In vivo tracking of [89Zr]Zr-labeled engineered extracellular vesicles by PET reveals organ-specific biodistribution based upon the route of administration.

Extracellular vesicles (EVs) have garnered increasing interest as delivery vehicles for multiple classes of therapeutics based on their role as mediators in an important, natural intercellular communication system. We recently described a platform to allow the design, production and in vivo study of human EVs with specific properties (drug or tropism modifiers). This article seeks to compare and expand upon historical biodistribution and kinetic data by comparing systemically and compartmentally administered labeled engineered EVs using in vivo and ex vivo techniques. METHODS: EVs were surface-labeled to high radiochemical purity and specific activity with 89Zirconium deferoxamine ([89Zr]Zr-DFO) and/or cy7-scrambled antisense oligonucleotide (Cy7-ExoASOscr), or luminally loaded with GFP for in vivo tracking in rodents and non-human primates (NHPs). Positron Emission Tomography (PET) and subsequent immunohistochemistry (IHC) and autoradiography (ARG) cross-validation enabled assessment of the anatomical and cellular distribution of labeled EVs both spatially and temporally. RESULTS: Over time, systemic administration of engineered EVs distributed preferentially to the liver and spleen (Intravenous, IV), gastrointestinal tract and lymph nodes (Intraperitoneal, IP) and local/regional lymph nodes (Subcutaneous, SC). Immunostaining of dissected organs displaying PET signal revealed co-localization of an EV marker (PTGFRN) with a subset of macrophage markers (CD206, F4/80, IBA1). Compartmental dosing into NHP cerebrospinal fluid (CSF) resulted in a heterogenous distribution of labeled EVs depending upon whether the route was intrathecal (ITH), intracisterna magna (ICM) or intracerebroventricular (ICV), compared to the homogeneous distribution observed in rodents. Thus anatomically, ITH administration in NHP revealed meningeal distribution along the neuraxis to the base of the skull. In contrast ICM and ICV dosing resulted in meningeal distribution around the skull and to the cervical and thoracic spinal column. Further characterization using IHC shows uptake in a subset of meningeal macrophages. CONCLUSIONS: The present studies provide a comprehensive assessment of the fate of robustly and reproducibly labeled engineered EVs across several mammalian species. The in vivo distribution was observed to be both spatially and temporally dependent upon the route of administration providing insight into potential targeting opportunities for engineered EVs carrying a therapeutic payload.

Solving an Old Dogma: Is it an Arteriole or a Venule?

There are very few reliable methods in the literature to discern with certainty between cerebral arterioles and venules. Smooth muscle cells (SMC) and pericytes are present in both arterioles and venules, so immunocytochemistry for markers specific to intramural cells (IMC) is unreliable. This study employed transmission electron microscopy (TEM) and a canine brain to produce robust criteria for the correct identification of cerebral arterioles and venules based on lumen:vessel wall area, tested against the less accurate lumen diameter:vessel wall thickness. We first used morphology of IMC to identify two distinct groups of vessels; group 1 with morphology akin to venules and group 2 with morphology akin to arterioles. We then quantitatively assessed these vessels for lumen:vessel wall area ratio and lumen diameter:wall thickness ratio. After assessing 112 vessels, we show two distinct groups of vessels that can be separated using lumen:vessel wall area (group 1, 1.89 -10.96 vs. group 2, 0.27-1.57; p < 0.001) but not using lumen diameter:vessel wall thickness where a substantial overlap in ranges between groups occurred (group 1, 1.58-22.66 vs. group 2, 1.40-11.63). We, therefore, conclude that lumen:vessel wall area is a more sensitive and preferred method for distinguishing cerebral arterioles from venules. The significance of this study is wide, as cerebral small vessel disease is a key feature of vascular dementia and understanding the pathogenesis relies on correct identification of vessels.

The perivascular pathways for influx of cerebrospinal fluid are most efficient in the midbrain.

