microscopic anatomy, immunohistochemistry, and his- topathology. The viewer will be fully engaged in the learning experience by the use of computer graphics and numerous images of normal ocular structures and spontaneous and treatment-induced lesions. Although the emphasis is on toxicologic pathology of the eye and associated extraocular structures, this CD-ROM also provides a valuable resource for those working in the area of diagnostic pathology. Ocular Collection Proto- col for the Laboratory Rabbit, Dog, and Monkey will be available free of charge near the end of 2008 by requesting a copy at the 2008 ESTP poster session or by contacting Dr. Jerry Hardisty at Experimental Pathol- ogy Laboratories, Inc. (jhardisty@epl-inc.com) doi: 10.1016/j.etp.2009.02.089 P04 Histopathological investigation of Wilson slices from developmental toxicity studies Christine Ru¨ hl-Fehlert, Ute Bach, Ana-Maria Klaus, Martin Rosenbruch Bayer HealthCare AG, Global Drug Discovery, Toxico- logical Pathology, 42096 Wuppertal, Germany In developmental toxicity studies, the investigation of soft tissues from rat fetuses is routinely performed using Wilson’s free hand razor cross sectioning technique. The unstained slices are investigated with a stereomicroscope for developmental variations or malformations. How- ever, for some findings the correlation with tissue structures or their categorization may remain equivocal based on this technique. Histopathology may then be used for further clarification since the slices are prefixed in a conventional fixative (e.g. Davidson’s solution) and thus give good technical results when paraffin histo- technique is applied. Examples of the usefulness of the combination of Wilson slices and histopathology are presented. A cyst-like structure at the mouth floor proved to be part of the oral cavity and was hence no abnormal finding. A case of enlarged laryngeal lumen could be traced back by histology to a differing section plane. In the eyes, retinal folding as a developmental anomaly could be distinguished from artificial retinal detachment and folding. These examples show that in developmental toxicity studies, histopathology may be valuable for the differentiation between technical artifacts and spontaneous or induced changes in soft tissues. doi: 10.1016/j.etp.2009.02.090 P05 A novel dual-labelling technique for the immuno-histo- chemical demonstration of T-lymphocyte subsets in FFPE rat lymphoid tissue Kevin J. Randall, Gail Pearse AstraZeneca, Alderley Park, UK Immunotoxicology has developed into an integral regulatory requirement of the toxicological assessment of xenobiotics. Enhanced pathological assessment of tissues can provide genuine insight into perturbations of lymphoid cell populations. To facilitate this we have endeavoured to develop a panel of immunohistochem- ical techniques to demonstrate T-cells and T-cell subsets in formalin-fixed paraffin-embedded rat lymphoid tis- sues. We were successful in developing methods for CD3 and CD8 but failed to arrive at a satisfactory technique for the direct demonstration of CD4 in these tissues. Taking the assumption that the majority of mature T-cells are either CD4+ or CD8+ we have combined our methods for CD3 and CD8 in a novel dual-labelling IHC method to simultaneously demonstrate CD3, CD8 and, by implication, CD4. doi: 10.1016/j.etp.2009.02.091 P06 Gene expression profiling in toxicological studies using FFPE tissues C. Schmitt, A. Walijew, P. Hewitt, J.H. Harleman Institute of Toxicology, Merck Serono Research, 64239 Darmstadt, Germany Large numbers of formalin-fixed paraffin-embedded (FFPE) tissues from toxicological studies have been accumulated over the years in the archives. Although RNA extracted from FFPE tissue is significantly degraded, new technologies are allowing their use for gene expression analysis. In this study, the cDNA- mediated annealing, selection, extension and ligation (DASL TM ) assay from Illumina Inc. and the WT- Ovation TM FFPE-System from NuGEN Inc. were used. Both methods, compared to standard technologies, do not need intact mRNA poly-A tails for cDNA synthesis. The impact of formalin fixation time and RNA extraction method on RNA quality and gene expression in both technologies was evaluated. Furthermore, the comparability of gene expression data from FFPE to fresh frozen (FF) tissue was determined. Technically, livers from 3 untreated rats were fixed for different times in formalin. Using RNA extracted with either High Pure RNA Paraffin (Roche) or RNeasy s FFPE Kits (Qiagen), the DASL TM assay was performed, ARTICLE IN PRESS Abstracts / Experimental and Toxicologic Pathology 61 (2009) 387–413 404