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Clinical and pathological effects of short-term cyanide repeated dosing to goats.

The purpose of this work is to determine and describe the effects of subacute cyanide toxicity to goats. Eight female goats were divided into two groups. The first group of five animals was treated with 8.0 mg KCN kg(-1) body weight day(-1) for seven consecutive days. The second group of three animals was treated with water as controls. Complete physical examination, including observation for behavior changes, was conducted before and after dosing. One treated animal was euthanized immediately after dosing. Later, two of the remaining treated animals and a control goat were euthanized after a 30-day recovery period. Euthanized animals were necropsied and tissues were collected and prepared for histologic studies. Clinical signs in treated goats were transient and included depression and lethargy, mild hyperpnea and hyperthermia, arrhythmias, abundant salivation, vocalizations, expiratory dyspnea, jerky movements and head pressing. Two goats developed convulsions after day 3 of treatment. One animal developed more permanent behavioral changes as she became less dominant and aggressive. Histologic changes included mild hepatocellular vacuolation and degeneration, mild vacuolation and swelling of the proximal convoluted tubules of the kidneys and spongiosis of the white matter (status spongiosis) of the cerebral white tracts, internal capsule, cerebellar peduncles, spinal cord and peripheral nerves. In summary, sub-lethal cyanide intoxication in goats resulted in behavioral changes, and during the treatment period animals showed delayed signs of toxicity. Significant histologic lesions in goats were observed and need to be characterized further.

Animals↗

Polyester prostheses as substitutes in the thoracic aorta of dogs. I. Evaluation of commercial prostheses.

Using canine models, a representative selection of polyester or Dacron vascular prostheses, including woven, knitted, and velour types, were evaluated for their relative healing characteristics and for their structural changes during implantation. Following residence periods ranging from 4 h to 6 months at the site of the thoracic aorta, the dogs were sacraficed, and the grafts were excized for measurement of the thrombogenicity of the flow surface and for pathological examination by light microscopy and SEM. The kidneys were also removed and examined for infarcts caused by any trapped circulating emboli. The extent of healing, the presence of embolizing nuclei, and the thrombogenicity and morphology of the lumen surface were also assessed. The healing characteristics of each type of device proved similar. Velour fabrics exhibited more extensive encapsulation, but frequently their internal capsules failed to incorporate all the fibers. In all cases, cellular development on the lumen was limited to areas contiguous to the anastomoses. The initial porosity of the devices as measured by water permeability did not appear to influence the healing sequence to a significant extent. The grafts did exhibit differences in structural stability depending on whether they were of a knitted or woven construction. We suggest that users consider these different mechanical and structural properties when making their choice of a graft. Despite these differences, we believe that the healing process is far more host dependent than graft dependent.

Angiography↗

Evaluating the Dialine vascular prosthesis knitted from an alternative source of polyester yarns.

The sudden and unilateral decision by E. I. DuPont de Nemours & Co., Inc., to withdraw its polymers for use in implantable devices has presented the medical device industry with an immediate and serious challenge to find alternative sources of biomaterials. In France, the company Cardial S.A. has already taken steps to find an alternative polyester yarn to replace Dacron by developing a new arterial prosthesis knitted from polyester yarns supplied by Rhône-Poulenc Fibres. This article describes an in vitro and in vivo study of this French device, called the Dialine prosthesis, with a view to determining its relative performance compared to current American and British prostheses, which rely on DuPont's Dacron yarn. In addition to analyses of the morphology and textile structure, and measurements of its physical and chemical properties, the Dialine graft was implanted as a thoracoabdominal bypass in dogs for periods ranging from 4 h to 6 months. In addition to our pathologic and histologic observations, we cleaned and evaluated the explanted prostheses for in vivo changes in dimensions, strength, and crystalline microstructure. The Dialine graft was found to differ structurally from other polyester prostheses because it is warp-knitted from a mixture of flat and texturized yarns with finer filaments. Its denser structure has a lower water permeability, greater flexibility and ease of handling, satisfactory strength, and dimensional stability, and it presents different textures on its luminal and external surfaces. The in vivo trial demonstrated that it has excellent biocompatibility and biostability over 6 months. With no thrombi observed on the luminal surface after 3 months, it has a faster rate of healing, generates compact external and internal capsules with a thinner neointima, and has an overall milder inflammatory response than is normally observed with Dacron-based prostheses.

