First Report of Bacterial Blight of Sugar Beet Caused by Pseudomonas syringae pv. aptata in Georgia, USA.

Sugar beet (Beta vulgaris L.) is not currently a commercial crop in Georgia, but experimental plantings as a winter rotational crop are promising in terms of yield and industrial sugar production (T. Brenneman, personal communication). A disease outbreak of suspected bacterial origin occurred in sugar beet plots (experimental lines Beta Seed energy beet 'BTS ENC115,' 'BTS EGC184,' 'BTS EGC195,' and 'BTS 1EN6702') in Tift Co., GA, in December 2012, at ~35% incidence. Foliar symptoms included circular to irregular spots, each with a tan center and dark margin. Ten leaves/experimental line with leaf spot symptoms were collected, and bacterial isolations made on King's B agar medium. After 48 h of incubation, cream-colored, fluorescent yellow, round colonies with smooth margins were isolated. The isolates were each gram negative, oxidase negative, non-pectolytic on potato, arginine dihydrolase negative, produced levan, and gave a hypersensitivity response (HR) on tobacco. These characteristics indicated that the isolates belonged to Pseudomonas syringae van Hall LOPAT group Ia (3). The 16S-23S rRNA (internal transcribed regions) (1) from four foliar isolates (SB-1, SB-2, SB-3, and SB-4), one/experimental line, was amplified, and the resultant PCR products were sequenced and BLAST searched in GenBank. The 16S-23S rRNA sequences matched those of P. syringae pv. syingae (Pss) (KF023189) and P. syringae pv. aptata (Psa) (AY342167.1) with 96 to 98% and 97 to 99% sequence identity, respectively. Also, the percent similarity of the 16S-23S rRNA sequences among the four isolates was >99% (KJ922021 to 24 for SB-1 to SB-4, respectively). The four test isolates also had ≤89 and ≤99% similarity with Pss and Psa, respectively, when tested with BIOLOG (Hayward, CA). In addition, four sugarbeet isolates along with a type strain of Psa (NCPPB 3539) were amplified using a PCR primer pair that detected the presence of the avrPphE gene, an avirulence gene present in Psa but absent in Pss (2). The type strain of Pss (NCPPB 1770) was not amplified using this primer pair. BOX-PCR analysis gave identical banding patterns for the four isolates as that of a type strain of Psa. In two independent experiments, 3-week-old seedlings of the sugar beet cv. Beta EGR099 (n = 10 seedlings/isolate/experiment) were spray-inoculated with a sterilized water suspension of 1 × 108 CFU/ml of each of the isolates. All of the inoculated seedlings developed symptoms (water-soaked lesions that developed into necrotic spots) 10 days after inoculation (DAI) in greenhouse conditions (~30°C and ~80% RH). All of the seedlings inoculated with the type strain of Psa also produced typical bacterial blight symptoms at 10 DAI. In contrast, five control seedlings inoculated with sterilized water remained asymptomatic, and target bacterial colonies were not re-isolated from the leaves of these plants. Bacterial colonies were re-isolated from symptomatic seedlings, and showed similar characteristics based on physiological tests, BIOLOG profile, BOX-PCR analysis, and positive amplification with the avrPphE PCR assay, which indicated that these strains were Psa. To our knowledge, this is the first report of Psa in sugarbeet in Georgia. The fact that a Psa strain was also isolated from a sugar beet seed lot (data not shown) suggested that the pathogen may have been introduced on contaminated seeds. Knowledge of the presence of Psa in the agro-ecosystem of Georgia may encourage scientists to implement integrated management practices for this pathogen. References: (1) C. Guasp et al. Int. J. Syst. Evol. Microbiol. 50:1629, 2000. (2) Y. Inoue and Y. Takikawa. Page 687 in: Presentations 6th Int. Conf. Pseudomonas syringae Pathovars and Related Pathogens, 2003. (3) R. A. Lelliot et al. J. Appl. Bacteriol. 29:470, 1966.

Effect of Simultaneous Water Deficit Stress and Meloidogyne incognita Infection on Cotton Yield and Fiber Quality.

