Rodent Anatomy Research Articles

Subiculum–BNST structural connectivity in humans and macaques

Invasive tract-tracing studies in rodents implicate a direct connection between the subiculum and bed nucleus of the stria terminalis (BNST) as a key component of neural pathways mediating hippocampal regulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. A clear characterisation of the connections linking the subiculum and BNST in humans and non-human primates is lacking. To address this, we first delineated the projections from the subiculum to the BNST using anterograde tracers injected into macaque monkeys, revealing evidence for a monosynaptic subiculum-BNST projection involving the fornix. Second, we used in vivo diffusion MRI tractography in macaques and humans to demonstrate substantial subiculum complex connectivity to the BNST in both species. This connection was primarily carried by the fornix, with additional connectivity via the amygdala, consistent with rodent anatomy. Third, utilising the twin-based nature of our human sample, we found that microstructural properties of these tracts were moderately heritable (h2 ∼ 0.5). In a final analysis, we found no evidence of any significant association between subiculum complex-BNST tract microstructure and indices of perceived stress/dispositional negativity and alcohol use, derived from principal component analysis decomposition of self-report data. Our findings address a key translational gap in our knowledge of the neurocircuitry regulating stress.

The nasal cavity in agoutis (Dasyprocta spp.): a micro-computed tomographic and histological study

Abstract Nasal anatomy in rodents is well-studied, but most current knowledge is based on small-bodied muroid species. Nasal anatomy and histology of hystricognaths, the largest living rodents, remains poorly understood. Here, we describe the nasal cavity of agoutis (Dasyprocta spp.), the first large-bodied South American rodents to be studied histologically throughout the nasal cavity. Two adult agoutis were studied using microcomputed tomography, and in one of these, half the snout was serially sectioned and stained for microscopic study. Certain features are notable in Dasyprocta. The frontal recess has five turbinals within it, the most in this space compared to other rodents that have been studied. The nasoturbinal is particularly large in dorsoventral and rostrocaudal dimensions and is entirely non-olfactory in function, in apparent contrast to known muroids. Whether this relates solely to body size scaling or perhaps also relates to directing airflow or conditioning inspired air requires further study. In addition, olfactory epithelium appears more restricted to the olfactory and frontal recesses compared to muroids. At the same time, the rostral tips of the olfactory turbinals bear at least some non-olfactory epithelium. The findings of this study support the hypothesis that turbinals are multifunctional structures, indicating investigators should use caution when categorizing turbinals as specialized for one function (e.g., olfaction or respiratory air-conditioning). Caution may be especially appropriate in the case of large-bodied mammals, in which the different scaling characteristics of respiratory and olfactory mucosa result in relative more of the former type as body size increases.

Research progress of animal models on orthodontic tooth movement

Orthodontic tooth movement animal models are important carriers for studying orthodontic tooth movement. Experimental animals that can be modeled include: rats, mice, dogs, rabbits, etc. How to select suitable animal models for different scientific problems is very important. Therefore, this paper reviews the types and characteristics of orthodontic tooth movement animal models, and focuses on the similarities and differences of rodent anatomy, modeling methods and considerations. It is found that there is a lack of unified modeling standards for orthodontic tooth movement animal models. Thus appropriate animal models should be selected according to actual needs.

Structural connectivity-based segmentation of the human entorhinal cortex

The medial (MEC) and lateral entorhinal cortex (LEC), widely studied in rodents, are well defined and characterized. In humans, however, the exact locations of their homologues remain uncertain. Previous functional magnetic resonance imaging (fMRI) studies have subdivided the human EC into posteromedial (pmEC) and anterolateral (alEC) parts, but uncertainty remains about the choice of imaging modality and seed regions, in particular in light of a substantial revision of the classical model of EC connectivity based on novel insights from rodent anatomy. Here, we used structural, not functional imaging, namely diffusion tensor imaging (DTI) and probabilistic tractography to segment the human EC based on differential connectivity to other brain regions known to project selectively to MEC or LEC. We defined MEC as more strongly connected with presubiculum and retrosplenial cortex (RSC), and LEC as more strongly connected with distal CA1 and proximal subiculum (dCA1pSub) and lateral orbitofrontal cortex (OFC). Although our DTI segmentation had a larger medial-lateral component than in the previous fMRI studies, our results show that the human MEC and LEC homologues have a border oriented both towards the posterior-anterior and medial-lateral axes, supporting the differentiation between pmEC and alEC.