Although there are no conventional lymphatic vessels in the brain, fluid and solutes drain along basement membranes (BMs) of cerebral capillaries and arteries towards the subarachnoid space and cervical lymph nodes. Convective influx/glymphatic entry of the cerebrospinal fluid (CSF) into the brain parenchyma occurs along the pial-glial BMs of arteries. This project tested the hypotheses that pial-glial BM of arteries are thicker in the midbrain, allowing more glymphatic entry of CSF. The in vivo MRI and PET images were obtained from a 4.2-year-old dog, whereas the post-mortem electron microscopy was performed in a 12-year-old dog. We demonstrated a significant increase in the thickness of the pial-glial BM in the midbrain compared with the same BM in different regions of the brain and an increase in the convective influx of fluid from the subarachnoid space. These results are highly significant for the intrathecal drug delivery into the brain, indicating that the midbrain is better equipped for convective influx/glymphatic entry of the CSF.

The structure of the perivascular compartment in the old canine brain: a case study.

Dilatation of periarteriolar spaces in MRI of the ageing human brains occurs in white matter (WM), basal ganglia and midbrain but not in cerebral cortex. Perivenous collagenous occurs in periventricular but not in subcortical WM.Here we test the hypotheses that (a) the capacity for dilatation of periarteriolar spaces correlates with the anatomical distribution of leptomeningeal cells coating intracerebral arteries and (b) the regional development of perivenous collagenous in the WM correlates with the population of intramural cells in the walls of veins.The anatomical distribution of leptomeningeal and intramural cells related to cerebral blood vessels is best documented by electron microscopy, requiring perfusion-fixed tissue not available in human material. We therefore analysed perfusion-fixed brain from a 12-year-old Beagle dog as the canine brain represents the anatomical arrangement in the human brain. Results showed regional variation in the arrangement of leptomeningeal cells around blood vessels. Arterioles are enveloped by one complete layer of leptomeninges often with a second incomplete layer in the WM. Venules showed incomplete layers of leptomeningeal cells. Intramural cell expression was higher in the post-capillary venules of the subcortical WM when compared with periventricular WM, suggesting that periventricular collagenosis around venules may be due to a lower resistance in the venular walls. It appears that the regional variation in the capacity for dilatation of arteriolar perivascular spaces in the white WM may be related to the number of perivascular leptomeningeal cells surrounding vessels in different areas of the brain.

Three-Dimensional Dosimetry for Radiation Safety Estimates from Intrathecal Administration.

Intrathecal administration is of growing interest for drug delivery, and its utility is being increasingly investigated through imaging. In this work, the 3-dimensional Voxel-Based Internal Dosimetry Application (VIDA) and 4D Extended Cardiac Torso Phantom (XCAT) were extended to provide radiation safety estimates specific to intrathecal administration. Methods: The 3-dimensional VIDA dosimetry application Monte Carlo simulation was run using a modified XCAT phantom with additional and edited cerebrospinal fluid (CSF) regions to produce voxel-level absorbed dose per unit cumulated activity maps for 9 selected source regions. Simulation validation was performed to compare absorbed dose estimates for common organs in a preexisting dosimetry tool (OLINDA/EXM). Dynamic planar imaging data were acquired in 6 healthy subjects using administered volumes of 5 or 15 mL (n = 3 each) of 185 MBq of 99mTc-diethylenetriaminepentaacetic acid. Absorbed dose was estimated for each subject using the intrathecal-specific dosimetry application. Results: Simulation results were within 6% of OLINDA estimates for common organs. Absorbed dose estimates were highest (0.3-0.8 mGy/MBq) in the lumbar CSF space. A whole-body effective dose estimate of 0.003 mSv/MBq was observed. An administered volume dependency was observed with a 15-mL volume, resulting in lower absorbed dose estimates for several intrathecal and nonintrathecal regions. Conclusion: The intrathecal-specific VIDA implementation enables tailored dosimetry estimation for regions most relevant in intrathecal administration. Absorbed doses are highly localized to CSF and spinal regions and should be taken into consideration when designing intrathecal imaging studies. A potentially interesting relationship was observed between absorbed dose and administered volume, which merits further investigation.

