Spontaneous histopathology in New Zealand White rabbits: ten years of control data.

The historical control database of a multinational laboratory services provider was queried for all histopathologic findings in New Zealand White rabbits which were used as control animals during a ten-year period (2011-2020). The query included all evaluated tissues, with or without microscopic findings, in studies conducted for safety testing for regulatory approval by the U.S. Food and Drug Agency (FDA) or the U.S. Environmental Protection Agency. A second query included studies conducted in the United Kingdom for control rabbits used in studies compliant with the Healthcare Products Regulatory Agency (MHRA) and/or the European Medicines Agency (EMA), which provide regulatory oversight in the United Kingdom and European Union, respectively. Infiltrates of inflammatory (mixed or mononuclear) cells were commonly noted in various organs including heart, digestive tract, muscle, thyroid, kidney, urinary bladder, eyelid, ocular structures, harderian gland, lacrimal gland, and lung. Mineralization was noted in aorta, kidney, urinary bladder, and ovary. Also noted were degeneration/necrosis in the myocardium, and intramuscular injection sites of the skin, degeneration/regeneration of muscle and diaphragm, ectopic tissue in the pancreas and thyroid, basophilic foci in salivary gland, increased/decreased vacuolation in adrenal gland, increased/decreased lymphocytic cellularity of lymph nodes, intrasinusoidal erythrocytes in lymph nodes, thymic atrophy, increased adipocytes in bone marrow, inflammatory cell foci in the liver and gall bladder, lacrimal gland atrophy, renal tubule basophilia, degeneration/regeneration, and dilatation; oviduct cyst; in the testis, degeneration/atrophy, cellular debris, dilatation, decreased sperm and segmental hypoplasia of seminiferous tubules; and squamous metaplasia of the testis and seminal vesicle.

Revealing the mechanism of action of a first-in-class covalent inhibitor of KRASG12C (ON) and other functional properties of oncogenic KRAS by 31P NMR.

Individual oncogenic KRAS mutants confer distinct differences in biochemical properties and signaling for reasons that are not well understood. KRAS activity is closely coupled to protein dynamics and is regulated through two interconverting conformations: state 1 (inactive, effector binding deficient) and state 2 (active, effector binding enabled). Here, we use 31P NMR to delineate the differences in state 1 and state 2 populations present in WT and common KRAS oncogenic mutants (G12C, G12D, G12V, G13D, and Q61L) bound to its natural substrate GTP or a commonly used nonhydrolyzable analog GppNHp (guanosine-5'-[(ß,γ)-imido] triphosphate). Our results show that GppNHp-bound proteins exhibit significant state 1 population, whereas GTP-bound KRAS is primarily (90% or more) in state 2 conformation. This observation suggests that the predominance of state 1 shown here and in other studies is related to GppNHp and is most likely nonexistent in cells. We characterize the impact of this differential conformational equilibrium of oncogenic KRAS on RAF1 kinase effector RAS-binding domain and intrinsic hydrolysis. Through a KRAS G12C drug discovery, we have identified a novel small-molecule inhibitor, BBO-8956, which is effective against both GDP- and GTP-bound KRAS G12C. We show that binding of this inhibitor significantly perturbs state 1-state 2 equilibrium and induces an inactive state 1 conformation in GTP-bound KRAS G12C. In the presence of BBO-8956, RAF1-RAS-binding domain is unable to induce a signaling competent state 2 conformation within the ternary complex, demonstrating the mechanism of action for this novel and active-conformation inhibitor.

Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing.

Dorsal root ganglia (DRG), trigeminal ganglia (TG), other sensory ganglia, and autonomic ganglia may be injured by some test article classes, including anti-neoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, nerve growth factor inhibitors, and aminoglycoside antibiotics. This article reviews ganglion anatomy, cytology, and pathology (emphasizing sensory ganglia) among common nonclinical species used in assessing product safety for such test articles (TAs). Principal histopathologic findings associated with sensory ganglion injury include neuron degeneration, necrosis, and/or loss; increased satellite glial cell and/or Schwann cell numbers; and leukocyte infiltration and/or inflammation. Secondary nerve fiber degeneration and/or glial reactions may occur in nerves, dorsal spinal nerve roots, spinal cord (dorsal and occasionally lateral funiculi), and sometimes the brainstem. Ganglion findings related to TA administration may result from TA exposure and/or trauma related to direct TA delivery into the central nervous system or ganglia. In some cases, TA-related effects may need to be differentiated from a spectrum of artifactual and/or spontaneous background changes.

