Size variation of trichospores of Harpella melusinae in larval black flies

Trichospores of Harpella melusinae in larval black flies from four streams in northwestern South Carolina were measured. The longest fresh trichospore was 242 microm, 38% longer than the reported maximum length of trichospores for this species. After staining with lactophenol cotton blue, trichospore length was significantly reduced by up to 24.4% in fresh larvae and up to 4.9% in fixed larvae. Mean trichospore length differed significantly between seasons and between sampling sites but did not differ significantly between middle and final instars. Trichospore length correlated significantly with host size. We suggest that taxonomic descriptions of trichomycetes should include measurements of fresh, fixed and stained trichospores.

Effects of erythrocyte flexibility on microvascular perfusion and oxygenation during acute anemia

Responses to exchange transfusion using red blood cells (RBCs) with normal and reduced flexibility were studied in the hamster window chamber model during acute moderate isovolemic hemodilution to determine the role of RBC membrane stiffness in microvascular perfusion and tissue oxygenation. Erythrocyte stiffness was increased by 30-min incubation in 0.02% glutaraldehyde solution, and unreacted glutaraldehyde was completely removed. Filtration pressure through 5-μm pore size filters was used to quantify stiffness of the RBCs. Anemic conditions were induced by two isovolemic hemodilution steps using 6% 70-kDa dextran to a hematocrit (Hct) of 18% (moderate hemodilution). The protocol continued with an exchange transfusion to reduce native RBCs to 75% of baseline (11% Hct) with either fresh RBCs (RBC group) or reduced-flexibility RBCs (GRBC group) suspended in 5% albumin at 18% Hct; a plasma expander (6% 70-kDa dextran; Dex70 group) was used as control. Systemic parameters, microvascular perfusion, capillary perfusion [functional capillary density (FCD)], and oxygen levels across the microvascular network were measured by noninvasive methods. RBC deformability for GRBCs was significantly decreased compared with RBCs and moderate hemodilution conditions. The GRBC group had a greater mean arterial blood pressure (MAP) than the RBC and Dex70 groups. FCD was substantially higher for RBC (0.81 ± 0.07 of baseline) vs. GRBC (0.32 ± 0.10 of baseline) and Dex70 (0.38 ± 0.10 of baseline) groups. Microvascular tissue Po2 was significantly lower for Dex70 and GRBC vs. RBC groups and the moderate hemodilution condition. Results were attributed to decreased oxygen uploading in the lungs and obstruction of tissue capillaries by rigidified RBCs, indicating that the effects impairing RBC flexibility are magnified at the microvascular level, where perfusion and oxygenation may define transfusion outcome.

Formaldehyde exposure induces histopathological and morphometric changes in the rat testis

Formaldehyde is a chemical which is traditionally used for fixing cadavers and routine histopathology techniques. It is vaporised during the dissection and practical study of a cadaver. Previous studies have shown that this vapour may cause clinical symptoms such as throat, eye, skin and nasal irritation. This study was designed to determine the histopathology and morphometrics of the rat testis when all the experimental animals were exposed to formaldehyde for 18 weeks. The study was performed in 2004 on 28 albino Wistar rats of 6-7 postnatal weeks. The rats were divided into three case groups (E1: 4 h/d, 4 d/w; E2: 2 h/d, 4 d/w; E3: 2 h/d, 2 d/w) and one control group. The testes specimens were sectioned at 5 microm and stained with the haematoxylin and eosin staining technique for histological and morphometrical studies. We found a severe decrease in germ cells associated with spermatogenesis arrest in the E1 group. A decrease in germ cells and a thickening of the basal membrane of the seminiferous tubules were seen in E2. Displacement of Sertoli and germinal cells were also found in the E3 group. The mean seminiferous tubular diameter and seminiferous epithelial height in the experimental groups were decreased in comparison with the control group and the differences were statistically significant (p < 0.05). The findings of this study revealed that chronic formaldehyde exposure can cause histopathological and morphometric changes to the seminiferous epithelium in rats and that these changes depend on the duration of the formaldehyde exposure.

Specimen Shrinkage and Its Influence on Margin Assessment in Breast Cancer

OBJECTIVE

The determination of tumour-free margin in breast cancer is crucial in deciding subsequent patient management. To exemplify the phenomenon of margin contraction during specimen preparation for histopathological analysis, we quantified the shrinkage of breast specimens as a result of formalin fixation.