Cooled radiofrequency ablation produces enhanced thermal lesions and leads to beneficial neuroadaptions in vivo

Purpose: Thermal radiofrequency ablation (RF) is a minimally invasive procedure used to denervate the pain-transmitting peripheral nerves in chronic pain patients. Standard RF (SRF) and cooled RF (CRF) are two commonly used thermal ablation technologies hypothesized to provide pain relief by temporarily blocking signaling of the pain-transmitting sensory nerves and eliminating perception of pain in the central nervous system (CNS). CRF overcomes the lesion size limitations inherent to SRF administered at 80°C by circulating fluid around a 60°C probe tip to remove heat from tissue adjacent to the electrode, thereby delivering energy within a larger radius. Although previous ex vivo studies have evaluated RF lesion size, the underlying central and/or peripheral mechanisms for RF-induced pain relief have not been characterized. Here, we present the first in vivo analysis of pathophysiological changes that occur in response to either SRF or CRF. We hypothesize that enhanced delivery of thermal energy provided by CRF correlates with sustained peripheral and/or CNS neuroadaptations. To test this hypothesis, we evaluated functional, structural, and biochemical responses in rodents exposed to sciatic nerve (SN) RF. Methods: As previously reported, sciatic nerve RF ablations can be performed in rats to mimic clinical applications allowing for rapid assessment of changes that occur over extended durations in humans. (Note: Two weeks of a rat lifespan corresponds to one human year.) In one group, male Lewis rats were exposed to recommended human clinical parameters of SRF (90s, 22-gauge, 5mm active tip, 80°C) or CRF (150s, 17-gauge, 2mm active tip, 60°) on the SN and assessed for immediate changes. Another group of Lewis rats were exposed to optimized levels of SRF (50s) or CRF (80s) to allow for long-term evaluation with minimal collateral damage to surrounding tissues and severe adverse events. Power output was recorded to calculate total energy delivered from the generator. Following ablation, rats were assessed for nerve function (electromyography, EMG) and lesion volume (9.4T Bruker MR scanner). EMG measurements were also taken repeatedly over the course of 12 weeks. At necropsy, nerves were harvested for histological analysis (H&E). A subsequent study exposed male Lewis rats to a pain phenotype in which local inflammation was induced via Freund’s complete adjuvant (FCA) injection in the left hind paw prior to ablation. Rats in the pain study were evaluated weekly via von-Frey for changes in left hind paw mechanosensitivity. At day 35 post-ablation necropsy, brains were collected for immunohistochemical analysis of CNS protein expression in brain regions known to be impacted by chronic pain. Results: Utilizing human clinical parameters, CRF delivered ∼3.5 times greater energy than SRF in vivo and remained consistent when optimized for the smaller rodent anatomy. In histological images of CRF nerves, a region of lesser thermal damage (pink) was flanked by regions of more severe damage (purple), paralleling the thermal profile of CRF lesions observed ex vivo. In images from SRF nerves, only a single thermal damage region was observed. High resolution MRI visualization of lesions immediately post-ablation (t=0) suggest larger volumetric lesions in CRF groups. Significantly greater attenuation in compound motor action potential (CMAP) amplitude was found immediately after ablation in and for up to 6 weeks post-ablation in CRF treated nerves, similar to the nerve-transection control group. A return of function was found as early as 4 weeks in SRF treated nerves. By week 8, both CRF and SRF treated groups show signs of return-to-function. A greater magnitude and duration of decreased mechanical sensitivity (up to 21 days) was found in rats treated with CRF compared to rats treated with SRF (7-14 days). Interestingly, CGRP expression in the central and basolateral amygdala was attenuated in CRF-treated rats 35 days post-ablation, relative both to SRF-treated and untreated FCA-Sham controls. Conclusions: Recent clinical results report CRF ablation provides pain relief that lasts more than twelve months. Enhanced lesion volume, a greater impact on nerve function and differential CNS neuroadaptions may elucidate the mechanisms underlying pain relief provided by CRF to chronic pain patients. Further work is warranted to the understand mechanistic differences between SRF and CRF procedures and their impact on pain related outcomes.

