Michio Fujita

Effect of Tyrosine Kinase Inhibition by Imatinib Mesylate on Mast Cell Tumors in Dogs

BACKGROUND Imatinib mesylate is a small molecule targeted at dysregulated protein-tyrosine kinase. Mutation of c-kit exon 11, which induces constitutive phosphorylation of KIT, is one of the mechanisms for the development or progression of mast cell tumor (MCT) in dogs. The purpose of this study was to examine the therapeutic potential of imatinib mesylate in canine MCT. HYPOTHESIS Imatinib mesylate has activity against MCT in dogs, and response to treatment can be correlated to presence of mutation within exon 11 of c-kit. ANIMALS Twenty-one dogs with MCT with gross tumor burden and median tumor size of 7.2 cm (range, 1.0-25.3 cm) before treatment. METHODS Tumors were analyzed for mutation of c-kit exon 11. Imatinib mesylate was administered PO to the dogs at a dose of 10 mg/kg daily for 1-9 weeks. RESULTS Ten of 21 dogs (48%) had some beneficial response to imatinib mesylate treatment within 14 days of treatment initiation. All 5 dogs with a demonstrable c-kit mutation in exon 11 responded to the drug (1 complete remission, 4 partial remission). CONCLUSIONS AND CLINICAL IMPORTANCE Imatinib mesylate has clinical activity against MCT in dogs. Response could not be predicted based on presence of absence of a mutation in exon 11 of c-kit.

A canine study of cold water drowning in fresh versus salt water.

OBJECTIVE To compare the pathophysiologic changes occurring during drowning in cold fresh water and cold salt water with reference to viability. DESIGN Randomized, prospective, controlled submersion experiments in two contrasting cold liquids. SETTING A laboratory at a large university-affiliated medical institution. SUBJECTS Thirteen healthy, anesthetized mongrel dogs. Three dogs served as controls and were immersed but not submerged. The remainder were submerged in cold fresh water or cold salt water (4 degrees C). INTERVENTIONS Catheters were placed in the femoral artery, right carotid artery and right internal jugular vein. Electrocardiogram, pneumogram, and rectal temperatures were measured continuously during submersion/immersion. MEASUREMENTS AND MAIN RESULTS Cold water submersion with drowning produced a large initial decrease in carotid artery temperature (approximately 7.5 degrees C in the first 2 mins) compared with a minor decrease (approximately 0.8 degrees C with immersion). No significant differences were noted in the rate of decrease of temperature between drowning in fresh water and salt water. During cold fresh water drowning, aspiration produced gross hemodilution with an average increase in body weight of 16.5%. Hematocrit values, serum sodium concentrations, and osmolality decreased while serum potassium concentrations, catecholamines, and free hemoglobin increased. All measured biochemical data (except PaO2) remained at viable levels. By contrast, during cold salt water drowning, average body weight increased by only 6%, with hemoconcentration and a shrinkage of vascular volume. Hematocrit and hemoglobin values increased by 30%, but initial plasma free hemoglobin values remained unchanged. Serum sodium concentrations, osmolality, and potassium concentrations increased rapidly to critical levels. CONCLUSIONS On submersion in cold water, all of the experimental animals developed tachypnea immediately, followed by aspiration with predictable effects. The biochemical and pathophysiologic changes in cold water drowning approximated those changes reported for warm water drowning for both fresh and salt water with one exception and continued aspiration of cold water produced extremely rapid core cooling as long as the circulation remained intact. This process of acute submersion hypothermia may protect the brain temporarily from lethal damage, as reported in cases of cold fresh water drowning. Concentrations of circulating catecholamines increased exponentially in both groups of test animals. Clinically, their acute effects on the circulation, compounded by significant hypothermia and extreme anoxia, must hamper the detection of residual circulation at rescue and may play a role in sudden death from cold water in the absence of drowning.

Diffusion-weighted imaging in kainic acid-induced complex partial status epilepticus in dogs.

