Miguel Bussiere

Evidence that the Major Membrane Lipids, Except Cholesterol, Are Made in Axons of Cultured Rat Sympathetic Neurons

Abstract: Membrane lipids and proteins required for axonal growth and regeneration are generally believed to be synthesized in the cell bodies of neurons and transported into the axons. However, we have demonstrated recently that, in cultured rat sympathetic neurons, axons themselves have the capacity to synthesize phosphatidylcholine, sphingomyelin, and phosphatidylethanolamine. In these experiments, we employed a compartment model of neuron culture in which pure axons grow in a fluid environment separate from that containing the cell bodies. In the present study, we again used compartmented cultures to confirm and extend the previous results. We have shown that three enzymes of phosphatidylcholine biosynthesis via the CDP‐choline pathway are present in axons. We have also shown that the rate‐limiting step in the biosynthesis of phosphatidylcholine by this route in neurons, and locally in axons, is catalyzed by the enzyme CTP:phosphocholine cytidylyltransferase. The biosynthesis of other membrane lipids, such as phosphatidylserine, phosphatidylethanolamine derived by decarboxylation of phosphatidylserine, phosphatidylinositol, and fatty acids, also occurs in axons. However, the methylation pathway for the conversion of phosphatidylethanolamine into phosphatidylcholine appears to be a quantitatively insignificant route for phosphatidylcholine synthesis in neurons. Moreover, our data provided no evidence for the biosynthesis of another important membrane lipid, cholesterol, in axons.

Elevation of Ceramide within Distal Neurites Inhibits Neurite Growth in Cultured Rat Sympathetic Neurons

Sphingolipids are abundant constituents of neuronal membranes and have been implicated in intracellular signaling. We show that two analogs of glycosphingolipid biosynthetic intermediates, fumonisin B1 (which inhibits dihydroceramide synthesis) and DL-1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP) (which inhibits glucosylceramide synthesis) decrease glycosphingolipid synthesis in rat sympathetic neurons. Although both fumonisin and PPMP inhibit glycosphingolipid synthesis, these inhibitors have differential effects on ceramide metabolism in axons. threo-PPMP, but not erythro-PPMP or fumonisin, induces an accumulation of [3H]palmitate-labeled ceramide and impairs axonal growth. Moreover, exogenously added, cell-permeable C6-ceramide, but not C6-dihydroceramide, mimicks the effect of PPMP. Our studies suggest that the lipid second messenger ceramide acts in distal axons, but not cell bodies, as a negative regulator of neurite growth.

Outcome in small aneurysms (<4 mm) treated by endovascular coiling

Background Coiling of small aneurysms can be technically challenging. These aspects of coiling tend to be less problematic in medium to large aneurysms as they are more accommodating of microcatheters and coils. When physicians are asked their opinion regarding aneurysm coilability in small aneurysms, the decision often lies in the operators feeling that they could reasonably exclude the aneurysm with a complication rate similar to larger aneurysms. The purpose of our study was to investigate the feasibility, intraprocedural rupture rates and long term durability of endovascular coiling for small (≤4 mm) aneurysms compared with non-small (>4 mm) aneurysms. To control for factors such as vessel tortuosity and aneurysm location, a control group was chosen matched to the study group both in age and aneurysm location. Materials and methods A retrospective review of 360 intracranial aneurysms coiled at our institution between 2003 and 2008 was performed. For the control group, intracranial aneurysms coiled in the same period matched to location and age were chosen. Results The frequency of intraprocedural perforations was 4/34 (0.12) and 3/68 (0.04) for the small and non-small cohort, respectively (p=0.22). All patients who had a perforation in the small aneurysm groups had a good clinical outcome compared with 1/3 in the non-small group (two mortalities). The frequency of recanalization for the small and non-small groups was 3/34 (0.09) and 23/68 (0.33), respectively (p=0.006). There was no retreatments in the small aneurysm group and five (0.07) in the non-small group (p=0.116). Conclusion Coiling of small (≤4 mm) aneurysms is feasible with a reasonable complication rate. There is a non-significant increase in frequency of intraprocedural rupture with coiling of small aneurysms compared with controls matched to aneurysm location and age but this is not associated with increased morbidity. Coiling of small aneurysms leads to durable results at long term follow-up.

Early Rivaroxaban Use After Cardioembolic Stroke May Not Result in Hemorrhagic Transformation: A Prospective Magnetic Resonance Imaging Study.

Background and Purpose— Early anticoagulation after cardioembolic stroke remains controversial because of the potential for hemorrhagic transformation (HT). We tested the safety and feasibility of initiating rivaroxaban ⩽14 days after cardioembolic stroke/transient ischemic attack. Methods— A prospective, open-label study of patients with atrial fibrillation treated with rivaroxaban ⩽14 days of transient ischemic attack or ischemic stroke (National Institute of Health Stroke Scale <9). All patients underwent magnetic resonance imaging <24 hours of rivaroxaban initiation and day 7. The primary end point was symptomatic HT at day 7. Results— Sixty patients (mean±SD age 71±19 years, 82% stroke/18% transient ischemic attack) were enrolled. Median (interquartile range) time from onset to rivaroxaban was 3 (5) days. At treatment initiation, median National Institute of Health Stroke Scale was 2 (4), and median diffusion-weighted imaging volume was 7.9 (13.7) mL. At baseline, HT was present in 25 (42%) patients (hemorrhagic infarct [HI]1=19, HI2=6). On follow-up magnetic resonance imaging, no patients developed symptomatic HT. New asymptomatic HI1 developed in 3 patients, and asymptomatic progression from HI1 to HI2 occurred in 5 patients; otherwise, HT remained unchanged at day 7. Conclusions— These data support the safety of rivaroxaban initiation ⩽14 days of mild–moderate cardioembolic stroke/transient ischemic attack. Magnetic resonance imaging evidence of petechial HT, which is common, does not appear to increase the risk of symptomatic HT.

