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  • 1
    ISSN: 1432-1440
    Keywords: Supernormal conduction ; Bundle branch block ; His bundle electrogram ; Programmed atrial stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A programmed atrial stimulation at a driving rate of 100/min was performed in a 47-year-old woman with left bundle branch block. Supernormal conduction lasting 40 ms was revealed within the right bundle branch. After autonomic blockade (0.2 mg propranolol/kg body weight and 0.04 mg atropine/kg body weight) the position and duration of the supernormal conduction did not change. This suggests that the autonomic nervous system has no influence on the supernormal phase of conduction in the human intraventricular conduction system.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1335
    Keywords: Liver cells ; Cell cycle ; DNA alkylation ; O6-Methylguanine repair
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To compare the formation and persistance of alkylated DNA bases in the G1- and S-phase compartments in liver in vivo, regnerating rat liver was exposed to [14C]dimethylnitrosamine (0.57 mg/kg, IP injection) or N-[methyl 14C]-N-nitrosourea (3.3 mg/kg, intraportal injection) during the G1 phase of the cell cyle (12 h after partial hepatectomy), or at 24 h after partial hepatectomy with 30% hepatocytes in DNA synthesis, or at 43 h after partial hepatectomy, 4 h after an hydroxyurea block from 14 to 39 h after operation with 80% hepatocytes in DNA synthesis. At 120 min after dimethylnitrosamine and 90 s, 5, 10, or 60 min after the intraportal pulse of N-methyl-N-nitrosourea the molar fractions of 7-methylguanine (7megua), O6-methylguanine (O6megua), and 3-methyladenine (3mead) and of metabolically labeled guanine were determined from DNA hydrolysates by Sephadex-G10 radiochromatography. After dimethylnitrosamine only minor differences were observed for 7megua formation in the three groups; the 3mead/7megua ratio remained constant irrespective of the number of cells in S phase. In contrast, the O6megua/7megua ratio revealed a loss of O6megua, the extent of which appeared proportional to the fraction of DNA-synthesizing cells in the liver. The rapid loss of O6megua in S-phase cells was confirmed after intraportal administration of N-methyl-N-nitrosourea. During the first 10 min after the methylnitrosourea pulse the O6megua/7megua ratio was constant in G1 cells and dropped from 90 s to 10 min by about 15% in liver containing 30% S-phase cells and by about 40% with 80% cells in DNA synthesis. DNA-synthesizing hepatocytes are apparently endowed with a higher O6megua DNA transferase activity than nonproliferating liver cells. The rapid, though exhaustible elimination of O6megua during S-phase might result in partial protection of DNA-synthesizing cells from base-mispairing and/or from hypomethylation at G-C sites.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2072
    Keywords: Phencyclidine ; Secobarbital ; Diazepam ; Eye tracking ; Smooth-pursuit eye movement ; Rhesus monkeys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Rhesus monkeys were trained to track a moving disk using a procedure in which responses on a lever were reinforced with water delivery only when the disk, oscillating in a horizontal plane on a screen at a frequency of 0.4 Hz in a visual angle of 20°, dimmed for a brief period. Pursuit eye movements were recorded by electrooculography (EOG). IM phencyclidine, secobarbital, and diazepam injections decreased the number of reinforced lever presses in a dose-related manner. Both secobarbital and diazepam produced episodic jerky-pursuit eye movements, while phencyclidine had no consistent effects on eye movements. Lever pressing was disrupted at doses which had little effect on the quality of smooth-pursuit eye movements in some monkeys. This separation was particularly pronounced with diazepam. The similarities of the drug effects on smooth-pursuit eye movements between the present study and human studies indicate that the present method using rhesus monkeys may be useful for predicting drug effects on eye tracking and oculomotor function in humans.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2072
    Keywords: d-Methylamphetamine ; Tolerance ; Neurotoxicity ; Dopamine ; DRL Schedule ; Amphetamines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The long-term neurochemical and behavioral effects of repeated d-methylamphetamine (d-MA) administration were investigated using four male rhesus monkeys trained to lever-press for food on a DRL-40 s schedule of reinforcement. Dose-response curves for d-MA (0.0625–2.0 mg/kg), apomorphine (0.025–0.4 mg/kg), and haloperidol (0.005–0.04 mg/kg) on responding showed that repeated d-MA administration (0.5–16.0 mg/kg/day) decreased sensitivity to d-MA and to apomorphine but increased sensitivity to haloperidol. At 3–6 months after the last injection of d-MA, a 48.1% decrease in caudate dopamine (DA) was observed, with the frontal cortex, midbrain, and ponsmedulla showing no significant change. A trend toward increasing concentrations of norepinephrine was noted in the same brain areas, but only in the frontal cortex did this change reach significance. Specific binding of 3H-spiroperidol to caudate membrane preparations was not changed, while the V max of the caudate DA re-uptake process declined 32%, with no change in K m. These results suggest that exposure of DA neurons in the caudate nucleus to high concentrations of d-MA can lead to nerve terminal degeneration.
    Type of Medium: Electronic Resource
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