Identical Threshold Research Articles

Renal vascular response to interruption of the renin-angiotensin system in normal man

We assessed the role of the renin-angiotensin system in the response of the renal circulation to restriction of sodium intake in 38 normal patients. Both saralasin (10 to 30 ng/kg/min), an angiotensin antagonist, and SQ 20881 (30 to 300microgram/kg), a converting enzyme inhibitor, induced a dose-related increase in renal blood flow (xenon 133 washout) only when the resin-angiotension system was activated by restriction of sodium intake to 10 MEq/day. Increasing doses of saralasin (100 to 1,000 ng/kg/min) reduced renal blood flow, presumably due to the angiotensin-like action of this partial agonist. The renal vascular response to SQ 20881 paralleled the endocrine response: An identical threshold dose (30 microgram/kg) increased renal blood flow and reduced plasma angiotensin II concentration, which fell despite a progressive rise of plasma renin activity. Plasma bradykinin concentration did not change in response to SQ 20881, which also blocks kininase II. Both agents also induced a small but consistent and statistically significant reduction in arterial blood pressure, which will be important in assessing the pathogenetic significance of a blood pressure reduction in patients with hypertension. This study indicates that angiotensin mediates the renal vascular response to restriction of salt intake in normal man and provides an approach to assessing the role played by angiotensin in the pathogenesis of functional renal disease.

Color properties of the contrast flash effect: Monoptic vs dichoptic comparisons

Color properties of the contrast flash effect: Monoptic vs dichoptic comparisons

Slow PIII component of the carp electroretinogram.

The slow PIII component of the electroretinogram (ERG) was studied in the isolated, aspartate-treated carp retina. Although the latter is richly populated with cones, slow PIII appeared to reflect almost exclusively the activity of rods; e.g. the spectral sensitivity of the potential paralleled closely the rod pigment curve, its operating range (i.e. the V-log I curve) was limited to 3 log units above absolute threshold, and raising background intensities to photopic levels produced saturation of the increment threshold function without evidence of a cone-mediated segment. Only after bleaching away a significant fraction of the porphyropsin was it possible to unmask a small photopic contribution to slow PIII, as evidenced by a displacement in the action spectrum to longer wavelengths. The spatial distribution of the slow PIII voltage within the retina (Faber, D.S. 1969. Ph.D. Thesis. State University of New York. Buffalo, N.Y.; Witkovsky, P.J. Nelson, and H. Ripps. 1973. J. Gen Physiol. 61:401) and its ability to survive aspartate treatment indicate that this potential arises in the Müller (glial) fiber. Additional support for this conclusion is provided by the slow rise time (several seconds) and long temporal integration (up to 40s) of the response. In many respects the properties of slow PIII resemble those of the c-wave, a pigment epithelial response also subserved by rod activity. On the other hand, the receptoral (fast PIII) and the b-wave components of the ERG behave quite differently. Unlike slow PIII, response saturation could not be induced, since both potentials are subserved by cones when the stimulus conditions exceed the limits of the scotopic range. Receptors appear to govern light adaptation at photopic background levels; both fast PIII and b-wave manifest identical incremental threshold values over this range of intensities. However, under scotopic conditions, the sensitivity of the b-wave is affected by luminous backgrounds too weak to alter fast PIII threshold, indicating a postreceptoral stage of adaptation.

The effects of edge sharpness and exposure duration on detection threshold

Paнee былo пoкaзaнo, хтo нa пopoг oбнapyжeиия тecтoвoгo oбьeктa влияeт хeткocть гpaниц зтoгo oбъeктa. Hacтoящee иccлeдoвaниe пoдтвepждaeт, хтo пopoг oбнapyжeния выщe для тecтoвoгo oбъeктa c иeяcными oхepтaииями, ecли длитeльнocть зкcпoзиции вeликa. Ho былo пoкaзaнo, хтo, ecли вpeмя зкcпoзиции мaлo, тo тecты c хeткими и иeхeткими кpaями имeют oдинaкoвыe пopoги. Paзлихиe в peзyльтaтaх вocпpиятия cтимyлoв пpи кpaткoй и длитeльнoй зкcпoзиции тaкжe знaхитeльнoe. Peзyхьтaты oбcyжцaютcя в paмкaх мoдeли, бaзиpyющeйcя нa тopмoзных взaимoдeйcтвиях.

Recognition of the landolt ring as a function of its orientation.

AbstractUnder identical experimental conditions recognition thresholds have been determined for four orientations of the Landolt Ring (six observes and 2168 presentations). The results show that the differences (preferences) between the visual angle thresholds of the four orientations for each subject and for the four averages, do not differ significantly.

Co-Ordination of Pedal-Disk Detachment in the Sea Anemone Calliactis Parasitica

ABSTRACT Electrical activity has been recorded from the sphincter region of Calliactis parasitica during the behavioural sequence in which the anemone detaches from the substrate and attaches to a Buccinum shell. The ectodermal slow-conduction system (SS1) fires repetitively, the majority of observed pulses occurring in the period prior to detachment (a typical example is 25 SS1 pulses at an average frequency of 1 pulse/ 7 sec.). Shell-tentacle contact is essential for stimulation of SS1 activity. Mechanical stimulation of the column excites the SS1, and 30 stimuli at a frequency of about one shock/5 sec. give pedal disk detachment. Electrical stimulation of the ectoderm excites the SS1 and about 30 stimuli at frequencies between one shock/3 sec. and one shock/9 sec. produce detachment. Detachment and the SS1 have an identical stimulus threshold. It is concluded that detachment is co-ordinated by the SS1.

