Microwave fixation method for cytochemistry. For conventional electron microscopy, enzymo-immunocytochemistry, autoradiography elemental distribution studies and staining methods

Mechanotransduction of stem cells for tendon repair

Tendon is a mechanosensitive tissue that transmits force from muscle to bone. Physiological loading contributes to maintaining the homeostasis and adaptation of tendon, but aberrant loading may lead to injury or failed repair. It is shown that stem cells respond to mechanical loading and play an essential role in both acute and chronic injuries, as well as in tendon repair. In the process of mechanotransduction, mechanical loading is detected by mechanosensors that regulate cell differentiation and proliferation via several signaling pathways. In order to better understand the stem-cell response to mechanical stimulation and the potential mechanism of the tendon repair process, in this review, we summarize the source and role of endogenous and exogenous stem cells active in tendon repair, describe the mechanical response of stem cells, and finally, highlight the mechanotransduction process and underlying signaling pathways.

Microwave-assisted technology for the clearing and staining of arbuscular mycorrhizal fungi in roots

The use of microwave irradiation as a source of energy to clear and stain intra-radical arbuscular mycorrhizal fungi propagules has been tested on a variety of indigenous and cultivated herbaceous plants. The aim of the study was to evaluate the efficiency of microwave irradiation on root softening, fungi tissue staining, and preservation of DNA integrity for subsequent molecular analyses. The proposed methodology has been adapted from the standard procedures used to detect and quantify mycorrhizal root colonization levels. Using a domestic microwave oven, tissue clearing and staining required together between 30 s and 1.5 min of microwave treatment to be completed, depending the diameter size of the roots. The well-performing chemical stains tested were acid fuchsin, trypan blue, and aniline blue. The acid fuchsin clearing and staining processes, as performed, were also demonstrated to preserve DNA integrity for further molecular analyses. Irradiation by microwaves has been used with success in our laboratory within the frame of several studies. It offers considerable time saving over traditional method, reducing processing times from several hours to a few minutes while decreasing considerably the amount of chemicals and energy required to perform analyses.

Glucocorticoid Generates ROS to Induce Oxidative Injury in the Hippocampus, Leading to Impairment of Cognitive Function of Rats

The present study attempted to clarify whether over-secretion of glucocorticoids in the serum caused by increased hypothalamus-pituitary-adrenal activity induces oxidative stress in the rat brain, and how the stress causes the emergence of cognitive deficits. When rats were subcutaneously injected with corticosterone, lipid hydroperoxides and protein carbonyls increased markedly in the hippocampus in association with a decrease in activity of antioxidative enzymes, such as superoxide dismutase, catalase and glutathione peroxidase. These results suggest that high-level corticosterone in the serum induces reactive oxygen species (ROS), leading to oxidative damage in the hippocampus. After administration of corticosterone to rats, glucose and superoxide levels in the serum increased markedly. Furthermore, pyramidal cell apoptosis was observed to accompany the loss of glucocorticoid receptors at the cornus ammonis 1 region of the hippocampus. Rats injected with corticosterone showed marked deficits in memory function. The present results imply that ROS generated from the glycation reaction of increased glucose levels caused by gluconeogenesis activation through glucocorticoid with proteins in the serum attack the hippocampus to induce neurodegeneration, resulting in cognitive deficits in rats.

Elevation by oxidative stress and aging of hypothalamic-pituitary-adrenal activity in rats and its prevention by vitamin e

The present study was conducted in order to determine whether oxidative stress during aging involves dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis in association with the emergence of cognitive deficits. When young rats were subjected to oxidative stress in the form of hyperoxia, thiobarbituric acid reactive substances, conjugated diene and lipid hydroperoxides increased markedly in the HPA axis. Vitamin E inhibited such increases in lipid peroxides in each organ. Levels of corticotrophin-releasing hormone in the hypothalamus and plasma levels of adrenocorticotrophic hormone and corticosterone were markedly elevated in young rats exposed to hyperoxia. However, young rats fed vitamin E-supplemented diets showed no abnormal hormone secretion, even after being subjected to hyperoxia. Furthermore, glucocorticosteroid receptors (GR) in pyramidal cells in the Cornus ammonis 1 region of the hippocampus in young rats were markedly decreased by oxidative stress. Similar phenomena were also observed in normal aged rats and young rats fed vitamin E-deficient diet kept in a normal atmosphere. Vitamin E supplementation prevented the decrease in GR in the hippocampus and the increase in corticosterone secretion caused by hyperoxia. These results suggest that oxidative stress induces oxidative damage in the hippocampus and the HPA axis during aging, resulting in a cognitive deficit in rats, and that negative-feedback inhibition on HPA activity was markedly dampened due to an increase in corticosterone levels caused by loss of GR.

