Intraosseous contrast administration for coelomic computed tomography angiography in green iguanas (Iguana iguana): Preliminary findings show promise as an alternative to the intravenous route.

Computed tomography is commonly used to evaluate the reptile coelom. One challenge in the acquisition of contrast-enhanced CT studies in reptiles is the difficulty in placing intravenous catheters due to the poor conspicuity of peripheral vessels. To overcome these limitations, intraosseous catheterization of the long bones (humerus, femur, and tibia) can be used. The purpose of this prospective study was to assess the feasibility and diagnostic value of contrast-enhanced CT of the coelom using a femoral intraosseous route for contrast administration. Twelve healthy juvenile green iguanas were enrolled. In 9 of 12 iguanas, vascular phases were obtained, providing strong, homogeneous enhancement of the arterial and venous tree concurrently. In these nine cases, Phase #1, acquired 60 s after beginning the injection of contrast medium, provided maximal contrast between the hepatic parenchyma and hepatic vasculature. In the remaining three cases, injection failure resulted from intracortical placement of the catheter tip. Histological examination of the liver, kidneys, and femur was performed to determine the pathomorphological correlates of the CT findings; in a third of patients, some degree of contrast-induced renal toxicity was documented, which in mammalians shows potential for reversibility. Four iguanas had iatrogenic structural damage to the femoral growth plates attributed to intraosseous catheter placement. A femoral intraosseous route can be used in green iguanas for iodinated contrast medium administration for CT angiography. For the greatest contrast between coelomic organs and vascular structures, at least one postcontrast acquisition 60 s after initiation of contrast administration is recommended when using this technique.

Evaluation of two nephrocystostomy techniques for ureteral bypass in cats.

OBJECTIVE: To describe two techniques for nephrocystostomy (NCT) in cats. STUDY DESIGN: Experimental study. ANIMALS: Twelve, adult, purpose-bred, cats. METHODS: A simple NCT (n = 3) or bladder cuff NCT (n = 9) was performed in the right or left kidneys. For simple NCT, an 8F catheter was placed through the caudal pole into the renal pelvis and the bladder was sutured around the catheter. For bladder cuff NCT, a 6 mm defect was removed from the caudal pole and a cuff of bladder mucosa was advanced and sutured into the renal pelvis. A 10F catheter was placed through the defect into the renal pelvis and the bladder wall was sutured around the catheter. Catheters were removed 41-118 days post-surgery. Computed tomography (CT) was performed 25 days after catheter removal for the simple NCT and 30 (n = 6) and 90 (n = 3) days after catheter removal for bladder cuff NCT. Histological evaluation of the nephrocystostomy site was performed. RESULTS: All simple NCTs became obstructed after catheter removal. All bladder cuff NCTs were patent, and CT revealed contrast flow into the bladder. Hematuria, clot-associated urethral obstruction, catheter dislodgement, and bladder infection occurred variably after surgery. Histological findings consisted of smooth epithelialization of the NCT and degenerative changes in the caudal pole of the kidney. CONCLUSION: Bladder cuff NCT was feasible in normal cats and remained patent for 90 days. Methods to limit nephrostomy track hemorrhage should be investigated. Degenerative changes may be related to vascular impairment from the bladder cuff sutures. CLINICAL SIGNIFICANCE: Complete ureteral bypass was possible in cats using only native tissues.

MRI of the live fish brain at 3 Tesla: Feasibility, technique and interspecies anatomic variations.

Advances in aquatic animal medicine and continued growth of the fish hobbyist and aquaculture communities have led to a developing interest in antemortem diagnostic imaging of aquatic species. The aims of this prospective, pilot study were to determine whether advanced neuroimaging can be safely achieved in live fish using clinically available equipment, to optimize imaging parameters, and to develop a comparative MRI atlas of a few fish species of economic or research value. Two each of channel catfish (Ictalurus punctatus), koi (Cyprinus rubrofuscus), and grass carp (Ctenopharyngodon idella) of at least 30 cm in length were individually anesthetized for 3 Tesla (3T) magnetic resonance imaging (MRI) of the brain. All fish achieved an adequate anesthetic level for prolonged immobilization during imaging. Diagnostic quality images were obtained for all subjects; however, the spatial resolution was maximized with larger fish. Imaging protocols were optimized for standard neuroimaging sequences. Additionally, inversion times for fluid-attenuation inversion recovery (FLAIR) sequences were adapted to the naturally high protein content of fish pericerebral fluid. Following imaging, the fish successfully recovered from anesthesia, were humanely euthanized, and were immediately processed to assess brain histopathology. Necropsy confirmed the sex and health status of each fish. A limited comparative MRI atlas was created of the brains of these species for clinical reference. Findings from the current study supported the use of 3T MRI as an adjunct diagnostic test for fish with suspected neurologic disease and provided a limited anatomic atlas of the teleost brain for use as a reference.

