Visible Limb Research Articles

Enhanced Expression of Limb Malformations and Axial Skeleton Alterations in legless Mutants by Transplacental Exposure to Retinoic Acid

This manuscript reports on the limb malformations and axial skeleton alterations found in legless fetuses and their heterozygote and wild-type littermates transplacentally exposed to all-trans-retinoic acid via a single intraperitoneal injection on Day 7, 8, 9, 9.5, 10, 10.5, or 11 of gestation. The most surprising aspect of the results was the temporal sensitivity of the legless mouse limb to exogenous retinoic acid. On Day 11, when both fore- and hindlimbs of nonmutant embryos can be made abnormal by retinoic acid and other teratogens, retinoic acid did not increase the frequency or severity of legless hindlimb defects and forelimb malformations were only slightly enhanced. On the other hand, retinoic acid administration on Day 7 exacerbated forelimb malformations in legless fetuses at a time when visible emergence of the affected structure is still 48 hr away. Heterozygote and wild-type fetuses had no limb malformations at this time point. A similar phenomenon was observed with hindlimb malformations after retinoic acid exposure on Day 8 except for a few mild limb malformations in heterozygotes at a high dose of retinoic acid. This early hypersensitivity of fore- and hindlimbs was followed by a period of reduced sensitivity (Day 8 forelimb; Day 9 hindlimb) when even very high doses (50 mg/kg) induced minimal changes in the typical legless malformation pattern. Subsequent]y, at the time of visible limb bud emergence (Day 9 forelimbs; Day 10 hindlimbs), sensitivity to exogenous retinoic acid was again detected. Surprisingly, the altered malformation patterns induced by retinoic acid in lgl mutants were nearly identical to those from earlier, preemergence exposure. A number of axial skeleton alterations were induced in legless fetuses by retinoic acid, especially after exposure on Days 7, 8, or 9. Posterior truncations were particularly noteworthy, showing a graded response in which frequency and severity of truncation were worst in lgl/lgl fetuses; heterozygotes gave an intermediate response, and wild-type fetuses were least affected. This exacerbation of the legless phenotype by exogenous retinoic acid coupled with the similarity between legless and retinoid malformations suggest that the legless mutation has altered endogenous retinoid homeostasis or a downstream retinoid-responsive gene.

850 μm Observations of the 11 July 1991 Total Solar Eclipse

We present observations of the 11 July 1991 total solar eclipse made from the Caltech Submillimeter Observatory. The 850 μm limb is extended 3380±140 km above the visible limb, and there is a 10% brightening at the extreme limb. The measured limb height agrees with previous work at shorter and longer wavelengths. The run of limb heights with wavelength is well fit by a single electron density scale height. We argue that there is no need to invoke spicule geometry to explain the observations.

Near IR Observations of the 11 July 1991 Total Solar Eclipse from Mauna Kea, Hawaii

Near IR total eclipse measurements have provided clear evidence during both 2nd and 3rd contacts for a limb extension of about 125 km for wavelengths in the range containing the CO fundamental vibration-rotation bands between 4.3 and 5.5 μm, when compared to the limb at nearby shorter wavelengths. This is interpreted as a “flash” spectrum in the CO lines, with the above extension representing the outer level of the CO emission layer. This height can be compared to the τCO = 1.0 level incorporated into recent representative atmospheric models (Ayres and Wiedemann, 1989) which is 90 km above the visible limb for a semi-empirical “hot chromosphere” model (Avrett, 1985) and 220 km for a “cool” radiative equilibrium model based upon work by Anderson (1989).

Pluto's Radius and Atmosphere: Results from the Entire 9 June 1988 Occultation Data Set

We have analyzed all photometric observations of the 9 June 1988 occultation of the star P8 by Pluto in order to derive the radius of Pluto and certain parameters of its atmosphere. Our analysis is based on a "haze" model; but where relevant, we also discuss the thermal gradient model. With either model, the occultation observations yield a diameter for the limb of Pluto that is significantly larger than that found from mutual event observations by D. J. Tholen and M. W. Buie (1989, Bull. Am. Astron. Soc. 21, 981-982), but is in good agreement with the value from E. F. Young (1992, Ph.D. thesis, Massachusetts Institute of Technology). For a clear atmosphere (i.e., the thermal gradient model), we find the radius of the solid surface of Pluto and, obviously, also of the limb, to be 1195 ± 5 km. If the haze model is correct, the solid surface of the planet falls below 1180 ± 5 km, but the radius of the visible limb would be in the haze layer between 1185 and 1200 km. The degree to which the structure of Pluto's atmosphere is globally homogeneous is also discussed.