METHODS

Fifty consecutive mastectomy and wide excision specimens were prospectively appraised. The closest free margin and maximal tumour diameter of fresh, unprepared specimens were recorded. These measurements were compared with the corresponding parameters following tissue fixation.

RESULTS

Following formalin fixation, the mean closest free margin of the specimens was found to have decreased from 10.28 mm to 6.78 mm (34%). The reduction of the mean diameter of the tumour itself was less significant, from 41.74 mm to 39.88 mm (4.5%).

CONCLUSION

Breast specimens undergo shrinkage after histological fixation, losing more than a third of their original closest free margin, whilst the tumour itself does not shrink substantially. This phenomenon has vital implications in the accuracy of margin analysis and consequent decisions on further management, including re-operation and the institution of adjuvant radiotherapy.

Two percent formalin retention enemas for hemorrhagic radiation proctitis: a preliminary report

PURPOSE

The short-term safety and efficacy of 2 percent formalin administered as a retention enema for hemorrhagic radiation proctitis was studied.

METHODS

A group of 24 patients with hemorrhagic radiation proctitis who received radical radiotherapy were administered 2 percent formalin as a retention enema and the treatment was followed up from 1 to 29 (mean, 15.34) weeks. The enema was performed on an outpatient basis under sedation with pentazocine and promethazine with a retention time of two minutes. The symptoms and proctoscope findings were graded and converted into a numeric score, ranging from 1 to 4. The mean improvements in scores before treatment and after the last follow-up were analyzed for statistical significance by using the paired t-test.

RESULTS

There was complete cessation of bleeding in 47.8 percent of patients and very negligible bleeding in 30.4 percent. A total of 78.2 percent responded positively to treatment with 2 percent formalin retention enema. More than one application was required in 34.7 percent of the patients. The procedure was well tolerated and most of the side effects were mild. Side effects were diarrhea in 23.5 percent, abdominal pain and tenesmus in 8.8 percent, and fever with vomiting in 2.9 percent of patients. There was a statistically significant reduction in bleeding and proctoscopy scores (P<0.01). None of the patients in this study required surgery to palliate their symptoms.

CONCLUSIONS

Two percent formalin when given as a retention enema is a safe, inexpensive, and effective intervention for hemorrhagic radiation proctitis. Any trained health worker using simple precautions can perform this procedure. The long-term efficacy and safety of 2 percent formalin retention enemas need further assessment with randomized, controlled trials.

Comparison of miRNA expression patterns using total RNA extracted from matched samples of formalin-fixed paraffin-embedded (FFPE) cells and snap frozen cells

Background

Archival formalin-fixed paraffin-embedded (FFPE) tissues have limited utility in applications involving analysis of gene expression due to mRNA degradation and modification during fixation and processing. This study analyzed 160 miRNAs in paired snap frozen and FFPE cells to investigate if miRNAs may be successfully detected in archival specimens.

Results

Our results show that miRNA extracted from FFPE blocks was successfully amplified using Q-RT-PCR. The levels of expression of miRNA detected in total RNA extracted from FFPE were higher than that extracted from snap frozen cells when the quantity of total RNA was identical. This phenomenon is most likely explained by the fact that larger numbers of FFPE cells were required to generate equivalent quantities of total RNA than their snap frozen counterparts.

Conclusion

We hypothesise that methylol cross-links between RNA and protein which occur during tissue processing inhibit the yield of total RNA. However, small RNA molecules appear to be less affected by this process and are recovered more easily in the extraction process. In general miRNAs demonstrated reliable expression levels in FFPE compared with snap frozen paired samples, suggesting these molecules might prove to be robust targets amenable to detection in archival material in the molecular pathology setting.