Use of computed tomography and magnetic resonance imaging to assess a case of spinal injury in a Showa koi Cyprinus carpio.

OBJECTIVE: A privately owned, 4-year-old female Showa koi (ornamental variant of Common Carp Cyprinus carpio) was presented for erratic swimming, air gasping, water spitting, and abnormal orientation in the water column. Initial physical examination revealed an obese patient with no external abnormalities except a small plaque localized to filaments on a right gill hemibranch. METHODS: The fish was anesthetized using AQUI-S 20E (10% eugenol solution) at 50 mg/L to facilitate diagnostic evaluation. Biopsy of the gill lesion yielded no significant findings. Whole-body computed tomography confirmed an excess of adipose tissue and mild scoliosis, with narrowing of the 10th-11th intervertebral space. A weight loss plan and need for repeat assessment were recommended. RESULT: The patient's original abnormal behaviors resolved over the following weeks, but it subsequently became hyporexic and depressed. Full-body magnetic resonance imaging (MRI) showed extensive alteration of vertebral centra, with multifocal compression of the spinal cord. Due to the patient's declining clinical condition and the grave prognosis based on MRI findings, the patient was humanely euthanized. CONCLUSION: Postmortem examination showed severe transmural myelomalacia associated with a vertebral subluxation. This case demonstrates the practical application of advanced cross-sectional imaging that has not been commonly afforded to fish or other lower vertebrates.

Mediastinal Serous Cavity Mesothelioma in Two Dogs.

The mediastinal serous cavity (MSC)-well documented but seldom recognized in the caudal mediastinum-is embryologically derived from the omental bursa. Mesothelioma arising from the MSC in two dogs is described. Both dogs presented with acute life-threatening hemorrhagic pleural effusion. Contrast computed tomography revealed a large solitary spherical-to-cylindrical tumor in the caudal mediastinum with variably thick, contrast-enhancing walls with lobular to frond-like proliferations that arose circumferentially and projected internally into a single, variably sized, fluid-attenuating lumen. The wall and lumen corresponded to the serous membrane and serous cavity of the MSC. Surgical exploration confirmed that both tumors arose from the mediastinum. Both had similar histologic findings, and special stains were necessary for definitive diagnosis. The tumor was nonresectable in one dog, and it was euthanized intraoperatively. The other survived 7 mo. An MSC mesothelioma should be considered a possible cause of hemothorax in dogs that may be detected on thoracic radiography and computed tomography. Differential diagnoses include esophageal foreign body or neoplasm, paraesophageal diaphragmatic hernia, MCS empyema, and pulmonary adenocarcinoma, with thoracic computed tomography helping to rule out foreign body and diaphragmatic hernia. For confirmed neoplasms, histochemistry and immunohistochemistry should be performed to differentiate between mesothelioma and pulmonary adenocarcinoma.

Intramuscular Grade 1 fibrosarcoma: Magnetic resonance imaging findings in 2 dogs.

Two adult neutered male dogs were presented for evaluation of firm, painless masses arising within muscle: an 8-year-old German wirehaired pointer dog with an accessory tricipital growth, and a 3-year-old German shepherd dog with a gracilis muscle growth. Magnetic resonance imaging (MRI) characteristics suggested malignant behavior, with a central fluid-like portion with a hyperenhancing lining, a nidus of disorganized tissue, and an extensive reactive zone, whereas histopathology was consistent with low-grade fibrosarcoma. This report describes histologically low-grade, yet biologically high-grade intramuscular fibrosarcoma, in which MRI provided detailed information on tumor behavior and assisted with biopsy and surgical planning.