Scientific and Regulatory Policy Committee Points to Consider: Sampling, Processing, Evaluation, Interpretation, and Reporting of Test Article-Related Ganglion Pathology for Nonclinical Toxicity Studies.

Certain biopharmaceutical products consistently affect dorsal root ganglia, trigeminal ganglia, and/or autonomic ganglia. Product classes targeting ganglia include antineoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, and anti-nerve growth factor agents. This article outlines "points to consider" for sample collection, processing, evaluation, interpretation, and reporting of ganglion findings; these points are consistent with published best practices for peripheral nervous system evaluation in nonclinical toxicity studies. Ganglion findings often occur as a combination of neuronal injury (e.g., degeneration, necrosis, and/or loss) and/or glial effects (e.g., increased satellite glial cell cellularity) with leukocyte accumulation (e.g., mononuclear cell infiltration or inflammation). Nerve fiber degeneration and/or glial reactions may be seen in nerves, dorsal spinal nerve roots, spinal cord, and occasionally brainstem. Interpretation of test article (TA)-associated effects may be confounded by incidental background changes or experimental procedure-related changes and limited historical control data. Reports should describe findings at these sites, any TA relationship, and the criteria used for assigning severity grades. Contextualizing adversity of ganglia findings can require a weight-of-evidence approach because morphologic changes of variable severity occur in ganglia but often are not accompanied by observable overt in-life functional alterations detectable by conventional behavioral and neurological testing techniques.

The Influence of Geographical Origin, Age, Sex, and Animal Husbandry on the Spontaneous Histopathology of Laboratory Cynomolgus Macaques (Macaca Fascicularis): A Contemporary Global and Multisite Review of Historical Control Data.

To investigate the influence of geographical origin, age, and sex on toxicologically relevant spontaneous histopathology findings in cynomolgus macaques (Macaca fascicularis), we performed a comparative analysis of historical control data (HCD) from 13 test sites that included 3351 animals (1645 females and 1706 males) sourced from Mauritius, China, Vietnam, and Cambodia, aged from 2 to 9.5 years, and from 446 toxicology studies evaluated between 2016 and 2021. The most common findings were mononuclear infiltrates in the kidney, liver, brain, and lung, which showed highest incidences in Mauritian macaques, and heart, salivary glands, and gastrointestinal tract (GIT), which showed highest incidences of mononuclear infiltrates in mainland Asian macaques. Developmental and degenerative findings were more common in Mauritian macaques, while lymphoid hyperplasia and lung pigment showed higher incidences in Asian macaques. Various sex and age-related differences were also present. Despite origin-related differences, the similarities in the nature and distribution of background lesions indicate that macaques from all geographical regions are suitable for toxicity testing and show comparable lesion spectrum. However, in a toxicity study, it is strongly recommended to use animals from a single geographical origin and to follow published guidelines when using HCD to evaluate and interpretate commonly diagnosed spontaneous lesions.

NMR 1H, 13C, 15N backbone resonance assignments of the T35S and oncogenic T35S/Q61L mutants of human KRAS4b in the active, GppNHp-bound conformation.

RAS proteins cycling between the active-form (GTP-bound) and inactive-form (GDP-bound) play a key role in cell signaling pathways that control cell survival, proliferation, and differentiation. Mutations at codon 12, 13, and 61 in RAS are known to attenuate its GTPase activity favoring the RAS active state and constitutively active downstream signaling. This hyperactivation accounts for various malignancies including pancreatic, lung, and colorectal cancers. Active KRAS is found to exist in equilibrium between two rapidly interconverting conformational states (State1-State2) in solution. Due to this dynamic feature of the protein, the 1H-15N correlation cross-peak signals of several amino acid (AA) residues of KRAS belonging to the flexible loop regions are absent from its 2D 1H-15N HSQC spectrum within and near physiological solution pH. A threonine to serine mutation at position 35 (T35S) shifts the interconverting equilibrium to State1 conformation and enables the emergence of such residues in the 2D 1H-15N HSQC spectrum due to gained conformational rigidity. We report here the 1HN, 15N, and 13C backbone resonance assignments for the 19.2 kDa (AA 1-169) protein constructs of KRAS-GppNHp harboring T35S mutation (KRAST35S/C118S-GppNHp) and of its oncogenic counterpart harboring the Q61L mutation (KRAST35S/Q61L/C118S-GppNHp) using heteronuclear, multidimensional NMR spectroscopy at 298 K. High resolution NMR data allowed the unambiguous assignments of 1H-15N correlation cross-peaks for all the residues except for Met1. Furthermore, 2D 1H-15N HSQC overlay of two proteins assisted in determination of Q61L mutation-induced chemical shift perturbations for select residues in the regions of P-loop, Switch-II, and helix α3.

