Means for efficient electron beam generation in wide-aperture open-discharge light sources

The interaction of a plasma in the accelerating gap of an open discharge with a strong external electric field and with the cathode surface has been investigated theoretically and experimentally. In a pulsed nanosecond discharge, the ion inertia and plasma screening of the electric field cause a fast growth of the electric field E in the cathode region and a decrease in the length of the latter. Along with a reduction of the electron multiplication factor at high electric fields, this leads to a substantial decrease in the ion flux toward the cathode, which allows one to develop highly efficient open-discharge light sources with a long lifetime and low cathode sputtering. In this respect, continuous and quasi-continuous discharges are less advantageous because of the smaller increase in the electric field in the cathode region. The Townsend coefficients of charge multiplication and electron emission at high electric fields typical of open discharges have been measured for the first time. Fast ions and atoms extracted from the plasma of the accelerating gap significantly affect the cathode emission properties. In particular, photoemission is enhanced by more than one order of magnitude and becomes the main mechanism for electron generation. This also increases the efficiency and lifetime of open-discharge light sources.     

Aging-related changes in the sensitivity of the system of respiratory control and the intensity of free-radical processes in humans

Results of a comparative study of the sensitivity of the system of respiratory control to increases in the CO₂ concentration and the intensity of free-radical processes in young and elderly subjects are described. It is shown that normal (natural) aging is accompanied by a decrease in the sensitivity of the respiratory system to hypercapnic stimulation and a parallel significant decrease in the activity of catalase in the blood of examined subjects. Mechanisms responsible for the modifications of the sensitivity of the system of respiratory control to hypercapnia are discussed; these shifts can be at least partly related to changes in the intensity of production of free radicals observed in elderly subjects. Neirofiziologiya/Neurophysiology, Vol. 40, No. 1, pp. 53–57, January–February, 2008.     

Oculomotor activities in monkeys with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced syndrome of parkinsonism

In twoMacaca rhesus monkeys that received repeated N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injections (single dose 0.2 mg/kg, i.m.; cumulative dose 11.2–13.3 mg), changes in characteristics of spontaneous saccadic eye movements and vestibulo-ocular reflex (VOR) were evaluated. With the development of severe behavioral disturbances, amplitude of spontaneous saccadic eye movements gradually decreased. Pronounced changes in duration of saccadic eye movements, frequency of spontaneous saccades, and their pattern were observed. No changes in parameters of VOR slow component were recorded, but high total MPTP doses suppressed fast phase of the reflex.Neirofiziologiya/Neurophysiology, Vol. 25, No. 3, pp. 184–190, May–June, 1993.     

Neuronal responses in the cat substantia innominata during instrumental conditioned reflex

Neuronal spike activity in the substantia innominata was investigated when establishing the instrumental conditioned reflex of lever-pressing with food reinforcement during chronic experiments on cats. Spike activity changed in 44.3% of neurons during this process; 24.3% responded directly to conditioned acoustic stimulation. Reactions associated with conditioned reflex movement were less pronounced. Response of peak intensity and duration was observed during food reinforcement, when the reaction occasionally occurred 500 msec in advance of the reinforcement provided. Involvement of cholinergic substantia innominata neurons in reinforcement is thought to be responsible for the persistence of residual effects in neocortical neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 796–804, November–December, 1989.     

Uptake of GABA by rat brain synaptic vesicles isolated by a new procedure.

Uptake of GABA was demonstrated in rat brain synaptic vesicles which were prepared by a new and efficient procedure. The uptake activity co-purified with the synaptic vesicles during the isolation procedure. The purity of the vesicle fraction was rigorously examined by analysis of marker enzymes and marker proteins and also by immunogold electron microscopy using antibodies against p38 (synaptophysin). Contamination by other cellular components was negligible, indicating that GABA uptake by the synaptic vesicle fraction is specific for synaptic vesicles and not due to the presence of other structure possessing GABA uptake or binding activities. GABA uptake was ATP dependent and similar to the uptake of glutamate, which was assayed for a comparison. Both uptake activities were independent of sodium. They were inhibited by the uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, indicating that the energy for the uptake is provided by an electrochemical proton gradient. This gradient is generated by a proton ATPase of the vacuolar type as suggested by the effects of various ATPase inhibitors on neurotransmitter uptake and proton pumping. Competition experiments revealed that the transporters for GABA and glutamate are selective for the respective neurotransmitters.     