Fibrosarcome intramusculaire de Grade 1 chez deux chiens : Imagerie par résonance magnétique. Ce rapport de cas décrit des fibrosarcomes intramusculaires de bas grade histologique mais au comportement biologique de haut grade ainsi que leur imagerie par résonance magnétique (IRM) chez deux chiens mâles castrés évalués pour des masses musculaires fermes et indolores : un Braque Allemand de 8 ans avec une masse originant de la branche accessoire du muscle triceps, et un Berger Allemand de 3 ans avec une masse au muscle gracile. L'IRM a révélé une zone centrale liquide bordée d'une mince couche au rehaussement marqué, adjacent à un foyer de tissu désorganisé, entourés par une zone réactive étendue. L'histopathologie des lésions révèle un fibrosarcome et malgré la présence d'anomalies histologiques de bas grade, l'infiltration des muscles adjacents est documentée par microscopie et les caractéristiques d'imagerie sont celles associées chez l'humain avec un comportement malin.(Traduit par les auteurs).

Diagnosis and treatment of epidural empyema in a pygmy goat.

A mixed-breed pygmy goat was presented for nonambulatory tetraparesis. Neurological examination was consistent with a C6 to T2 myelopathy. Initially, the goat was treated medically. Forty-three days later, magnetic resonance imaging (MRI) revealed an extradural mass compressing the cervical spinal cord. Magnetic resonance attributes of the mass were consistent with a slow-growing, fluid-poor lesion. The spinal cord was surgically decompressed. Epidural empyema secondary to Fusobacterium necrophorum was identified. Postoperative care consisted of anti-inflammatory medication, antimicrobials, and physical therapy. Ability to walk occurred by day 14 after surgery. Despite prolonged recumbency before surgery, the goat was clinically normal, and antimicrobials were discontinued on day 60 after surgery. Key clinical message: Epidural empyema can cause a compressive myelopathy which may result in varying degrees of paresis/paralysis. Clinical resolution and return of normal function occurred following the use of MRI to plan surgical decompression combined with extended use of antimicrobials.

Diagnostic et traitement d'un empyème épidural chez une chèvre pygmée. Une chèvre naine fut présentée pour tétraparésie non-ambulatoire, neuro-localisée au segment C6-T2. Un traitement conservateur fut initialement instauré. Quarante-trois jours plus tard, une IRM révéla une compression sévère de la moelle épinière cervicale par une masse extradurale faiblement liquide et à croissance lente. La moelle épinière fut chirurgicalement décompressée. Un empyème épidural secondaire à Fusobacterium necrophorum fut identifié. Des soins postopératoires à base d'anti-inflammatoires, d'antibiotiques ainsi qu'une rééducation physique furent instaurés. L'animal recouvra la capacité de marcher 14 jours plus tard. Malgré un décubitus prolongé, 60 jours après la chirurgie la chèvre était normale et les antimicrobiens furent interrompus.Message clinique clé :L'empyème épidural peut provoquer une myélopathie compressive pouvant entraîner divers degrés de parésie/ paralysie. La résolution clinique et le retour de la fonction normale sont survenus après l'utilisation de l'IRM pour planifier la décompression chirurgicale combinée à une utilisation prolongée d'antimicrobiens.(Traduit par Karin Gendron et Maëva Barozzi).

The pathogenesis of paraesophageal empyema in dogs and constancy of radiographic and computed tomography signs are linked to involvement of the mediastinal serous cavity.

The mediastinal serous cavity is a normal anatomic space in the caudal mediastinum. Aims of this anatomic and case series study were to describe the signs of pathologic expansion of the mediastinal serous cavity observed during computed tomography (CT), review the underlying anatomy, perform a literature review, and evaluate the medical records of several dogs with mediastinal serous cavity empyema (paraesophageal empyema). The mesothelial lined mediastinal serous cavity is a cranial extension of the omental bursa, separated from the peritoneal cavity by the diaphragm, in the dorsal part of the caudal mediastinum, to the right of the esophagus, between the heart base and diaphragm. In five adult, large-breed dogs with surgically and histologically confirmed paraesophageal empyema, macroscopic plant material was found at surgery in two dogs, adherence to adjacent lung was present in three different dogs, accessory lobectomy was performed in two dogs with subacute-chronic pyogranulomatous pneumonia, and one dog had concurrent pyothorax and mediastinitis, but none had esophageal abnormalities. This study expands our understanding of the pathogenesis and basis for the imaging appearance of paraesophageal empyema in dogs by clarifying the underlying anatomic structures that direct development of this condition. The term empyema accurately describes this condition because the purulent material accumulates within an existing body cavity. The study also provides initial evidence that the development of paraesophageal empyema might be due to local extension of lung disease, such as foreign body migration or pneumonia. Computed tomography was helpful for diagnosis, assessing size, and determining the spread of disease.