A comparison of the pharmacokinetics and NMDAR antagonism-associated neurotoxicity of ketamine, (2R,6R)-hydroxynorketamine and MK-801.

With the increasing use of ketamine as an off-label treatment for depression and the recent FDA approval of (S)-ketamine for treatment-resistant depression, there is an increased need to understand the long-term safety profile of chronic ketamine administration. Of particular concern is the neurotoxicity previously observed in rat models following acute exposure to high doses of ketamine, broadly referred to as 'Olney's lesions'. This type of toxicity presents as abnormal neuronal cellular vacuolization, followed by neuronal death and has been associated with ketamine's inhibition of the N-methyl-d-aspartate receptor (NMDAR). In this study, a pharmacological and neuropathological analysis of ketamine, the potent NMDAR antagonist MK-801, and the ketamine metabolite (2R,6R)-hydroxynorketamine [(2R,6R)-HNK)] in rats is described following both single dose and repeat dose drug exposures. Ketamine dosing was studied up to 20 mg/kg intravenously for the single-dose neuropathology study and up to 60 mg/kg intraperitoneally for the multiple-dose neuropathology study. MK-801 dosing was studied up to 0.8 mg/kg subcutaneously for both the single and multiple-dose neuropathology studies, while (2R,6R)-HNK dosing was studied up to 160 mg/kg intravenously in both studies. These studies confirm dose-dependent induction of 'Olney's lesions' following both single dose and repeat dosing of MK-801. Ketamine exposure, while showing common behavioral effects, did not induce wide-spread Olney's lesions. Treatment with (2R,6R)-HNK did not produce behavioral effects, toxicity or any evidence of Olney's lesion formation. Based on these results, future NMDAR-antagonist neurotoxicity studies should strongly consider taking pharmacokinetics more thoroughly into account.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Dog.

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the societies of toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in most tissues and organs from the dog used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions, lesions induced by exposure to test materials, and relevant infectious and parasitic lesions. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Neuroanatomy and Sampling of Central Projections for the Visual System in Mammals Used in Toxicity Testing.

Visual system toxicity may manifest anywhere in the visual system, from the eye proper to the visual brain. Therefore, effective screening for visual system toxicity must evaluate not only ocular structures (ie, eye and optic nerve) but also multiple key brain regions involved in vision (eg, optic tract, subcortical relay nuclei, and primary and secondary visual cortices). Despite a generally comparable pattern across species, the neuroanatomic organization and function of the visual brain in rodents and rabbits exhibit appreciable differences relative to nonrodents. Currently recognized sampling practices for general toxicity studies in animals, which are based on easily discerned external neuroanatomic landmarks and guided by extant stereotaxic brain atlases, typically will permit histopathologic evaluation of many brain centers involved in visual sensation (eg, optic chiasm, optic tract, dorsal lateral geniculate nucleus, primary and secondary visual cortices) and often some subcortical brain nuclei involved in light-modulated nonvisual activities needed for visual attention and orientation (eg, rostral colliculus in quadrupeds, termed the superior colliculus in bipeds; several cranial nerve nuclei). Pathologic findings induced by toxicants in the visual brain centers are similar to those that are produced in other brain regions.

Semiquantitative Methods for GFP Immunohistochemistry and In Situ Hybridization to Evaluate AAV Transduction of Mouse Retinal Cells Following Subretinal Injection.

The goal of this study was to develop methods for the evaluation of green fluorescent protein (GFP) and GFP transcript biodistribution in paraformaldehyde-fixed paraffin-embedded (PFPE) eye sections to assess the effectiveness of Adeno-associated virus (AAV) gene delivery in an experimental ocular toxicity study. Female C57BL/6NTac mice were administered AAV2-enhancedGFP vector once via subretinal injection. One group also received anti-inflammatory therapy (meloxicam). Immunohistochemistry (IHC) and RNA in situ hybridization (ISH) for GFP were performed on PFPE serial eye sections and evaluated using semiquantitative methods. On day 43, GFP labeling in both IHC and ISH sections was greatest in the retinal pigment epithelium, compared with other retinal layers in which expression was negative to moderate. Despite the presence of IHC GFP labeling in the photoreceptor layer (PRL) in some animals, only low numbers of transduced cells were detected by ISH in the PRL. Simultaneous analysis of IHC and ISH may be needed for comprehensive assessment of gene transduction and protein biodistribution. This study demonstrates approaches for semiquantitative evaluation of IHC and ISH that allow interpretation and reporting of GFP expression in toxicity studies.