Description of the terminal branches of the abdominal aorta in capybaras Hydrochoerus hydrochaeris Linnaeus, 1766 (Mammalia: Rodentia)

The capybara Hydrochoerus hydrochaeris Linnaeus, 1766 (Mammalia: Rodentia) is the largest rodent in the world, with great economic potential. Exceeding 80 kg, the animal always lives close to water bodies and its hierarchical flocks have a single dominant male. Current study analyzes the structure and positioning of the terminal branches of the capybara's abdominal aorta to identify clinical pathologies, surgical and radiological procedures, and to contribute towards the knowledge of the rodent's anatomy. The abdominal aorta and its final branches (internal iliac artery, external iliac artery and median sacral artery) of six animals were dissected. Results showed that the organs were very similar to those registered in the literature for other species of rodents.

Architecture of the Entorhinal Cortex A Review of Entorhinal Anatomy in Rodents with Some Comparative Notes.

The entorhinal cortex (EC) is the major input and output structure of the hippocampal formation, forming the nodal point in cortico-hippocampal circuits. Different division schemes including two or many more subdivisions have been proposed, but here we will argue that subdividing EC into two components, the lateral EC (LEC) and medial EC (MEC) might suffice to describe the functional architecture of EC. This subdivision then leads to an anatomical interpretation of the different phenotypes of LEC and MEC. First, we will briefly summarize the cytoarchitectonic differences and differences in hippocampal projection patterns on which the subdivision between LEC and MEC traditionally is based and provide a short comparative perspective. Second, we focus on main differences in cortical connectivity, leading to the conclusion that the apparent differences may well correlate with the functional differences. Cortical connectivity of MEC is features interactions with areas such as the presubiculum, parasubiculum, retrosplenial cortex (RSC) and postrhinal cortex, all areas that are considered to belong to the “spatial processing domain” of the cortex. In contrast, LEC is strongly connected with olfactory areas, insular, medial- and orbitofrontal areas and perirhinal cortex. These areas are likely more involved in processing of object information, attention and motivation. Third, we will compare the intrinsic networks involving principal- and inter-neurons in LEC and MEC. Together, these observations suggest that the different phenotypes of both EC subdivisions likely depend on the combination of intrinsic organization and specific sets of inputs. We further suggest a reappraisal of the notion of EC as a layered input-output structure for the hippocampal formation.

Intrahepatic Vascular Anatomy in Rats and Mice--Variations and Surgical Implications.

IntroductionThe intra-hepatic vascular anatomy in rodents, its variations and corresponding supplying and draining territories in respect to the lobar structure of the liver have not been described. We performed a detailed anatomical imaging study in rats and mice to allow for further refinement of experimental surgical approaches.MethodsLEWIS-Rats and C57Bl/6N-Mice were subjected to ex-vivo imaging using μCT. The image data were used for semi-automated segmentation to extract the hepatic vascular tree as prerequisite for 3D visualization. The underlying vascular anatomy was reconstructed, analysed and used for determining hepatic vascular territories.ResultsThe four major liver lobes have their own lobar portal supply and hepatic drainage territories. In contrast, the paracaval liver is supplied by various small branches from right and caudate portal veins and drains directly into the vena cava. Variations in hepatic vascular anatomy were observed in terms of branching pattern and distance of branches to each other. The portal vein anatomy is more variable than the hepatic vein anatomy. Surgically relevant variations were primarily observed in portal venous supply.ConclusionsFor the first time the key variations of intrahepatic vascular anatomy in mice and rats and their surgical implications were described. We showed that lobar borders of the liver do not always match vascular territorial borders. These findings are of importance for the design of new surgical procedures and for understanding eventual complications following hepatic surgery.

