A weighted and directed interareal connectivity matrix for macaque cerebral cortex

Retrograde tracer injections in 29 of the 91 areas of the macaque cerebral cortex revealed 1,615 interareal pathways, a third of which have not previously been reported. A weight index (extrinsic fraction of labeled neurons [FLNe]) was determined for each area-to-area pathway. Newly found projections were weaker on average compared with the known projections; nevertheless, the 2 sets of pathways had extensively overlapping weight distributions. Repeat injections across individuals revealed modest FLNe variability given the range of FLNe values (standard deviation <1 log unit, range 5 log units). The connectivity profile for each area conformed to a lognormal distribution, where a majority of projections are moderate or weak in strength. In the G_{29 × 29} interareal subgraph, two-thirds of the connections that can exist do exist. Analysis of the smallest set of areas that collects links from all 91 nodes of the G_{29 × 91} subgraph (dominating set analysis) confirms the dense (66%) structure of the cortical matrix. The G_{29 × 29} subgraph suggests an unexpectedly high incidence of unidirectional links. The directed and weighted G_{29 × 91} connectivity matrix for the macaque will be valuable for comparison with connectivity analyses in other species, including humans. It will also inform future modeling studies that explore the regularities of cortical networks.

Weight consistency specifies regularities of macaque cortical networks

To what extent cortical pathways show significant weight differences and whether these differences are consistent across animals (thereby comprising robust connectivity profiles) is an important and unresolved neuroanatomical issue. Here we report a quantitative retrograde tracer analysis in the cynomolgus macaque monkey of the weight consistency of the afferents of cortical areas across brains via calculation of a weight index (fraction of labeled neurons, FLN). Injection in 8 cortical areas (3 occipital plus 5 in the other lobes) revealed a consistent pattern: small subcortical input (1.3% cumulative FLN), high local intrinsic connectivity (80% FLN), high-input form neighboring areas (15% cumulative FLN), and weak long-range corticocortical connectivity (3% cumulative FLN). Corticocortical FLN values of projections to areas V1, V2, and V4 showed heavy-tailed, lognormal distributions spanning 5 orders of magnitude that were consistent, demonstrating significant connectivity profiles. These results indicate that 1) connection weight heterogeneity plays an important role in determining cortical network specificity, 2) high investment in local projections highlights the importance of local processing, and 3) transmission of information across multiple hierarchy levels mainly involves pathways having low FLN values.

Analysis of pentacyclic triterpenes by LC-MS. A comparative study between APCI and APPI

The analytical performances of three atmospheric-pressure sources, electrospray (ESI), atmospheric-pressure chemical ionization (APCI), and atmospheric-pressure photoionization (APPI), were evaluated for the analysis of pentacyclic triterpenes in liquid chromatography-mass spectrometry (LC-MS). Among these sources, APPI and APCI are particularly well adapted to sensitive analyses of pentacyclic triterpenes by LC-MS. Detection parameters were optimized for both the sources, and the effects of three dopants (toluene, acetone and anisole) on the detection (sensitivity and ion fingerprints in MS spectra) were studied in detail for APPI-MS.The limits of quantification were measured under selected ion monitoring conditions, in the range of 0.005-0.015 mg l(-1) and 0.002-0.84 mg l(-1) in APPI and APCI, respectively, depending on the studied pentacyclic triterpene. Overall, APPI was found more sensitive than APCI in positive ion mode, whereas APCI shows the greatest sensitivity for acidic triterpenes in negative ion mode.Following this study, the developed LC-MS method was used for the characterization of pentacyclic triterpenes in three plant extracts. High amounts of betulinic acid, betulinic aldehyde and betulinic aldehyde acetate were observed in plane bark. The main component of birch bark is betulin and extracts of okoume resin exhibit high amounts of alpha- and beta-amyrin.

[Giant cystic widening of Virchow-Robin spaces, case report]

INTRODUCTION

Virchow-Robin spaces are very well-known anatomical and radiological entities. However, the observation of giant cystic widening of Virchow-Robin spaces is anecdotic. We report herein the case of a patient presenting with giant cystic widening of Virchow-Robin spaces located in both cerebral hemispheres.

OBSERVATION

A 26-year-old female presented with numbness of left arm and then, of both arms. CT scan showed many hypodensities located in the two hemispheres. Neurologic examination was normal. MR imaging allowed the diagnosis of giant cystic widening Virchow-Robin spaces in T2, T2*, T1 gadolinium and Flair weighted images. Neuropsychological investigations were normal.

CONCLUSION

Giant cystic widening of Virchow-Robin spaces are extremely rare entities. MR imaging helps the diagnosis. Only extreme dilatation of Virchow-Robin perivascular spaces close to ventricular system must be watched and treated in case of an obstructive hydrocephalus risk. When located in cerebral hemispheres, these dilatations are mostly asymptomatic and must not be confused with a cystic tumoral disease.

Comparison of optimized and standard diffusion-weighted imaging at 1.5T for the detection of acute lesions in patients with transient ischemic attack

SUMMARY

The high rate of normal diffusion-weighted imaging (DWI) in patients with transient ischemic attack (TIA) raises the question as to its sensitivity for detecting small ischemic lesions. We compared standard and optimized DWI in 36 consecutive patients with TIA. Optimized DWI was positive in more patients than standard DWI (19 versus 16; P < .001) and showed more lesions (56 versus 42; P = .002). At 1.5T, optimizing DWI decreases the rate of false-negative DWI in patients with TIA.