OBJECTIVE To investigate diffusion-weighted imaging (DWI) in status epilepticus, a canine model of kainic acid (KA)-induced complex partial status epilepticus (CPSE) was produced. In order to validate its usefulness, MR imaging was carried out at various times following onset of CPSE followed by histopathology. MATERIAL AND METHODS Six normal dogs were used in this study. In each dog, a cannula was stereotactically inserted into the left amygdala. One week after surgery, all dogs were imaged at MRI. Pre-injection imaging consisted of T2 weighted (T2W) imaging, fluid attenuated inversion recovery (FLAIR), and DWI. Two weeks after surgery, five dogs received intraamygdaloid KA microinjections. One dog was used as a control. MRI was carried out at 3, 6, 12, 24 and 48 h after onset of CPSE. Animals were euthanized immediately after MRI for histopathological evaluation. The average of each apparent diffusion coefficient (ADC) in the regions of interest was calculated from each DWI. RESULTS At 3 and 6 h, DWI hyperintensity and low ADC were found in the injected amygdala, without any T2W and FLAIR imaging changes. At 12 and 24 h, all imaging showed hyperintensity with higher ADC in the amygdala and the hippocampus. At 48 h, all imaging techniques showed continued hyperintensity, but ADC showed a trend towards normalization. This increasing hyperintensity in DWIs were in agreement with the degree of histopathology during CPSE. SUMMARY This study suggests that DWI is a useful imaging method for finding the epileptic focus or for examining potential epileptic brain damage in status epilepticus.

A familial spontaneous epileptic feline strain: A novel model of idiopathic/genetic epilepsy

A spontaneous epileptic model of cats has not been described previously. Recently, we identified familial epileptic cats and investigated their clinical features. These epileptic cats are healthy except for the presence of recurrent seizures that are typically a focal limbic seizure with secondary generalization. Furthermore, generalized seizures were induced by vestibular stimulation in some cats. This spontaneous epileptic cat strain may be a valuable model for idiopathic/genetic epilepsy.

EVALUATION OF DYSTROPHIC DOG PATHOLOGY BY FAT-SUPPRESSED T2-WEIGHTED IMAGING

Duchenne muscular dystrophy (DMD) is a devastating muscle disorder that is characterized by progressive muscle necrosis, fibrosis, and fatty infiltration. To examine the temporospatial pathological changes, a noninvasive evaluation method such as magnetic resonance imaging (MRI) is needed. The aim of this study was to precisely assess muscle necrosis and inflammation based on a sequence of T2‐weighted imaging (T2WI), gadolinium‐enhanced imaging, and selective fat suppression, chemical shift selective T2‐weighted imaging (CHESS‐T2WI), on a 3.0‐Tesla MRI unit in 3‐month‐old and 7‐year‐old dogs with canine X‐linked muscular dystrophy (CXMDJ), a suitable animal model for DMD. The results show that CHESS‐T2WI was more sensitive and useful from the early to late stages of CXMDJ than T2WI or contrast enhancement imaging in the evaluation of muscle necrosis, because these latter sequences can be influenced by fatty infiltration or interstitial connective tissues.Muscle Nerve, 2009

Complex partial status epilepticus induced by a microinjection of kainic acid into unilateral amygdala in dogs and its brain damage

OBJECTIVE In order to investigate kainic acid (KA)-induced amygdaloid seizure and seizure-induced brain damage in dogs, and to compare these findings with that in other species, a KA-induced seizure model in dogs was produced. MATERIAL AND METHODS Normal beagle dogs were used. A Teflon cannula for KA injection was inserted into the left amygdala, and cortical or depth electrodes were positioned. One week after surgery, 1.5 microg of KA was microinjected into the left amygdala. EEGs and the behavior of the animals were monitored for 2 months after KA injection. In addition, neuron-specific enolase levels in the cerebrospinal fluid (CSF-NSE) were measured intermittently. At 2 months after the injection, histopathological studies were performed. RESULTS KA-treated dogs showed limbic seizures that started from the left amygdala within 30 min after injection. The seizures developed into complex partial status epilepticus (CPSE), and started independently from the bilateral amygdala during the CPSE. The CPSE lasted for 1-3 days, and the animals showed no spontaneous seizures during the 2-month observation period. A significant increase in CSF-NSE was observed immediately after CPSE. Histopathologically, extensive necrosis, which formed large cavity lesions, was observed around the bilateral amygdala. SUMMARY A microinjection of KA into unilateral amygdala in dogs induced CPSE. The seizures elicited independently from bilateral amygdala, and bilateral limbic structures suffered extensive injury. In addition, CSF-NSE was demonstrated as a useful marker of acute neuronal damage.

