On the microstructural origin of brain white matter hydraulic permeability

Brain microstructure plays a key role in driving the transport of drug molecules directly administered to the brain tissue, as in Convection-Enhanced Delivery procedures. The proposed research analyzes the hydraulic permeability of two white matter (WM) areas (corpus callosum and fornix) whose three-dimensional microstructure was reconstructed starting from the acquisition of electron microscopy images. We cut the two volumes with 20 equally spaced planes distributed along two perpendicular directions, and, on each plane, we computed the corresponding permeability vector. Then, we considered that the WM structure is mainly composed of elongated and parallel axons, and, using a principal component analysis, we defined two principal directions, parallel and perpendicular, with respect to the axons’ main direction. The latter were used to define a reference frame onto which the permeability vectors were projected to finally obtain the permeability along the parallel and perpendicular directions. The results show a statistically significant difference between parallel and perpendicular permeability, with a ratio of about two in both the WM structures analyzed, thus demonstrating their anisotropic behavior. Moreover, we find a significant difference between permeability in corpus callosum and fornix, which suggests that the WM heterogeneity should also be considered when modeling drug transport in the brain. Our findings, which demonstrate and quantify the anisotropic and heterogeneous character of the WM, represent a fundamental contribution not only for drug-delivery modeling, but also for shedding light on the interstitial transport mechanisms in the extracellular space.

Understanding the effect of the brain microstructure on spatial drug distribution is pivotal to designing effective treatment strategies for neurological disorders (1).The recent introduction of an innovative technique called Convection-Enhanced Delivery (CED) in the neurosurgical scenario opened up the possibility to deliver chemotherapeutic agents to brain tumors and, more recently, gene therapy for Parkinson’s disease and antiseizure agents for epilepsy (2–4). In CED, the main idea is to use convection to augment the local concentration of a drug by directly infusing in the brain tissue (5). Usually, one or more catheters are stereotactically placed in the region of interest and then anchored to a pump that can inject a drug at certain flow rate, which is usually of the order of microliters per minute (6). By using CED, it is possible to achieve a much higher spatial distribution of the drug because the pressure gradient allows infusing over a larger volume with respect to other methods (5).Despite CED having shown promising results in the field of neurological drug delivery, clinical trials did not succeed in demonstrating benefits in terms of life expectancy for patients (5–7). Indeed, for CED to be effective, it is necessary to have a sufficiently high concentration of drug in the regions occupied by the diseased tissue. However, a number of factors, such as catheter design, catheter placement, and infusion protocol, which are often very difficult to control, influence the drug-distribution and concentration profile. Accordingly, clinicians would significantly benefit from making use of numerical models able to predict the drug distribution and concentration in the preoperative phase (5, 6). A predictive model allows the surgeon to test different scenarios in terms of catheter setup and infusion settings in the preoperative phase to decide the best way to operate on the patient.Although several models devoted to tackling the above scenario have been developed in the last 20 y (8–12), there are still important discrepancies between prediction and reality, thus suggesting the need for more refined and comprehensive approaches (1). In particular, the brain extracellular space (ECS) spatial organization is identified as a pivotal factor for drug transport, as highlighted by ref. 13. However, there exists only a limited number of studies that have tried to understand the relation between ECS and hydraulic permeability, a fundamental parameter for modeling CED, which is also the subject of an important controversy (14, 15).Recent advances in imaging and three-dimensional (3D) reconstruction of brain structures at the cellular level have laid the first milestone toward a deeper understanding of the ECS spatial organization role. For example, ref. 14 used the neuropil reconstruction (gray matter) by ref. 16 to compare advective and diffusive transport within the interstitial space. Tools have also been developed (17) to perform a detailed analysis of other fibrous soft tissues, such as those developed to study the meniscus microstructure, in which the fluid flows during the transmission of the load to the articular cartilage, and to link the local tissue microstructure to the zonal variation of elastic and viscoelastic properties of the tissue (18).In this work, we use the dataset obtained using focused ion-beam scanning electron microscopy (FIB-SEM) to provide two-dimensional (2D) and 3D tissue microstructural information, as provided by ref. 19, to examine the permeability of two white matter (WM) structures, corpus callosum (CC) and fornix (FO). By integrating the information acquired by simulating a convective flow between the axons and the principal component analysis (PCA) performed on the axons’ centerline, we determine and, in doing so, confirm the ability to predict the strongly anisotropic character of the WM in terms of hydraulic permeability. Moreover, comparing the two WM structures, we reveal the significant difference between different WM areas. The relations between ECS and WM anisotropy and heterogeneity are here systematically discussed and represent an important contribution not only for CED modeling, but also for understanding interstitial solute transport.     