Effects of low-level formaldehyde exposure on synaptic plasticity-related gene expression in the hippocampus of immunized mice

We examined the effects of inhalative exposure to formaldehyde (FA, 400 ppb) on N-methyl-D-aspartate (NMDA) receptor subunits (NR2A and NR2B), dopamine receptor subtypes (D1 and D2), cyclic AMP responsive element-binding protein (CREB)-1, CREB-2, FosB/DeltaFosB, and transient receptor potential vanilloid receptor (TRPV1) in the hippocampus of ovalbumin-immunized mice using quantitative real-time PCR. Western blot analyses for pCREB were performed. The mRNA levels of NR2A, D1 and D2 receptors, and CREB-1 were significantly increased by FA, but NR2B, CREB-2, FosB/DeltaFosB, and TRPV1 mRNA levels remained unchanged. Treatment with MK-801 normalized the mRNA levels induced by FA. There was no significant effect of FA exposure and MK-801 treatment on the protein level of pCREB. These results indicate that FA exposure selectively up-regulates hippocampal gene expression in immunologically sensitized mice. The FA effects are presumably mediated by glutamatergic neurotransmission through NMDA receptors.

Mast cell heterogeneity between two different species of Hoplias sp. (Characiformes: Erythrinidae): response to fixatives, anatomical distribution, histochemical contents and ultrastructural features

Mast cells from two erythrinid species: Hoplias malabaricus and Hoplias lacerdae, were studied in several tissues throughout the body using light and electron microscopy. Mast cells were found in all organs studied, but were especially abundant in the gastrointestinal tract, and were always in association with connective tissue. These cells showed different characteristics between the two species studied, like varied morphology, anatomical distribution, density, basophilic/eosinophilic staining and heparin content. In H. malabaricus, the tissues fixed with Helly's solution contained mast cells that were basophilic, metachromatic and had heparin in their cytoplasmic granules, while the tissues fixed with Karnovsky's solution contained eosinophilic and orthochromatic mast cells in which heparin was not detected. In H. lacerdae, the use of both fixatives resulted in mast cells that were eosinophilic, orthochromatic, with no identifiable heparin content. Exclusively in H. malabaricus oesophagus, the mast cells were additionally seen among the epithelial cells. The ultrastructural studies performed in hindgut fixed with Karnovsky's solution revealed that the cytoplasmic granules seen in H. lacerdae mast cells were better preserved than in H. malabaricus mast cells. The latter had electron-lucent granules that were often merged, forming channels. The present study demonstrated that mast cells from two species belonging to the same genus or even mast cells from the same species but under different fixatives can present heterogeneous characteristics, possibly due to their functional properties or to their sensitivity to fixatives.

Artifactual dendritic beading in rat spinal cord induced by perfusion with cold saline and paraformaldehyde

Extensive dendritic beading of MAP2 (microtubule-associated protein 2) immunoreactivity has previously been observed in the contused rat spinal cord. However, we have also observed dendritic beading in occasional uninjured animals. The purpose of this study was to examine the possibility that perfusion conditions contributed to the dendritic beading. Under deep anesthesia, uninjured rats (adult female Long-Evans, 200-225 g) were transcardially perfused with 0.9% saline solution followed by 4% paraformaldehyde at cold (4 degrees C) or warm (20 degrees C) temperature, and at a low (20 ml/min) or high (50 ml/min) flow rate. Dendrites were visualized by MAP2 immunoreactivity. The results demonstrate that perfusion with cold solutions at a high flow rate induces pronounced dendritic beading, and when perfused at a low flow rate, results in moderate dendritic beading. Warm perfusates did not induce dendritic beading when administered at a low flow rate, but occasional beading was observed with a high flow rate. Western blots revealed spectrin breakdown, but not MAP2 loss, in rats perfused with cold saline solution at a high flow rate, conditions that also resulted in dendritic beading. These findings demonstrate that dendritic morphology is sensitive to both temperature and flow rate of the perfusate. Warm fixative and a low perfusion flow rate minimized the perfusion-induced dendritic beading.

Investigation of alloreactive NK cells in mixed lymphocyte reactions using paraformaldehyde-silenced target cells

Mixed lymphocyte reactions (MLRs) remain central to the characterization of cellular allo-interactions. Here we show that irradiation, as used to 'silence' a given cell-population in unidirectional ('one-way') MLRs, is unable to abolish cytokine-production even at doses much higher than usually applied. By contrast, using target cells silenced via a formaldehyde-based fixation-protocol, we demonstrate feasibility to detect - in a true one-way reaction - secretion of IFNgamma by alloreactive NK cells. This simple, fixation-based protocol provides an accurate, robust and time-efficient means for assessing alloreactivity, avoiding cytokine-production by the MLR stimulator cells.

