2+ acts at the same binding site as L-glutamate does since the value of the limiting slope of double logarithmic plots for the action of glutamate was increased in the presence of Ni2+. The potentiation of GP in the presence of Ni2+ cannot be ascribed to competition between Ni2+ and Ca2+ since GP amplitude did not show any dependence on the concentration of Ca2+. Nickel ions did not alter the reversal potential of excitatory postsynaptic current (EPSC) and glutamate current (GC) under the voltage clamp condition, whereas the amplitude of GC was potentiated in the presence of Ni2+. The time constant of the decay of EPSC showed a weak voltage dependency: the more depolarized the membrane, the more prolonged the time constant. In the presence of 1 mM Ni2+ the amplitude of miniature EPSCs (MEPSCs) increased and the half decay time was prolonged significantly. These results suggest that Ni2+ interacts with charged groups near the glutamate receptor-channel complex so that the kinetics of the channel are altered.

Dorsal unpaired median neurons of the cockroach metathoracic ganglion.

On the dorsal surface in the metathoracic ganglion of the cockroach Periplaneta americana, eight large and a number of small somata described by Crossman et al., (1971) were reexamined. These eight large cells (40-60 micron in diameter) could be divided into three different types by Lucifer yellow or nickel injection, depending on the branching of their axons. No neuron was found which sent axons into either the anterior or posterior connectives. In the mesothoracic ganglion an interganglionic H-shaped DUM neuron was found which had four axons, one into each anterior and posterior connective.

Potent excitatory effect of maitotoxin on Ca channels in the insect skeletal muscle.

The effect of maitotoxin (MTX), the most potent marine toxin as yet known, was studied using the skeletal muscle of the larval meal worm, Tenebrio molitor. In normal saline, Tenebrio muscles responded with the spike to direct stimulation. In the saline containing tetraethylammonium (TEA) the all-or-none action potential which had characteristic plateau was elicited by membrane depolarization. When MTX (5 X 10(-9) to 10(-8) g/ml) in the TEA saline was added, the plateau of action potential was prolonged more than in the saline containing TEA alone. Furthermore, MTX lowered the threshold, so that action potentials were readily evoked in the saline containing MTX. In either case, effects, of MTX were antagonized by Co2+. These results suggest that MTX activates the voltage-dependent Ca2+ channels in the insect muscle.

Presynaptic effect of streptomycin on the insect neuromuscular junction.

The effect of streptomycin on the neuromuscular junction of the cockroach leg muscle was studied by means of intracellular electrodes. The miniature excitatory postsynaptic potential (MEPSP) frequency decreased in the presence of 1 mM streptomycin. Double logarithmic plots of the quantal content against the external calcium concentration in the absence and presence of streptomycin suggested the competition for a common site of presynaptic membrane at insect neuromuscular junctions.

Effect of lanthanum ions on neuromuscular transmission in insects.

The effect of extracellular lanthanum on neuromuscular transmission was studied in cockroach leg muscle and larval mealworm ventral muscle by means of microelectrodes. Miniature excitatory postsynaptic potential (MEPSP) frequency was markedly increased after lanthanum was added, in the presence and absence of calcium. The potentiation by La3+ was suppressed in a high Ca2+ saline and enhanced in the absence of Ca2+. Lanthanum ions blocked neuromuscular transmission at a concentration as low as 0.1 mM. The quantal content estimated by the failure method was reduced by 80% in the presence of 0.1 mM-La3+. The reduction in the EPSP amplitude by La3+ may be due to a decrease in the amount of transmitter released by a nerve impulse. The response to L-glutamate applied iontophoretically was also reduced in the presence of La3+. It seems unlikely that La3+ and L-glutamate were competing for a common binding site on the postsynaptic membrane since the apparent maximum of the dose-response curve for glutamate-induced depolarization was reduced in the presence of La3+. External recording of MEPSPs showed that adding lanthanum to the bathing medium increased the time constant of decay of the potential. These results suggest that lanthanum does indeed have a postsynaptic action in addition to its prejunctional action in insect muscle fibres.

A dual effect of cobalt ions on the spontaneous release of transmitter at insect motor nerve terminals.

1. The effect of extracellular cobalt on the frequency of miniature excitatory post-synaptic potentials (MEPSPs) was studied in cockroach leg muscle fibres that had been depolarized with 20.8 mM-K saline. 2. Cobalt ions had a dual effect on the spontaneous release of transmitter, an inhibitory action being followed by an acceleratory. A reciprocal relationship between Ca2+ and Co2+ was found for both the inhibitory and acceleratory effects. 3. The equilibrium dissociation constant for Co2+ as a competitive antagonist of spontaneous release ranged from 0.4 to 0.65 mM. It is concluded that Co2+ is much more potent than Mg2+ in suppressing spontaneous transmitter release at the insect neuromuscular junction. The antagonism by extracellular Co2+ appears to occur only at the external surface site on the terminal membrane.

Effect of uncoupling agents of oxidative phosphorylation on the spontaneous release of transmitter from insect motor nerve terminals.

1. The effect of uncoupling agents of oxidative phosphorylation, potassium warfarin and carbonylcyanide-p-trifluoromethoxy-phenylhydrazone (p-CCP), on the spontaneous release of transmitter was studied at the neuromuscular junction of cockroach muscles. 2. The agents produced a large increase in the frequency of occurrence of miniature excitatory postsynaptic potentials (MEPSPs). This increase also was observed in calcium-free saline. 3. The results may be explained on the hypothesis that the increase in the spontaneous release is due to the increase in free calcium concentration derived from an intracellular origin in the terminal. The mitochondria may play an important role in regulating the intracellular calcium concentration in the nerve terminals of insect muscles.

The statistical analysis of spontaneous transmitter release at individual junctions on cockroach muscle.

1. Miniature excitatory post-synaptic potentials (MEPSPs) were recorded extra- and intracellularly from the coxal depressor muscle of the cockroach, Periplaneta americana. 2. Statistical analysis of the time intervals between MEPSPs showed that the variance-to-mean curve for the extracellular data sets lay significantly above the line predicted for a Poisson process. A shuffling procedure, however, made the series almost random. 3. The serial correlation coefficients for the extracellular data sets exceeded the confidence limits for various lags and most of them were positive. In comparison with the intensity function, the departure from the random process appeared to be mainly due to large positive correlation of intervals. 4. It is concluded that in insect neuromuscular junctions, the spontaneous release of transmitter at individual sites is more clustered than that predicted by a Poisson process.

Curare has a voltage-dependent blocking action on the glutamate synapse.

The skeletal muscle of members of Orthoptera and Diptera receives an innervation which is probably glutaminergic. Recent study of the ventral muscle fibres in the larvae of the beetle, Tenebrio molitor, has revealed that the transmitter action can be mimicked by the iontophoretic application of L-glutamate to the junctional sites at which the extracellular excitatory postsynaptic potentials (e.p.s.ps) could be recorded (D.Y. and H.W., unpublished observation). Contrary to the evidence favouring glutamate as a transmitter of junctional excitation in insects, some investigators have found that curare (+)tubocrarine, TC), a classic acetylcholine (ACh) antagonist, suppresses the neurally evoked muscle potentials in the fly Sacophaga, and Tenebrio. Here, we have analysed the action of curare on the neuromuscular junction of Tenebrio larvae and found that curare blocked the glutaminergic transmission by antagonising the transmitter at the postsynaptic site.