Anisotropic and heterogeneous diffusion in the turtle cerebellum: implications for volume transmission

1993 ◽  
Vol 70 (5) ◽  
pp. 2035-2044 ◽  
Author(s):  
M. E. Rice ◽  
Y. C. Okada ◽  
C. Nicholson
Keyword(s):  
Time Course ◽  
Granular Layer ◽  
Volume Fraction ◽  
Molecular Layer ◽  
Extracellular Volume ◽  
Striking Difference ◽  
Volume Transmission ◽  
Anisotropic Porous Media ◽  
Parallel Fibers ◽  
Ion Shifts

1. Measurements of extracellular diffusion properties were made in three orthogonal axes of the molecular and granular layers of the isolated turtle cerebellum with the use of iontophoresis of tetramethylammonium (TMA+) combined with ion-selective microelectrodes. 2. Diffusion in the extracellular space of the molecular layer was anisotropic, that is, there was a different value for the tortuosity factor, lambda i, associated with each axis of that layer. The x- and y-axes lay in the plane parallel to the pial surface of this lissencephalic cerebellum with the x-axis in the direction of the parallel fibers. The z-axis was perpendicular this plane. The tortuosity values were lambda x = 1.44 +/- 0.01, lambda y = 1.95 +/- 0.02, and lambda z = 1.58 +/- 0.01 (mean +/- SE). By contrast, the granular layer was isotropic with a single tortuosity value, lambda Gr = 1.77 +/- 0.01. 3. These data confirm the applicability of appropriately extended Fickian equations to describe diffusion in anisotropic porous media, including brain tissue. 4. Heterogeneity between the molecular and granular layer was revealed by a striking difference in extracellular volume fraction, alpha, for each layer. In the molecular layer alpha = 0.31 +/- 0.01, whereas in the granular layer alpha = 0.22 +/- 0.01. 5. Volume fraction and tortuosity affected the time course and amplitude of extracellular TMA+ concentration after iontophoresis. This was modeled by the use of the average parameters determined experimentally, and the nonspherical pattern of diffusion in the molecular layer was compared with the spherical distribution in the granular layer and agarose gel by computing isoconcentration ellipsoids. 6. One functional consequence of these results was demonstrated by measuring local changes in [K+]o and [Ca2+]o after microiontophoresis of a cerebellar transmitter, glutamate. The ratios of ion shifts in the x- and y-axes in the granular layer were close to unity, with a ratio of 1.04 +/- 0.08 for the rise in [K+]o and 1.03 +/- 0.17 for the decrease in [Ca2+]o. In contrast, ion shifts in the molecular layer had an x:y ratio of 1.44 +/- 0.14 for the rise in [K+]o and 2.10 +/- 0.42 for the decrease in [Ca2+]o. 7. These data demonstrate that the structure of cellular aggregates can channel the migration of substances in the extracellular microenvironment, and this could be a mechanism for volume transmission of chemical signals. For example, the preferred diffusion direction of glutamate along the parallel fibers would help constrain an incoming excitatory stimulus to stay "on-beam."

scholarly journals Dopamine-Mediated Volume Transmission in Midbrain Is Regulated by Distinct Extracellular Geometry and Uptake

2001 ◽  
Vol 85 (4) ◽  
pp. 1761-1771 ◽  
Author(s):  
Stephanie J. Cragg ◽  
Charles Nicholson ◽  
June Kume-Kick ◽  
Lian Tao ◽  
Margaret E. Rice
Keyword(s):  
Point Source ◽  
Time Course ◽  
Volume Fraction ◽  
Extracellular Volume ◽  
Brain Slices ◽  
Extracellular Volume Fraction ◽  
Receptor Activation ◽  
Substantia Nigra Pars Compacta ◽  
Volume Transmission ◽  
Carbon Fiber Microelectrodes