Pathological study of pulp treated with chemicals after Er:YAG laser preparation

OBJECTIVE

The aim of this study was to clarify pulp reaction following cavity preparation with an Er:YAG laser and subsequent treatment with topically applied chemicals to achieve a high resin bond strength.

BACKGROUND DATA

The application of chemicals has been found to effectively remove or reform the denatured layer produced by Er:YAG laser irradiation and has been proposed as a new strategy for improving resin bond strength. However, very little is known about pulp reaction to chemical procedures.

METHODS

Class 5 dentin cavities were prepared with an Er:YAG laser in 128 teeth in nine adult dogs. The teeth were then coated with glutaraldehyde (GA group), or phosphoric acid and sodium hypochlorite (PA group) to reform or remove the denatured layer. All the cavities were then restored with composite resin. In the control group, no chemical application was carried out prior to restoration. The animals were sacrificed immediately after, and at 7 and 90 days following treatment. The treated teeth were then extracted for histopathological examination of the pulp.

RESULTS

Pathological evaluation of the pulp indicated a good condition in each group at each of the three observation time points. No bacterial growth was observed on the cavity walls or bacterial invasion into the dentinal tubules or pulp chambers in any of the groups at any of the observation periods.

CONCLUSION

Our findings suggest that the application of chemicals to remove or reform denatured layers is effective in obtaining better composite resin restoration with no pulp damage.

[Adaptation of an immunohistochemistry protocol for the detection of Leptospira spp. in samples of formaldehyde-fixed tissue]

The immunohistochemistry technique was evaluated in tissue samples fixed in formaldehyde saline solution 10 % and included in paraffin to be used as a lab method allowing to identify leptospires in tissues. Samples obtained from the experimental inoculation of 8 guinea pigs carriers of L. interrogans Pomona isolated from a clinical case were used. The disease was reproduced in a lab model. The histologic sections of the kidneys of the animals inoculated were subjected to histopathological studies, immunofluorescence, Warthin-Starry stain, and immunohistochemistry technique using formaldehyde-fixed samples. This technique proved to be an efficient tool for the diagnosis of leptospirosis.

Green fluorescent protein as a tracer in chimeric tissues: the power of vapor fixation

Green fluorescent protein (GFP) and its variants, small, highly soluble proteins, are routinely used as reporters for patterns of gene expression and the origin of cells in transplantation experiments. When not linked as fusion proteins to other polypeptides, they distribute rapidly in the cytoplasm of a given cell, thus allowing real-time observations on living material. For histological analysis, previous bath fixation of whole organs or tissues seemed obligatory, because, during drop fixation of sections, GFP rapidly leaks from cells whose membrane has been damaged by freezing and/or sectioning. The fluorescence of GFP and its derivatives is retained upon fixation, but most enzyme and antigenic activities of interest will be lost in the whole sample as a consequence of formaldehyde (FA) fixation. We have therefore developed an alternative method to fix GFP in frozen tissue sections by FA vapor. This method prevents leakage and redistribution of GFP and allows any cytochemical method to be applied to unfixed adjacent serial sections.

Evaluation of fixative solutions for ultrastructural analysis of brown spider Loxosceles intermedia (araneae: sicariidae) tissues

In view of the widely varying compositions of fixative solutions used for studying spiders, five different fixative formulas were tested for fixing male brown-spider (Loxosceles intermedia) gonad tissues. The brown spider represents a public health problem in Curitiba (Paraná State, Brazil). Morphological study of its gonads may aid in understanding the reproductive strategies of this species, and possibly in developing a reproduction control program. The fixatives tested contained glutaraldehyde alone or combined with paraformaldehyde, and the buffers cacodylate or phosphate, with or without the addition of sucrose or sodium chloride as osmolytes. Those containing 2.5% glutaraldehyde and 2% paraformaldehyde in 100 mM phosphate buffer with 200 mM sucrose, or in 200 mM sodium cacodylate, satisfactorily preserved mitochondria, the Golgi apparatus, and the membranes in general. These formulas were nearly isosmotic (439 mOsm/kg H2O and 455 mOsm/kg H2O respectively) to brown spider hemolymph (478 mOsm/kg H2O). With respective to the fixative agents, a glutaraldehyde-paraformaldehyde combination resulted in optimal fixation of Loxosceles intermedia cells. For other species of spiders, hemolymph osmolality should be considered, but the fixative formulas cited above would also probably yield good results.