Structural and antigenic preservation of plant samples by microwave-enhanced fixation, using dedicated hardware, minimizing heat-related effects

We explored the use of microwave technology in fixation with the objective of achieving quicker fixation regimes, lower concentrations of toxic and volatile reagents, and enhanced antigen detection. We used a modified domestic microwave oven (900 W) and a low-power (5 W) microwave bench. The work was done on plant materials. The oven was supplemented with a cooling device, a stirring system, and a record of the sample temperature and the time of effective irradiation. The sample, immersed in a fixative solution of 1% paraformaldehyde (PFA) in PBS, was irradiated for only 10 minutes. The sample temperature did not exceed 37 degrees C. In these mild conditions, the quality of the (ultra)structural preservation of the samples, morphometrically assessed, was at the same level as obtained with the same fixative, using conventional methods. On the contrary, samples fixed in the same conditions without irradiation showed a poor structural preservation. The antigenic preservation of the irradiated samples was excellent, since the labeling levels of two nucleolar proteins, detected by immunogold, were three times higher than in conventionally fixed samples. In the so-called microwave bench, the pathway of microwaves is guided, so that low-power microwaves directly hit the sample and there is no dispersion of energy. Temperature of fixative did not increase after microwave irradiation. Fixation in the bench with either 4% PFA, or 1% PFA, for 20 minutes resulted in structural preservation of samples similar in quality as obtained with conventional fixation and in a similar or better level of antigen preservation. Therefore, controlling temperature and effective irradiation is crucial in order to obtain optimal structural and antigen preservation with microwave-enhanced fixation. The dramatic differences observed between microwave-irradiated samples and samples fixed in the same conditions without irradiation, strongly support the existence of specific effects of microwaves on fixation, independent from the mere heating of the samples.

Selective uptake of [14C]2-deoxyglucose by neurons and astrocytes: high-resolution microautoradiographic imaging by cellular 14C-trajectography combined with immunohistochemistry

At the moment, there is no direct in vivo evidence of the relative amount of glucose taken up and metabolized by glial cells and neurons, respectively. Therefore, we developed a specific high cellular resolution beta-trajectory approach that allows recording and identification of individual tracks of electrons emitted during disintegrations of 14C. We used [14C]2-deoxyglucose (2DG), which is an analog of glucose and is not metabolized further than the first phosphorylation by hexokinase; this property allows localization of the tracer within the cell type where it is phosphorylated. The present technical approach associated a method of cellular trajectography mainly characterized by the high thickness of the emulsion (15 microm), which permits following of the trajectory of individual electrons. This technique was improved to preserve the in vivo label of diffusible compounds such as 2DG and 2DG-6P and associated with immunohistochemical detection of neurons and astrocytes. beta-Track counting of labeled compounds was performed in 5 microm glial fibrillary acidic protein (GFAP)- and microtubule-associated protein (MAP)2-immunolabeled paraffin adjacent sections. Of 3,075 counted beta-tracks, 53.0% were localized in astrocytes on GFAP-labeled sections and 60.1% in neurons on MAP2-labeled sections. These data represent the first in vivo evidence of the compartmentation of uptake and metabolism of glucose in neurons and astrocytes.

Bisphenol A induces apoptosis in central neural cells during early development of Xenopus laevis

Bisphenol A (BPA), known to be a xenoestrogen, is widely used in industry and dentistry. In the present study, we investigated the effects of BPA on the early development of Xenopus laevis embryos. Stage 6 embryos were exposed to 10-100 microM BPA. Developmental abnormalities were observed when the embryos were exposed to at least 20 microM BPA, with marked developmental abnormalities, such as crooked vertebrae and developmental defects of the head and abdomen, detected in all embryos up to stage 40. Interestingly, apoptosis occurred specifically in central nervous tissue cells of the brain and spinal cord, as assessed by histological analysis. BPA-induced malformations and apoptosis were not observed in embryos exposed to BPA after stage 10. When embryos were exposed to 10 microM 17beta-estradiol (E2), abnormalities were also observed until stage 40. However, the abnormalities induced by BPA and E2 were different and E2 exposure did not induce apoptosis in the central nervous system. Our results indicated that the developmental abnormalities and apoptosis induced by BPA exposure were not inhibited by the addition of E2. In conclusion, we demonstrated that BPA induced marked malformations and specific apoptosis of central nervous system cells during early development of X. laevis embryos, and that these BPA effects appeared to be due to non-estrogenic activities on developmental processes.

Microwave procedures for electron microscopy and resin-embedded sections

Microwaves now have well-established applications in routine light microscopy. They are employed in tissue fixation and to accelerate a wide spectrum of staining procedures. Besides producing superior preservation of cellular antigens through microwave fixation, this form of irradiation has been employed for antigen retrieval, a procedure that has been a major factor in the optimization of immunolabelling in paraffin sections and cytological preparations. A commercial tissue processor has recently been developed which employs microwaves in a markedly accelerated, one-step processing of tissue blocks, completing the procedure within a fraction of conventional times. Microwaves have also been successfully applied in a variety of molecular techniques such as in situ hybridization and polymerase chain reaction. The adoption of microwaves in electron microscopic procedures has been slower, largely because the requirement for speed in processing is not as great, except in diagnostic samples. However, as this review will show, there are equally as many innovative applications of microwaves in electron microscopy. Microwaves have been employed for rapid processing of fine needle aspiration biopsy samples, in keeping with the requirement for speed in this method of diagnosis. Ultrafast fixation of tissue samples has resulted in the better demonstration of cellular enzymes and proteins. It has been clearly shown that microwave-stimulated on grid staining in uranyl acetate and lead citrate produces more consistent results and without background precipitation. Microwaves can be used to hasten resin polymerization and exposure to microwaves results in antigen retrieval in both resin-embedded thick sections and for immuno-electron microscopy. Immunolabelling shows enhanced sensitivity and the technique is anticipated to contribute greatly to the optimization of immuno-electron microscopy. The potential for greatly accelerated preparation of samples for electron microscopy exists but is yet to be fully realized.