Characterization of the 5-HT2C receptor agonist lorcaserin on efficacy and safety measures in a rat model of diet-induced obesity.

The 5-HT2C receptor agonist lorcaserin (Belviq®) has been Food and Drug Administration (FDA) approved for the treatment of obesity. The present study is a back translational investigation into the effect of 28-day lorcaserin treatment in a diet-induced obesity (DIO) model using male, Sprague-Dawley rats. An assessment of drug effect on efficacy and multiple safety endpoints including cardiac function was undertaken. Lorcaserin (1-2 mg/kg SC b.i.d.) significantly reduced percentage body weight gain compared to vehicle-treated controls (VEH: 10.6 ± 0.4%; LOR 1: 7.6 ± 1.2%; LOR 2: 5.4 ± 0.6%). Measurement of body composition using quantitative magnetic resonance (QMR) imaging indicated this change was due to the selective reduction in body fat mass. Modest effects on food intake were recorded. At the completion of the treatment phase, echocardiography revealed no evidence for valvulopathy, that is, no aortic or mitral valve regurgitation. The pharmacokinetics of the present treatment regimen was determined over a 7-day treatment period; plasma C min and C max were in the range 13-160 ng/mL (1 mg/kg b.i.d.) and 34-264 ng/mL (2 mg/kg b.i.d.) with no evidence for drug accumulation. In sum, these studies show an effect of lorcaserin in the DIO model, that in the context of the primary endpoint measure of % body weight change was similar to that reported clinically (i.e., 3.0-5.2% vs. 3.2%). The present studies highlight the translational value of obesity models such as DIO, and suggest that assuming consideration is paid to nonspecific drug effects such as malaise, the DIO model has reasonable forward translational value to help predict clinical outcomes of a new chemical entity.

Comparison of bronchoalveolar lavage fluid obtained by manual aspiration with a handheld syringe with that obtained by automated suction pump aspiration from healthy dogs.

OBJECTIVE: To compare bronchoalveolar lavage (BAL) fluid obtained by manual aspiration (MA) with a handheld syringe with that obtained by suction pump aspiration (SPA) in healthy dogs. ANIMALS: 13 adult Beagles. PROCEDURES: Each dog was anesthetized and bronchoscopic BAL was performed. The MA technique was accomplished with a 35-mL syringe attached to the bronchoscope biopsy channel. The SPA technique was achieved with negative pressure (5 kPa) applied to the bronchoscope suction valve with a disposable suction trap. Both aspiration techniques were performed in each dog in randomized order on opposite caudal lung lobes. Two 1 mL/kg aliquots of warm saline (0.9% NaCl) solution were infused per site. For each BAL fluid sample, the percentage of retrieved fluid was calculated, the total nucleated cell count (TNCC) and differential cell count were determined, and semiquantitative assessment of slide quality was performed. Comparisons were made between MA and SPA techniques for each outcome. RESULTS: 1 dog was removed from the study because of illness. The mean percentage of fluid retrieved (mean difference, 23%) and median TNCC (median distribution of differences, 100 cells/µL) for samples obtained by SPA were significantly greater than those for samples obtained by MA. CONCLUSIONS AND CLINICAL RELEVANCE: In healthy dogs, BAL by SPA resulted in a significantly higher percentage of fluid retrieval and samples with a higher TNCC than did MA. Further evaluation of aspiration techniques in dogs with respiratory tract disease is required to assess whether SPA improves the diagnostic yield of BAL samples.

Noninvasive measurements of body composition and body water via quantitative magnetic resonance, deuterium water, and dual-energy x-ray absorptiometry in cats.

