Death initiates a cascade of physiological and biochemical alterations in organs and tissues, resulting in microscopic changes that challenge the histopathological evaluation. Moreover, the brain is particularly susceptible to artifacts owing to its unique composition and its location within the cranial vault. The aim of this study was to compile and illustrate the microscopic changes in the central nervous system (CNS) of rats subjected to delayed postmortem fixation. It also scrutinizes the influence of exsanguination and cooling methods on the initiation and progression of these alterations. Twenty-four Wistar Han outbred rats (RccHan™: WIST) were sacrificed and stored either at room temperature (18-22°C) or under refrigeration (2-4°C). Necropsies were conducted at different time points postmortem (i.e., 0.5 h, 1 h, 4 h, 8 h, 12 h, 24 h, 36 h, 48 h, 7 days and 14 days). Brain sections underwent simultaneous digital evaluation by 14 pathologists until a consensus was reached on terminology, key findings, and intensity levels. Microscopic observations varied among cell types. Glial cells were similarly affected throughout the CNS and showed pericellular halo, chromatin condensation and nuclear shrinkage. Neurons showed two types of postmortem changes as most of them showed progressive shrinkage, cytoplasmic dissolution and karyorrhexis whereas others acquired a dark-neuron-like appearance. Neuronal changes showed marked differences among neuroanatomical locations. Additional postmortem changes encompassed: granulation and microcavitation in neuropil and white matter; retraction spaces; detachment of ependyma, choroid plexus, and leptomeninges. Severity of findings after 48 h at room temperature was higher than after seven days under refrigeration and similar to or slightly lower than after 14 days under refrigeration. No clear differences were observed related to the sex or weight of the animals or their exsanguination status. This work elucidates the onset and progression of autolytic changes in the brains of Wistar Han rats, offering insights to accurately identify and enhance the histopathological evaluation.
Bisphenol A (BPA), an endocrine-disrupting chemical and environmental pollutant, has been reported by many researchers to induce male reproductive toxicity in different experimental models. In this study, we investigated whether long-term exposure for two months to 25 µg/kg body weight (low dose) of BPA affects spermatogenesis or sperm quality in young Istrian Pramenka rams exposed via diet. We evaluated body and testicular weights, histopathology of testes and epididymides, and sperm analyses, and compared these parameters between the group of treated rams and the control group of rams. Although there were some differences between the two groups, these differences were not large or statistically significant. The only statistically significant difference was the lower epithelial height of seminiferous tubules in treated rams, compared to control rams. In addition to assessing toxicity, BPA concentrations in the blood plasma of treated rams were determined after the first administration, and the toxicokinetic parameters of total BPA were calculated. In this study, no major signs of altered reproduction in rams were detected.
We examined a 110-week-old RccHanTM: WIST Wistar male rat from a carcinogenicity study. No clinical signs were observed, and the rat was sacrificed at the end of the study. Macroscopically, within the midline of the sphenoid bone, was a 10 mm, non-infiltrative, soft, heterogeneous mass. Microscopic evaluation showed an expansile, cystic proliferation, consisting of two patterns of epithelial lining: well-differentiated areas lined by a single layer to a pseudostratified, ciliated-cuboidal epithelia with Goblet cells compatible with Rathke's cleft cyst; and poorly differentiated ones that formed irregular papillary projections, covered by atypical epithelia with squamous differentiation and hyperkeratosis compatible with areas of craniopharyngioma. Pleomorphisms were high in atypical areas with up to 2-3 mitotic figures per high power field. Within the cystic cavities, there was abrupt keratinization, mucus, cholesterol clefts, and foci of foamy macrophages. Immunohistochemistry revealed strong pancytokeratin immunolabelling of neoplastic cells confirming the epithelial origin. Well-differentiated epithelial lining showed cytokeratin-20 and cytokeratin-8 immunoreactivity, whereas the atypical squamous epithelium presented with a loss of cytokeratin-20 positive signal and weak to moderate positivity with cytokeratin-8. Areas compatible with a Rathke's cleft cyst and craniopharyngioma were considered to co-exist in the same mass.
The discussion on whether the Sprague Dawley (SD), the Fischer F344, or the Hannover Wistar rat is the most appropriate model for toxicity studies in rodents is ongoing. A substantial quantity of data on these strains concerning their source, diet, and housing conditions have been published. Generally, before starting a toxicology program in rodents, it should be taken into account that oncogenicity studies will be required for the majority of compounds successfully completing development. Survival, body weight development, incidence, type, time of onset of age-dependent lesions and neoplasms, as well as some special considerations of the rat model selected may be decisive. Therefore, an understanding of the historical background data is essential. These aspects demonstrate why the use of a specific rat model should be carefully considered at the beginning of the toxicology program.
Models, Animal , Neoplasms, Experimental/pathology , Toxicity Tests/methods , Animals , Body Weight , Carcinogens/metabolism , Carcinogens/toxicity , Female , Male , Neoplasms, Experimental/chemically induced , Organ Size , Rats , Rats, Inbred F344 , Rats, Sprague-Dawley , Rats, Wistar
Many variables may affect the outcome of continuous infusion studies. The results largely depend on the experience of the laboratory performing these studies, the technical equipment used, the choice of blood vessels and hence the surgical technique as well the quality of pathological evaluation. The latter is of major interest due to the fact that the pathologist is not involved until necropsy in most cases, i.e. not dealing with the complicated surgical or in-life procedures of this study type. The technique of tissue sampling during necropsy and the histology processing procedures may influence the tissues presented for evaluation, hence the pathologist may be a source of misinterpretation. Therefore, ITO proposes a tissue sampling procedure and a standard nomenclature for pathological lesions for all sites and tissues in contact with the port-access and/or catheter system.