Clinical and molecular analysis of GM2 gangliosidosis in two apparent littermate kittens of the Japanese domestic cat

This case report documents clinical and molecular findings in two littermate kittens of the Japanese domestic cat with GM2 gangliosidosis variant 0. Analysis included detailed physical, magnetic resonance imaging, biochemical, pathological and genetic examinations. At first, these littermate kittens showed typical cerebellar signs at approximately 2 months of age. About 2 months later, they progressively showed other neurological signs and subsequently died at about 7 months of age. Magnetic resonance imaging just before the death showed an enlarged ventricular system, T1 hyperintensity in the internal capsule, and T2 hyperintensity in the white matter of the whole brain. Histological findings suggested a type of lysosomal storage disease. Biochemical studies demonstrated that the kittens were affected with GM2 gangliosidosis variant 0, and a DNA assay finally demonstrated that these animals were homozygous for the mutation, which the authors had identified in a different family of the Japanese domestic cat. The findings in the present cases provide useful information about GM2 gangliosidosis variant 0 in Japanese domestic cats.

Pharmacokinetics and toxicity of zonisamide in cats

With the eventual goal of making zonisamide (ZNS), a relatively new antiepileptic drug, available for the treatment of epilepsy in cats, the pharmacokinetics after a single oral administration at 10 mg/kg and the toxicity after 9-week daily administration of 20 mg/kg/day of ZNS were studied in healthy cats. Pharmacokinetic parameters obtained with a single administration of ZNS at 10 mg/day were as follows: Cmax=13.1 μg/ml; Tmax=4.0 h; T1/2=33.0 h; areas under the curves (AUCs)=720.3 μg/mlh (values represent the medians). The study with daily administrations revealed that the toxicity of ZNS was comparatively low in cats, suggesting that it may be an available drug for cats. However, half of the cats that were administered 20 mg/kg/day daily showed adverse reactions such as anorexia, diarrhoea, vomiting, somnolence and locomotor ataxia.

Magnetic resonance volumetry of the hippocampus in familial spontaneous epileptic cats

A strain of familial spontaneous epileptic cats (FSECs) with typical limbic seizures was identified in 2010. The electroencephalographic features suggested that an epileptogenic zone is present in the mesial temporal structures (i.e., amygdala and/or hippocampus). In this study, visual evaluations and quantitative analyses were performed by using 3D MR hippocampal volumetry in comparing FSECs with age-matched controls. Visual hippocampal asymmetries were seen in 8 of 14 (57.1%) FSECs. The FSEC group showed a significantly higher asymmetric ratio (4.15%) than the control group (0.99%). The smaller side of hippocampal volume (HV) (0.206 cm(3)) in FSECs was significantly smaller than the mean HV in controls (0.227 cm(3)). However, the means of left and right HVs and total HVs in FSECs showed no differences because the laterality of hippocampal atrophy was different in each individual. Therefore, since FSECs represent a true model of spontaneous epilepsy, hippocampal volumetry should be evaluated in each individual as well as in human patients. The significant asymmetry of HV suggests the potential for hippocampal atrophy in FSECs.

Electroencephalographic features of familial spontaneous epileptic cats

A feline strain of familial spontaneous epileptic cats (FSECs) with typical limbic seizures was identified in 2010, and have been maintained as a novel animal model of genetic epilepsy. In this study, we characterized the electroencephalographic (EEG) features of FSECs. On scalp EEG under sedation, FSECs showed sporadic, but comparatively frequent interictal discharges dominantly in the uni- or bilateral temporal region. Bemegride activation was performed in order to evaluate the predisposition of epileptogenicity of FSECs. The threshold doses of the first paroxysmal discharge, clinical myoclonus and generalized convulsion in FSECs were significantly lower than those in control cats. Chronic video-intracranial EEG monitoring revealed subclinical or clinical focal seizures with secondarily generalization onset from the unilateral amygdala and/or hippocampus. Clinical generalized seizures were also recorded, but we were unable to detect the onset site. The results of the present study show that FSECs resemble not only feline kindling or the kainic acid model and El mouse, but also human familial or sporadic mesial temporal lobe epilepsy. In addition, our results indicate that FSECs are a natural and valuable model of mesial temporal lobe epilepsy.