Reciprocal regulation of choline acetyltransferase and choline kinase in sympathetic neurons during cholinergic differentiation

The regulation of the synthesis of acetylcholine and phosphatidylcholine in rat sympathetic neurons was examined in the context of cholinergic differentiation. We demonstrate that the activities of choline acetyltransferase (ChAT) and choline kinase (CK) are inversely affected by treatment of sympathetic neurons with retinoic acid, utilized as an agent that induces cholinergic differentiation. Whereas ChAT specific activity increased 2- to 4-fold after 12 days of treatment with 5 microM retinoic acid, CK specific activity decreased by 25-30%. These changes in enzyme activities were essentially reflected in the incorporation of [methyl-3H]choline into ACh and the metabolites of the CDP-choline pathway for phosphatidylcholine synthesis. When sympathetic neurons were treated under high potassium conditions (50 mM) for 12 days, the specific activity of CK increased 1.3-fold whereas the activity of ChAT decreased by up to 90%. Furthermore, experiments in which the incorporation of [methyl-3H]choline into ACh and the metabolites of the CDP-choline pathway was measured in the absence of Na+ or in the presence of hemicholinium-3 (HC-3), demonstrate that CK has access to the same pool of choline utilized by ChAT. These results provide evidence that the activities of ChAT and CK may be inversely regulated during the process of cholinergic differentiation.

Extracranial Venous abnormalities: A true pathological finding in patients with multiple sclerosis or an anatomical variant?

AbstractObjectiveTo evaluate the extracranial venous anatomy with contrast-enhanced MR venogram (CE-MRV) in patients without multiple sclerosis (MS), and assess the prevalence of various venous anomalies such as asymmetry and stenosis in this population.Materials and methodsWe prospectively recruited 100 patients without MS, aged 18–60 years, referred for contrast-enhanced MRI. They underwent additional CE-MRV from skull base to mediastinum on a 3T scanner. Exclusion criteria included prior neck radiation, neck surgery, neck/mediastinal masses or significant cardiac or pulmonary disease. Two neuroradiologists independently evaluated the studies to document asymmetry and stenosis in the jugular veins and prominence of collateral veins.ResultsAsymmetry of internal jugular veins (IJVs) was found in 75 % of subjects. Both observers found stenosis in the IJVs with fair agreement. Most stenoses were located in the upper IJV segments. Asymmetrical vertebral veins and prominence of extracranial collateral veins, in particular the external jugular veins, was not uncommon.ConclusionIt is common to have stenoses and asymmetry of the IJVs as well as prominence of the collateral veins of the neck in patients without MS. These findings are in contrast to prior reports suggesting collateral venous drainage is rare except in MS patients.Key Points• The venous anatomy of the neck in patients without MS demonstrates multiple variants • Asymmetry and stenoses of the internal jugular veins are common • Collateral neck veins are not uncommon in patients without MS • These findings do not support the theory of chronic cerebrospinal venous insufficiency • MR venography is a useful imaging modality for assessing venous anatomy

CTA source images as a predictor of final infarct volume are time-dependent.

Avascularity on CT angiography source images (CTASI) may better predict final infarct volume in acute stroke as compared to early ischemic changes on non-contract CT1-4. These CTASI findings may represent infarct core and help determine the extent of salvageable tissue3. However, the extent of avascularity on CTASI may overestimate infarct volume if transit of contrast is prolonged due to proximal artery occlusion. We present a case where CT-perfusion (CTP) and time-resolved CT-angiography (CTA) identified salvageable tissue thought to be infarcted on CTASI. An 81-year-old female with a history of atrial fibrillation anticoagulated with warfarin with no concurrent antiplatelet therapy presented to the emergency department with acute right hemiplegia and global aphasia. The international normalized ratio (INR) was subtherapeutic at 1.7. Initial CT showed no early ischemic changes (Figure A). CT-angiography showed a left M1 occlusion with reduced filling of the distal vessels (Figure B). CT-angiography images were acquired on a 320 slice scanner (ToshibaAquilion One, Japan). The scanning parameters were as follows: 80kv, 100mA, one second rotation, volume acquisition. Thirty ccs of intravenous contrast (Iopamidol, Bracco, Princton, NJ) was injected at a rate of 5 cc/sec. A total of 18 volumes were acquired (13 volumes every second with one second interval followed by five volumes with five second interval). A large area of avascularity in the middle cerebral artery (MCA) territory seen CTASI suggested a large infarct core with minimal penumbra (Figure C). Conversely, CTP revealed a large area of cerebral blood flow / cerebral blood volume mismatch and suggested a small infarct core. This was corroborated by MTT acquired at 12 seconds. (Figures D-F). Using the time-resolved CTA function of the Toshiba Aquilion ONETM volume CT scanner, we reprocessed the original CTASI images obtained two seconds from the original acquisition and revealed contrast within vessels in the left MCA territory, presumably filling via leptomeningeal collaterals (Figures G-H). Consistent with the CTP findings, these images suggested relatively oligemic but potentially salvageable tissue. The patient received intravenous tPA 29 minutes after symptom onset, and was then transferred to the angiography suite for possible intra-arterial therapy. Groin