Effects of Local Melatonin Application on Implant Osseointegration

Purpose: The aim of this study was to assess the effect of local melatonin administration on bone osseointegration around implants in rabbit tibiae. Material and Methods: Ten female, 6‐month‐old New Zealand rabbits were randomly divided into two groups: the experimental group, where five rabbits were treated with local application of melatonin (3 mg) to implant sites when placed into the rabbit tibia, and the control group, those who where without additive materials. Four weeks later, animals were sacrificed; tibiae were dissected from soft tissues and fixed in buffered formaldehyde, and then included in methacrylate. Histological sections were performed to be studied under light microscopy and analyzed morphometrically to evaluate the amount of bone to implant contact (BIC), trabecular area density, and cortical area density. One‐way analysis of variance test was used for statistical evaluation. p < .05 was considered to be significant. Results: Histological evaluation showed more trabecular reaction in the melatonin group. Morphometrical analysis showed a statistically significant increase in trabecular BIC in the melatonin group when compared with the control group (24.61% ± 2.87 vs 13.62% ± 1.44; p < .01). Cortical BIC was decreased in the melatonin group, without statistical significance (71.08 ± 3.63 vs 76.28 ± 2.57; p = 0.31). Trabecular area density was increased significantly in the melatonin group (8.68 ± 1.61 vs 4.02 ± 0.36; p < .05). Cortical area density was decreased significantly in the melatonin group (91.31 ± 1.6 vs 95.7 ± 0.5; p < .05). Conclusion: Within the limitation of this animal study, local melatonin application at the time of implant placement might induce more trabecular bone at implant contact and higher trabecular area density.     

Impact of Chronic Simulated Snoring on Carotid Atherosclerosis in Rabbits

Background and Purpose

Chronic simulated snoring was induced in rabbits to determine the impact of snoring on the development of atherosclerosis.

Methods

The pressure wave of induced snoring at the carotid bifurcation of rabbits was acquired by gently pressing the airway. This wave was then simulated using custom-made mechanical devices. Twelve rabbits were used in this study, seven of which were assigned to the experimental group and the remaining five formed the control group. All of the rabbits were raised on a 1% high-cholesterol diet. Either working or sham devices were positioned at the ventral center of the neck in each rabbit. At the end of a 2-month observation period, all of the rabbits were sacrificed by perfusion fixation, the carotid arteries harvested, and the carotid atherosclerosis histology reviewed.

Results

All of the rabbits survived to the end of the experimental period. Blood sampling revealed the presence of hypercholesterolemia in both groups, with no significant difference between them. The presence and degree of atherosclerosis did not differ significantly between the groups.

Conclusions

The findings of this study show the feasibility of making a chronic simulated snoring rabbit model. However, the causative role of snoring in carotid atherosclerosis was not detected in this animal study.     

液氮冷冻联合Nd:YAG激光对兔耳静脉作用的效果观察

目的:观察液氮冷冻联合Nd:YAG激光照射对兔耳静脉的作用,评估该方法治疗静脉畸形的可行性。方法:将65只白兔随机分为4组。A、B、C为实验组,每组20只;D组为空白对照组,5只。以兔耳背中央静脉为实验模型,A组行液氮冷冻及Nd:YAG激光照射,B组行液氮冷冻,C组行Nd:YAG激光照射,D组不做处理。分别于实验处置后1、3、7、14、21 d对兔耳背中央静脉进行大体、光镜及电镜观察。结果:A组静脉血管内皮细胞、管壁平滑肌及构架结构均有明显损伤破坏,管腔内血栓形成,最终静脉闭锁。B、C组虽有血管内皮细胞损伤及血栓形成,但随后血栓逐渐溶解,血管修复。结论:冷冻联合激光照射对兔耳静脉有较强的损伤作用,具有治疗静脉畸形的可能性。     

Effect of chondroitinase ABC on adhesion and behavior of synovial membrane‐derived mesenchymal stem cells in rabbit partial‐thickness chondral defects