An investigation of the problem of two-layered immunohistochemical staining in paraformaldehyde fixed sections

In sections of paraformaldehyde fixed brain tissue, stained using immunohistochemical methods, the distribution of staining within the sections is not uniform. Whilst stained cells are seen at the top and bottom surfaces, the central thicknesses of the sections contain little or no immunoreactivity. This presents a major problem for quantification, as each section contains a population of cells that is not visualized by the staining method. Following extensive investigation of this phenomenon, we report that the failure of full thickness, immunohistochemical staining is not a failure of the immunohistochemical methodology per se, nor is it related directly to the thickness of the sections used. Rather, the problem lies in the chemistry of the tissue itself, and originates during fixation of the tissues using paraformaldehyde-based perfusion methods, which render the cell membranes impermeable to one or more components of the staining protocol. We show that this impermeability is affected by addition of membrane-disrupting agents to the fixative, and by a reduction of exposure to paraformaldehyde during fixation. The present investigation contributes to the development of new fixation protocols, optimised for use in both immunohistochemical methods and morphometric analyses.

ThromboFix platelet stabilizer: advances in clinical platelet analyses by flow cytometry?

Platelet flow cytometry is restricted by spontaneous platelet activation in unfixed samples or by significant alterations of platelet performance caused by the use of fixatives. Aim of this study was to evaluate the new platelet stabilizer ThromboFix for clinical diagnostics.

METHODS

Whole blood samples with or without addition of a weak (ADP) or strong (TRAP-6) agonist were fixed with either ThromboFix or paraformaldehyde (PFA) and stored for different periods of time for up to 7 days. Samples were then incubated with either CD41 and CD62P or CD42b and CD45 monoclonal antibodies and analyzed by flow cytometry.

RESULTS

The numbers of platelets, microparticles and aggregates remained stable for 7 days after treatment with ThromboFix but not with PFA due to an increasing aggregate formation after 3 days. Platelet activation was restricted to less than 1% of CD62P positive events in resting samples without a significant difference compared to an unfixed reference sample. Fixation, however, significantly reduced CD62P expression after stimulation (P < 0.05). Stabilized by ThromboFix, the level of platelet activation remained unchanged in resting and ADP stimulated samples for 7 days but decreased moderately with time after a strong stimulation with TRAP-6 (P < 0.01). After PFA fixation, intact CD62P antigen disappeared from the platelet surface within hours (P < 0.01). ThromboFix reduced the formation of platelet-leukocyte conjugates significantly (P < 0.05) and, in contrast to PFA, failed to stabilize the already formed conjugates.

CONCLUSION

In clinical situations without immediate access to a flow cytometer, ThromboFix is helpful in the flow cytometric analysis of the platelet activation marker CD62P. It should not be used for the investigation of platelet-leukocyte conjugate formation.

Primer: tissue fixation and preservation for optimal molecular analysis of urologic tissues

Appreciation of the different methods of tissue handling is a prerequisite to obtaining accurate and biologically relevant tissue-based information. When a tissue sample is removed from its environment, biological changes are induced within its constituent cell population. It is inevitable that artefacts will be induced through obtaining and processing tissues, irrespective of whether the samples comprise a few cells derived by fine-needle aspiration or larger specimens obtained surgically. Depending upon the level of sophistication of the analytical methods subsequently employed, such changes might be irrelevant, or might result in acquisition of spurious data. While even brief ischemia alters expression of some genes, detectable by appropriate molecular techniques, the same changes might make no appreciable difference to tissue histomorphology. Furthermore, the phenotype of viable cells is known to change during tissue collection and handling. For example, transitional epithelial cells voided in urine are not phenotypically identical to those retained within the urothelium. Such phenotypic changes are temporary and might be of little consequence to subsequent analyses. Surprisingly, many cells in tissues preserved in an ischemic state can remain viable for several hours, and are believed to remain genotypically stable in the short term.

