Chronic stress, but not hypercaloric diet, impairs vascular function in rats

The aim of this study was to evaluate vascular and metabolic effects of chronic mild unpredictable stress (CMS) and hypercaloric diet (HD) without carbohydrate supplementation in rats. Male Sprague-Dawley rats were randomly assigned to four groups: Control, HD, CMS, and HD plus CMS. CMS consisted of the application of different stressors for 3 weeks. The rats were killed 15 days after CMS exposure. The HD group presented higher plasma lipid concentrations, without changes in fasting glucose concentration, glucose tolerance test, and vascular function and morphology, in comparison with the control group. Stressed rats presented higher fasting blood concentration of insulin, higher homeostasis model assessment index values and area under the curve in an oral glucose tolerance test, in comparison with non-stressed rats. CMS increased the plasma concentrations of corticosterone and lipids, and the atherogenic index values, without change in high-density lipoprotein level. CMS increased intima-media thickness and induced endothelium-dependent supersensitivity to phenylephrine, and lowered the relaxation response to acetylcholine in the thoracic aorta isolated from rats fed with control or HD, in comparison with non-stressed groups. CMS effects were independent of diet. In non-stressed rats, the HD induced dyslipidemia, but did not change glucose metabolism, vascular function, or morphology. The data from this study indicate that CMS promotes a set of events which together can contribute to impair function of the thoracic aorta.

Proatherosclerotic effects of chronic stress in male rats: altered phenylephrine sensitivity and nitric oxide synthase activity of aorta and circulating lipids

The aim of this study was to analyze the effects of chronic mild unpredictable stress (CMS) on the vasoconstrictor response and morphology of the thoracic aorta and serum lipid profiles in rats. Male Sprague-Dawley rats were submitted to CMS, which consisted of the application of different stressors for 7 days per week across 3 weeks. The rats were sacrificed 15 days after CMS exposure. CMS induced supersensitivity to the vasoconstrictor effect of phenylephrine in endothelium-intact thoracic aortic rings without changes in aortic rings without endothelium, or pre-incubated with nitric oxide (NO) synthesis inhibitor. Rats submitted to CMS showed hypertrophy of the intima and tunica media of thoracic aorta, increased serum levels of triglycerides, total cholesterol, very low-density lipoprotein cholesterol, low-density lipoprotein cholesterol and atherogenic index, without changes in high-density lipoprotein cholesterol levels, when compared with control rats. These data indicate that CMS induces physiological and morphological changes that may contribute to the development of atherosclerosis by mechanisms related to deficiency in NO production and dyslipidemia.

Ciliated fibroblasts in mouse connective tissues: a comparison between methods for estimating their frequency

The frequency of ciliated fibroblasts in skin, gingiva, molar and incisor periodontal ligaments and incisor enamel-related periodontium of the mouse was estimated by straight counting or by methods based on the probability of observing a basal body in relation to other cell structures. Transmission electron microscopy of ultra-thin sections mounted in single slot grids was used. The results obtained with these methods differed, but indicated that periodontal ligament fibroblasts from molars or incisors generally had a higher ciliation index than the fibroblasts from skin and gingiva. These differences may not be real since the detection of cilia and/or centriolar structures seems to depend very much upon the plane of sectioning relative to the long axis of the fibroblasts, a situation which favours the more regularly arranged periodontal fibroblasts. This arrangement makes the periodontal tissues, particularly those of rodent incisors, a valuable model for studying ciliation in vivo because of the prompt response to experimental manipulation.

Alveolar bone remodelling pattern of the rat incisor under different functional conditions as shown by minocycline administration

Remodelling of the socket surrounding the continuously growing and erupting rat incisor was examined in teeth under normo, hyper and hypofunctional conditions. Cross-sections of the mandible were observed under fluorescence microscopy, where minocycline labelling evidenced bone remodelling. Animals had received minocycline (10 mg/day) during the experimental period. Control animals (from all three groups) received vehicle alone and samples from these animals were not fluorescent. Minocycline did not interfere with the eruption rates in any of the functional conditions studied. Normofunctional (impeded) incisors showed constant osteogenic activity in the alveolar bone facing the periodontal ligament in all regions of the incisor. Under hypofunctional (unimpeded) and hyperfunctional (impeded) conditions, osteogenesis in the region close to the alveolar crest was markedly increased in the mesial wall of the socket. The labial alveolar bone, facing the enamel-related periodontium, was almost entirely formed during the experimental period in all the groups, but in hyper and hypofunctional teeth the newly formed bone was thicker and contained a substantial amount formed before the experimental period. In the more apical regions of the socket no marked differences between the three functional conditions were found. The similar bone remodelling shown in hypo and hyperfunctional teeth might indicate that there are common factors causing this pattern. Consideration of possible factors appear to rule out the eruption rate, which is very different under these two functional conditions.

Glycol methacrylate: an alternative method for embedding subcutaneous implants

The aim of this investigation was to study the use of glycol methacrylate (GMA) as an embedding material for rat subcutaneous tissue, which received implants of tubes with endodontic sealer. After fixation, the specimens were dehydrated in a growing alcohol series up to 95%, immersed in infiltration GMA solution and then in embedding solution. The blocks were cut into 3.0 microm sections and stained with hematoxylin-eosin. The quality of cell definition and staining allowed a quantitative analysis of the cells infiltrated in the end of the tubes. It was also possible to identify each type of inflammatory cell. Moreover, it was possible to distinguish clearly chronic from acute inflammatory cells. The GMA technique is easy to execute and reproducible, and provides a better definition of tissue cells, thus permitting definition of the degree of the inflammatory process. Therefore, it is an excellent alternative for the evaluation of the biocompatibility of endodontic sealers.

The effect of lead on the eruption rates of incisor teeth in rats

The effects of lead on the continuously erupting rat incisors under normo-, hyper- and hypofunctional conditions were investigated. Left lower incisors of 20 rats were rendered unimpeded (hypofunctional) by cutting them out of occlusion every 2 days; the right lower incisors of these rats were considered hyperfunctional. Measurements on normally growing teeth (normofunctional) were carried out in a group of ten rats whose teeth were not cut but only marked every 2 days. On day 7 of the experiment, half of the rats from these two groups were given a single intraperitoneal injection of lead acetate (40 mg/kg), and the other half received sodium acetate (22 mg/kg). Another group of 15 rats was used to obtain blood samples for lead determination 1 h, and 10, 20, and 30 days after lead administration. Animals were killed on day 32. Hypofunctional incisors from lead-treated rats erupted more slowly than control ones (P<0.05). These results show a previously unreported toxic effect of heavy metals.

An electron microscopic study of dental plaque of the rat incisor

Because rat incisors continuously erupt they provide an opportunity for the study of dental plaque at all stages of its development. The youngest plaque would be visible at the gingival margin of the tooth as it erupts, and the older plaque higher on the tooth. The ultrastructural features of these plaques were studied by transmission electron microscopy. Cocci and short rods colonized the cementum surface, forming a monolayer. The plaque had a maximum thickness of about 40 microns, with the inner third rich in fibrillar matrix and the organisms forming microcolonies perpendicular to the tooth surface. Cells were haphazardly distributed in a loose matrix on the surface of the plaque. In the area of plaque disorganization the cementum was covered by isolated groups of bacteria and the matrix had holes in it. The rat mandibular incisor may provide a unique model for study of how plaque on cementum is initially formed, matures and finally is degraded.