Spontaneous Background and Procedure-Related Microscopic Findings and Common Artifacts in Ocular Tissues of Laboratory Animals in Ocular Studies.

Identification of test article-related microscopic findings in ocular toxicology studies requires a working knowledge of the artifacts and procedure-related or background findings commonly encountered in such studies. The objective of this article is to provide a mini-atlas of the artifacts and procedure-related or spontaneous background findings commonly observed in ocular tissues from animals in toxicology studies of ocular drug candidates. Artifacts in the eye are often related to collection or fixation procedures and include swelling and vacuolation of lens fibers, separation of the neuroretina from the retinal pigment epithelium (RPE), and vacuolation of the optic nerve. Common in-life procedure-related findings include intravitreal injection needle tracks in the sclera and ciliary body pars plana and foci of RPE hypertrophy and/or hyperpigmentation at subretinal injection sites. Common background findings include corneal mineralization, uveal mononuclear cell infiltrates, and peripheral displacement of photoreceptor nuclei in the retina. A few uncommon spontaneous background findings that may be confused with test article-related findings, such as bilateral optic atrophy in macaques, are also included.

Proliferative and Nonproliferative Lesions of the Rat and Mouse Central and Peripheral Nervous Systems: New and Revised INHAND Terms.

Harmonization of diagnostic terminology used during the histopathologic analysis of rodent tissue sections from nonclinical toxicity studies will improve the consistency of data sets produced by laboratories located around the world. The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a cooperative enterprise of 4 major societies of toxicologic pathology to develop a globally accepted standard vocabulary for proliferative and nonproliferative lesions in rodents. A prior manuscript (Toxicol Pathol 2012;40[4 Suppl]:87S-157S) defined multiple diagnostic terms for toxicant-induced lesions, common spontaneous and age-related changes, and principal confounding artifacts in the rat and mouse central nervous system (CNS) and peripheral nervous system (PNS). The current article defines 9 new diagnostic terms and updates 2 previous terms for findings in the rodent CNS and PNS, the need for which has become evident in the years since the publication of the initial INHAND nomenclature for findings in rodent neural tissues. The nomenclature presented in this document is also available electronically on the Internet at the goRENI website (http://www.goreni.org/).

Large sternal exostoses presenting as stridor: A surgical and anesthetic challenge.

BACKGROUND AND AIMS: Large osteochondroma arising from chest wall and sternum is uncommon and presentation with airway compression is further uncommon. METHODS: Here we present a case of large chest wall osteochondroma as a part of hereditary multiple exostoses in a 9-year-old boy presented with a history of stridor and shortness of breath. The bony mass of the right chest wall was extending up to a suprasternal notch and compressing the trachea. RESULTS: The case was successfully managed by initial femoro-femoral cardiopulmonary bypass under local anesthesia before the induction of anesthesia to prevent respiratory collapse, followed by debulking surgery was done.

Autologous bone marrow mononuclear cell transplantation in patients with chronic traumatic brain injury- a clinical study.