The effect of formalin storage on the apical microleakage of obturated canals

Infection control guidelines recommend disinfection of extracted teeth in 10% formalin for 2 weeks before use. Although extracted teeth are routinely used for in vitro endodontic research, the potential influence of formalin has not been evaluated. The purpose of this study was to investigate the effect of formalin storage on the apical seal integrity of obturated canals. There were 100 single-rooted human teeth decoronated, accessed, and randomly divided into four groups. Group 1 was composed of specimens that were instrumented and obturated after extraction without storage in formalin. Groups 2, 3, and 4 were stored in formalin for 2, 4, and 8 weeks, respectively, before treatment. Canals were instrumented to a master apical file size #7 ProFile .04 Taper Series 29 and obturated with Obtura II thermoplasticized gutta-percha and Roth 801 sealer. The teeth were immersed in India ink, cleared, and the greatest extent of linear dye leakage was measured. Microleakage testing displayed significantly less microleakage after 2 and 4 weeks of formalin storage. Leakage measurements after 4 weeks of storage were 62.3% lower than nonfixed specimens. The 8-week storage group demonstrated lower dye penetration compared with the nonfixed group; however, the difference was not statistically significant. Within the scope of this study, storage of extracted teeth in formalin for 2 and 4 weeks resulted in a significant decrease in apical microleakage compared with nonfixed specimens.

An ELISA-based method for the quantification of incorporated BrdU as a measure of cell proliferation in vivo

In this study, we describe a new rapid and versatile method to determine the BrdU content of DNA in brain tissues dissected from BrdU-treated rats. Different to already existing BrdU ELISAs the method is suitable for the assessment of BrdU incorporation in ex vivo experiments as it is based on the analysis of tissue extracts instead of immobilized cells. The method comprises the preparation of DNA extracts from dissected tissues, the immobilization of BrdU-containing DNA with an anti-BrdU antibody and quantification of the incorporated BrdU by a peroxidase-conjugated anti-BrdU antibody. Validating the new assay in vitro, we found a clear-cut dependency of the ELISA signal from the time SKNSH neuroblastoma cells had been exposed to BrdU. Parallel studies with existing ELISAs and a parallel immunocytochemical determination of BrdU positive cells revealed comparable results. In vivo experiments showed a virtually linear relationship between the BrdU immunoreactivity in the hippocampus and the time rats have been exposed to BrdU. Repeating the determination of the BrdU content of the same set of tissue samples revealed reproducible relative differences of the ELISA signals. This was true for protocols using purified DNA as well as crude DNA extracts. For the sensitivity and reproducibility of the method heat denaturation of the DNA prior to the analysis in the ELISA was crucial. In rats treated with electroconvulsion the BrdU content of the hippocampus, determined by the new ELISA, was increased to 225% of controls. In a parallel immunohistochemical study, the number of BrdU positive cells was comparably increased to 251% of controls. The assay thus provides a rapid method to detect changes of cell proliferation in dissected brain tissues and other proliferative tissues. With appropriate protocols, the assay may also be used to assess the generation of particular cell types like neurons in neurogenic areas.

Effect of fixation and embedding on Raman spectroscopic analysis of bone tissue

Raman spectroscopy provides valuable information on the physicochemical properties of hard tissues. While the technique can analyze tissues in their native state, analysis of fixed, embedded, and sectioned specimens may be necessary on certain occasions. The information on the effects of fixatives and embedding media on Raman spectral properties is limited. We examined the effect of ethanol and glycerol as fixatives and a variety of embedding media (Araldite, Eponate, Technovit, glycol methacrylate, polymethyl methacrylate, and LR white) on Raman spectral properties (mineralization, crystallinity, and carbonation) measured from the cortical bone of mouse humeri. Humeri were fixed in ethanol or glycerol, followed by embedding in one of the media. Nonfixed, freeze-dried, and fixed but not embedded sections were also examined. Periosteal, endosteal, and midosteal regions of the intracortical envelope were analyzed. Raman spectra of fixative solutions and embedding media were also recorded separately in order to examine the specifics of overlap between spectra. We found significant effects of fixation, embedding, and anatomical location on Raman spectral properties. The interference of ethanol with tissue seemed to be relatively less pronounced than that of glycerol. However, there was no single combination of fixation and embedding that left Raman spectral parameters unaltered. We conclude that careful selection of a fixation and embedding combination should be made based on the parameter of interest and the type of tissue. It may be necessary to process multiple samples from the tissue, each using a combination appropriate for the Raman parameter in question.