Angiography↗

Sequential diffusion-weighted magnetic resonance imaging study of lysophosphatidyl choline-induced experimental demyelinating lesion: an animal model of multiple sclerosis.

PURPOSE: To differentiate the surrounding edema from the focal demyelinating lesion during the early phase of the lesion using an apparent diffusion coefficient (ADC), and to monitor the changes in ADCs during the complete progression of a lysophosphatidyl choline (LPC)-induced experimental demyelinating lesion, an animal model of multiple sclerosis (MS). MATERIAL AND METHODS: Eighteen rats divided into two groups-demyelinating lesion (group I, N = 12) and vehicle group (saline injected; group II, N = 6)-were studied. A 0.2-microl quantity of 1% LPC solution in isotonic saline was injected in the rat brain internal capsule (IC) area to create the demyelinating lesion. Six rats were used exclusively for histology. Diffusion-weighted (DW) images were acquired at different diffusion weightings on the 3rd, 5th, 10th, 15th, and 20th days after LPC injection. ADC was measured from three regions of interest (ROIs) within the IC: focal demyelinating lesion (area A), surrounding area of the lesion (area B), and contralateral IC area (area C). RESULTS: Histology revealed demyelination of the IC area during the early phase of lesion progression up to day 10 and remyelination thereafter. Elevated ADCs were observed for the surrounding edematous area (area B), compared to the focal demyelinating lesion (area A) during the early phase of the demyelination process, while substantial reduction of ADCs was noticed during remyelination for both regions. CONCLUSION: Measurement of ADC showed clear differentiation of the surrounding edema from the LPC-induced focal demyelinating lesion in rats, especially during the early phase of the lesion progression.

Analysis of Variance↗

Directional diffusion in relapsing-remitting multiple sclerosis: a possible in vivo signature of Wallerian degeneration.

PURPOSE: To examine the role of directional dependence of the apparent diffusion coefficients in the evaluation of normal-appearing brain regions of patients with relapsing-remitting multiple sclerosis. MATERIALS AND METHODS: The role of diffusion tensor eigenvalues was investigated in the normal-appearing brain regions for 18 patients with relapsing-remitting multiple sclerosis and 15 age-matched normal controls. RESULTS: The isotropic apparent diffusion was increased in all regions. However, reduced anisotropy was significant only in regions with high anisotropy, including the corpus callosum and the internal capsule, and was due to increased diffusion tensor eigenvalues corresponding to diffusion transverse to the fibers without significant increase along the fibers. This characteristic pattern of changes in diffusion tensor eigenvalues has been observed previously in cases of Wallerian degeneration. Low-anisotropy regions corresponded to gray matter and gray/white interface regions. Since fiber tract orientations are not determined for regions of low anisotropy, this characteristic pattern of diffusion change is not detectable in these regions. CONCLUSION: Examination of diffusion tensor eigenvectors may provide insight into the changes observed in diffusion and a signature of Wallerian degeneration in the normal-appearing white matter of relapsing-remitting multiple sclerosis patients.

Adult↗

Tractography-based quantitation of diffusion tensor imaging parameters in white matter tracts of preterm newborns.

PURPOSE: To evaluate the feasibility of performing diffusion tensor tractography (DTT) to map and quantify the pyramidal white matter tracts of premature newborns. MATERIALS AND METHODS: Fourteen diffusion tensor MRI (DTI) examinations of nine premature newborns were evaluated. DTT was performed to segment bilateral pyramidal tracts, using a fiber-tracking algorithm originating in the cerebral peduncle (CP) and filtering through the posterior limb of the internal capsule (PLIC) and precentral gyrus (PCG). Voxels containing the resulting tracts were then used for quantitation of DTI parameters along the tract. The DTT-based tract measurements were compared with standard manually placed region-of-interest (ROI) measurements at four locations along the pyramidal tract, and the reproducibility of each technique was evaluated. RESULTS: DTT demonstrated improved reproducibility over manual ROI measurement for pyramidal tract quantitation and was less subject to intra-operator variability (P < 0.0001, Fisher test for equal variance). In general, the anatomic locations and measurements obtained with the two techniques were in good agreement, although some systematic differences were identified in the PLIC and CP. CONCLUSION: Fiber DTT is feasible in premature newborns, provides more reproducible tract measurements than manual ROI methods, and allows quantitation along the entire tract for more detailed DTI assessment of white matter maturation.

Diffusion Magnetic Resonance Imaging↗

Electrophysiological alterations in subthalamic neurons after unilateral dopamine depletion in the rat.