Investigating the accuracy of microstereotactic-body-radiotherapy utilizing anatomically accurate 3D printed rodent-morphic dosimeters.

Sophisticated small animal irradiators, incorporating cone-beam-CT image-guidance, have recently been developed which enable exploration of the efficacy of advanced radiation treatments in the preclinical setting. Microstereotactic-body-radiation-therapy (microSBRT) is one technique of interest, utilizing field sizes in the range of 1-15 mm. Verification of the accuracy of microSBRT treatment delivery is challenging due to the lack of available methods to comprehensively measure dose distributions in representative phantoms with sufficiently high spatial resolution and in 3 dimensions (3D). This work introduces a potential solution in the form of anatomically accurate rodent-morphic 3D dosimeters compatible with ultrahigh resolution (0.3 mm(3)) optical computed tomography (optical-CT) dose read-out. Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from contours defined on x-ray CT data sets of rats and mice, and using these molds to create tissue-equivalent radiochromic 3D dosimeters from Presage. Anatomically accurate spines were incorporated into some dosimeters, by first 3D printing the spine mold, then forming a high-Z bone equivalent spine insert. This spine insert was then set inside the tissue equivalent body mold. The high-Z spinal insert enabled representative cone-beam CT IGRT targeting. On irradiation, a linear radiochromic change in optical-density occurs in the dosimeter, which is proportional to absorbed dose, and was read out using optical-CT in high-resolution (0.5 mm isotropic voxels). Optical-CT data were converted to absolute dose in two ways: (i) using a calibration curve derived from other Presage dosimeters from the same batch, and (ii) by independent measurement of calibrated dose at a point using a novel detector comprised of a yttrium oxide based nanocrystalline scintillator, with a submillimeter active length. A microSBRT spinal treatment was delivered consisting of a 180° continuous arc at 225 kVp with a 20 × 10 mm field size. Dose response was evaluated using both the Presage/optical-CT 3D dosimetry system described above, and independent verification in select planes using EBT2 radiochromic film placed inside rodent-morphic dosimeters that had been sectioned in half. Rodent-morphic 3D dosimeters were successfully produced from Presage radiochromic material by utilizing 3D printed molds of rat CT contours. The dosimeters were found to be compatible with optical-CT dose readout in high-resolution 3D (0.5 mm isotropic voxels) with minimal artifacts or noise. Cone-beam CT image guidance was possible with these dosimeters due to sufficient contrast between high-Z spinal inserts and tissue equivalent Presage material (CNR ∼10 on CBCT images). Dose at isocenter measured with optical-CT was found to agree with nanoscintillator measurement to within 2.8%. Maximum dose in line profiles taken through Presage and film dose slices agreed within 3%, with FWHM measurements through each profile found to agree within 2%. This work demonstrates the feasibility of using 3D printing technology to make anatomically accurate Presage rodent-morphic dosimeters incorporating spinal-mimicking inserts. High quality optical-CT 3D dosimetry is feasible on these dosimeters, despite the irregular surfaces and implanted inserts. The ability to measure dose distributions in anatomically accurate phantoms represents a powerful useful additional verification tool for preclinical microSBRT.

Emulation of human and rodent cardiac motion with a computer‐controlled cardiac phantom using DENSE MRI