Somatodendritic release of dopamine (DA) in midbrain is, at least in part, nonsynaptic; moreover, midbrain DA receptors are predominantly extrasynaptic. Thus somatodendritic DA mediates volume transmission, with an efficacy regulated by the diffusion and uptake characteristics of the local extracellular microenvironment. Here, we quantitatively evaluated diffusion and uptake in substantia nigra pars compacta (SNc) and reticulata (SNr), ventral tegmental area (VTA), and cerebral cortex in guinea pig brain slices. The geometric parameters that govern diffusion, extracellular volume fraction (α) and tortuosity (λ), together with linear uptake ( k′), were determined for tetramethylammonium (TMA+), and for DA, using point-source diffusion combined with ion-selective and carbon-fiber microelectrodes. TMA+-diffusion measurements revealed a large α of 30% in SNc, SNr, and VTA, which was significantly higher than the 22% in cortex. Values for λ and k′ for TMA+ were similar among regions. Point-source DA-diffusion curves fitted theory well with linear uptake, with significantly higher values of k′ for DA in SNc and VTA (0.08–0.09 s− 1) than in SNr (0.006 s− 1), where DA processes are sparser. Inhibition of DA uptake by GBR-12909 caused a greater decrease in k′ in SNc than in VTA. In addition, DA uptake was slightly decreased by the norepinephrine transport inhibitor, desipramine in both regions, although this was statistically significant only in VTA. We used these data to model the radius of influence of DA in midbrain. Simulated release from a 20-vesicle point source produced DA concentrations sufficient for receptor activation up to 20 μm away with a DA half-life at this distance of several hundred milliseconds. Most importantly, this model showed that diffusion rather than uptake was the most important determinant of DA time course in midbrain, which contrasts strikingly with the striatum where uptake dominates. The issues considered here, while specific for DA in midbrain, illustrate fundamental biophysical properties relevant for all extracellular communication.

scholarly journals Immunocytochemical demonstration of alpha-tubulin modification during axonal maturation in the cerebellar cortex.

1984 ◽  
Vol 98 (1) ◽  
pp. 347-351 ◽  
Author(s):  
R Cumming ◽  
R D Burgoyne ◽  
N A Lytton
Keyword(s):  
Cerebellar Cortex ◽  
Time Course ◽  
Staining Pattern ◽  
Molecular Layer ◽  
Parallel Fiber ◽  
Differential Staining ◽  
Germinal Layer ◽  
Progressive Change ◽  
Parallel Fibers ◽  
Alpha Tubulin

Previous light microscopic immunocytochemical studies using two monoclonal antibodies that recognise alpha-tubulin (YOL/34 and YL1/2) but differ in their isotypic specificity have shown that the unmyelinated parallel fiber axons in the cerebellar cortex are labeled with only one of the antibodies (YOL/34). We now show that at 10 d postnatally the parallel fibers are labeled with both antibodies, and that during development YL1/2 (but not YOL/34) immunoreactivity disappears progressively from parallel fibers in the lower regions of the molecular layer upwards towards the external germinal layer. By approximately 28 d postnatally, the differential staining pattern of parallel fibers by the antibodies is established throughout the molecular layer. The time course, light microscopic, and ultrastructural staining distribution corresponds to a progressive change in alpha-tubulin immunoreactivity as the parallel fibers form synaptic contacts. This modification of alpha-tubulin (which was not observed in Purkinje cell dendrites or Bergmann glia) may be related to the formation of a basic isotype of alpha-tubulin within parallel fiber axons at maturation.

scholarly journals The link between left ventricular extracellular volume determined by T1 myocardial mapping and gut microbiota composition in individuals with heart failure and preserved ejection fraction

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
A.N Kaburova ◽  
O.M Drapkina ◽  
S.M Uydin ◽  
M.V Vishnyakova ◽  
M.S Pokrovskaya ◽  
...  
Keyword(s):  
Heart Failure ◽  
Ejection Fraction ◽  
Gut Microbiota ◽  
Myocardial Fibrosis ◽  
Volume Fraction ◽  
Extracellular Volume ◽  
Left Ventricular ◽  
Diffuse Myocardial Fibrosis ◽  
Rrna Gene ◽  
Preserved Ejection Fraction