Successful medical management and rehabilitation of exercise-induced dorsal scapular luxation in an ultramarathon endurance sled dog with magnetic resonance imaging diagnosis of grade II serratus ventralis strain.

Dorsal displacement of the scapula in dogs is rare and often traumatic. This report describes dorsal luxation of the scapula in a sled dog. This case is unique given the injury was sport-related. Magnetic resonance imaging helped direct therapy and monitor healing; and medical management with rehabilitation resulted in full recovery and return to sport. One year after injury, the dog completed both a 482 km and a 1600 km endurance race, placing among the leading teams in the 1600-km race.

Traitement médical réussi d'une luxation scapulaire dorsale aiguë secondaire à la pratique du sport d'endurance chez un chien de traîneau et diagnostic par IRM d'une lésion du m. dentelé ventral. Le déplacement dorsal de la scapula est rare chez le chien et souvent d'origine traumatique. Ce rapport décrit une luxation scapulaire dorsale aiguë chez un chien de traîneau à l'effort. L'intérêt de ce cas tient à sa cause, associé à la pratique de l'activité sportive; à l'analyse des changements en IRM soutenant une thérapie ciblée consistant en un support médical ainsi que d'un programme de rééducation physique, résultant en un rétablissement complet. Un an après cette blessure, le chien termina des courses d'endurance de 482 km et de 1600 km, se classant lors de cette dernière parmi les meilleures équipes de la course.(Traduit par les auteurs).

What is the evidence? The issue of verifying correct needle position during epidural anaesthesia in dogs.

OBJECTIVES: To review the methods for verifying the needle position while performing epidural anaesthesia in dogs, and to discuss the advantages, disadvantages, usefulness and reliability of each technique in the experimental and clinical research setting. DATABASES USED: PubMed, Scopus, Google Scholar and the Basel University Library online catalogues; the latter, which was provided by the University of Berne, were used as databases. The results were filtered manually based on the titles and abstracts in order to narrow the field. CONCLUSIONS: Besides some drawbacks, including the potential side effects of contrast medium injection, which may limit its routine use in clinical patients, epidurography should still be regarded as one of the most reliable techniques to verify needle position in dogs. Ultrasonography, electrical nerve stimulation, loss of resistance and the hanging drop technique are regarded as less invasive than epidurography and, for this reason, their use may be more applicable to clinical patients. However, these methods have been described in only a few published reports, all of which involved a limited number of dogs. Finally, the detection of epidural pressure waves has been investigated more extensively in dogs, and the findings of these studies suggest that this technique may be used to verify epidural needle placement for experimental and clinical research, on condition that all the negative subjects are excluded from the study.

Assessment of Intrathecal Pressure in Chondrodystrophic Dogs With Acute Thoracolumbar Disk Disease.

OBJECTIVES: To assess intrathecal pressure (ITP) in chondrodystrophic dogs with thoracolumbar disk extrusion. STUDY DESIGN: Prospective cohort study. ANIMALS: Group 1: 11 chondrodystrophic dogs with thoracolumbar disk extrusion and present deep pain sensation. Group 2 (control): 3 healthy chondrodystrophic laboratory dogs without spinal disease. METHODS: Diagnosis was based on neurologic signs, magnetic resonance imaging (MRI) findings, and surgical confirmation. Blood pressure was maintained within physiologic range during anesthesia. A standardized surgical procedure was applied to minimize factors that could influence measurement readings. An extended hemilaminectomy was performed and ITP was measured with a fiber optic catheter. The catheter was inserted in the subarachnoid space 1 spinal segment caudal to the level of herniation and its tip was advanced to the site of compression. RESULTS: Significantly higher ITP occurred in chondrodystrophic dogs with acute thoracolumbar disk disease compared with controls. ITP was not associated with duration of clinical signs, neurologic status, outcome, degree of spinal cord compression, or signal intensity changes as assessed by MRI. CONCLUSION: Acute thoracolumbar disk disease leads to elevated ITP in chondrodystrophic dogs, which may contribute to increased compression of spinal cord parenchyma.