Both water deficit stress and Meloidogyne incognita infection can reduce cotton growth and yield, and drought can affect fiber quality, but the effect of nematodes on fiber quality is not well documented. To determine whether nematode parasitism affects fiber quality and whether the combined effects of nematode and drought stress on yield and quality are additive (independent effects), synergistic, or antagonistic, we conducted a study for 7 yr in a field infested with M. incognita. A split-plot design was used with the main plot factor as one of three irrigation treatments (low [nonirrigated], moderate irrigation, and high irrigation [water-replete]) and the subplot factor as 0 or 56 l/ha 1,3-dichloropropene. We prevented water deficit stress in plots designated as water-replete by supplementing rainfall with irrigation. Plots receiving moderate irrigation received half the water applied to the water-replete treatment. The severity of root galling was greater in nonfumigated plots and in plots receiving the least irrigation, but the amount of irrigation did not influence the effect of fumigation on root galling (no irrigation × fumigation interaction). The weights of lint and seed harvested were reduced in nonfumigated plots and also decreased as the level of irrigation decreased, but fumigation did not influence the effect of irrigation. Nematodes affected fiber quality by increasing micronaire readings but typically had little or no effect on percent lint, fiber length (measured by HVI), uniformity, strength, elongation, length (based on weight or number measured by AFIS), upper quartile length, or short fiber content (based on weight or number). Micronaire also was increased by water deficit stress, but the effects from nematodes and water stress were independent. We conclude that the detrimental effects caused to cotton yield and quality by nematode parasitism and water deficit stress are independent and therefore additive.

Prevention of cigarette smoking-induced platelet aggregate formation by aspirin.

The purpose of this study was to determine whether aspirin could prevent a decrease in the platelet aggregate ratio that we previously found after cigarette smoking. Twenty healthy nonsmokers, who had not taken aspirin in the preceding seven days, smoked two tobacco cigarettes without filters during a 20-minute period. The mean platelet aggregate ratios before and after smoking were 0.91 and 0.80, respectively. When the experiments were repeated 48 hours later and seven to 18 hours after the ingestion of one tablet of aspirin (0.32 g), there was no decrease in the platelet aggregate ratio after smoking. The mean post-smoking platelet aggregate ration after aspirin (0.93) was significantly higher than before aspirin. We conclude that aspirin prevented cigarette smoking-induced platelet aggregate formation.

"Normothermic range" temperature affects myocardial infarct size.

OBJECTIVES: This study tested the hypothesis that small changes in temperature above the hypothermic range may alter myocardial infarct size after acute coronary occlusion-reperfusion. A secondary hypothesis, that a correlation between temperature and infarct size may be independent of an associated change of heart rate, was also evaluated. METHODS: Eighteen pentobarbitone-anaesthetised, open chest rabbits underwent 30 min coronary artery occlusion and 3 h reperfusion at blood temperatures ranging from 35-42 degrees C, achieved and maintained using surface methods (not paced, group NP). In a second group of 11 animals, heart rate was held constant across the same range of temperatures (paced, group P), before and throughout coronary artery occlusion-reperfusion. Infarct sizes were assessed by the tetrazolium method. RESULTS: Target temperature was effectively controlled over the duration of the experimental protocol to within +/- 0.25 degrees C. Area at risk did not vary with temperature. Infarct size, normalised to area at risk, was correlated with temperature in both groups (infarct size = 7.9 x temp-250.0, r = 0.75, p = 0.0003, group NP; infarct size = 11.7 x temp-404.5, r = 0.88, p = 0.0004, group P). There was no significant difference between the slopes of these two lines (p = 0.18), indicating that the positive correlation between infarct size and temperature is not related to changes of heart rate. CONCLUSION: Temperatures in the range of 35-42 degrees C affect myocardial infarct size significantly, independent of heart rate.

Fluorescent vs. radioactive microsphere measurement of regional myocardial blood flow.