Traitement hormonal substitutif de la ménopause et risque vasculaire

Although experimental data and results of observational studies suggest that hormone replacement therapy (HRT) was associated with a reduction in the risk of heart disease, the results for stroke have been far less clear. Several recent randomized secondary prevention studies have found that HRT is not protective against the risk of coronary heart disease, stroke or progression of atherosclerosis. Moreover, an increased risk of stroke and first coronary event with hormone therapy has been found in low-risk healthy post menopausal women. In light of these findings, although the absolute risk of vascular event associated with HRT is low, most organizations recommend caution in using HRT. Hormone therapy should not be initiated to prevent vascular disease among postmenopausal women. There are numerous plausible explanations for the divergent findings from observational and randomized clinical trials of hormone therapy. Some discrepancies are certainly the result of methodological differences between the study designs. They also suggest other biological effects of hormone therapy than modification of classic vascular risk factors. Further studies should focus on identifying the mechanisms of risk and determining whether and how different regimens of hormone therapy influence vascular risk.

Management and Outcome of Patients with Transient Ischemic Attack Admitted to a Stroke Unit

BACKGROUND

The way in which patients with transient ischemic attack (TIA) are investigated and treated varies substantially worldwide. There are no data on the management and outcome of TIA patients admitted to a stroke unit. We assessed to what extent rapid management of TIA patients admitted to a stroke unit led to specific treatments which can prevent stroke and evaluated the early risk and predictors of stroke in these patients.

METHODS

From January 2003 to November 2005, 203 consecutive patients with a recent (<48 h) TIA were admitted to our stroke unit. All patients had a diffusion-weighted imaging (DWI) on admission, a standardized etiological workup, and were followed up to 3 months.

RESULTS

The median (interquartile range) time from TIA onset to admission to the stroke unit was 12 h (5-25). DWI revealed acute lesions in 64 patients (32%). Of the 203 patients, 147 (72%) were treated by antiplatelet therapy and 56 (28%) with high doses of heparin, soon after their admission. In addition, 7 patients (3%) had a carotid revascularization. The risk of stroke was 2.5% (95% CI, 0.3-4.7) at 1 week, and 3.5% (1.0-6.1) at 3 months. In multivariate analysis, a score > or =5 at the previously validated ABCD score (HR = 5.0; 1.0-25.8; p = 0.06) and the presence of DWI abnormalities (HR = 10.3; 1.2-86.7; p = 0.03) were independent predictors of stroke at 3 months.

CONCLUSION

Early management of TIA in a stroke unit leads to specific treatments in a significant proportion of cases. The presence of acute lesions on DWI and the ABCD score predict the 3-month risk of stroke after TIA.

Enhanced pelvic responses to stressors in female CRF-overexpressing mice

Acute stress affects gut functions through the activation of corticotropin-releasing factor (CRF) receptors. The impact of acute stress on pelvic viscera in the context of chronic stress is not well characterized. We investigated the colonic, urinary, and locomotor responses monitored as fecal pellet output (FPO), urine voiding, and ambulatory activity, respectively, in female and male CRF-overexpressing (CRF-OE) mice, a chronic stress model, and their wild-type littermates (WTL). Female CRF-OE mice, compared with WTL, had enhanced FPO to 2-min handling (150%) and 60-min novel environment (155%) but displayed a similar response to a 60-min partial restraint stress. Female CRF-OE mice, compared with WTL, also had a significantly increased number of urine spots (7.3 +/- 1.4 vs. 1.3 +/- 0.8 spots/h) and lower locomotor activity (246.8 +/- 47.8 vs. 388.2 +/- 31.9 entries/h) to a novel environment. Male CRF-OE mice and WTL both responded to a novel environment but failed to show differences between them in colonic and locomotor responses. Male WTL, compared with female WTL, had higher FPO (113%). In female CRF-OE mice, the CRF(1)/CRF(2) receptor antagonist astressin B and the selective CRF(2) receptor agonist mouse urocortin 2 (injected peripherally) prevented the enhanced defecation without affecting urine or locomotor responses to novel environment. RT-PCR showed that CRF(1) and CRF(2) receptors are expressed in the mouse colonic tissues. The data show that chronic stress, due to continuous central CRF overdrive, renders female CRF-OE mice to have enhanced pelvic and altered behavioral responses to superimposed mild stressors and that CRF(1)-initiated colonic response is counteracted by selective activation of CRF(2) receptor.

Reversible cerebral angiopathy

Reversible cerebral angiopathy (RCA) is responsible for disabling headache and potential stroke complications. Most patients respond poorly to analgesics. We describe four patients with typical RCA whose headache rapidly disappeared after IV nimodipine treatment was initiated.

[Brain imaging patterns after stroke]

The advent of new imaging techniques, such as diffusion-weighted sequences, has a great impact on the diagnostic imaging in stroke. The aim of the present paper is to review the brain imaging patterns after stroke, highlight the usefulness of imaging technique for the diagnosis and etiological work-up after stroke. Three causes of ischemic stroke (cerebral venous thrombosis, aortic arch atheroma, patent foramen ovale) are detailed.