Transplanted cells may have difficulty attaching to the surface of partial‐thickness chondral lesions because of the anti‐adhesive properties of the proteoglycan rich matrix. Therefore, the current study attempts to evaluate the effect of chondroitinase ABC (chABC) on the adhesion and behavior of transplanted synovial membrane‐derived mesenchymal stem cells (SDSCs) in rabbit partial‐thickness chondral defects. In ex vivo adhesion experiments, chABC treatment (0.1 U/ml) was increased in SDSC attachment to the cartilage explants, and significantly diminished by pretreatment with neutralizing antibody against fibronectin. In the in vivo experiments, 1 day and 4 weeks after the chABC treatment (0.1 and 1 U/ml), the immunoreactivity (IR) against CS‐56 (intact chondroitin sulfate antibody) was markedly decreased; however, the IR of 2B6 (stub of the chondroitin 4‐sulfate chain), 3B3 (stub of the chondroitin 6‐sulfate chain), and fibronectin was increased. At 12 weeks, this IR returned to normal except in the high‐dose chABC‐treated group (1 U/ml). Furthermore, the attachment of SDSCs to the chondral defects after chABC treatment was increased at 7 days compared with that in the chondral defects pretreated with saline. However, the tissue repaired by SDSCs was negatively stained for type II collagen at 12 weeks. In conclusion, these results showed that the exposure to fibronectin by chABC treatment enhances the attachment of SDSCs to partial‐thickness chondral defects. However, the tissue regenerated by SDSCs showed lack of hyaline cartilage regeneration. Thus, to understand the fate of transplanted MSCs in cartilage defect is very important for successful cell therapies. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1293–1301, 2013     

Effects of Hypercholesterolemia on Healing of Vascular Grafts

Small-diameter vascular grafts woven from bioresorbable lactide/glycolide copolymers have been successfully interposed into aortas of normal NZW rabbits. The current study examines the histologic and functional reactions to these bioresorbable grafts in severely hypercholesterolemic rabbits, a standard animal model of atherosclerosis. Sixty rabbits were placed on a 2% cholesterol, 6% peanut oil atherogenic diet. Baseline serum cholesterols and triglycerides were measured and repeated at operation 3 months later. Woven polyglactin 910 (PG910) grafts were interposed into infrarenal aortas. Fifty-two rabbits died on the diet or within 3 days of surgery and eight survived operation (normal NZW rabbit operative mortality is < 10%). Cholesterol levels rose from 63 to 1989, p <. 001. Of the eight survivors, five died after 3 weeks, and one died after 21/2 months. Two were sacrificed at 2 and 4 months. Four aortic disruptions with retroperitoneal hematomas, one pseudoaneurysm, and one diffuse aneurysm were observed, greater than in normal rabbits, p <. 001. Inspection revealed severe atherosclerosis. Histologically, 3-week explants showed only small areas of neointima with myofibroblasts and endothelial cells; the outer capsules were infiltrated by lipid-laden macrophages. Graft material in 2-to 4-month explants was replaced by tissue with histologic atherosclerosis. More severe atherosclerosis was observed in native aortas at the perianastomotic areas than the more distant aortic segments. Abundant intracellular lipid was seen also in splenic histiocytes and hepatic cells with evidence of micronodular cirrhosis. Macrophages phagocytizing bioresorbable prostheses may release growth factors mediating the formation of a cellular tissue conduit. Severe hypercholesterolemia may alter monokine release from macrophages resulting in a weakened prosthesis/tissue complex.     

Assessment of the Thrombogenic Effect of Fibrin Sealant Dressing in a Vascular Surgery Model in Rabbits

This study's objective was to investigate the potential thrombogenic effects of thrombin-containing fibrin sealant dressings (FSD) in a vascular repair model. Oval-shaped pieces of the rabbit abdominal aorta and vena cava were excised, the injuries were repaired with FSD, and animals were allowed to recover. Thrombus formation was examined by (1) an infusion of indium-labeled platelets into the rabbits following FSD application and estimation of total number of platelets attached to the wounds at 2, 4, and 6 h later (short-term effect, n = 12); and by (2) morphological and histological examinations of the vessels and dressings on days 1, 3, and 7 after repair operation in another group of rabbits (long-term effect, n = 12). Application of FSD sealed the vascular injures and produced immediate hemostasis that was stable up to 1 week. The highest numbers of platelets (both native and labeled) adhered to the arterial and venous repair sites were 6.5 × 10⁶ and 4.4 × 10⁷, respectively, 6 h after operation. The adhered platelets, however, did not form a visible and clinically significant thrombus. In long-term experiments, no evidence of thrombus was found in the lumens of the repaired vessels or on the dressings, and no microthrombi were detected histologically in other tissues at any time point. Although vena caval injuries showed signs of healing at day 7 postoperatively, the aortic wounds expanded progressively (pseudoaneurysm) and were prone to rupture at later times. Thus, direct exposure of FSD does not cause intravascular thrombosis or thrombotic events in rabbits. The dressing appears to be safe and effective for short-term repair of vascular injuries. It may also allow healing of minor venous defects, but cannot replace conventional surgical techniques (suturing) for permanent repair of arterial damages.     