OBJECTIVES: This study compared simultaneous regional myocardial blood flow (RMBF) measurements using fluorescent microspheres (FM) and radiolabeled microspheres (RM). The utility of an internal standard during processing was also examined. METHODS: Paired FM and RM were injected into the left atrium of 9 anaesthetised rabbits. RMBF was altered by use of either regional ischaemia or (-)-N6-(2-phenylisopropyl)-adenosine. Radioactivity of blood reference and tissue samples was quantitated using standard methods. Samples were then digested with potassium hydroxide and microspheres recovered by vacuum filtration, with an additional label of FM as the internal standard. FM labels were extracted using Carbitol acetate and quantitated using fluorescence spectroscopy. Agreement between the fluorescent and radioactive methods was assessed using both orthogonal regression and difference-against-mean analyses. RESULTS: Using recovery-uncorrected data, the slope of the orthogonal regression of RM and FM-determined RMBF was not statistically different from 1, but the intercept was statistically different from 0 [-0.03(0.01), P = 0.005] and the mean RMBF by each method differed from one another [1.24(0.08) vs. 1.17(0.08) ml.min-1.g-1, P = 0.0002]. The mean +/- 2 s.d. of the differences of RMBF (RM minus FM) was +0.07 +/- 0.30 ml.min-1.g-1. Although recovery of FM from tissue averaged 97.6(1.2)%, use of the internal standard to correct for losses substantially improved the agreement between RM and FM-determined RMBF: the orthogonal regression slope was not statistically different from 1, the intercept was not statistically different from 0, and the means of the flows were not different. The mean +/- 2 s.d. of the differences of RMBF was -0.01 +/- 0.22 ml.min-1.g-1. The internal standard also improved RMBF estimates from samples with simulated large spillage during processing. CONCLUSION: Fluorescent microspheres are an equivalent alternative to radiolabeled microspheres for the estimation of RMBF. Although the overall recovery of microspheres using this technique was high, use of an internal standard is recommended for correction of random losses.

Extension of myocardial necrosis into normal epicardium followng hypotension during experimental coronary occlusion.

In an effort to determine the manner in which hypotension following experimental coronary occlusion affects myocardial infarct size, the left anterior descending coronary artery was occluded in 22 barbiturate anaesthetised dogs, the chest was closed, and the dogs allowed to recover. Thirty minutes following coronary occlusion, seven dogs were haemorrhaged to a mean arterial pressure of 8.2 +/- 0.3 kPa (62 +/- 2 mmHg) and maintained at this pressure; no intervention was undertaken in control dogs. Twenty-four hours after coronary occlusion infarct size in control and hypotensive animals was determined. The hypotensive group developed larger percentages of necrosis of the left ventricles distal to the site of occlusion than did the control dogs (37.8 +/- 2.3 vs 30.4 +/- 1.4 (P less than 0.01)). Although the percentage of infarcted endocardium did not change significantly, the infarction of epicardium was 45% larger in the hypotensive group (34.4 +/- 3.3% vs 23.7 +/- 1.9%, P less than 0.01). Regional myocardial blood flow (RMBF) was determined by means of radioactive microspheres in 5 dogs following coronary occlusion before and after hypotension. RMBF following haemorrhage fell by an equal proportion, 61.9 +/- 3.3% in normal tissue and 61.2 +/- 2.4% in ischaemic zones. In conclusion, hypotension caused infarct extension into the epicardium, ie, into tissue that does not become necrotic under control conditions.

Anaesthetics alter the magnitude of infarct limitation by ischaemic preconditioning.