Evaluation of a Novel Screw Position in a Type III Distal Phalanx Fracture Model: An Ex Vivo Study.

OBJECTIVE: Mechanical evaluation of a novel screw position used for repair in a type III distal phalanx fracture model and assessment of solar canal penetration (SCP). STUDY DESIGN: Experimental study. SAMPLE POPULATION: Disarticulated equine hooves (n = 24) and 24 isolated distal phalanges. METHODS: Hooves/distal phalanges cut in a sagittal plane were repaired with 1 of 2 different cortical screw placements in lag fashion. In group 1 (conventional screw placement), the screw was inserted halfway between the proximal border of the solar canal (SC) and the subchondral bone surface on a line parallel to the dorsal cortex, whereas in group 2, the screw was inserted more palmar/plantar, where a perpendicular line drawn from the group 1 position reached the palmar/plantar cortex. Construct strength was evaluated by 3-point bending to failure. SCP was assessed by CT imaging and macroscopically. RESULTS: Screws were significantly longer in group 2 and in forelimbs. Group 2 isolated distal phalanges had a significantly more rigid fixation compared with the conventional screw position (maximum point at failure 31%, bending stiffness 41% higher). Lumen reduction of the SC was observed in 13/52 specimens (all from group 2), of which 9 were forelimbs. CONCLUSIONS: More distal screw positioning compared with the conventionally recommended screw position for internal fixation of type III distal phalangeal fractures allows placement of a longer screw and renders a more rigid fracture fixation. The novel screw position, however, carries a higher risk of SCP.

Pulmonary Echinococcus multilocularis metastasis in a dog.

A young adult Labrador retriever dog was presented for surgical debulking of hepatic alveolar echinococcosis. Computed tomography detected hepatomegaly with multiple large cavitary masses with extension of tissue from a lesion wall into the caudal vena cava and numerous nodules in all lung lobes. Following euthanasia, histology confirmed parasitic vesicles with granulomatous reaction in all lesions, and polymerase chain reaction (PCR) established the causative agent to be Echinococcus multilocularis. This report is the first to present imaging features of pulmonary E. multilocularis granulomata in a dog.

Métastases pulmonaires d'Echinococcus multilocularischez un chien. À l'examen par tomodensitométrie d'un Labrador retriever jeune adulte référé pour résection de lésions hépatiques d'échinococcose alvéolaire, une hépatomégalie avec présence de larges masses cavitaires fut mise en évidence, de même que l'extension de la paroi d'une lésion à l'intérieur de la veine cave caudale, et de nombreux nodules pulmonaires. Après euthanasie, des vésicules parasitiques associés à une réaction granulomateuse furent confirmés histologiquement dans toutes les lésions évaluées, et E. multilocularis fût démontré par PCR être l'agent causal. Ce rapport de cas est le premier à présenter les caractéristiques de lésions pulmonaires d'E. multilocularis chez le chien.(Traduit par les auteurs).

The 5' UTR of HIV-1 full-length mRNA and the Tat viral protein modulate the programmed -1 ribosomal frameshift that generates HIV-1 enzymes.