The present study examined the effects of unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta (SNc) on electrophysiological properties of subthalamic neurons (STN) in adult rats. Most neurons displayed regular spontaneous tonic firing patterns in both control and lesioned animals; however, the percentage of neurons with spontaneous burst firing at hyperpolarized membrane potentials was increased significantly in lesioned animals compared with controls (45% vs. 14% respectively). In the presence of bicuculline, a gamma-aminobutyric acid type A (GABAA) receptor antagonist, electrical stimulation of the internal capsule produced monosynaptic excitatory postsynaptic potentials (EPSPs) in almost all recorded neurons. DA (50 microM) increased the amplitude and/or duration of the EPSPs in neurons from both groups, whereas the DA D1 receptor agonist SKF 81297 (10 microM) produced a significant increase in amplitude and/or duration of EPSPs in neurons from the lesioned group only. This latter increase was blocked by pretreatment with the DA D1 antagonist SCH 23390 (10 microM). These data suggest that unilateral degeneration of DA neurons in the SNc changes firing properties and enhances electrophysiological responsiveness of STN neurons to activation of DA D1 receptors.

Action Potentials↗

Fetal cortical astrocytes migrate from cortical homografts throughout the host brain and over the glia limitans.

The cerebral cortices from 14-day gestation rat embryos were prelabeled with Phaseolus vulgaris leucoagglutin (PHAL) and then homografted into freshly made implantation pockets in the host cerebral cortex. Animals were sacrificed at 30 and 60 days postimplantation (DPI). Paraffin sections were double labeled for the presence of glial fibrillary acidic protein (GFAP), a specific marker for astrocytes, and PHAL, utilized as a marker for transplant-derived cells. Transplant-derived astrocytes were found on the glia limitans along the entire circumference of the brain, in the hippocampal commissure, corpus callosum, internal capsule, entopeduncular nucleus, habenular commissure, brachium of the superior colliculus, optic tract, optic chiasm, and sensory root of the trigeminal nerve. Transplanted astrocytes entered the spaces of Virchow-Robin, and migrated along parenchymal blood vessels and between the ependymal and subependymal layers of the third and lateral ventricles. The presence of basal lamina or parallel nerve fiber bundles was a common factor for these migration routes.

Animals↗

Human malignant astrocytoma xenografts migrate in rat brain: a model for central nervous system cancer research.

Fresh cells from two grade 3 human malignant astrocytomas were prelabeled with Phaseolus vulgaris leucoagglutin (PHAL) and then xenografted into freshly made implantation pockets in rat host cerebral cortex. Animals were sacrificed at 7, 14, 21 days, and 1 month postimplantation (DPI). Paraffin sections were double-labeled for the presence of glial fibrillary acidic protein (GFAP), a specific marker for astrocytes and differentiated astrocytoma cells, and PHAL, utilized as a marker for graft-derived cells. Grafted human astrocytoma cells were found on the glia limitans along the entire circumference of the brain, in the corpus callosum, internal capsule, entopeduncular nucleus, optic tract, and median eminence. In addition, astrocytoma cells were observed in the cingulum, habenula, arcuate, and supraoptic nucleus. Astrocytoma cells entered the spaces of Virchow-Robin, and migrated along parenchymal blood vessels and between the ependymal and subependymal layers of the third and lateral ventricles. The corpus callosum was a major migration route for the astrocytoma cells. The presence of basal lamina or parallel nerve fiber bundles was a common factor for these migration routes. The migration of the human astrocytoma xenografted cells in the rat brain followed the spread of human malignant astrocytomas in the human brain and is a valuable basic science tool in brain cancer research.

Animals↗

Brain regional distribution of physostigmine and its relation to cerebral blood flow following intravenous administration in rats.

3H-labeled physostigmine (50 micrograms.kg-1) was administered intravenously to rats, and its concentration in brain tissue and spinal cord was assessed by quantitative autoradiography. Regional cerebral blood flow (rCBF) was measured with iodo-14C-antipyrine autoradiography in control rats and in animals injected i.v. with a dose of physostigmine similar to that used for the distribution studies. Tissue concentration of 3H-physostigmine was correlated with rCBF for 37 brain regions. A high degree of correlation was found at 0.5 min after drug injection, r (correlation coefficient) = 0.87. This association decreased at later times (5 min r = 0.73, 12 min r = 0.24). Structures with high cholinesterase activity (caudate-putamen, amygdala, hippocampus) showed greater retention of physostigmine over time. The highest initial physostigmine concentrations were found in regions lacking a blood-brain barrier (pineal bland, median eminence, choroid plexus) (range = 10.4-23.8 nCi/mg) and the lowest in white matter (corpus callosum, internal capsule, hippocampus commisure, spinal cord dorsal column) (range = 1.2-2.6 nCi/mg). Initial concentrations of the drug in the areas in which physostigmine induced vasodilatation (motor, sensory, temporal and occipital cortex, claustrum, and superior collicullus) were not different from concentrations in areas of comparable basal rCBF in which no such effect was observed. Variations in drug access to brain regions, then, do not explain the topographical variations of the cerebrovascular action of physostigmine.