OBJECTIVE: The aim was to determine whether three commonly used animal anaesthetics alter the magnitude of infarct limitation achieved with ischaemic preconditioning. METHODS: Eighty four anaesthetised non-preconditioned and preconditioned open chest rabbits underwent a 30 min coronary occlusion followed by 3 h reperfusion. Ischaemic preconditioning was achieved with 5 min coronary occlusion beginning 15 min before the 30 min coronary occlusion. The anaesthetics studied were: pentobarbitone (30 mg.kg-1 intravenously +30-50 mg.kg-1.h-1 intravenously), isoflurane (1.5-2.5% end expiratory), and ketamine/xylazine (cocktail of 67 mg ketamine and 6.7 mg xylazine.ml-1, 1 ml.kg-1 intramuscularly +0.3-1.3 ml.kg-1.h-1 intramuscularly). Area at risk was delineated with ZnCdS particles and infarction assessed with tetrazolium. RESULTS: There were no significant differences in area at risk, heart rate, arterial pressure, and temperature between non-preconditioned and preconditioned hearts. Although infarct size was not significantly different among non-preconditioned hearts for each anaesthetic regimen (p = NS), the magnitude of infarct limitation with preconditioning varied with the anaesthetic employed (decrease in infarct size from control values of 81%, 44%, and 33% for pentobarbitone, isoflurane and ketamine/xylazine, respectively, p = 0.0145 for comparison of the three magnitudes, two factor ANOVA). CONCLUSION: Anaesthetic regimens affect the degree of infarct size limitation seen with ischaemic preconditioning.

Long-term changes in psychological symptomatology associated with HIV serostatus among male injecting drug users.

OBJECTIVE: To examine long-term changes in psychological symptomatology from 6 to 24 months after notification of HIV serostatus among male injecting drug users (IDU). DESIGN: Self-report and interview data were collected at 6-month intervals as part of a longitudinal study monitoring HIV infection and risk-associated behaviors among IDU. SETTING: A community-based methadone-maintenance clinic. PARTICIPANTS: Ninety-seven male IDU (81 HIV-seronegative, 16 HIV-seropositive), including both methadone-maintained and out-of-treatment IDU. MAIN OUTCOME MEASURES: Analyses of long-term changes in psychological symptomatology associated with HIV serostatus among male IDU. RESULTS: Analyses of long-term changes in psychological symptomatology between groups revealed no significantly greater levels of overall psychological distress or significant elevations on subscales of the Symptom Checklist-90 for HIV-seropositive compared with HIV-seronegative male IDU. Also, no significantly higher scores on the Beck Depression Inventory or the psychiatric composite score of the Addiction Severity Index were observed between groups. CONCLUSIONS: Our results suggest that HIV-seropositive male IDU do not express greater levels of psychological symptomatology from 6 to 24 months following notification of seropositivity compared with HIV-seronegative male IDU. Several explanations for these findings are considered. Future work should examine why male IDU do not report significant and long-term elevations in symptoms post-notification of HIV seropositivity. Also, studies of changes in psychological symptomatology as a function of HIV serostatus among female IDU need to be conducted to assess implications for treatment interventions among this underserved population.

Indigo carmine inhibits endothelium-dependent and -independent vasodilation.

To investigate the potential mechanisms by which indigo carmine produces hypertension, we tested the hypothesis that indigo carmine inhibits endothelium-dependent vasodilation and determined the possible site of the inhibition (endothelium versus smooth muscle). Using isolated rat thoracic aortic rings that were precontracted with phenylephrine, we examined vasodilatory responses to acetylcholine, histamine, and Ca2+ ionophore A23187 (in endothelium-intact rings) and sodium nitroprusside and isoproterenol (in endothelium-denuded rings) in the presence and absence of indigo carmine. In addition, the effects of methylene blue on the acetylcholine- and sodium nitroprusside-induced vasodilation were compared with those of indigo carmine. Indigo carmine (10(-6), 10(-5), and 10(-4) mol/L) significantly inhibited receptor- and non-receptor-mediated endothelium-dependent vasorelaxation. Indigo carmine (10(-4) mol/L) also inhibited endothelium-independent vasorelaxation induced by sodium nitroprusside (an activator of vascular smooth muscle soluble guanylyl cyclase), although to a lesser extent than vasodilation from acetylcholine, histamine, and Ca2+ ionophore A23187. In contrast, indigo carmine (10(-4) mol/L) had no effect on the vasodilation induced by isoproterenol (an activator of adenylyl cyclase), indicating that indigo carmine selectively inhibits nitric oxide-mediated responses. Methylene blue, a known inhibitor of soluble guanylyl cyclase, inhibited both acetylcholine- and sodium nitroprusside-induced vasorelaxation. The inhibition was also greater in the acetylcholine- than the sodium nitroprusside-induced vasodilation. These results suggest that indigo carmine, like methylene blue, may inhibit endothelium-dependent relaxation by a mechanism that involves two levels. The major action of indigo carmine appears to be at the level of nitric oxide generation and/or release from the endothelial cell. In addition, indigo carmine appears to inhibit vascular smooth muscle guanylyl cyclase. Thus, indigo carmine may elevate blood pressure by interfering with these nitric oxide-mediated vasodilatory mechanisms.