OBJECTIVE: To compare quantitative magnetic resonance (QMR), dual-energy x-ray absorptiometry (DXA), and deuterium oxide (D2O) dilution methods for measurement of total body water (TBW), lean body mass (LBM), and fat mass (FM) in healthy cats and to assess QMR precision and accuracy. ANIMALS: Domestic shorthair cats (58 and 32 cats for trials 1 and 2, respectively). PROCEDURES: QMR scans of awake cats performed with 2 units were followed by administration of D2O tracer (100 mg/kg, PO). Cats then were anesthetized, which was followed by QMR and DXA scans. Jugular blood samples were collected before and 120 minutes after D2O administration. RESULTS: QMR precision was similar between units (coefficient of variation < 2.9% for all measures). Fat mass, LBM, and TBW were similar for awake or sedated cats and differed by 4.0%, 3.4%, and 3.9%, respectively, depending on the unit. The QMR minimally underestimated TBW (1.4%) and LBM (4.4%) but significantly underestimated FM (29%), whereas DXA significantly underestimated LBM (9.2%) and quantitatively underestimated FM (9.3%). A significant relationship with D2O measurement was detected for all QMR (r(2) > 0.84) and DXA (r(2) > 0.84) measurements. CONCLUSIONS AND CLINICAL RELEVANCE: QMR was useful for determining body composition in cats; precision was improved over DXA. Quantitative magnetic resonance can be used to safely and rapidly acquire data without the need for anesthesia, facilitating frequent monitoring of weight changes in geriatric, extremely young, or ill pets. Compared with the D2O dilution method, QMR correction equations provided accurate data over a range of body compositions.

Noninvasive measurements of body composition and body water via quantitative magnetic resonance, deuterium water, and dual-energy x-ray absorptiometry in awake and sedated dogs.

OBJECTIVE: To compare quantitative magnetic resonance (QMR), dual-energy x-ray absorptiometry (DXA), and deuterium oxide (D2O) methods for measurement of total body water (TBW), lean body mass (LBM), and fat mass (FM) in healthy dogs and to assess QMR accuracy. ANIMALS: 58 Beagles (9 months to 11.5 years old). PROCEDURES: QMR scans were performed on awake dogs. A D2O tracer was administered (100 mg/kg, PO) immediately before dogs were sedated, which was followed by a second QMR or DXA scan. Jugular blood samples were collected before and 120 minutes after D2O administration. RESULTS: TBW, LBM, and FM determined via QMR were not significantly different between awake or sedated dogs, and means differed by only 2.0%, 2.2%, and 4.3%, respectively. Compared with results for D2O dilution, QMR significantly underestimated TBW (10.2%), LBM (13.4%), and FM (15.4%). Similarly, DXA underestimated LBM (7.3%) and FM (8.4%). A significant relationship was detected between FM measured via D2O dilution and QMR (r(2) > 0.89) or DXA (r(2) > 0.88). Even though means of TBW and LBM differed significantly between D2O dilution and QMR or DXA, values were highly related (r(2) > 0.92). CONCLUSIONS AND CLINICAL RELEVANCE: QMR was useful for determining body composition in dogs and can be used to safely and rapidly acquire accurate data without the need for sedation or anesthesia. These benefits can facilitate frequent scans, particularly in geriatric, extremely young, or ill pets. Compared with the D2O dilution method, QMR correction equations provided accurate assessment over a range of body compositions.

Comparison between manual aspiration via polyethylene tubing and aspiration via a suction pump with a suction trap connection for performing bronchoalveolar lavage in healthy dogs.