Animals↗

Microelectrode recordings in the pallidum.

The internal segment of the globus pallidus (GPi) is being targeted in neurosurgical procedures to treat Parkinson's disease and dystonia. Precise targeting of the pallidal complex is important in determining the efficacy of the surgical intervention and for the avoidance of adverse effects. Intraoperative microelectrode recording can be used to characterize the patterns of activity and receptive field properties of single pallidal neurons and to identify important bordering structures, including the optic tract and internal capsule. Because the clinical features of movement disorders can be differentially affected as a function of location within the pallidal complex, further refinements in intraoperative targeting may become important.

Brain Mapping↗

Lower stimulation frequency can enhance tolerability and efficacy of pallidal deep brain stimulation for dystonia.

We report the case of a patient with medically refractory primary dystonia who was treated with bilateral pallidal deep brain stimulation. Stimulation at 130 Hz or higher, by means of the more ventral contacts generated capsular side effects, which made their use impractical. Consequently, the patient was treated for 9 months at 130 to 185 Hz, by means of the more dorsal contacts, achieving modest results. By reducing the stimulation frequency to 80 Hz, we were able to activate the ventral contacts without inducing side effects. Within days, the patient experienced a dramatic improvement in function that has persisted for 1 year. A further reduction in stimulation frequency to 60 Hz resulted in a worsening of his symptoms. We conclude that chronic stimulation at frequencies of <100 Hz may be efficacious in dystonia and may enhance the tolerability of stimulation by means of contacts that are positioned posteroventrally within the internal globus pallidus, nearer the internal capsule.

Deep Brain Stimulation↗

Reproducibility of relaxation and spin-density parameters in phantoms and the human brain measured by MR imaging at 1.5 T.

The reproducibility of T1, T2, and proton density, measured in phantoms and the human brain was evaluated by proton imaging techniques. The sequence used to derive T1 and density values was a multiple-saturation recovery which consists of four pairs of 90 degrees pulses, followed by a 180 degrees phase reversal pulse, generating four T1-weighted images. T2 was derived from a multiple-echo sequence, generating four T2-weighted images. The data were analyzed by fitting the pixel intensities to the respective equations by means of nonlinear multiparameter least-squares analysis. Short-term reproducibility between four consecutive scans was evaluated to be 1-4% depending on location with a phantom covering the entire span of physiologic T1 and T2 values. A second phantom containing a series of identical samples served to study the dependence of the apparent T1 and T2 on position, both radially and axially, with respect to magnet isocenter. Reproducibility across the field of view was found to be better than 7% (T1 and T2). This phantom was further used to evaluate effects of long-term reproducibility, which at each location varied from 5-14% (T1) and 2-10% (T2). Finally, interinstrument reproducibility, tested by means of the same protocol on three different instruments, all operating at the same magnetic field and using largely identical hardware for each location, was found to be 1-14% (T1) and 2-10% (T2). The positional dependence of the apparent relaxation times appears to be systematic and may be due to variations in the effective field, caused by magnet and rf inhomogeneity. Finally, brain tissue relaxation and spin-density data were determined using the same protocol in 37 scans performed on 27 normal volunteers. The tissues analyzed were putamen, thalamus, caudate nucleus, centrum semiovale, internal capsule, and corpus callosum. Excellent accordance was further obtained between left and right hemispheres.

Brain↗

Magnetic resonance imaging of experimental demyelinating lesions.