Model for assessment of mobility of toes and healing of tendons in rabbits

Abstract

Repair of a transected flexor tendon will, despite careful technique and early rehabilitation, usually result in a restricted range of movement. This is mainly because adhesions form between the tendon and the surrounding structures. Our aim was to establish an experimental model in rabbits for future studies on new techniques to reduce the formation of adhesions after zone II repair of flexor tendons. In rabbits' hind paws the metatarsal bones II, IV, and V were removed and the flexor tendon was freed to the metatarsophalangeal (MTP) joint. The digits were secured in a specifically-designed biomechanical testing device comprising a servo-hydraulic actuator that was designed to apply controlled force or displacement. The tests were videotaped with a digital force-monitor behind the tested digit. Paper printouts from the recordings were obtained for 0, 0.5, 1, 2, 3, 4, and 5 Newton (N) and metatarsophalangeal, proximal interphalangeal, and distal interphalangeal, angles and distances between metatarsophalangeal joints and claws were measured. The tensile strength of the tendon was evaluated by a load-to-failure test. The continuous data obtained from the experiments were used to calculate functional stiffness at the selected forces. The model allows for unique continuous recordings of mobility of toes, thereby indirectly quantifying the presence of adhesions and the assessment of tensile strength. The data are reproducible, and there is little variation between the digits tested. The model is primarily intended to compare data among treated and non-treated digits of methods to limit the formation of adhesions after tendons have been repaired.     

Subarachnoid blood infusion versus raised intracranial pressure: Effects on the amino acid pattern in the extracellular fluid of the rabbit hippocampus

Abstract

In order to evaluate the role of a hemorrhage versus that of a transient increase in intracranial pressure in subarachnoid hemorrhage, the two components were induced separately in rabbits. Extracellular glutamate, sampled from the hippocampus with microdialysis, was used to evaluate the degree of CNS tissue damage. In four rabbits, autologous arterial blood was infused in the cisterna magna in a volume that would not affect the intracranial pressure. The other group of animals was infused with saline to elevate the intracranial pressure from 10 to > 100 mmHg. The increase of intracranial pressure per se did not induce significant changes in extracellular glutamate. However, 20-60 min after infusion of blood, a significant glutamate increase was recorded. Furthermore, aspartate, alanine, glycine and serine were also raised. The results indicate that blood in the subarachnoid space damages the brain primarily by inducing ischemia. Furthermore, the parameters employed gave no indication that an increase in intracranial pressure had a deleterious effect on CNS tissue. [Neurol Res 1999; 21: 404-408]     

Comparison of spontaneously released endothelium-derived relaxing factor in cerebral and extracerebral arteries in rabbits

Abstract

To investigate regional differences in spontaneously released endothelium-derived relaxing factor (EDRF), a bioassay of spontaneously released EDRF was performed on rabbit basilar, ear; common carotid and thoracic arteries using an isometric tension measurement technique and a measurement of cyclic guanosine monophosphate (cCMP) content in the vascular smooth muscle. The amount of spontaneously released EDRF was higher in the basilar artery than in any other arteries examined (p < 0.01). The levels of cCMP were 57.3 ± 4.4 (n = 7) in basilar, 26.5±4.3 (n = 6) in ear; 24.5±2.3 (n = 11) in common carotidand 30.3 ±3.8 pmol/g tissue (n = 8) in thoracic artery with endothelium, while endothelium-denuded arteries showed 24.2 ± 6.6 (n = 5), 17.5 ± 5.1 (n = 6), 20.1 ± 2.9 (n = 7) and 14.4 ± 2.3 pmol/g tissue (n = 8) in the same order. Haemoglobin (10~5 m, incubated with the artery for 5 min, significantly reduced the level of cGMP in all vessels with endothelium: 35.3±4.4 (basilar), 76.0 + 2.7 (ear), 14.0±1.9 (common carotid) and 8.7 ±1.2 pmol/g tissue (thoracic artery). Since endothelium-dependent relaxation is associated with a rise in the cGMP content of the smooth muscle cell, the data of cGMP measurement in addition to the bioassay of spontaneously released EDRF in tension measurement suggests that the spontaneous release of EDRF is much greater in the basilar artery than in extracerebral arteries. It is concluded that the intensity of the spontaneously released EDRF is relatively higher in the intracerebral artery than in the extracerebral artery. [Neurol Res 1993; 15: 327-332]