Prieto, J. | Search bioRxiv

bioRxiv2019

Altered hypothalamic diffusivity in Parkinsonian autonomic dysfunction

The pathophysiological basis of autonomic symptoms in Parkinsons disease remains incompletely understood. The hypothalamus plays a key regulatory role in autonomic function and has been shown to be affected in Parkinsons disease. Here, using diffusion magnetic resonance imaging, we investigated whether microstructural properties of the hypothalamus differ in Parkinsons disease patients with high compared to low autonomic symptom burden.\n\nParkinsons disease patients with low (n=25) and high (n=25) autonomic symptom burden were identified from a larger pool, based on scores from a questionnaire assessing autonomic symptoms in Parkinsons disease (SCOPA-AUT). In each patient, we first segmented the hypothalamus manually, based on anatomical landmarks. Diffusivity measures were then extracted from the hypothalamus. Diffusivity measures calculated in the brainstem and the putamen were used to assess the specificity of the results.\n\nRelative to patients with low autonomic symptom burden, patients with high burden showed increased mean, axial, and radial diffusivity in the hypothalamus. In contrast, we did not find significant group differences in any of these measures extracted from the brainstem or the putamen.\n\nThese results reveal consistent differences in the microstructural properties of the hypothalamus between patients with low and high autonomic symptom burden. Hypothalamic diffusivity properties can thus potentially be used as an imaging marker to assist in the identification of therapeutic targets for autonomic dysfunction in Parkinsons disease.

neuroscience↗

bioRxiv2019

HydroShoot: a functional-structural plant model for simulating hydraulic structure, gas and energy exchange dynamics of complex plant canopies under water deficit - application to grapevine (Vitis vinifera L.)

This paper aims at presenting HydroShoot, a functional-structural plant model (FSPM) that is developed to simulate gas-exchange rates of complex plant canopies under water deficit conditions, by scaling up gas-exchange rates from the leaf to the canopy levels. The main hypothesis is that simulating both the hydraulic structure of the shoot together with the energy budget of individual leaves is the asset for successfully achieving this up-scaling task. HydroShoot was hence built as the ensemble of three interacting modules: hydraulic which calculates the distribution of xylem water potential across shoot hydraulic segments, energy which calculates the complete energy budget of individual leaves, and exchange which calculates net assimilation and transpiration rates of individual leaves. HydroShoot was coupled with irradiance interception and soil water balance models, and was evaluated on virtual and real grapevines having strongly contrasted canopies, under well-watered and water-deficit conditions. HydroShoot captured accurately the impact of canopy architecture and the varying soil water deficit conditions on plant-scale gas-exchange rates and leaf-scale temperature and water potential distributions. Both shoot hydraulic structure and leaf energy budget simulations were, as postulated, required to adequately scaling-up leaf to canopy gas-exchange rates. Notwithstanding, simulating the hydraulic structure of the shoot was found far more necessary to adequately performing this scaling task than simulating leaf energy balance. That is, the intra-canopy variability of leaf water potential was a better predictor of the reduction of whole plant gas-exchange rates under water deficit than the intra-canopy variability of leaf temperature. We conclude therefore that simulating the shoot hydraulic structure is a prerequisite if FSPM's are to be used to assess gas-exchange rates of complex plant canopies as those of grapevines. Finally HydroShoot is available through the OpenAlea platform (https://github.com/openalea/hydroshoot) as a set of reusable modules.

plant biology↗