An animal model of central nervous system demyelination was created by injecting rat internal capsules with lysophosphatidylcholine (LPC). The resulting chemically induced demyelinating lesions were readily visible in T1-weighted spin-echo, T2 weighted spin-echo, and inversion-recovery magnetic resonance imaging (MRI) sequences. Changes in lesions were followed over 8 weeks and correlated with histopathology. Histologically, lesions were characterized initially by an acute, inflammatory phase with edema and blood-brain barrier breakdown, followed by macrophage-mediated removal of myelin debris and finally by remyelination after 3 to 4 weeks. MRI can differentiate lesion stages in the LPC model and may be useful in investigating mechanistic aspects of the demyelinating process. In addition the well-localized lesions may be amenable to study by techniques of volume-localized NMR spectroscopy.

Animals↗

Diffusion imaging of experimental allergic encephalomyelitis.

Diffusion-weighted magnetic resonance imaging (MRI) was compared with T2-weighted MRI in longitudinal studies of experimental allergic encephalomyelitis (EAE), an animal model of multiple sclerosis, in five monkeys (Macaca fascicularis). In a region of the brain that had highly directional myelinated fibers (internal capsule) sequential changes were identified on diffusion-weighted images on and before the day these changes were detected on conventional T2-weighted images. Changes were also identified on diffusion-weighted images in brain areas that did not develop T2-weighted abnormalities. This result suggests that diffusion-weighted image intensities are sensitive to pathologic conditions of the brain that can not be seen on T2-weighted images.

Animals↗

In vivo measurement of T2 distributions and water contents in normal human brain.

Using a 32-echo imaging pulse sequence, T2 relaxation decay curves were acquired from five white- and six gray-matter brain structures outlined in 12 normal volunteers. The water contents of white and gray matter were 0.71 (0.01) and 0.83 (0.03) g/ml, respectively. All white-matter structures had significantly higher myelin water percentages (signal percentage with T2 between 10 and 50 ms) than all gray-matter structures. The range in geometric mean T2 of the main peak for both white and gray matter was from 70 to 86 ms. T2 distributions from the posterior internal capsules and splenium of the corpus callosum were significantly wider (width is related to water environment inhomogeneity) than those from any other white- or gray-matter structures. Thus, quantitative measurement and analysis of T2 relaxation reveals differences in brain tissue water environments not discernible on conventional MR images. These differences may make short T2 components reliable markers for normal myelin.

Adult↗

Retrospective measurement of the diffusion tensor eigenvalues from diffusion anisotropy and mean diffusivity in DTI.

A simple theoretical framework to compute the eigenvalues of a cylindrically symmetric prolate diffusion tensor (D) from one of the rotationally-invariant diffusion anisotropy indices and average diffusivity is presented and validated. Cylindrical or axial symmetry assumes a prolate ellipsoid shape (lambdaparallel=lambda1>lambdaperpendicular=(lambda2+lambda3)/2; lambda2=lambda3). A prolate ellipsoid with such symmetry is largely satisfied in a number of white matter (WM) structures, such as the spinal cord, corpus callosum, internal capsule, and corticospinal tract. The theoretical model presented is validated using in vivo DTI measurements of rat spinal cord and human brain, where eigenvalues were calculated from both the set of diffusion coefficients and a tensor analysis. This method was used to retrospectively analyze literature data that reported tensor-derived average diffusivity, anisotropy, and eigenvalues, and similar eigenvalue measurements were obtained. The method provides a means to retrospectively reanalyze literature data that do not report eigenvalues. Other potential applications of this method are also discussed.

Adult↗

Serial in vivo MR tracking of magnetically labeled neural spheres transplanted in chronic EAE mice.

Neural stem cell (NSC) transplantation has been shown to attenuate the severity of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Central to the future success of NSC transplantation in MS is the ability of transplanted cells to migrate from the site of transplantation to relevant foci of disease. Using magnetically labeled mouse neurospheres and human embryonic stem cell (hESC)-derived neurospheres, we applied serial magnetic resonance imaging (MRI) to assess the biodynamics of transplanted cell migration in a chronic mouse EAE model. Magnetic labeling did not affect the in vitro and in vivo characteristics of cells as multipotential precursors. Cell migration occurred along white matter (WM) tracts (especially the corpus callosum (CC), fimbria, and internal capsule), predominantly early in the acute phase of disease, and in an asymmetric manner. The distance of cell migration correlated well with clinical severity of disease and the number of microglia in the WM tracts, supporting the notion that inflammatory signals promote transplanted cell migration. This study shows for the first time that hESC-derived neural precursors also respond to tissue signals in an MS model, similarly to rodent cells. The results are directly relevant for designing and optimizing cell therapies for MS, and achieving a better understanding of in vivo cell dynamics and cell-tissue interactions.

Animals↗