Submillimeter observations of the 1991 July 11 total solar eclipse

We present observations of the 1991 July 11 total solar eclipse at 850 μm made with the Caltech Submillimeter Observatory (CSO) on Mauna Kea. We find that the 850 μm limb is 3380±140 km above the visible limb. We also find that there is a 10% limb brightening in the outer 7″ of the solar disk, and we measure a central brightness temperature of 6400±700 K. These results require that the upper chromosphere not be in hydrostatic equilibrium, with a higher electron density than is predicted by the standard (VAL) model

High-temperature flares observed in broadband soft X-rays

Broadband soft solar X-rays monitored by the GOES satellites have been used to detect high-temperature flares (> 25 MK). The data suggest that there are two general categories of high-temperature flares: those that are intrinsically hot and recur repeatedly in particular active regions and those that show enhanced temperatures because of their proximity to the solar limb. Intrinsically hot flares associate with gamma-ray flares and impulsive hard X-ray flares. Hot flares show a small incidence with gradual hard X-ray flares, but those cases are either extremely intense flares or limb flares. The apparently hot flares occur near the visible limb, which suggests the strong thermal stratification of flare plasmas as demonstrated by over-the-limb events; even on the visible disk near the limb, the lower, cooler plasmas are somehow partially occulted.

Submillimeter solar limb profiles determined from observations of the total solar eclipse of 1988 March 18

Observations were made of the extreme solar limb in six far-infrared wavelength bands ranging from 30 to 670 micron using the Kuiper Airborne Observatory during the total eclipse of the sun on 1988 March 18. By observations of the occultation of the solar limb by the moon, it was possible to obtain a spatial resolution of 0.5 arcsec normal to the limb. The solar limb was found to be extended with respect to the visible limb at all of these wavelengths, with the extension increasing with wavelength. Limb brightening was observed to increase slightly with increasing wavelength, and no sign of a sharp emission spike at the extreme limb was found at any of these wavelengths. The observations can be well fitted by a chromospheric model incorporating cool dense spicules in the lower chromosphere.

A model for nonexercising hindlimb muscles in exercising animals

Nonexercising muscles appear to be metabolically active during exercise. Animal models for this purpose have not been established. However, we have been able to teach animals to run on their forelimbs while their hindlimbs are suspended above the treadmill with no visible limb movement. To document that indeed this mode of exercise does not provoke additional muscle activity, we have compared the levels of neural activation of the soleus and plantaris muscles using a computer analysis of the electromyographic interference pattern, recorded from bipolar fine wire electrodes implanted across each muscle. Via computer analyses of the electromyographic interference patterns the frequencies and amplitudes of motor unit action potentials were obtained. The data were sampled during 20 s of every minute of observation. Comparisons were made in four conditions: (i) resting on the treadmill while bearing weight on the hindlimbs (normal rest), (ii) running on the treadmill (15 m/min, 8% grade) on all four limbs (normal exercise), (iii) resting while the hindlimbs were suspended in a harness above the treadmill (suspended rest), and (iv) exercising with the forelimbs (15 m/min, 8% grade) while the hindlimbs were suspended above the treadmill (suspended exercise). All four experimental conditions were carried out for 90 min each and were performed by each animal. The results clearly show that muscle activities (frequencies and amplitudes), when the hindlimbs are suspended above the treadmill, at rest or during exercise, are lower than the activities in these same muscles when the animals are at rest, supporting only their body weight. Activities in the same muscles during exercise were from 300 to 2000% greater than during hindlimb suspension.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropathies with prolonged conduction block, single and grouped fasciculations, localized limb myokymia