Experimental pathogenicity of Candida albicans and Candida dubliniensis with continuous and discontinuous fringes morphotypes

A possible correlation between the presence of discontinuous fringes and high virulence has been previously suggested. The aim of this study was to compare the pathogenicity of Candida albicans and Candida dubliniensis with continuous and discontinuous fringes morphotypes on mice. For C. albicans, two discontinuous fringe morphotype isolates (PN 69, PN 74), two continuous fringe morphotype isolates (N 60, N 33) and one reference strain were used. For C. dubliniensis, three discontinuous fringe morphotype isolates (97487, 97464, 97519), two continuous fringe morphotype isolates (97040, 98026) and one reference strain were used. Swiss male mice were inoculated with a standardised suspension of the microorganisms and observed for 35 days. The pathogenicity of the isolates was analysed according to parameters proposed previously. Three isolates were considered pathogenic: PN 74, N 60 and 98026. Strain N 60 killed the highest amount of mice (80%). Animals inoculated with C. albicans did not show differences on survival estimate. Candida dubliniensis 98026 was more pathogenic than samples 97464 and 97519. On the other hand, the sample 97487 showed a higher pathogenicity when compared with 97040 (Kaplan–Meier test, P = 0.008). Strains with continuous fringe morphotypes were also associated with Candida sp. virulence in vivo.     

Investigation on the interaction mechanism between the electrochemically produced benzophenone radical-anions and various monomers

The decay caused by the interaction between methacrylonitrile, methylmethacrylate, acrylonitrile, and methylacrylate and benzophenone radical-anions produced through electrolytical reduction of benzophenone in dimethylformamide in the presence of tetraethyl-ammonium perchlorate as background electrolyte, has been investigated at various temperatures by using the polarographic and amperometric techniques. Owing to the interaction with the monomers, the benzophenone radical-anions fully reoxidate to benzophenone. Moreover, decay rates will depend on the square radical-anions and first power monomer concentration and are inversely proportional to the concentration of unaltered benzophenone present in the system. The experimental results are interpreted on the basis of a kinetic scheme which comprises the dismutation of benzophenone radical-anions to dianions and benzophenone, and subsequent electronic transfer from dianions to monomers.     

Anomalies in the fractional precipitation of polyvinylchloride

An accurate fractional precipitation, using tetrahydrofuran as solvent and water as nonsolvent, of polyvinylchloride prepared by a strictly homogeneous polymerization process, shows that the anomalies in the fractionation are associated, as main factor, to the more crystalline part of PVC. In fact, the first fractions exhibit a markedly higher degree of crystallinity than the successive fractions and the unfractionated polymer, as determined by X-ray diffraction. Nuclear magnetic resonance indicates a slightly more syndiotactic configuration of the first fractions with respect to the others.     

Electroinitiated cationic polymerization of ethyl and i-butyl vinyl ethers

The electroinitiated cationic polymerization of ethyl and i-butyl vinyl ethers has been studied under various experimental conditions using NaB(C₆H₅)₄ as background electrolyte. Differring from other electrolytes with higher oxidation potentials, the NaB(C₆H₅)₄ allows appreciable current intensities and the polymerizations can occur at moderate rates. The monomer to polymer conversion presents a slightly sigmoidal shape as a function of the quantity of electricity and at a fixed quantity of electricity is independent from the current intensities. The molecular weights of the polymers are substantially controlled by chain transfer to monomers and solvents: the relative chain transfer constants are reported. The reaction temperature affects remarkably the molecular weights while the influence of dielectric constant of the reaction medium is negligible. An interpretation is given of the effect of NaB(C₆H₅)₄ electrolyte on the initiation mechanism and on the resulting conditions of polymerization.     

