Signs of the principle body axes prior to primitive streak formation in the rabbit embryo

An early common element during anterior-posterior axis formation amongst amniotes is the primitive streak, running longitudinally in the two-layered embryonic disc. In mammals the primordium of this transient structure is the first definite morphological sign of the anterior-posterior axis, while in avian embryos the axis is visible and apparently defined earlier. Here we scrutinize suggestions that in mammals also there are earlier signs of axis formation by using correlative low and high-resolution light microscopy on tissues from rabbit embryos at 6.3 and 6.5 days post-conception, i.e. immediately before and after primitive streak formation. A series of semithin sections were cut from resin-embedded embryonic discs that had been photographed previously at low power. In embryos at 6.5-days post-conception the primitive streak is as long as up to half the diameter of the embryonic disc, extending anteriorly from a thickening, here called the posterior node, at the posterior margin, which contains the first mesoderm cells ingressing from the epiblast. On both sides of the primitive streak there is a triangular area that appears light in surface views of fixed embryos and correlates with stretches of low-columnar simple epithelium in an otherwise high-columnar pseudostratified epiblast. Within the anterior margin, which has a sharper contour than the rest of the circumference of the embryonic disc, there is a narrow, crescent-shaped dark zone caused by increased cellular height and number in both epiblast and hypoblast. These characteristics of the anterior margin are also found at 6.3 days post-conception, at which stage there is no sign of a primitive streak or a posterior node. The posterior margin, in contrast, is ill-defined in these earlier embryos, or there is a light crescent within the posterior margin, which has the same histological characteristics as the bilateral posterior triangular areas of primitive streak stages. Because the anterior differentiation occurs prior to primitive streak formation and is a sign of both the anterior-posterior and the transverse axes of the embryonic disc, and because some of its histological characteristics are found in primate and human embryos, we propose to name this structure the anterior marginal crescent and to add it to the list of transient structures that gradually establish the principal body axes in mammals. The anterior manifestation of body axes in mammals is thus essentially different from axis development in the avian embryo, where differentiation of these axes is first manifest at the posterior margin.Supported by the Deutsche Forschungsgemeinschaft (Vi 151/1-1); part of the results were presented at the First Joint Meeting of the Anatomical Society of Great Britain and Ireland and of the Anatomische Gesellschaft, Southampton, December 1994, and will be published in abstract form (J Anat, in press)     

Hard tissue laser ablation mechanisms

The aim of this work is the experimental and theoretical investigation of the influence of variable laser parameters (wavelength, fluence, pulse repetition rate) and of the optical and thermophysical properties of bone tissue (absorption coefficient, tissue inhomogeneity) as well as of the sample thickness on ablation thresholds and ablation rate. Ablation and perforation experiments were conducted using a semiconductively pre-ionized transverse excitation atmospheric pressure (TEA) carbon dioxide (CO₂) laser (10.6m and a sliding discharge TEA [hydrogen fluoride (HF)] laser (2.9m). The experimental data are discussed with respect to the following ablation mechanisms: thermal melting and vaporization process, pressure oscillation of gases released by the thermal decomposition of collagen and/or apatite, stresses due to the expansion of superheated water.     

Holmium: YAG laser surgery in obliterated cochleas: an experimental study in human cadaver temporal bones

A pulsed holmium: YAG laser ( = 2120 nm) was used to reopen the basal turn of artificially obliterated human cochleas in freshly dissected cadavers. This allowed intracochlear insertion of the stimulation electrode of a cochlear implant under simulated surgical conditions. Laser energy was transmitted through a 400-m nylon fiber via the opened facial recess directly to the round window niche. At an energy level of 500 mJ per 2.5 s pulse, a repetition rate of 2 Hz, and an exposure time of 20–30 s, the photo-ablative mechanism of laser-bone interaction led to a 8–10 mm recanalization of the basal turn of the cochlea without damaging surrounding structures. The artificial bony occlusion and the recanalized basal turn of the cochlea were visualized by means of computed tomography and studied under light microscopy, using a histologic thin-section technique.Presented at the XVth World Congress of Otorhinolaryngology, Istanbul, Turkey, 23 June 1993     

上皮植入性虹膜囊肿的激光治疗

目的：观察Ｎｄ：ＹＡＧ激光治疗上皮植入性虹膜囊肿的疗效。方法：治疗前详细了解囊肿与周围组织的关系,首先激穿囊肿前壁,使腔内液体引流,然后降低能量,照射囊肿后壁及周围组织,以尽可能破坏上皮细胞,减少复发。激光治疗单脉冲能量为０．４ＭＪ,每次治疗总量为２０～３５ＭＪ。结果：所有治疗眼的视力均有不同程度提高。经术后６个月～１年的随访观察,未见明显复发。结论：激光治疗上皮植入性虹膜囊肿,既可破坏囊壁的上皮细胞,又可避免和减少囊肿邻近组织的损伤及反应,以尽可能多地保留和恢复有效视功能,以避免患者因再次手术所带来的痛苦,疗效满意     

微血管舒张功能障碍及体外反搏的改善作用

目的：通过测定微血管血流灌注来反映微血管的舒张功能,同时观察体外反搏治疗改善冠心病患者微血管舒张功能障碍的效果。方法：应用激光多普勒血流量计（ＬＤＦ） ,测量５８ 个被观察者的前臂皮肤在反应性充血前后微血管血流灌注增加比值,评价血流介导的微血管舒张功能。结果：冠心病组、高胆固醇血症组及吸烟组微血管舒张功能明显低于对照组,比值分别为１．８３±０．３７、２．６３±０．５１、３．１９ ±０．５６ 比３．５６±０．３６ ;Ｐ分别＜ ０．０１,＜０．０１,＜ ０．０５。冠心病组反搏治疗前后比,其微血管的舒张功能明显提高,比值为１．８３±０．３７ 比２．５４±０．４３; Ｐ＜０．０１。结论：ＬＤＦ可检测冠心病患者明显的微血管舒张功能障碍及高胆固醇血症者和吸烟者微血管功能的异常;体外反搏治疗可改善冠心病患者的微血管舒张功能。     

颈椎椎间盘与后部结构断层解剖及影像学研究

选用43具青年尸体,蛛网膜下腔注入铸型造影剂,低温冷冻,以椎间盘为中心制作断层标本,同时选取40例正常健康人进行超声、CT及MR扫描图像分析.发现同组中不同椎间盘水平测量数据的大小不同;解剖学与影像学各测量结果进行比较无显著性差异.     