Effects of paraformaldehyde fixation on nicotinic acetylcholine receptor binding in adult and developing rat brain sections

In vitro receptor autoradiography requires unfixed tissue sections, but incubation and washing procedures often result in substantial tissue damage in sections from developing brain, hindering quantitative and qualitative analysis. Formaldehyde fixation greatly preserves morphology. However, fixation can interfere with pharmacological properties of receptors, increase in non-specific background labeling, or even destroy ligand binding sites. Two mild fixation protocols, 0.2% paraformaldehyde (pFA) and pFA vapor fixation, were compared for their ability to improve tissue morphology in postnatal day 7 (P7) brain slices and maintain binding of [125I]-epibatidine and [125I]-alpha-bungarotoxin to heteromeric and homomeric nicotinic acetylcholine receptors, respectively. Fixation greatly improved the ability of P7 brain slices to withstand incubation and washing procedures during binding, resulting in minimal or no loss of tissue after prior 0.2% pFA or vapor fixation, respectively. In adults, distribution pattern of [125I]-epibatidine was identical in fixed and unfixed slices, with no difference in total and non-specific labeling. Distribution of [125I]-alphaBTX labeling was similarly unaffected by 0.2% pFA fixation, but vapor fixation increased total and non-specific binding signal. Thus, mild fixations greatly improve tissue quality during receptor binding procedures and can preserve pharmacological properties of nicotinic acetylcholine receptors. However, different receptors or ligands might exhibit differential sensitivity to fixation protocols.

[The investigation of FFA fixative solution for retina]

PURPOSE

To search for an effective fixative solution for retina.

METHODS

One group of retinas were fixed in an admixture of formalin, dehydrated alcohol and glacial acetic acid (FFA). The other group of retinas were fixed in 10% neutral formalin.HE and immunohistochemistry were performed. Then compare the difference under the light microscope.

RESULTS

The structure of the retinas fixed in FFA fixative solution was clear. The cells were arranged and compacted. Few exfoliation of the tissue from the glass slide was observed.

CONCLUSION

FFA fixative solution is superior to 10% neutral formalin for the fixation of retina.

Direct quantification of gene expression in homogenates of formalin-fixed, paraffin-embedded tissues

Formalin-fixed, paraffin-embedded (FFPE) tissues represent an important source of archival materials for gene expression profiling. We report here the development of a modified branch DNA assay that allows direct quantification of messenger RNA (mRNA) transcripts in homogenates from FFPE tissue sections without the need for RNA isolation and reverse transcription into cDNA. Formalin fixation essentially has no effect on the branch DNA assay, and RNA degradation only marginally reduces the signal by 2- to 3-fold. Under the same conditions, formalin fixation and RNA degradation greatly reduces real-time reverse transcription PCR (RT-PCR) efficiency, reducing signals by as much as 15- and 1400-fold, respectively. Although both technologies can generate biologically meaningful expression profiles from FFPE human lung tumor specimens, the branch DNA assay is more sensitive than real-time RT-PCR under the conditions tested. Our results therefore suggest that the branch DNA assay is an ideal tool for retrospective analysis of gene expression in archival tissues.

Effects of fixation, dehydration and staining on dimensions of myxosporidan

The effects of fixation, dehydration and staining on the morphological dimensions of myxo- and microsporidan spores were tested. Seven fixatives, two dehydrants and five stains were tested. Ten % formalin produced the least shrinkage and provided the best cytological detail of fixed material in both types of spores. All fixatives caused shrinkage of myxosporidan spore length and polar capsule length. Spore capsule width and polar capsule width were unaffected by 10% formalin. Ethyl alcohol caused no significant change in spore width. Microsporidan spore length shrunk with all fixatives, but spore width was generally unaffected. Dehydration, with either isopropyl alcohol or acetone, produced additional, significant shrinkage. The influence of stains on spore size was negligible. Heidenhains iron hematoxylin followed by eosin, and Mallory's analine-blue collagen stain, effectively stained myxo- and microsporidan spores.