Dichloroacetate reduces plasma lactate levels but does not reduce infarct size in rabbit myocardium.

Dichloroacetate (DCA), an activator of pyruvate dehydrogenase (PDHC), enhances postischemic mechanical recovery of isolated hearts. It is not known whether this is secondary to reduced infarction or preservation of contractile function in viable cardiomyocytes. This study investigated the effect of DCA on myocardial infarct size. Anesthetized open chest rabbits underwent regional coronary occlusion and reperfusion. DCA (300 mg/kg plus 150 mg/kg 1 h later) was administered intravenously either before occlusion (DCA-O; n = 8) or at reperfusion (DCA-R; n = 7). Control rabbits (n = 8) received saline vehicle. Myocardial PDHC activity was measured after administration of 300 mg/kg i.v. DCA in 10 separate rabbits. DCA reduced plasma lactate levels and increased PDHC activity by 76%, from 2.79 +/- .30 mumol/min.g-1 to 4.92 +/- .44 mumol/min.g-1 (p < .005). However, infarct size in DCA-treated animals was not significantly different from Control (60 +/- 5% DCA-O, 57 +/- 6% DCA-R, 58 +/- 7% Control). We conclude that stimulation of pyruvate dehydrogenase does not limit infarct size.

Mitral insufficiency after pericardiectomy for constrictive pericarditis.

We report the case of a 24-year-old man in whom a clinical syndrome developed while he was on active military duty in Saudi Arabia that was subsequently diagnosed as constrictive pericarditis. Phrenic nerve to phrenic nerve pericardiectomy and posterior pericardial release successfully relieved the ventricular constriction with a resultant increase in the cardiac index from 1.9 to 3.8 L.min-1.m-2. Transesophageal echocardiographic monitoring during the operation disclosed trace mitral regurgitation before median sternotomy. The severity of the regurgitation noticeably increased to the moderate level immediately after pericardial resection. This echocardiographic finding had improved 1 week later, but the regurgitation still was greater than baseline. Mitral valve function had returned to baseline by 4 weeks after the operation. Possible mechanisms of this evolving pattern of perioperative mitral valve dysfunction are discussed.

A new technique for measuring aortic root pressure during infusion of cardioplegic solution.

Aortic root pressure is an important factor in determining the distribution of cardioplegic solutions. Previously, in order to measure this parameter, it was necessary to insert a separate catheter into the aortic root during cardioplegic infusion. An alternative method for measuring aortic root pressure is described that is both simple and accurate and obviates the need for a second aortic root catheter.

Effects of aortic occlusion on regional spinal cord blood flow and somatosensory evoked potentials in sheep.

Somatosensory evoked potentials (SEPs) were recorded continuously during aortic occlusion in sheep, with simultaneous measurement of spinal cord blood flow (SCBF) by radiolabeled microspheres. Aortic occlusion was associated with disappearance of the SEPs in seven of nine sheep in 7.8 +/- 4.1 (SD) minutes. SCBF at the time of initial cross clamping and 30 minutes after the onset of ischemia revealed a severe reduction in white and gray matter flow in the thoracolumbar cord. Release of the aortic clamp was associated with reactive hyperemia in these ischemic regions. In two animals, the SEP persisted during aortic cross clamping. The total SCBF in the thoracic and lumbar regions of these two animals exceeded 20 ml/100 g/min after 30 minutes of ischemia and was significantly greater than the flow recorded in sheep whose evoked response disappeared. The relation between spinal cord ischemia and evoked potential alterations is discussed in detail.

