Qualitative and Quantitative Neuropathology Approaches Using Magnetic Resonance Microscopy (Diffusion Tensor Imaging) and Stereology in a Hexachlorophene Model of Myelinopathy in Sprague-Dawley Rats.

It is well established that hexachlorophene, which is used as an antibacterial agent, causes intramyelinic edema in humans and animal models. The hexachlorophene myelinopathy model, in which male Sprague-Dawley rats received 25 to 30 mg/kg hexachlorophene by gavage for up to 5 days, provided an opportunity to compare traditional neuropathology evaluations with magnetic resonance microscopy (MRM) findings. In addition, stereology assessments of 3 neuroanatomical sites were compared to quantitative measurements of similar structures by MRM. There were positive correlations between hematoxylin and eosin and luxol fast blue stains and MRM for identifying intramyelinic edema in the cingulum of corpus callosum, optic chiasm, anterior commissure (aca), lateral olfactory tracts, pyramidal tracts (py), and white matter tracts in the cerebellum. Stereology assessments were focused on the aca, longitudinal fasciculus of the pons, and py and demonstrated differences between control and treated rats, as was observed using MRM. The added value of MRM assessments was the ability to acquire qualitative 3-dimensional (3-D) images and obtain quantitative measurements of intramyelinic edema in 26 neuroanatomical sites in the intact brain. Also, diffusion tensor imaging (fractional anisotropy [FA]) indicated that there were changes in the cytoarchitecture of the white matter as detected by decreases in the FA in the treated compared to the control rats. This study demonstrates creative strategies that are possible using qualitative and quantitative assessments of potential white matter neurotoxicants in nonclinical toxicity studies. Our results lead us to the conclusion that volumetric analysis by MRM and stereology adds significant value to the standard 2-D microscopic evaluations.

NTP/NIEHS Global Contributions to Toxicologic Pathology.

National Toxicology Program (NTP) pathologists are engaged in important initiatives that have significant global impact. These initiatives build on its leadership in pathology peer review and publications in the areas of toxicologic pathology, clinical pathology, and laboratory animal medicine. Over the past decade, NTP/National Institute of Environmental Health Sciences research initiatives have focused on cancer and noncancer hazard identification, with the goal of understanding cellular and molecular mechanisms of disease. New initiatives of significant global impact include the web-based nonneoplastic lesion atlas and an NTP partnership with international scientists to investigate molecular mechanisms at the whole genome level, which will be used to inform potential mechanisms of environmental exposures in human cancers. Also, we are dedicated to contributing to pathology and toxicology organizations through service on executive committees and editorial boards, participating in international projects and symposiums, and providing training for future leaders in toxicologic pathology. Herein, we provide highlights of our global contributions.

Impact of Environmental Enrichment Devices on NTP In Vivo Studies.

The goal of this study was to determine whether the use of nesting material or polycarbonate shelters as enrichment devices would have an impact on end points commonly measured during the conduct of the National Toxicology Program (NTP) 13-week studies. The study design was consistent with the NTP 13-week toxicity studies. Harlan Sprague-Dawley (HSD) rats and their offspring and B6C3F1/N mice were assigned to control (unenriched) and enriched experimental groups. Body weight, food and water consumption, behavioral observations, fecal content, clinical pathology, gross pathology, organ weights, and histopathology were evaluated. Enriched male mice and male and female rats exhibited decreased feed intake without a subsequent decrease in body weight; this may have been the result of the nesting material reducing the effect of cold stress, thereby allowing for more efficient use of feed. There were statistical differences in some hematological parameters; however, these were not considered physiologically relevant since all values were within the normal range. Gross pathology and histopathological findings were background changes and were not considered enrichment-related. Nesting material and shelters were used frequently and consistently and allowed animals to display species-typical behavior. There was no significant impact on commonly measured end points in HSD rats and B6C3F1/N mice given enrichment devices.

Effects of Buprenorphine, Chlorhexidine, and Low-level Laser Therapy on Wound Healing in Mice.

Systemic buprenorphine and topical antiseptics such as chlorhexidine are frequently used in research animals to aid in pain control and to reduce infection, respectively. These therapeutics are controversial, especially when used in wound healing studies, due to conflicting data suggesting that they delay wound healing. Low-level laser therapy (LLLT) has been used to aid in wound healing without exerting the systemic effects of therapies such as buprenorphine. We conducted 2 studies to investigate the effects of these common treatment modalities on the rate of wound healing in mice. The first study used models of punch biopsy and dermal abrasion to assess whether buprenorphine HCl or 0.12% chlorhexidine delayed wound healing. The second study investigated the effects of sustained-released buprenorphine, 0.05% chlorhexidine, and LLLT on excisional wound healing. The rate of wound healing was assessed by obtaining photographs on days 0, 2, 4, 7, and 9 for the punch biopsy model in study 1, days 0, 1, 2, 4, 6, 8, 11, and 13 for the dermal abrasion model in study 1, and days 0, 3, 6, and 10 for the mice in study 2. Image J software was used to analyze the photographed wounds to determine the wound area. When comparing the wound area on the above days to the original wound area, no significant differences in healing were observed for any of the treatment groups at any time period for either study. Given the results of these studies, we believe that systemic buprenorphine, topical chlorhexidine, and LLLT can be used without impairing or delaying wound healing in mice.