Fourteen patients presented prolonged conduction block (CB) related to hereditary neuropathy with liability to pressure palsies (n = 7), neuropathy with proximal multifocal persistent CB (n = 2), radiation plexopathy (n = 3) and chronic acquired polyneuropathy (n = 2). All subjects presented both single and grouped fasciculation potentials that resulted in visible limb myokymia in 9 patients. This ectopic activity was recorded only in muscles affected by the CB, was more important in severe or complete CB, and often arose from terminal branches of blocked axons. These fasciculations and grouped fasciculations therefore appear to be causally related to the CB. In the presence of localized myokymia, a prolonged CB should be suspected.

Aerosol optical depth and planetary albedo in the visible from the Solar Mesosphere Explorer

The Solar Mesosphere Explorer (SME) satellite has observed the visible sunlight scattered at the earth's limb since early 1982. By using a radiative transfer model including multiple scattering and albedo effects, observations at 20°N latitude have been interpreted in terms of aerosol optical depth. The ratio of aerosol extinction to Rayleigh extinction at 431.8 nm shows a large increase after the eruption of El Chichon. A maximum ratio of 5 at 36 km and larger than 11 at 30 km occurs in the summer of 1982 followed by a decrease through 1983 and 1984. Aspects of the aerosol time evolution appear to be consistent with other observations and model predictions. Quantitative differences exist between inferred SME and lidar extinction coefficients, possibly due to the different wavelengths of the measurements and to the different scattering phase functions used in the two analyses. It is also shown that visible limb radiances provide information on the planetary albedo, which shows an increase from the equator to the poles with a maximum in the winter hemisphere and a minimum in the summer hemisphere.

Myokymia induced by timber rattlesnake venom: [formula omitted], J.F. Brick, K. Apelgren and J.E. Riggs (Dept. of Neurology, West Virginia University Medical Center, Morgantown, WV 26506, U.S.A.)

Fourteen patients presented prolonged conduction block (CB) related to hereditary neuropathy with liability to pressure palsies (n = 7), neuropathy with proximal multifocal persistent CB (n = 2), radiation plexopathy (n = 3) and chronic acquired polyneuropathy (n = 2). All subjects presented both single and grouped fasciculation potentials that resulted in visible limb myokymia in 9 patients. This ectopic activity was recorded only in muscles affected by the CB, was more important in severe or complete CB, and often arose from terminal branches of blocked axons. These fasciculations and grouped fasciculations therefore appear to be causally related to the CB. In the presence of localized myokymia, a prolonged CB should be suspected.

Extreme limb profiles of the sun at far-infrared and submillimeter wavelengths

Thirty, 50, 100, and 200 microns solar limb intensity profiles determined with arcsecond resolution from airborne observations of the occultation of the solar limb during the total eclipse of July 31, 1981, are presented. Two points of particular importance emerge: (1) the longer-wavelength (100 and 200 micron) limbs are significantly brighter than disk center. At 200 microns the extreme limb is about 1.22 times the brightness of disk center. This is consistent with the 6000 K temperature-plateau structure of the model chromospheres of Vernazza, Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45, 635); and (2) the longer wavelength limbs are extended significantly further above the visible limb than Vernazza, Avrett, and Loeser predict. These results provide a strong basis for modeling of the solar chromosphere free from the assumption of gravitational-hydrostatic equilibrium.

El Chichon and “mystery cloud” aerosols between 30 and 55 km: Global observations from the SME visible spectrometer

Visible limb radiances measured by the Solar Mesophere Explorer (SME) are used to obtain volume scattering ratios for aerosol loading in the 30‐55 km altitude range of the stratosphere. Global maps of these ratios are presented for the period January, 1982 to August, 1984. Significant aerosol scattering from the "mystery cloud" and El Chichon aerosol layers are found above 30 km. A timescale of approximately 2 months between the appearance of the aerosol at 30.5 km and at 37.5 km is consistent with vertical transport of aerosol or vapor by eddy diffusion above 30 km. An anticorrelation exists between aerosol scattering and stratospheric temperatures. Periods of lower stratospheric temperatures may account for the formation of aerosol between 40 and 55 km altitude.