BACKGROUND: Chronic Traumatic Brain Injury (TBI) is one of the common causes of longterm disability worldwide. Cell transplantation has gained attention as a prospective therapeutic option for neurotraumatic disorders like TBI. The postulated mechanism of cell transplantation which includes angiogenesis, axonal regeneration, neurogenesis and synaptic remodeling, may tackle the pathology of chronic TBI and improve overall functioning. METHODS: To study the effects of cell transplantation, 50 patients with chronic TBI were enrolled in an open label non-randomized study. The intervention included intrathecal transplantation of autologous bone marrow mononuclear cells and neurorehabilitation. Mean follow up duration was 22 months. Fifteen patients underwent second dose of cell transplantation, 6 months after their first intervention. Percentage analysis was performed to analyze the symptomatic improvements in the patients. Functional independence measure (FIM) was used as an outcome measure to evaluate the functional changes in the patients. Statistical tests were applied on the pre-intervention and post-intervention scores for determining the significance. Comparative Positron Emission Tomography- computed tomography (PET CT) scans were performed in 10 patients to monitor the effect of intervention on brain function. Factors such as age, multiple doses, time since injury and severity of injury were also analyzed to determine their effect on the outcome of cell transplantation. Adverse events were monitored throughout the follow up period. RESULTS: Overall 92% patients showed improvements in symptoms such as sitting and standing balance, voluntary control, memory, oromotor skills lower limb activities, ambulation, trunk & upper limb activity, speech, posture, communication, psychological status, cognition, attention and concentration, muscle tone, coordination, activities of daily living. A statistically significant (at p ≤ 0.05 with p-value 0) improvement was observed in the scores of FIM after intervention on the Wilcoxon signed rank test. Better outcome of the intervention was found in patients with mild TBI, age less than 18 years and time since injury less than 5 years. Ten patients who underwent a repeat PET CT scan brain showed improved brain metabolism in areas which correlated to the symptomatic changes. Two patients had an episode of seizures which was managed with medication. They both had an abnormal EEG before the intervention and 1 of them had previous history and was on antiepileptics. No other major adverse events were recorded. CONCLUSION: This study demonstrates the safety and efficacy of cell transplantation in chronic TBI on long term follow up. Early intervention in younger age group of patients with mild TBI showed the best outcome in this study. In combination with neurorehabilitation, cell transplantation can enhance functional recovery and improve quality of life of patients with chronic TBI. PET CT scan brain should be explored as a monitoring tool to study the efficacy of intervention.

LRRK2 inhibitors induce reversible changes in nonhuman primate lungs without measurable pulmonary deficits.

The kinase-activating mutation G2019S in leucine-rich repeat kinase 2 (LRRK2) is one of the most common genetic causes of Parkinson's disease (PD) and has spurred development of LRRK2 inhibitors. Preclinical studies have raised concerns about the safety of LRRK2 inhibitors due to histopathological changes in the lungs of nonhuman primates treated with two of these compounds. Here, we investigated whether these lung effects represented on-target pharmacology and whether they were reversible after drug withdrawal in macaques. We also examined whether treatment was associated with pulmonary function deficits. We conducted a 2-week repeat-dose toxicology study in macaques comparing three different LRRK2 inhibitors: GNE-7915 (30 mg/kg, twice daily as a positive control), MLi-2 (15 and 50 mg/kg, once daily), and PFE-360 (3 and 6 mg/kg, once daily). Subsets of animals dosed with GNE-7915 or MLi-2 were evaluated 2 weeks after drug withdrawal for lung function. All compounds induced mild cytoplasmic vacuolation of type II lung pneumocytes without signs of lung degeneration, implicating on-target pharmacology. At low doses of PFE-360 or MLi-2, there was ~50 or 100% LRRK2 inhibition in brain tissue, respectively, but histopathological lung changes were either absent or minimal. The lung effect was reversible after dosing ceased. Lung function tests demonstrated that the histological changes in lung tissue induced by MLi-2 and GNE-7915 did not result in pulmonary deficits. Our results suggest that the observed lung effects in nonhuman primates in response to LRRK2 inhibitors should not preclude clinical testing of these compounds for PD.

Cell transplantation as a novel therapeutic strategy for autism spectrum disorders: a clinical study.

BACKGROUND: Autism spectrum disorders [ASD] is a lifelong disability mainly affecting the development, communication, social interaction and behavior of an individual. Cell transplantation is emerging as a potential therapeutic strategy for ASD. Our previously published proof of concept study showed beneficial effects of cell transplantation in ASD. This study shows effect of cell transplantation in a larger sample size of ASD patients. METHODS: 254 patients diagnosed with ASD on DSM V criteria were enrolled in this open label non-randomized study. The intervention included intrathecal transplantation of autologous bone marrow mononuclear cells and neurorehabilitation. On mean follow up of 7.50 months, percentage analysis was performed on all symptomatic changes. Changes in outcome measures, Indian Scale for Assessment of Autism [ISAA] and Childhood Autism Rating Scale [CARS], were analyzed statistically using Wilcoxon Signed-Rank Test. Comparative analysis of Positron Emission Tomography [PET CT] scan brain, performed before and 6 months after intervention, was done in 86 patients to monitor the outcome at cellular level. Change in the standardized uptake values was statistically evaluated using T-Test [P≤0.05]. RESULTS: Improvements were observed in eye contact, attention and concentration, hyperactivity, sitting tolerance, social interaction, stereotypical behavior, aggressiveness, communication, speech, command following and self-stimulatory behavior. Statistically significant improvement was observed in scores of ISAA and CARS after intervention. A significantly better outcome of the intervention was found in patients at younger age and with shorter duration of disease [<5 years from time of diagnosis]. 86 patients who underwent a repeat PET CT scan showed improved brain metabolism after intervention in areas which correlated to the symptomatic changes. No major procedure related adverse events were recorded. However, 5 patients, with history of seizure and abnormal EEG, had an episode of seizure which was managed using medications. Outcome of intervention in these patients was not affected by seizures as improvements were observed in them. CONCLUSION: The results of this study indicate that autologous bone marrow mononuclear cells in combination with neurorehabilitation are a safe and effective treatment modality for ASD. It improves the quality of life of patients and helps them to integrate in mainstream lifestyle.