OBJECTIVE: To compare the diagnostic quality of bronchoalveolar lavage (BAL) fluid acquired from healthy dogs by manual aspiration via polyethylene tubing (MAPT) and via suction pump aspiration (SPA) with a suction trap connection. ANIMALS: 12 healthy adult Beagles. PROCEDURES: BAL was performed with bronchoscopic guidance in anesthetized dogs. The MAPT was performed with a 35-mL syringe attached to polyethylene tubing wedged in a bronchus via the bronchoscope's biopsy channel. The SPA was performed with 5 kPa of negative pressure applied to the bronchoscope's suction valve via a suction trap. The MAPT and SPA techniques were performed in randomized order on opposite caudal lung lobes of each dog. Two 1 mL/kg lavages were performed per site. Samples of BAL fluid were analyzed on the basis of a semiquantitative quality scale, percentage of retrieved fluid, and total nucleated and differential cell counts. Results were compared with Wilcoxon signed rank tests. RESULTS: Percentage of BAL fluid retrieved (median difference, 16.2%), surfactant score (median difference, 1), and neutrophil count (median difference, 74 cells/µL) were significantly higher for SPA than for MAPT. A higher BAL fluid epithelial cell score was obtained via MAPT, compared with that for samples obtained via SPA (median difference, 1). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that in healthy dogs, SPA provided a higher percentage of BAL fluid retrieval than did MAPT. The SPA technique may improve the rate of diagnostic success for BAL in dogs, compared with that for MAPT. Further evaluation of these aspiration techniques in dogs with respiratory tract disease is required.

Incidence of and risk factors for seizures after myelography performed with iohexol in dogs: 503 cases (2002-2004).

OBJECTIVE: To establish the incidence of and risk factors for seizures following myelography performed with iohexol in dogs. DESIGN: Retrospective case series. ANIMALS: 503 dogs. PROCEDURES: Medical records were searched for dogs that underwent myelography between April 2002 and December 2004. Data extracted included body weight, breed, age, sex, volume and dose of iohexol, site of injections, location of lesion, duration of anesthesia, surgical procedures immediately after myelography, use of acepromazine, and presence or absence of seizures. RESULTS: 15 (3%) dogs had postmyelographic seizures. Risk factors significantly associated with seizures were size of dogs (large dogs were 35.35 times as likely to have seizures as were small dogs), location of contrast medium injection (dogs in which iohexol was injected into the cerebellomedullary cistern were 7.4 times as likely to have seizures as were dogs in which iohexol was injected into the lumbar cistern), location of lesion (dogs with lesions at the level of the cervical portion of the vertebral column were 4.65 times as likely to develop seizures as were dogs with lesions in other regions), and total volume of iohexol. Mean ± SD total volume of iohexol was 11.73 ± 5.52 mL (median, 10.5 mL [range, 3.0 to 21.0 mL]) for dogs that had seizures and 4.57 ± 4.13 mL (median, 3.5 mL [range, 0.75 to 45.0 mL]) for those that did not. CONCLUSIONS AND CLINICAL RELEVANCE: Large-breed dogs with cervical lesions and large volumes of iohexol injected into the cerebellomedullary cistern had the highest risk of seizures. The use of contrast medium volumes > 8 mL in large dogs should be avoided, with preference given to injections into the lumbar cistern.

Migration of cells from the yolk sac to hematopoietic tissues after in utero transplantation of early and mid gestation canine fetuses.

BACKGROUND: In utero hematopoietic cell transplantation offers a means of early intervention for the treatment of diseases before birth. Delivery of cells to the yolk sac is a minimally invasive approach that results in low levels of chimerism. However, there is little information on the optimal doses, timing of delivery, and migration of transplanted cells from the yolk sac into the fetus. METHODS: Varying cell doses of mesenchymal stromal cells or bone marrow mononuclear cells labeled with fluorescent supraparamagnetic iron oxide nanoparticles and a fluorescent intracellular dye, 5- and 6-([(4-chloromethyl)benzoyl]-amino) tetramethylrhodamine, were transplanted under ultrasound guidance to the yolk sacs of day 25 or day 35 canine fetuses. Ex vivo whole body fluorescence imaging and microscopy of tissue sections were correlated with the presence of iron oxide in injected and control fetuses. RESULTS: Day 25 and day 35 recipients showed similar survival rates after injection of cells into yolk sacs, although increased fetal morality was associated with cell doses greater than 10 cells/kg to day 25 fetuses. The fluorescence and iron oxide signals were predominantly localized to the abdominal regions, with no fluorescence visible in yolk sacs. Microscopy of tissues revealed colocalization of fluorophore with iron oxide in donor cells detected in the fetal livers and bone marrow of recipients 7 and 17 days after receiving mesenchymal stromal cells or bone marrow mononuclear cells. CONCLUSIONS: These studies demonstrated that cells injected into the yolk sacs of early gestation canine fetuses migrate to recipient hematopoietic tissues. Thus, yolk sac injection offers a safe and effective approach for engraftment of cells to fetal hematopoietic tissues.