Damage to DNA in bacterioplankton: a model of damage by ultraviolet radiation and its repair as influenced by vertical mixing.

A model of UV-induced DNA damage in oceanic bacterioplankton was developed and tested against previously published and novel measurements of cyclobutane pyrimidine dimers (CPD) in surface layers of the ocean. The model describes the effects of solar irradiance, wind-forced mixing of bacterioplankton and optical properties of the water on net DNA damage in the water column. The biological part includes the induction of CPD by UV radiation and repair of this damage through photoreactivation and excision. The modeled damage is compared with measured variability of CPD in the ocean: diel variation in natural bacterioplankton communities at the surface and in vertical profiles under different wind conditions (net damage as influenced by repair and mixing); in situ incubation of natural assemblages of bacterioplankton (damage and repair, no mixing); and in situ incubation of DNA solutions (no repair, no mixing). The model predictions are generally consistent with the measurements, showing similar patterns with depth, time and wind speed. A sensitivity analysis assesses the effect on net DNA damage of varying ozone thickness, colored dissolved organic matter concentration, chlorophyll concentration, wind speed and mixed layer depth. Ozone thickness and mixed layer depth are the most important factors affecting net DNA damage in the mixed layer. From the model, the total amplification factor (TAF; a relative measure of the increase of damage associated with a decrease in ozone thickness) for net DNA damage in the euphotic zone is 1.7, as compared with 2.1-2.2 for irradiance weighted for damage to DNA at the surface.

Adrenergic activation confers cardioprotection mediated by adenosine, but is not required for ischemic preconditioning.

BACKGROUND: The aim of this study was to determine whether (1) adrenergic activation is cardioprotective, (2) adrenergic cardioprotection occurs via adenosine receptor activation, and (3) ischemic preconditioning requires alpha-adrenergic activation. METHODS: Anesthetised open chest rabbits underwent 30 min coronary occlusion and 3 h reperfusion. Ischemic preconditioning was elicited with 5 min coronary occlusion and 10 min reperfusion. Activation of adrenergic receptors with endogenous norepinephrine was achieved with tyramine (0.28 mg/kg/min intravenously for 5 min). Adenosine receptors were blocked with 8-p-sulfophenyl theophylline (10 mg/kg intravenously), alpha 1-adrenergic receptors were selectively blocked with prazosin (0.1 mg/kg intravenously), and alpha-adrenergic receptors were blocked with phentolamine (4 mg/kg intravenously). RESULTS: Ischemic preconditioning reduced risk-adjusted infarct volume by 79% (P < 0.0005). This protection was attenuated by adenosine receptor blockade. Tyramine infusion resulted in a 1305% change from baseline plasma norepinephrine concentration (P < or = 0.01), and reduced infarct volume by 55% (P = 0.01). Adenosine receptor blockade abolished this protection. Blockade of alpha 1-adrenergic receptors with prazosin failed to abolish ischemic preconditioning (79 versus 89% reduction in infarct volume, without and with prazosin, respectively). Similarly, non-selective blockade of alpha-adrenergic receptors also failed to abolish ischemic preconditioning (79 versus 57% reduction without and with phentolamine, respectively). CONCLUSIONS: We conclude that the cardioprotection of ischemic preconditioning and alpha-adrenergic activation both involve adenosine, but ischemic preconditioning does not require alpha-adrenergic activation.

The effect of sympathectomy on blood flow in bone. Regional distribution and effect over time.