Autophagy of Sensory Neurons in the Trigeminal and Dorsal Root Ganglia of Cynomolgus Monkeys (Macaca fascicularis).

Although necrosis and apoptosis are uncommon, autophagy of sensory neurons (ASN) in trigeminal and dorsal root ganglia is a very common, spontaneous finding in cynomolgus monkeys (Macaca fascicularis). Data from one author's (Butt) laboratory showed 12 of 22 studies (year range 2017 to 2019) that included the evaluation of sensory ganglia from cynomolgus monkeys had at least one control animal with ASN. Autophagy of sensory neurons is characterized by a distinct cell membrane, cytoplasm filled with autolysosomes, disintegrated nuclear membrane, and/or globules of degraded chromatin. Since these changes are consistent with autophagy and indicate an irreversible state, a diagnosis of autophagy is preferred instead of necrosis or degeneration. Sensory ganglia are not commonly evaluated in nonclinical toxicology investigations so many pathologists may be unaware of this common change. Especially due to the typically small group size of monkey studies, the observation of this change in sensory ganglia may lead to a faulty interpretation that this change is due to the test article. This article describes the light microscopic and ultrastructural characteristics of neuronal autophagy in trigeminal and dorsal root ganglia and provides historical control data of the incidence of this change in cynomolgus monkeys.

Atlas of Normal Microanatomy, Procedural and Processing Artifacts, Common Background Findings, and Neurotoxic Lesions in the Peripheral Nervous System of Laboratory Animals.

The ability to differentiate among normal structures, procedural and processing artifacts, spontaneous background changes, and test article-related effects in the peripheral nervous system (PNS) is essential for interpreting microscopic features of ganglia and nerves evaluated in animal species commonly used in toxicity studies evaluating regulated products and chemicals. This atlas provides images of findings that may be encountered in ganglia and nerves of animal species commonly used in product discovery and development. Most atlas images are of tissues from control animals that were processed using routine methods (ie, immersion fixation in neutral-buffered 10% formalin, embedding in paraffin, sectioning at 5 µm, and staining with hematoxylin and eosin) since these preparations are traditionally applied to study materials produced during most animal toxicity studies. A few images are of tissues processed using special procedures (ie, immersion or perfusion fixation using methanol-free 4% formaldehyde, postfixation in glutaraldehyde and osmium, embedding in hard plastic resin, sectioning at 1 µm, and staining with toluidine blue), since these preparations promote better stabilization of lipids and thus optimal resolution of myelin sheaths. Together, this compilation provides a useful resource for discriminating among normal structures, procedure- and processing-related artifacts, incidental background changes, and treatment-induced findings that may be seen in PNS tissues of laboratory animals.

Incidental Ultrastructural Findings in the Sural Nerve and Dorsal Root Ganglion of Aged Control Sprague Dawley Rats in a Nonclinical Carcinogenicity Study.

Xenobiotic-induced peripheral nerve damage is a growing concern. Identifying relative risks that a new drug may cause peripheral nerve injury over long periods of administration is gathering importance in the evaluation of animal models. Separating out age-related changes in peripheral nerves of rats caused by compression injury from drug-induced effects has been difficult. Biopsy of the sural nerve is utilized in humans for investigations of peripheral neuropathy, because it is largely removed from the effects of nerve compression. This study used transmission electron microscopy to identify incidental findings in the sural nerves and dorsal root ganglia of aged control rats over time. The goal was to establish a baseline understanding of the range of possible changes that could be noted in controls compared to rats treated with any new investigative drug. In this evaluation, most sural nerve fibers from aged control rats had few ultrastructural abnormalities of pathologic significance. However, glycogenosomes, polyglucosan bodies, swollen mitochondria, autolysosomes, split myelin, Schwann cell processes, and endoneural macrophages with phagocytosed debris (considered an indication of ongoing degenerative changes) were occasionally noted.