Effects of hypercapnia, hypocapnia, and hyperoxemia on brain morphometrics determined by use of T1-weighted magnetic resonance imaging in isoflurane-anesthetized dogs.

OBJECTIVE: To evaluate the effects of various combinations of PaCO2 and PaO2 values on brain morphometrics. ANIMALS: 6 healthy adult dogs. PROCEDURES: A modified Latin square design for randomization was used. Dogs were anesthetized with propofol (6 to 8 mg/kg, IV), and anesthesia was maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). Three targeted values of PaCO2 (20, 40, and 80 mm Hg) and 2 values of PaO2 (100 and 500 mm Hg) were achieved in each dog, yielding 6 combinations during a single magnetic resonance (MR) imaging session. When the endpoints were reached, dogs were given at least 5 minutes for physiologic variables to stabilize before T1-weighted MR images were obtained. Total brain volume (TBV) and lateral ventricular volume (LVV) were calculated from manually drawn contours of areas of interest by use of a software program, with each dog serving as its own control animal. Three blinded investigators subjectively evaluated the lateral ventricular size (LVS) and the cerebral sulci width (CSW). Brain morphometric values were compared among the target blood gas states. RESULTS: No significant differences in TBV were found among target states. The LVV was significantly greater during hypocapnia, compared with hypercapnia at the same PaO2 value. With regard to the subjective evaluations, there were no significant differences among evaluators or among combinations of PaO2 and PaCO2 values. CONCLUSIONS AND CLINICAL RELEVANCE: The changes observed in LVV during hypocapnia and hypercapnia may serve as a potential confounding factor when neuromorphometric evaluations are performed in anesthetized dogs.

Effects of hypercapnia, hypocapnia, and hyperoxemia on blood oxygenation level-dependent signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in isoflurane-anesthetized dogs.

OBJECTIVE: To assess the effects of alterations in PaCO(2) and PaO(2) on blood oxygenation level-dependent (BOLD) signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in brains of isoflurane-anesthetized dogs. ANIMALS: 6 healthy dogs. PROCEDURES: In each dog, anesthesia was induced with propofol (6 to 8 mg/kg, IV) and maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). During 1 magnetic resonance imaging session in each dog, targeted values of PaCO(2) (20, 40, or 80 mm Hg) and PaO(2) (100 or 500 mm Hg) were combined to establish 6 experimental conditions, including a control condition (PaCO(2), 40 mm Hg; PaO(2), 100 mm Hg). Dogs were randomly assigned to different sequences of conditions. Each condition was established for a period of >or= 5 minutes before susceptibility-weighted imaging was performed. Signal intensity was measured in 6 regions of interest in the brain, and data were analyzed by use of an ANCOVA and post hoc Tukey-Kramer adjustments. RESULTS: Compared with control condition findings, BOLD signal intensity did not differ significantly in any region of interest. However, signal intensities in the thalamus and diencephalic gray matter decreased significantly during both hypocapnic conditions, compared with all other conditions except for the control condition. CONCLUSIONS AND CLINICAL RELEVANCE: In isoflurane-anesthetized dogs, certain regions of gray matter appeared to have greater cerebrovascular responses to changes in PaCO(2) and PaO(2) than did others. Both PaO(2) and PaCO(2) should be controlled during magnetic resonance imaging procedures that involve BOLD signaling and taken into account when interpreting findings.