Anomalous Thresholds in Unitary Theories

Consistency requirements for a Mandelstam representation are shown to imply identical anomalous threshold properties in perturbation theory and any unitary theory without the need to continue in external masses.

Field Dependence of Photoelectric Emission from Molybdenum

Photoelectric emission from a 5-mil single-crystal molybdenum wire was measured at 1000°K with accelerating fields from 0.8 to 142 kv/cm and monochromatic light in the range 238 to 297 mμ. Above 3.6 kv/cm, the data are in good agreement with Fowler-Schottky theory. Apparent threshold energies increase from 4.44 to 4.52 ev with increasing illumination energy, as is expected from emitters of nonuniform work function. Two illumination directions, separated azimuthally by 90°, give identical results. Fowler plots yield identical thresholds of 4.41 ev at room temperature and 1000°K and a Richardson-plot determination of the thermionic emission constants yields eφ**=4.33 ev and A**=38 amp/cm2-deg2. The multiplicity of apparent work functions measured on a single specimen, as well as the marked dissimilarity in the emission constants of molybdenum in sheet and wire form, are explained in terms of patch effect. The theory for the periodic deviation from the photoelectric Schottky effect is extended to describe emitters at elevated temperatures. No evidence for the predicted deviation appears in the experimental photoelectric Schottky data.

Innervation zone and propagation velocity in human muscle.

Summary.The innervation of the brachial biceps was found to be localised to a narrow band in the proximal third of the short head and in the distal third of the long head. Counts of terminal nerve endings showed that 67 per cent of all endings were situated within 10 per cent of the muscle length.The action potential recorded with an electrode placed within the zone of innervation had an abrupt onset, and with two or more electrodes placed in the innervation zone near fibres of the same motor unit, the initial deflection of the action potential was simultaneous within 0.5 msec. This was seen up to electrode distances of 40 mm, along the longitudinal axis of the muscle, and indicates that the end plates of the same unit are scattered over this area. It excludes furthermore that propagation over the thin terminal nerve branches contributes to the action potential duration.When care was taken to place the electrodes distal to the site of innervation and an identical threshold to electrical stimulation had ensured that the electrodes led off from the same muscle fibres, the propagation velocity of the spike of the action potential released by voluntary effort varied over a narrow range. The mean value was 4.7 m/sec. with a maximal variation of 1.3 m/sec. within the same muscle (36.57° C). The small variation in velocity was unexpected in view of the threefold variation in diameter, but could be accounted for by the influence of the external resistance which was shown to be localised mainly in the interspaces between inactive fibres in situ.The propagation velocity during voluntary effort exceeded the velocity of electrically activated fibres by 0.7 m/sec.Differences in action potential duration during voluntary effort can mainly be attributed to the spatial dispersion of the site of innervation for the different fibres of the motor unit.

Propagation velocity in electrically activated muscle fibres in man.

Summary.The arrival time of muscle action potentials evoked by direct local stimulation was determined in 3 to 5 points of the brachial biceps.The stimulus artifact was reduced by stimulating with a bipolar electrode via a doubly screened transformer with the screen around the secondary coil connected to the muscle.It was ascertained that potentials from the same few fibres were picked up at the different electrodes as indicated by an identical threshold for the steep potentials of short duration.The propagation velocity was constant over 10–11 cm muscle length investigated and, therefore, the muscle fibres must pass uninterrupted over this distance.In ten subjects the propagation velocity varied between 3.3 and 5.2 m/sec. and averaged 4.02 ± 0.13 m/sec. (36.5°C.). In different regions of the same muscle it varied up to 15 per cent. There was no significant difference in the velocity over muscles from subjects of different age (3–74) years). The small variation in propagation velocity in spite of large differences in fibre circumference (2.5–3) times, 19 biopsies) suggest the presence of a mechanism which synchronizes the propagation of the impulses from a small group of simultaneously activated fibres.Differences in propagation velocity of the order of magnitude found with electrical stimulation can only account for a minor part of the variation in muscle action potential duration obtained with random leads at voluntary effort.

THE COURSE OF ROD DARK ADAPTATION AS INFLUENCED BY THE INTENSITY AND DURATION OF PRE-ADAPTATION TO LIGHT

An increase in the degree of light adaptation causes a decrease in the slope of the subsequent rod dark adaptation function and a displacement of the function to the right on the time axis. Over a wide range, these changes occur to the same extent whether the increase in the degree of light adaptation is produced by raising the intensity or by prolonging the exposure. Within these limits, the Bunsen-Roscoe reciprocity law applies to the intensity and duration of pre-exposure. Over a still wider range, dark adaptation has the same course following brief exposure to a bright light as it has following prolonged exposure to a dim light, provided the degree of light adaptation is the same in both instances (as indicated by identical initial dark adaptation thresholds).