Translation of the full-length messenger RNA (mRNA) of the human immunodeficiency virus type 1 (HIV-1) generates the precursor of the viral enzymes via a programmed -1 ribosomal frameshift. Here, using dual-luciferase reporters, we investigated whether the highly structured 5' untranslated region (UTR) of this mRNA, which interferes with translation initiation, can modulate HIV-1 frameshift efficiency. We showed that, when the 5' UTR of HIV-1 mRNA occupies the 5' end of the reporter mRNA, HIV-1 frameshift efficiency is increased about fourfold in Jurkat T-cells, compared with a control dual-luciferase reporter with a short unstructured 5' UTR. This increase was related to an interference with cap-dependent translation initiation by the TAR-Poly(A) region at the 5' end of the messenger. HIV-1 mRNA 5' UTR also contains an internal ribosome entry site (IRES), but we showed that, when the cap-dependent initiation mode is available, the IRES is not used or is weakly used. However, when the ribosomes have to use the IRES to translate the dual-luciferase reporter, the frameshift efficiency is comparable to that of the control dual-luciferase reporter. The decrease in cap-dependent initiation and the accompanying increase in frameshift efficiency caused by the 5' UTR of HIV-1 mRNA is antagonized, in a dose-dependent way, by the Tat viral protein. Tat also stimulates the IRES-dependent initiation and decreases the corresponding frameshift efficiency. A model is presented that accounts for the variations in frameshift efficiency depending on the 5' UTR and the presence of Tat, and it is proposed that a range of frameshift efficiencies is compatible with the virus replication.

The activity of the HIV-1 IRES is stimulated by oxidative stress and controlled by a negative regulatory element.

Initiation of translation of the full-length messenger RNA of HIV-1, which generates the viral structural proteins and enzymes, is cap-dependent but can also use an internal ribosome entry site (IRES) located in the 5' untranslated region. Our aim was to define, through a mutational analysis, regions of HIV-1 IRES that are important for its activity. A dual-luciferase reporter construct where the Renilla luciferase (Rluc) translation is cap-dependent while the firefly luciferase (Fluc) translation depends on HIV-1 IRES was used. The Fluc/Rluc ratio was measured in lysates of Jurkat T cells transfected with the dual-luciferase plasmid bearing either the wild-type or a mutated IRES. Deletions or mutations in three regions decreased the IRES activity but deletion or mutations of a stem-loop preceding the primer binding site increased the IRES activity. The wild-type IRES activity, but not that of an IRES with a mutated stem-loop, was increased when cells were treated with agents that induce oxidative stress. Such stress is known to be caused by HIV-1 infection and we propose that this stem-loop is involved in a switch that stimulates the IRES activity in cells infected with HIV-1, supporting the suggestion that the IRES activity is up-regulated in the course of HIV-1 replication cycle.

Biomechanical evaluation of the stabilizing function of the atlantoaxial ligaments under shear loading: a canine cadaveric study.

OBJECTIVES: To evaluate the stabilizing function of atlanto-axial ligaments in dogs. STUDY DESIGN: Cadaveric biomechanical study. ANIMALS: Beagle dog cadavers (n = 10). METHODS: The craniocervical region was collected from 10 Beagle cadavers, and the occipito-atlanto-axial region was prepared and freed from the surrounding muscles. Care was taken to preserve integrity of the atlantoaxial ligaments and atlantoaxial joint capsule. The atlanto-occipital joints were blocked with 2 diverging transarticular 1.8 mm positive threaded K-wires. Specimen extremities were embedded in polymethylmethacrylate (PMMA) and mounted on a simulator testing shear load at the atlantoaxial joint. Range of motion (ROM) and neutral zone (NZ) were determined with all ligaments intact, after cutting the apical ligament, both alar ligaments, the transverse ligaments and finally after cutting the dorsal atlantoaxial ligament. RESULTS: ROM increased similarly and stepwise during testing. The most significant increase was observed after transection of the alar ligaments. CONCLUSION: The alar ligaments seem to be the most important ligamentous structures for stabilization of the atlantoaxial joint under shear load.

Severe esophageal injuries occurring after general anesthesia in two cats: case report and literature review.

Two healthy cats underwent elective surgical procedures under general anesthesia. One developed severe esophagitis leading to esophageal rupture, mediastinitis, and pyothorax. The other cat developed esophageal stricture, diverticulum formation, and suspected iatrogenic perforation. Both cats had signs of dysphagia and regurgitation beginning a few days after anesthesia. The first cat also had severe dyspnea due to septic pleural effusion and pneumomediastinum. In the second cat, endoscopy revealed diffuse esophagitis, an esophageal stricture, and a large esophageal diverticulum. Rupture of the esophageal wall occurred while inflating the esophagus for inspection. Due to the poor prognosis, both cats were euthanized. Necropsy revealed severe esophageal changes. Postanesthetic esophagitis has been previously described in dogs and cats; however, severe life-threatening esophageal injuries rarely occur as a sequel to general anesthesia. To the authors' knowledge, esophageal rupture secondary to perianesthetic reflux has never been reported in cats.