Abstract Introduction Heart failure with preserved ejection fraction (HFpEF) represents a major challenge in modern cardiology. As described previously, in HFpEF comorbidities promote a systemic inflammatory state, leading to diffuse myocardial fibrosis resulting in myocardial stiffening. Gut dysbiosis which is considered as the novel source of chronic systemic inflammation has been actively investigated as the risk factor for the development and aggravation of cardiovascular diseases including heart failure. Cardiac magnetic resonance T1-mapping is a novel tool, which allows noninvasive quantification of the extracellular space and diffuse myocardial fibrosis. Moreover, the extracellular volume (ECV) fraction can be calculated, providing information on the relative expansion of the extracellular matrix, thus being a noninvasive alternative to myocardial biopsy studies. Purpose The research was aimed at investigating the correlation between the left ventricular ECV and gut microbial genera in patients with HFpEF. Methods 42 patients with confirmed HF-pEF (mediana and interquartile range of age 67 [64; 72] years, 47% men, body mass index <35 kg/m2 with no history of myocardial infarction or diabetes mellitus) were enrolled in the study. The patients underwent transthoracic echocardiography with Doppler study, HF-pEF was confirmed according to the recent ESC guidelines (based on E/e' ratio, N-terminal pro-B type natriuretic peptide >125 pg/ml and symptoms of heart failure). The intestinal microbiome was investigated using high-throughput sequencing of bacterial 16S rRNA gene. As the last step of research T1-myocardial mapping with the modified look-locker inversion-recovery protocol (MOLLI) sequence at 1.5 Tesla was performed to assess left ventricular extracellular volume fraction. Results The mean±std in ECV was 31.02±4.4%. The relative abundance (%) of the most prevalent phyla in gut microbiota was 48±22.5 for Firmicutes, 47.4±22.8 for Bacteroidetes and 1.5 [1.5; 2.5] for Proteobacteria. The analysis showed significant negative correlations between ECV and the following bacterial genera: Faecalibacterium (r=−0.35), Blautia (r=−0.43), Lachnoclostridium (r=−0.32). Moreover ECV positively correlated with Holdemania (r=0.4), Victivallis (r=0.38), Dehalobacterium (r=0.38), Enterococcus (r=0.33) and Catabacter (r=0.32). All correlation values with p<0.05. Conclusion We discovered both negative and positive significant correlations between ECV – the non-invasive marker of myocardial fibrosis and several bacterial genera, which may have negative impact on myocardial remodeling in HF-pEF. Funding Acknowledgement Type of funding source: None

Transmural heterogeneity of diffusion anisotropy in the sheep myocardium characterized by MR diffusion tensor imaging

2007 ◽  
Vol 293 (4) ◽  
pp. H2377-H2384 ◽  
Author(s):  
Yi Jiang ◽  
Julius M. Guccione ◽  
Mark B. Ratcliffe ◽  
Edward W. Hsu
Keyword(s):  
Diffusion Tensor Imaging ◽  
Volume Fraction ◽  
Diffusion Tensor ◽  
Extracellular Volume ◽  
Extracellular Volume Fraction ◽  
Left Ventricular ◽  
Fiber Direction ◽  
Significant Difference ◽  
Mr Diffusion ◽  
Mr Diffusion Tensor Imaging