AbstractIn this work, human myocardial motion is studied in an electrical and in an MRI‐compatible (pneumatic) version of a specialized, commercially available, human cardiac phantom at 1.5 Tesla using Displacement Encoding with Stimulated Echoes (DENSE). Work is extended to a prototype rodent phantom, designed, manufactured, implemented, and imaged on a high field (7 T) scanner using urethane‐elastomers under dynamic conditions. Mechanical properties of phantom composition (including commercially available urethane‐elastomers of variable elasticity, poly(glycerol) sebacate (PGS), and polyvinyl acetate (PVA)‐elastomeric samples were evaluated with dynamic mechanical analysis (DMA) and atomic force microscopy (AFM). Both phantoms were cyclically driven at 90–100 bpm and were molded to match accurately human and rodent anatomy. Constructed waveforms attained human and rodent torsions that ranged between 0–40° and 0–20°, respectively. The human phantom used PVA elastomer‐materials, whereas solid, cylindrical urethane‐elastomeric, and PGS samples were tested in the rodent phantom. Measured bulk storage moduli of elasticity varied between 0.7 and 1.06 MPa using the DMA, whereas AFM measurements independently confirmed the graded surface stiffness of elastomers and PGS samples. Displacement maps were generated with DENSE at time intervals ending at 25% of the cardiac cycle (due to the reduced DENSE‐MRI SNR at subsequent intervals) and yielded basal, middle, and apical longitudinal displacements that ranged between −4–6, −8–8, and −10–8 mm, respectively. Elicited in‐plane strain results yielded LV phantom values during the first five cardiac phases that ranged between 0.03–3.7% for Exx and 0.03–4.8% for Eyy. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 59–71, 2013.

SU‐GG‐J‐133: Dosimetric Characterization of an Accessory Designed to Irradiate Rodents Using the Gamma Knife Perfexion Treatment System (PFX)

Purpose: Dosimetric characterization of an accessory designed to irradiate rodents using the Gamma Knife Perfexion treatment system (PFX). Methods and Materials: A rodent holder assembly was designed to be compatible with the PFX for the irradiation of up to 6 anesthetized, immobilized mice in one session. The holder design includes modular plastic construction materials compatible with MR and CT image guidance. Rodent positions are aligned to the holder assembly through sighting of external features on each animal and are targeted using the stereotactic coordinate system of the PFX and the Leksell GammaPlan planning system (LGP). Currently, GammaPlan versions cannot easily model the mice on the rodent holder assembly. Co‐60 dose rates and isodose distributions for various radiation beam configurations and depths were determined using EBT radiochromic film and micro‐LiF TLDs in rodent‐sized polystyrene phantoms mounted on the assembly. Published tissue air ratios were spot‐checked using TPRs obtained in a special step‐wise tapered polystyrene phantom. Results: The measured dose rates using film agreed to within 7% of expected values computed from published TAR and Elekta output data. Dose rates are about 55–60% greater compared to Elekta 16cm sphere calibration. Maximum dose rates scale with the number of unblocked sources. Film dosimetry shows that the 4mm collimator irradiates an ellipsoidal volume with approximately a 3 mm diameter at the 90% isodose. Isodose distributions can be shaped by blocking sectors 3 and 7 to avoid specific rodent anatomy and the adjacent rodent positions on the holder assembly. Conclusion: Deviations from published data can be explained to result from attenuation of the dose rates by the rodent holder. Our dosimetric data supports the use of PFX for multiple‐rodent irradiation. The system can be used to determine response of rodent brain tissue and tumors to radiation and the effect of molecular radiation modifiers.

Distinct Cortical Anatomy Linked to Subregions of the Medial Temporal Lobe Revealed by Intrinsic Functional Connectivity

The hippocampus and adjacent cortical structures in the medial temporal lobe (MTL) contribute to memory through interactions with distributed brain areas. Studies of monkey and rodent anatomy suggest that parallel pathways converge on distinct subregions of the MTL. To explore the cortical areas linked to subregions of the MTL in humans, we examined cortico-cortical and hippocampal-cortical correlations using high-resolution, functional connectivity analysis in 100 individuals. MTL seed regions extended along the anterior to posterior axis and included hippocampus and adjacent structures. Results revealed two separate brain pathways that correlated with distinct subregions within the MTL. The body of the hippocampus and posterior parahippocampal cortex correlated with lateral parietal cortex, regions along the posterior midline including posterior cingulate and retrosplenial cortex, and ventral medial prefrontal cortex. By contrast, anterior hippocampus and the perirhinal/entorhinal cortices correlated with distinct regions in the lateral temporal cortex extending into the temporal pole. The present results are largely consistent with known connectivity in the monkey and provide a novel task-independent dissociation of the parallel pathways supporting the MTL memory system in humans. The cortical pathways include regions that have undergone considerable areal expansion in humans, providing insight into how the MTL memory system has evolved to support a diverse array of cognitive domains.