The presence of the TAR RNA structure alters the programmed -1 ribosomal frameshift efficiency of the human immunodeficiency virus type 1 (HIV-1) by modifying the rate of translation initiation.

HIV-1 uses a programmed -1 ribosomal frameshift to synthesize the precursor of its enzymes, Gag-Pol. The frameshift efficiency that is critical for the virus replication, is controlled by an interaction between the ribosome and a specific structure on the viral mRNA, the frameshift stimulatory signal. The rate of cap-dependent translation initiation is known to be altered by the TAR RNA structure, present at the 5' and 3' end of all HIV-1 mRNAs. Depending upon its concentration, TAR activates or inhibits the double-stranded RNA-dependent protein kinase (PKR). We investigated here whether changes in translation initiation caused by TAR affect HIV-1 frameshift efficiency. CD4+ T cells and 293T cells were transfected with a dual-luciferase construct where the firefly luciferase expression depends upon the HIV-1 frameshift. Translation initiation was altered by adding TAR in cis or trans of the reporter mRNA. We show that HIV-1 frameshift efficiency correlates negatively with changes in the rate of translation initiation caused by TAR and mediated by PKR. A model is presented where changes in the rate of initiation affect the probability of frameshifting by altering the distance between elongating ribosomes on the mRNA, which influences the frequency of encounter between these ribosomes and the frameshift stimulatory signal.

Imaging Ischemic and Hemorrhagic Disease of the Brain in Dogs.

Strokes, both ischemic and hemorrhagic, are the most common underlying cause of acute, non-progressive encephalopathy in dogs. In effect, substantial information detailing the underlying causes and predisposing factors, affected vessels, imaging features, and outcomes based on location and extent of injury is available. The features of canine strokes on both computed tomography (CT) and magnetic resonance imaging (MRI) have been described in numerous studies. This summary article serves as a compilation of these various descriptions. Drawing from the established and emerging stroke evaluation sequences used in the investigation of strokes in humans, this summary describes all theoretically available sequences. Particular detail is given to logistics of image acquisition, description of imaging findings, and each sequence's advantages and disadvantages. As the imaging features of both forms of strokes are highly representative of the underlying pathophysiologic stages in the hours to months following stroke onset, the descriptions of strokes at various stages are also discussed. It is unlikely that canine strokes can be diagnosed within the same rapid time frame as human strokes, and therefore the opportunity for thrombolytic intervention in ischemic strokes is unattainable. However, a thorough understanding of the appearance of strokes at various stages can aid the clinician when presented with a patient that has developed a stroke in the days or weeks prior to evaluation. Additionally, investigation into new imaging techniques may increase the sensitivity and specificity of stroke diagnosis, as well as provide new ways to monitor strokes over time.

Pancreatic Langerhans cell histiocytosis in a cat.

In contrast to pulmonary Langerhans cell histiocytosis (LCH), which is a proliferative disorder of Langerhans cells that affects the lungs and other organs of cats, LCH involving a single organ system has not been documented in cats, to our knowledge. Herein we describe a case of pancreatic LCH in a 9-y-old castrated male Domestic Shorthaired cat that was evaluated for possible renal transplantation. The cat was hypoglycemic, hyperinsulinemic, and azotemic. Ultrasound examination revealed a diffusely enlarged, normoechoic pancreas. The cat was euthanized because of severe renal azotemia and the possibility of pancreatic neoplasia. Grossly, the pancreas was enlarged, and both kidneys were pale white, firm, and had irregular capsular surfaces. Histologically, the pancreas was expanded with interlobular, intraparenchymal, and ductal clusters of round-to-polygonal cells admixed with fibrous connective tissue and scattered lymphocytes. Infiltrating cells had a moderate amount of eosinophilic cytoplasm, round-to-indented nuclei with finely stippled chromatin and 1 or 2 nucleoli, and were strongly immunoreactive for CD18, ionized calcium-binding adapter molecule 1, and e-cadherin. The morphologic and immunohistochemical features of the pancreatic changes were consistent with single-system LCH.