Use of multichannel electrogastrography for noninvasive assessment of gastric myoelectrical activity in dogs.

OBJECTIVE: To evaluate whether changes in gastric myoelectrical activity in healthy, awake dogs can be detected via multichannel electrogastrography (EGG). ANIMALS: 6 healthy hound-breed dogs. PROCEDURES: For each dog, 8-channel EGG was performed after food had been withheld for 12 hours and at 30 minutes after subsequent feeding; 60 minutes after feeding, atropine (0.04 mg/kg) was administered IM to induce ileus, and 30 minutes later, EGG was again performed. Mean cycles per minute (cpm) values of the dominant frequency (a measure of the rhythmicity of gastric electrical activity) and mean power ratios (ie, power measured after treatment divided by the power measured when food was withheld) were calculated. Motility of the gastric antrum was assessed via B-mode ultrasonography during the same phases; contractions determined ultrasonographically were correlated with EGG power for each channel in each phase. RESULTS: The criterion for stability (SD of the dominant frequency < 15% of the cpm value in at least 3 of the 8 EGG channels) was met in 4 of the 6 dogs (only in long-distance channels). The mean power ratios were significantly higher in the postprandial phase than in the ileus phase. Compared with the postprandial phase, significantly fewer contractions per minute were evident ultrasonographically in the ileus and food-withholding phases. There was a significant and good correlation between EGG power and ultrasonographic findings in all 8 channels. CONCLUSIONS AND CLINICAL RELEVANCE: Electrogastrography may be useful in assessing gastric myoelectrical activities in awake dogs with naturally occurring gastrointestinal disease, including gastric dilatation-volvulus.

The influence of posture and loading on interfacet spacing: an investigation using magnetic resonance imaging on porcine spinal units.

STUDY DESIGN: Basic scientific investigation using porcine spine segments and magnetic resonance imaging. OBJECTIVE: To quantify the effects of flexion-extension postures and loading history on the distance between the facet articular surfaces. SUMMARY OF BACKGROUND DATA: Increased axial twist motion is used clinically to indicate instability and has been implicated as a potential cause of low back pain. Recently, it has been demonstrated that larger twist angles can be achieved when coupled with forward flexion in vivo. These findings suggest a postural mechanism may be responsible for modulating how the facet joints articulate, thereby affecting the moment resisting capability of the facets and altering the load distribution between the facet joints and the disc. METHODS: Four porcine cervical spine motion segments (C3-C4) were exposed to a compressive preload. Two of these specimens were also exposed to 5000 repeats of flexion-extension motions. The interfacet spacing was measured from magnetic resonance images of 6 postures: neutral, maximum flexed, maximum extended, neutral-twisted, maximum flexed-twisted, and maximum extended-twisted. The range of axial twist angle was quantified in the neutral, flexed, and extended postures. RESULTS: Flexion-extension postures and loading history caused a difference in the interfacet spacing and twist angle measured. Repetitive loading and flexed postures independently increased the spacing and twist angle, whereas the preload condition and extended postures independently decreased the measures. The 2 specimens that underwent the preload only condition suffered no damage to the disc or vertebrae. Of the repetitively loaded specimens, 1 had a vertebral fracture with initiation of herniation, and the second had a complete herniation. CONCLUSION: The findings support a posture-dependent injury mechanism and may account for the previously reported in vivo posture-dependent passive rotational differences quantified for combined postures. The changes in spine mechanics and resulting load distribution due to coupled postures may be a key to understanding the formation of low back injuries and eventually clinical spine instability.

Suspected transient pseudohypoaldosteronism in a 10-day-old quarter horse foal.