The orientation of MRI-measured diffusion tensor in the myocardium has been directly correlated to the tissue fiber direction and widely characterized. However, the scalar anisotropy indexes have mostly been assumed to be uniform throughout the myocardial wall. The present study examines the fractional anisotropy (FA) as a function of transmural depth and circumferential and longitudinal locations in the normal sheep cardiac left ventricle. Results indicate that FA remains relatively constant from the epicardium to the midwall and then decreases (25.7%) steadily toward the endocardium. The decrease of FA corresponds to 7.9% and 12.9% increases in the secondary and tertiary diffusion tensor diffusivities, respectively. The transmural location of the FA transition coincides with the location where myocardial fibers run exactly circumferentially. There is also a significant difference in the midwall-endocardium FA slope between the septum and the posterior or lateral left ventricular free wall. These findings are consistent with the cellular microstructure from histological studies of the myocardium and suggest a role for MR diffusion tensor imaging in characterization of not only fiber orientation but, also, other tissue parameters, such as the extracellular volume fraction.

Abstract 17263: Pre-Clinical Left Ventricular Myocardial Remodeling in Patients With Friedreich’s Ataxia: A Cardiac MRI Study

Circulation ◽  
2018 ◽  
Vol 138 (Suppl_1) ◽  
Author(s):  
Karen A Takazaki1 ◽  
Thiago Quinaglia A. C. Silva ◽  
Alberto Martinez ◽  
Tomas Neilan ◽  
Ravi SHAH ◽  
...  
Keyword(s):  
Heart Failure ◽  
Volume Fraction ◽  
Extracellular Volume ◽  
Extracellular Volume Fraction ◽  
Friedreich’S Ataxia ◽  
Left Ventricular ◽  
Friedreich's Ataxia ◽  
Intracellular Water ◽  
Lv Mass ◽  
Burn Out

Background: Heart Failure (HF) is the most common cause of death in Friedreich’s ataxia (FRDA), an inherited mitochondrial disease. Myocardial fibrosis is a well-documented histopathological feature among FRDA patients with HF. Objectives: In this study we will investigate the myocardial extracellular volume fraction (ECV) and intracellular water lifetime (τ ic ), using T1-weighted CMR imaging, in a cohort of patients with FRDA without signs of heart failure. We will also investigate whether myocardial tissue phenotyping by CMR can highlight particular characteristics of LV remodeling in FRDA’s cardiomyopathy, beyond those currently assessed with imaging-based classification of disease severity. Methods: Twenty-six FRDA’s patients (age 26.6±9.3 years, 15 women) without signs of HF, and 10 healthy controls (32.6±7.3 years, 5 women) underwent cardiac magnetic resonance (CMR) studies for assessment of left ventricular (LV) function, myocardial T1, late gadolinium enhancement (LGE), extracellular volume fraction (ECV), and intracellular water-lifetime (τ ic ) as marker of cardiomyocyte size. Neurological decline was determined using the FRDA rating scale (FARS 3). Results: FRDA patients had normal LV ejection fraction (LVEF: 67.66±11.4 vs. 63.9±9.0, P=0.311), larger LV mass index (LVMASSi: 61.03±22.1 vs. 45±4.2g/m 2 , P<0.001), and decreased LV end-diastolic volume index (LVEDVi 53.42±12 vs. 75.7±16.1, P=0.002), compared with controls. ECV and τ ic , were increased in FRDA patients (ECV: 0.36±0.05 vs. 0.25±0.02, P<0.0001; τ ic : 0.13±0.07 vs. 0.06±0.03, P=0.001). ECV was positively associated with LV mass-to-volume ratio (r=0.628, P<0.001). FARS 3 correlated positively with disease duration (r=0.669, P<0.001), and negatively with τ ic , (r=0.478, P=0.039). LVMASSi and cardiomyocyte mass-index [(1–ECV)LVMASSi] declined with age, indicating that LV hypertrophy may transition to a “burn-out” phase with LV atrophy. Conclusions: LV hypertrophy in FRDA reflects an expansion of the myocardial interstitium and an increase in cardiomyocyte size. In contrast, the neurological decline was more likely with decreasing cardiomyocyte size, possibly an early sign of myocardial “burn-out” in FRDA.

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