The “efferent copy” hypothesis in saccadic programming in cats

Eye movements were investigated in cats while following a visual target. Wire coils implanted into the eyes served as transducers; the animal was placed in a revolving magnetic field (the magnetic search coil technique). The linear nature of amplitude-velocity relationships in saccadic eye movements was demonstrated. With combined head and eye movements, slope of plot was unrelated to maximum velocity of head movement over the entire test range (of up to 250 deg/sec); saccades decelerated when the head was immobile. Duration of gaze shift rose as it increased in amplitude. Amplitude of gaze was found to depend on head velocity. Experimentally obtained data on the interaction between head and eye movements when combined in following a target may be interpreted from the aspect of a mechanism operating to suppress saccadic signals by an efferent copy signal for head movement.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 631–637, September–October, 1988.     

Voltage dependence of acetylcholine-activated membrane conductance in sympathetic ganglion neurons

Acetylcholine-induced membrane conductance was investigated in superior cervical ganglion neurons using a patch-clamp technique. It was found that hyperpolarization and depolarization produce an increase and a reduction in acetylcholine (ACh) conductance. This reduction was unconnected with either reversal of the current induced by iontophoretic ACh application or the presence of Ca ions in the external solution. The time constant of relaxation (_r) of this current, produced by a jump in membrane potential, was found to increase e-fold when the membrane was hyperpolarized by 70 mV, matching the voltage dependence of ACh conductance. This led to the hypothesis that voltage-dependent ACh-induced conductance is entirely determined by the voltage dependence of nicotinic receptor channel gating kinetics.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 167–171, March–April, 1988.     

Glutathione synthetase in tobacco suspension cultures: catalytic properties and localization

Glutathione synthetase activity (EC 6.3.2.3) was analysed in ammonium sulfate precipitates of extracts l'rom photohetevotrophically grown cells of Nicotiana tabactm L. cv. Samsun by determination of glutathione as its monobromobimane derivative. Maximal enzyme activity was obtained at pH 8.0–9.0 in Tris-HCl and CHES as buffer systems. The enzyme showed an absolute requirement for Mg2+ and was slightly stimulated by K+. When Mg2+ was replaced by Mn2+ less synthetase activity was observed, and above 30 m M Mn2+ no activity was found. The enzyme was specific for glycine (KM = 0.308 m M ). No product formation was observed with ß -alanine and γ y-aminobutyrate using substrate conccntrations of 10 m M . The apparent KM values for γ -glutamylcysteine and γ -glutamyl- l -α-aminobutyrate were, respectively, 0.022 and 0.033 m M . By chloroplast Isolation ca 24% of the total glutathione synthetase activity of the cells could be shown to be localized in the chloroplasts, the rest being attributed to the cytoplasm of the tobacco cells.     

Effect of intracellular administration of L-tyrosine and L-phenylalanine upon voltage-dependent calcium current in PC 12 pheochromocytoma cells

Using the voltage clamp technique under conditions of intracellular perfusion, we investigated changes in high-threshold voltage-dependent calcium current (I_Ca) in the surface membrane of PC 12 cells caused by intracellular administration of the aromatic amino acids L-tyrosine and L-phenylalanine. Administration of L-tyrosine (20 mmole/1) prevented decrease in I_Ca caused by perfusion of the cell with an artificial saline solution and had a transient restorative effect upon the cell. Administration of L-phenylalanine (20 mM) quickened the decrease in amplitude of I_Ca observed in the control. These effect of aromatic amino acids are maintained when ATP (2 mM) in the intracellular solution is replaced by an equivalent quantity of ADP. The tyrosine hydroxylase blocker -methyl D,L-tyrosine (20 MM) had an effect upon I_Ca analogous to that of L-tyrosine.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 105–111, January–February, 1991.     

Electrophysiological analysis of corticofugal influences on preoptic neurons

Evoked potential (EPs) and responses of the medial (MPO) and lateral (LPO) preoptic region (RPO) and adjacent structures of the hypothalamus to stimulation of the prefrontal (area 8) and cingulate (area 24) cortex, piriform lobe (periamygdaloid cortex), and hippocampus (area CA3) were investigated in acute experiments on cats under ketamine anesthesia. The most pronounced EPs were observed in the RPO after stimulating the piriform and cingulate cortex. A close relation was found between neuronal responses and EP components. The majority of neurons responding to stimulation of various cortical structures were localized in the LPO, where primarily excitatory responses dominate. The MPO contained somewhat fewer neurons responding to cortical stimulation, and the dominant response here was primarily inhibitory. The ratio of inhibitory and excitatory responses in the LPO was 0.6:1 and in the MPO 5.8:1. Primarily in-inhibitory responses dominated also in the LPO zone adjacent to the bed nucleus stria terminalis (BST) and primarily excitatory in the region surrounding the supraoptic nucleus (SO) (respective ratios 4.9:1 and 0.7:1). The RPO is a broad convergence zone, where 3/4 of the neurons responded to stimuli of two and more cortical regions.A. M. Gorky Medical Institute, Ukrainian Minstry of Health, Donetsk. Translated from Neirofiziologiya, Vol. 23, No. 6, pp. 709–719, November–December, 1991.