准分子激光PRK术后的临床分析

目的 对１１１眼屈光范围球镜在－３．００￣－１７．００Ｄ及柱镜在－０．５０Ｄ￣－４．５０Ｄ范围的患者进行了ＰＲＫ术后的分析。方法 采用美国ＶＩＳＸ２０／２０Ｂ准分子激光系统的最新软件包进行角膜切削,并行术前后的主客观验光及角膜透明度检查。结果与结论 准分子激光ＰＲＫ术是目前理想的屈光手术之一,特别对于中低度近视尤为适合,对高度近视则其预见性稳定性较差,并发症的发生并未成为影响术后效果的主要因素。     

Semiconductor diode laser transscleral cyclophotocoagulation versus filtering surgery with Mitomycin-C

Both filtering surgery with Mitomycin-C and diode laser cyclophotocoagulation have proved to be effective alternatives in cases of glaucoma with poor surgical prognosis. The right eyes of 40 pigmented rabbits were randomly divided into 2 groups: Mitomycin-C group underwent filtering surgery with application of 0.4 mg/ml of Mitomycin-C whereas the diode laser (DL) group received 15 applications of 1.8 J (1800 mW. 1000 ms) distributed in 270°. Mean IOP showed statistical differences in two periods between days 3–13 and 45–60 — Mann-Whitney U test — with a higher IOP lowering in the DL group. The comparison of IOP survival curves (Log-Rank test) was not significant p = 0.070809. Ocular hypertension, hyphema and inflammatory signs were higher in the DL group, both in short and long term, but in terms of statistical significance only ocular hypertension showed differences p = 0.00011717 - Fisher exact test. Microscopic examination revealed patent sclerostomies in 60% of the MMC group eyes with different grades of fibroblastic proliferation. In the DL group we observed necrosis of the sclieral stroma and of the pigmented and unpigmented ciliary epithelium, with signs of thermal coagulation of the ciliary stroma and of the stromal vasculature. We must point out that the treatment with laser has proved to be more effective although both treatments showed very acceptable IOP lowering until 2 months after the surgery.     

Analysis of orthograde fast axonal transport and nonaxonal transport along the optic pathway of albino rabbits during increased and decreased intraocular pressure

Orthograde fast axonal and nonaxonal transport through the optic disc was studied quantitatively and autoradiographically in albino rabbits during elevated (30 or 50 mmHg), normal (13–15 mmHg) and decreased (0–4 mmHg) intraocular pressure (IOP). In cases of intraocular hypertension up to 50 mmHg, autoradiographic findings of a disturbed orthograde fast axonal transport were seen in the optic disc within 3 hr. The blockage was relatively mild and uniform, and was distributed adjacent to the extension line of sclera. Despite this histological evidence of blockage, a quantitative analysis showed no statistically significant decrease in axonally transferred radioactivity within 3 hr. Decrease in the transferred material was evident at 6 hr, and the extent of decrease was mild (ca. 20% at the most prominent portion). In cases of moderate intraocular hypertension (30 mmHg) for 6 hr, a quantitative analysis showed no decrease in axonal transport. After 3–6 hr of intraocular hypotension (0–4 mmHg), papilledema did not develop and autoradiographically there was no accumulatjon of axonal components. Axonally transferred material remained quantitatively at the same level as in the control animals. Nonaxonal transport along the optic nerve was doubly enhanced in cases of intraocular hypertension up to 50 mmHg, and was reduced to one thrid at level of 0–4 mmHg. Filtration of intraocular fluid through the optic disc appears to be the largest component of the nonoxonal transport.     

Induction of vascular haemostasis by Nd:YAG laser light in melanin-rich and melanin-free tissue

Haemostasis was effected in vessels of melanin-rich (MR: choroid) and melanin-free (MF: mesentery) rabbit tissue irradiated with a cw-Nd: YAG laser. The following parameters were employed: - pulse duration: 200 ms (MR) and 100ms (MF); focal spot diameter: 200 m (MR) and 80 m (MF); pulse energies: 100–250 mJ (MR) and 0.5-1J (MF); irradiances: 1.6–4.0kWcm^–2 (MR) and 1–2 × 10²kWcm² (MF). In melanin-rich tissue, laser energy is absorbed principally by melanin granules contained within the stromal melanocytes. The heat generated in these structures radiates into the surrounding tissue where it is dissipated. The damage thus incurred by the endothelium of blood vessels encompassed within this field triggers the haemostatic mechanism whereby blood flow is arrested. This effect is realized by the formation of an occluding plug of platelets, which is stabilized by the deposition of fibrin, particularly in capillaries, and to a lesser degree in larger vessels of the vascular lamina. In melanin-free tissue, haemoglobin serves as the primary site of energy absorption, which is thus shifted from the stroma to the vessel lumen. Irradiation of vessels in such tissue leads to thermocoagulation of plasma proteins and consequent stasis of blood flow.