Submillimeter extensions of the solar limb determined from observations of the total eclipse of 1981 July 31

First results are presented of observations of a lunar occultation of the solar limb made from the Kuiper Airborne Observatory in the 30 micrometr, 50 micrometer, 100 micrometer, and 200 micrometer continuum during the total solar eclipse of 1981 July 31. The solar limb was extended at the longer wavelengths up to 1000 km higher than predicted from smooth plane-parallel chromospheric models. Results at both second and third contact show the infrared limb extensions to be approximately 0.8, 15, 2.5 and 3.0 above the visible limb in the observed bands, respectively. A possible interpretation proposes chromospheric fine structure inhomogeneities of greater density than presently incorporated in models of the middle chromosphere.

Quiet Sun observations of the Ali autoionization lines ?1932 and ?1936

We present quiet Sun observations obtained during a rocket flight of the Al i autoionization lines λ1932 and λ1936 at solar pointings ranging from μ = 0.73 out to the visible limb. Absolute intensities are estimated to be accurate to approximately ±20%. These lines progressively weaken with decreasing μ but never go into emission before finally disappearing with the continuum just beyond the visible solar limb. The observations are compared with LTE line profiles computed through the quiet Sun atmosphere of Vernazza et al. (1976). We discuss several areas of disagreement between the synthetic and observed profiles.

Effects of ecdysterone, inokosterone and eyestalk ablation on limb regeneration in the fiddler crab, Uca pugilator

AbstractBilateral ablation of eyestalks or injection of either ecdysterone or inokosterone (two 25‐μg doses or five 10‐μg doses into crabs weighing on an average 1.5 g) caused precocious proecdysis and ecdysis in the fiddler crab, Uca pugilator. On a weight basis ecdysterone was more effective than inokosterone in exerting the effects. Whether the accelerated proecdysis was accompanied by regenerative limb growth depended on the degree of limb bud development at the time of treatment with ecdysones. Ecdysterone and inokosterone blocked the initiation of basal limb growth when administered as two 25‐μg doses into crabs exhibiting scar tissue without any visible limb bud. When injected into crabs with limb buds in various stages of basal limb growth exogenous ecdysones accelerated basal limb growth and led to proecdysial limb growth. The degree of acceleration of limb bud growth noticed within three to six days after injection of ecdysones into crabs with limb buds in early stages of basal limb growth was greater than that resulting from eyestalk ablation. In crabs with limb buds in later stages of basal growth, the degree of acceleration of limb bud growth evoked by exogenous ecdysones was similar to that resulting from eyestalk ablation. The final sizes of the limb buds preceding ecdysis in eyestalkless crabs and crabs injected with ecdysones depended on the proecdysial duration available for regeneration.The rate of proecdysial limb growth has been known to vary with the speed at which the crabs complete the proecdysial stages of the molt cycle. This study shows that the time required for the initiation and completion of the basal limb growth also varies depending on how soon the intact and eyestalkless crabs approach proecdysis and ecdysis.

Further Observations of the Structure of the Chromosphere-Corona Transition Region from Limb and Disk Intensities

Further observations of limb and disk intensity ratios of emission lines in the EUV solar spectrum were obtained on a Skylark rocket flight on 5 August 1971. Analysis of the data has shown that the observations support the existence of a steep rise in temperature in the transition region between Te ~ 6 × 104 K and 3 × 105 K. The average absolute height of the transition region above the visible limb has been measured with a greater accuracy than previously possible and is 1700 km ± 700 km. An independent method using arc-length measurements of spectrum lines gives an absolute height of 2100 km ± 850 km. Emission from lines which are optically thick in spicules is observed to extend to heights of 10000 km above the transition region. The observed decrease of Fen emission with height is consistent with current spicule statistics.

Intensity distribution in the Lyman-α line at the solar limb

The distribution of the solar intensity in the Lyman α line has been measured close to the visible limb. It is compared to a computation including LTE departures (as evaluated by Y. Cuny). As far as the profile of the line and the intensity (integrated over the line) are concerned, the interspicular model of Coates is the only one which seems to agree with the observations.