Considerable interest has developed in the role of the autonomic nervous system and its effect on blood flow in bone. Theories pertaining to the long-term physiological effect of sympathectomy on blood flow in bone have been controversial. This study employed the radioactive tracer-microsphere technique to investigate the influence of sympathectomy on regional blood flow in bone over time in dogs. Blood flow was measured in fifteen adult dogs, weighing eighteen to twenty kilograms, at one hour, one day, and one, two, three, four, and six weeks after a transperitoneal sympathectomy from the first to the sixth lumbar level. Absolute control flow values were consistent with those that have been reported previously and had lower standard errors. Blood flow in bone in the femoral regions increased by 24.0 to 41.0 per cent. Greater elevations, of 37.0 to 59.0 per cent, were noted in the tibial sections. The largest increases (58.0 to 67.0 per cent) were seen in the metatarsals and proximal phalanges. All elevated values for blood flow returned to control values by six weeks. The data support the hypothesis that surgical sympathectomy exerts a significant yet transient effect on blood flow in bone. Furthermore, the greater increase distally is the first physiological evidence to support previous anatomical work that concluded that the major site of sympathetic tone lies distally in the lower extremity of the dog.

Pseudarthrosis of the cervical spine after anterior arthrodesis. Treatment by posterior nerve-root decompression, stabilization, and arthrodesis.

Nineteen consecutive patients who had a symptomatic pseudarthrosis after a failed anterior cervical arthrodesis were treated by a posterior nerve-root decompression and arthrodesis. The indications for the operation were radiculopathy in the absence of myelopathy and evidence of a pseudarthrosis on lateral flexion and extension radiographs. The average duration of follow-up was forty-four months (range, twenty-four to fifty-four months). A solid fusion was achieved in all patients, and the radiculopathy was relieved in all but one. The motor weakness that had been present in four patients preoperatively resolved completely.

Application of Nomarski interference contrast microscopy as a thickness monitor in the preparation of transparent, SiC-based, cross-sectional TEM samples.

Reflected light optical microscopy using a Nomarski prism and a differential interference contrast filter have been employed in concert to achieve a technique that provides an accurate color reference for thickness during the dimpling and ion milling of transparent transmission electron microscopy samples of 6H-SiC(000 1) wafers. The samples had thin films of AIN, GaN, and Au deposited on the SiC substrate. A sequence of variously colored primary and secondary interference bands was observed when the SiC was thinner than 20 microm using an optical microscope. The color bands were correlated with the TEM sample thickness as measured via scanning electron microscopy. The interference contrast was used to provide an indication of the dimpling rate, the ion milling rate, and also the most probable location of perforation, which are useful to reduce sample breakage. The application of pressure during the initial cross-sectional preparation reduced the separation of the two halves of the sample sandwich and resulted in increased shielding of the film surface from ion milling damage.

Fusion of the occiput to the upper cervical spine. A review of 37 cases.

This is the first report of a large series of patients undergoing preoperative traction to reduce spinomedullary compression from cranial settling. In all cases, an attempt was made to reduce the malalignment with Gardner-Wells or halo traction before posterior fusion. One patient required an anterior retropharyngeal decompression of the odontoid performed as a one-stage procedure at the time of the posterior operation, and two required subsequent anterior transoral-transpharyngeal resection of the odontoid. From 1974 to 1989, 37 patients underwent posterior occipital cervical arthrodesis. All cases presented with neurologic deficit, and most had signs of brain stem compression, such as L'hermitte's sign or Ondine's curse. The most common cause of basilar impression was rheumatoid arthritis, neoplastic destruction, previously failed C1-C2 fusion, or Down's syndrome. Mean postoperative follow-up was 2 years and 10 months; the patients with less than 2 years' follow-up were followed until successful fusion. Eight of 9 patients with L'hermitte's sign or Ondine's curse and 10 of 12 patients with intractable occipital pain were relieved of their symptoms after reduction and triple-wire stabilization-fusion. Eighteen of 25 patients with long tract signs improved after surgery. Interestingly, 14 (93.3%) of 15 patients with myelopathy improved when successful preoperative reduction of their deformity occurred, whereas only 4 (40%) of 10 patients with fixed basilar impression improved (chi 2 = 8.57, P = .014). Symptoms such as Ondine's curse, L'hermitte's sign, intractable occipital headache, and myelopathy are usually relieved by skeletal traction and posterior fusion without need of an additional transmucosal anterior procedure.(ABSTRACT TRUNCATED AT 250 WORDS)