Anxiety and acceptance of gynecological laparoscopic operations

BACKGROUND: To evaluate the acceptance of gynecological laparoscopic operations. METHODS: A comparative analysis has been performed in a group of 32 women by analyzing a) the cognitive component, by means of 2 questionnaires administered before and after the operation and b) the emotional component, by evaluating the pre- and post-operative anxiety levels (State anxiety) and the constitutional ones (Trait anxiety) using the STAI Y test. The anxiety level of our group has been compared with that attributed to the general population by means of the Z test. Moreover, significant correlations have been searched between: 1) pre- and postoperative Trait and State anxiety, through the Pearson's correlation test; 2) the variables investigated by the two informational questionnaires and the anxiety measures, through the Student t test; 3) the informative variables themselves through the c2 test. RESULTS: Postoperative State anxiety is lower than that of the general population (p<0.05); a significant correlation exists between post- operative State and Trait anxiety (p<0.05); Trait anxiety is higher when fantasies linked to the operation are characterized by fear (p<0.05), and attribution of the decision to operate to the doctor (p<0.05); post-operative State anxiety is higher when the level of education is low (p<0.05) and the attribution of the decision to operate is to the doctor (p<0.05); a significant correlation exists between fantasies characterized by fear and the experience of postoperative pains, between postoperative pains and attribution of the decision to operate to the doctor (p<0.05) and between fantasies characterized by fear and attribution of the decision to operate to the doctor (p<0.05). CONCLUSIONS: Higher anxiety levels have been detected in the pre-operative phase, in less educated patients and when the decision to operate has been attributed to the doctor. A not wholly convinced personal attitude has been accompanied by preoperative fantasies characterized by fear and has resulted in subjectively more painful postoperative course.     

Seroprevalence study of tick borne encephalitis in Turin province

BACKGROUND: Tick borne encephalitis (TBE) virus is diffused in some European countries and it is transmitted by tick bites. In Italy Isodex ricinus represents the main vector of the infection, that rarely produces the neurologic manifestations, characterising the secondary phase of the same. METHODS: In Italy TBE has been little studied and this only in the Middle and Northern regions of the country. Seroepidemiological researches were done prevalently on subjects at high risk of tick bite, such as hunters or forest guards and especially in Trentino and Tuscany. No precise information about TBE virus diffusion was disposable in the Piedmont region and particularly in the Susa valley where, before our investigation failed the data about it. RESULTS: We found that usual hunters and wild boar breeders seem to be particularly exposed to the risk of TBE virus infection, but none neurologic involvement was detected in the anamnesis of the significantly seropositive subjects and also of the borderline ones, that we have studied, despite the limited number of these subjects. CONCLUSIONS: Nevertheless we hope for a following extension of our case report, also in consideration that rare cases of encephalitis of unknown etiology, are signalled in Piedmont.     

Electrochemically initiated cationic polymerization of trioxane in benzonitrile and nitrobenzene. Part II

Electrochemically initiated cationic polymerizations of trioxane in benzonitrile and in nitrobenzene have been carried out. In both of these solvents the polymerizations go on even when the current is switched off. In benzonitrile the polymerizations are affected, however, by a slow termination reaction probably involving the solvent. This leads to a satisfactory thermal stability of the polyoxymethylenes. Based on certain assumptions the specific propagation rate constants of trioxane polymerizations in both solvents and the corresponding activation energies have been deduced from the initial polymerization rates of experiments carried out at various concentrations of initiating species and at various temperatures.     

Teased-fiber technique for peripheral myelinated nerves: methodology and interpretation

Teased-fiber technique is the best approach for studying peripheral myelinated nerve fibers in their continuity. It enables the assessment of size of myelin segments formed by Schwann cells and characterization of pathologic changes affecting the internodia, the paranodal regions, and the invested axons. Fiber teasing is performed on prestained proximodistally oriented portions of peripheral nerves. Specimens about 10 mm long are stained for 24-48 hours in Sudan black and then transferred to glycerin, where, using a pair of fine forceps and a stereomicroscope, they are separated into smaller fiber bundles from which single fibers are isolated. The work is performed on a glass slide with an adhesive surface (albuminized or "superfrost"), on which the fibers are placed in strict proximodistal orientation. Following drying in an oven, the slides are mounted with glycerin-gelatine (same as used for frozen sections). The changes, when present, can usually be recognized during the preparation, but fibers are reexamined and changes confirmed in mounted slides. Photographic reconstruction of the fibers facilitates their assessment and enables the documentation of findings. The teased-fiber technique is auxiliary to histopathology, and to limit the workload and save costs, it can be performed on only a few specimens selected for better characterization of changes recognized or suspected in tissue sections. In particular, segmental demyelination and early stages of Wallerian or secondary axonal degeneration can be recognized in teased fibers. Segmental demyelination is characterized by loss of fully myelinated segments and their replacement by newly formed short and thin segments, remyelinating the preserved axon. The early stage of secondary axonal degeneration is recognized by formation of ovoidal fiber fragments in the midinternodal region.