Training Mouse Pathologists: Five Years of Pathology of Mouse Models of Human Disease Workshops

On September 10–16, 2006 the 5th annual workshop, Pathology of Mouse Models of Human Disease, for human and veterinary pathologists was held at the Fred Hutchinson Cancer Center in Seattle, WA. In this report we outline the rationale for setting up this workshop series, summarize our experience in its development, and outline our main goals and perspectives. The laboratory mouse has been critical to biomedical research since Clarence Cook Little defied the thoughts of the day nearly a century ago by creating the first inbred mouse strain (1). By the end of the millennium just a few years ago inbred mice, and more importantly, genetically engineered mice (GEMs), became the primary tool (2) for major genetic based biomedical breakthroughs. The development of this tool created a problem that has been evident for decades but brought to a head in recent years; whereas the technology to create mutant mice has become more or less routine, there is a shortage of experts to do the requisite histopathologic phenotyping in which accurate comparisons are made with human diseases. Veterinarians are trained in the pathology of multiple species but have only limited knowledge of human pathology, and their experience with laboratory mice is generally restricted to the diagnosis of infectious disease. Many veterinary pathologists gain expertise in toxicologic pathology while evaluating rodent tissues for the pharmaceutical industry, but few are trained in the nuances of mouse genetic pathology and the validation of human disease models. Physicians have extensive knowledge of Homo sapiens, but many are not well versed in the intricacies of rodent anatomy and physiology. We have struggled to redefine training programs and services which integrate veterinary and physician pathologists into a cohesive interdisciplinary approach on an institutional basis (3); however, the traditional Hippocratean, mentor-student approach to teaching medicine remains one of the most effective approaches. In 1999, Drs. Jerry Ward and John Sundberg organized the first large meeting to focus on this topic that was held at the National Institutes of

Computer simulation analysis of normal and abnormal development of the mammalian diaphragm.

BackgroundCongenital diaphragmatic hernia (CDH) is a birth defect with significant morbidity and mortality. Knowledge of diaphragm morphogenesis and the aberrations leading to CDH is limited. Although classical embryologists described the diaphragm as arising from the septum transversum, pleuroperitoneal folds (PPF), esophageal mesentery and body wall, animal studies suggest that the PPF is the major, if not sole, contributor to the muscular diaphragm. Recently, a posterior defect in the PPF has been identified when the teratogen nitrofen is used to induce CDH in fetal rodents. We describe use of a cell-based computer modeling system (Nudge++™) to study diaphragm morphogenesis.Methods and resultsKey diaphragmatic structures were digitized from transverse serial sections of paraffin-embedded mouse embryos at embryonic days 11.5 and 13. Structure boundaries and simulated cells were combined in the Nudge++™ software. Model cells were assigned putative behavioral programs, and these programs were progressively modified to produce a diaphragm consistent with the observed anatomy in rodents. Homology between our model and recent anatomical observations occurred under the following simulation conditions: (1) cell mitoses are restricted to the edge of growing tissue; (2) cells near the chest wall remain mitotically active; (3) mitotically active non-edge cells migrate toward the chest wall; and (4) movement direction depends on clonal differentiation between anterior and posterior PPF cells.ConclusionWith the PPF as the sole source of mitotic cells, an early defect in the PPF evolves into a posteromedial diaphragm defect, similar to that of the rodent nitrofen CDH model. A posterolateral defect, as occurs in human CDH, would be more readily recreated by invoking other cellular contributions. Our results suggest that recent reports of PPF-dominated diaphragm morphogenesis in the rodent may not be strictly applicable to man. The ability to recreate a CDH defect using a combination of experimental data and testable hypotheses gives impetus to simulation modeling as an adjunct to experimental analysis of diaphragm morphogenesis.