Intraoperative lesion characterization after focused ultrasound thalamotomy

OBJECTIVE Outcomes after focused ultrasound ablation (FUSA) for essential tremor remain heterogeneous, despite therapeutic promise. Clinical outcomes are directly related to the volume and location of the therapeutic lesions, consistent with CNS ablative therapies. Recent data demonstrate that postoperative diffusion MRI, specifically the quantification of intracellular diffusion by restricted diffusion imaging (RDI), can accurately characterize focused ultrasound lesions. However, it is unclear whether RDI can reliably detect focused ultrasound lesions intraoperatively (i.e., within a few minutes of lesioning) and whether the intraoperative lesions predict delayed clinical outcomes. METHODS An intraoperative imaging protocol was implemented that included RDI and T2-weighted imaging in addition to intraoperative MR thermography. Lesion characteristics were defined with each sequence and then compared. An imaging-outcomes analysis was performed to determine lesion characteristics associated with delayed clinical outcomes. RESULTS Intraoperative RDI accurately identified the volume and location of focused ultrasound lesions. Intraoperative T2-weighted imaging underestimated the lesion volume but accurately identified the location. Intraoperative RDI revealed that lesions of the ventral border of the ventral intermediate nucleus were significantly associated with postoperative tremor improvement. In contrast, the lesions extending into the inferolateral white matter were associated with postoperative ataxia. CONCLUSIONS These data support the acquisition of intraoperative RDI to characterize focused ultrasound lesions. Future research should test the histological correlates of intraoperative RDI and test whether it can be developed as feedback to optimize the current technique of FUSA.

Spatially heterogeneous microstructural development within subcortical regions from 9-13 years

During late childhood behavioral changes, such as increased risk-taking and emotional reactivity, have been associated with the maturation of cortico-subcortical circuits. Understanding microstructural changes in subcortical regions may aid our understanding of how individual differences in these behaviors emerge. Restriction spectrum imaging (RSI) is a framework for modelling diffusion-weighted imaging that decomposes the diffusion signal from a voxel into hindered and restricted compartments. This yields greater specificity than conventional methods of characterizing intracellular diffusion. Using RSI, we modelled voxelwise restricted isotropic, N0, and anisotropic, ND, diffusion across the brain and measured cross-sectional and longitudinal age associations in a large sample (n=8,039) from the Adolescent Brain and Cognitive Development (ABCD) study aged 9-13 years. Older participants had higher N0 and ND across subcortical regions. The largest associations for N0 were within the basal ganglia and for ND within the ventral diencephalon. Importantly, age associations varied with respect to the internal cytoarchitecture within subcortical structures, for example age associations differed across thalamic nuclei. This suggests that developmental effects may map onto specific cell populations or circuits and highlights the utility of voxelwise compared to ROI-wise analyses. Future analyses will aim to understand the relevance of this subcortical microstructural developmental for behavioral outcomes.

ATP-Dependent Diffusion Entropy and Homogeneity in Living Cells

Intracellular dynamics is highly complex, and includes diffusion of poly-dispersed objects in a non-homogeneous, out-of-equilibrium medium. Assuming non-equilibrium steady-state, we developed a framework that relates non-equilibrium fluctuations to diffusion, and generalized entropy in cells. We employed imaging of live Jurkat T cells, and showed that active cells have higher diffusion parameters (Kα and α) and entropy relative to the same cells after ATP depletion. Kα and α were related in ATP-depleted cells while this relation was not apparent in untreated cells, probably due to non-equilibrium applied work. Next we evaluated the effect of intracellular diffusion and entropy on the cell content homogeneity, which was displayed by the extent of its liquid–liquid phase separation (LLPS). Correlations between intracellular diffusion parameters, entropy and cell homogeneity could be demonstrated only in active cells while these correlations disappeared after ATP depletion. We conclude that non-equilibrium contributions to diffusivity and entropy by ATP-dependent mechanical work allow cells to control their content homogeneity and LLPS state. Such understanding may enable better intervention in extreme LLPS conditions associated with various cell malignancies and degenerative diseases.

Viscoadaptation controls intracellular reaction rates in response to heat and energy availability

Summary/AbstractCells must precisely orchestrate thousands of reactions in both time and space. Yet reaction kinetics are highly dependent on uncontrollable environmental conditions such as temperature. Here, we report a novel mechanism by which budding yeast influence reaction rates through adjustment of intracellular viscosity. This “viscoadaptation” is achieved by production of two carbohydrates, trehalose and glycogen, which combine to create a more viscous cellular environment in which biomolecules retain solubility. We demonstrate that viscoadaptation functions as both an acute response to temperature increase as well as a homeostatic mechanism, allowing cells grown at temperatures spanning from 22°C to 40°C to maintain equivalent rates of intracellular diffusion and diffusion-controlled chemical reactions. Multiple conditions that lower ATP trigger viscoadaptation, suggesting that viscoadaptation may be a general cellular response to low energy. Viscoadaptation reveals viscosity to be a tunable property of cells through which they can regulate diffusion-controlled processes dynamically in response to a changing environment.

Terasaki Spiral Ramps and Intracellular Diffusion

The sheet-like endoplasmic reticulum (ER) of eukaryotic cells has been found to be riddled with spiral dislocations, known as ‘Terasaki ramps’, in the vicinity of which the doubled bilayer membranes which make up ER sheets can be approximately modeled by helicoids. Here we analyze diffusion on a surface with locally helicoidal topological dislocations, and use the results to argue that the Terasaki ramps facilitate a highly efficient transport of water-soluble molecules within the lumen of the endoplasmic reticulum.

Super-resolution displacement mapping of unbound single molecules reveals nanoscale heterogeneities in intracellular diffusivity

Intracellular diffusion underlies vital processes of the cell. However, it remains difficult to elucidate how an average-sized protein diffuses in the cell with good spatial resolution and sensitivity. Here we report single-molecule displacement/diffusivity mapping (SMdM), a super-resolution strategy that enables the nanoscale mapping of intracellular diffusivity through the local statistics of instantaneous displacements of freely diffusing single molecules. We thus show that diffusion in the cytoplasm and in the nucleus to both be spatially heterogeneous at the nanoscale, and such variations in local diffusivity correlate strongly with the ultrastructure of the actin cytoskeleton and the chromosome, respectively. Moreover, we identify the net charge of the diffuser as a key determinant of diffusion rate: intriguingly, the possession of positive, but not negative, net charges significantly impedes diffusion, and the exact degree of slowdown is determined by the specific subcellular environments.