A 10-day-old quarter horse colt was presented for signs of disorientation and inability to nurse. Hydronephrosis/hydroureters, with concomitant pyelonephritis and a severe electrolytes disturbance, were diagnosed. The clinical findings closely resembled those described for a syndrome of transient pseudohypoaldosteronism in human neonates.

Ultrasound-guided fine needle aspiration in the diagnosis of peripheral nerve sheath tumors in 4 dogs.

Ultrasound-guided fine needle aspiration was used in establishing the diagnosis in 4 cases of malignant peripheral nerve sheath tumor. Sonographic and cytologic characteristics are discussed. Because of its availability and ease of use, axillary ultrasonography with fine needle aspiration can be an initial diagnostic step for suspected brachial plexus tumors.

Comparison of magnetic resonance imaging and myelography in 18 Doberman pinscher dogs with cervical spondylomyelopathy.

Eighteen Doberman pinscher dogs with clinical signs of cervical spondylomyelopathy (wobbler syndrome) underwent cervical myelography and magnetic resonance (MR) imaging. Cervical myelography was performed using iohexol, followed by lateral and ventrodorsal radiographs. Traction myelography was performed using a cervical harness exerting 9 kg of linear traction. MR imaging was performed in sagittal, transverse, and dorsal planes using a 1.5 T magnet with the spine in neutral and traction positions. Three reviewers independently evaluated the myelographic and MR images to determine the most extensive lesion and whether the lesion was static or dynamic. All reviewers agreed with the location of the most extensive lesion on MR images (100%), while the agreement using myelography was 83%. The myelogram and MR imaging findings agreed in the identification of the affected site in 13-16 dogs depending on the reviewer. MR imaging provided additional information on lesion location because it allowed direct examination of the spinal cord diameter and parenchyma. Spinal cord signal changes were seen in 10 dogs. Depending on the reviewer, two to four dogs had their lesions classified as dynamic on myelography but static on MR images. Myelography markedly underscored the severity of the spinal cord compression in two dogs, and failed to identify the cause of the signs in another. The results of this study indicated that, although myelography can identify the location of the lesion in most patients, MR imaging appears to be more accurate in predicting the site, severity, and nature of the spinal cord compression.

Morphologic and morphometric magnetic resonance imaging features of Doberman Pinschers with and without clinical signs of cervical spondylomyelopathy.

OBJECTIVE: To compare morphologic and morphometric features of the cervical vertebral column and spinal cord of Doberman Pinschers with and without clinical signs of cervical spondylomyelopathy (CSM; wobbler syndrome) detected via magnetic resonance imaging (MRI). ANIMALS: 16 clinically normal and 16 CSM-affected Doberman Pinschers. PROCEDURES: For each dog, MRI of the cervical vertebral column (in neutral and traction positions) was performed. Morphologically, MRI abnormalities were classified according to a spinal cord compression scale. Foraminal stenosis and intervertebral disk degeneration and protrusion were also recorded. Morphometric measurements of the vertebral canal and spinal cord were obtained in sagittal and transverse MRI planes. RESULTS: 4 of 16 clinically normal and 15 of 16 CSM-affected dogs had spinal cord compression. Twelve clinically normal and all CSM-affected dogs had disk degeneration. Foraminal stenosis was detected in 11 clinically normal and 14 CSM-affected dogs. Vertebral canal and spinal cord areas were consistently smaller in CSM-affected dogs, compared with clinically normal dogs. In neutral and traction positions, the intervertebral disks of CSM-affected dogs were wider than those of clinically normal dogs but the amount of disk distraction was similar between groups. CONCLUSIONS AND CLINICAL RELEVANCE: The incidence of intervertebral disk degeneration and foraminal stenosis in clinically normal Doberman Pinschers was high; cervical spinal cord compression may be present without concurrent clinical signs. A combination of static factors (ie, a relatively stenotic vertebral canal and wider intervertebral disks) distinguished CSM-affected dogs from clinically normal dogs and appears to be a key feature in the pathogenesis of CSM.