Biology subjects

Khadem, A.

Publications and source records attributed to Khadem, A..

5 recordsLinked to original sources

bioRxiv2022

Functional impairment of the Lateral Geniculate Nucleus in Multiple Sclerosis

Visual impairment is one of the early symptoms of Multiple sclerosis (MS) disease. The objective of this study is evaluating function of Lateral geniculate nucleus, which bridges visual information from retina to other higher order visual processing areas. We collected BOLD fMRI data from 19 MS and 19 control subjects by employing selective visual stimulation tasks to provoke the whole LGN, Magnocellular, Parvocellular, and Koniocellular pathways as part of LGN multilayer structure. Through statistical analysis, we observed a significant reduction (p<0.05) of the average BOLD signal from the whole LGN structure in MS group. Further investigations showed a significant reduction of BOLD signal (p<0.05) in response to Magno and Parvo stimuli compared to healthy controls that suggested a selective functional impairment emerging in primary visual pathways in MS. In summary, we showed functional abnormalities in LGN structure and its M and P subdivisions based on functional MRI.

bioengineering↗

bioRxiv2022

Key role of auxin cellular accumulation in totipotency and pluripotency acquisition

Genome editing and in vitro based-plant propagation require efficient plant regeneration system. Somatic embryogenesis (SE) or de novo shoot regeneration are two major systems that widely used for plant in vitro regeneration. Most SE or shoot regeneration protocols rely on the exogenous application of the synthetic auxin analog 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthylene acetic acid (NAA), whereas the natural auxins indole-3-acetic acid (IAA), 4-chloroindole-3-acetic acid (4-Cl-IAA) or indole-3-butyric acid (IBA) are not or less effective for plant regeneration. Although these synthetic auxins mimics the physiological activity of the main natural auxin IAA in many aspects, there are also clear differences that have been attributed to differences in stability or to different affinities for certain TIR1/AFB-Aux/IAA auxin co-receptor pairs. Here we show that the success of 2,4-D in inducing SE from Arabidopsis is related to ineffectiveness as substrate for auxin efflux, resulting in its intracellular 2,4-D accumulation. Reducing auxin efflux by addition of the auxin transport inhibitor naphthylphthalamic acid (NPA) also allowed natural auxins and other synthetic analogs to induce SE in Arabidopsis with similar efficiencies as 2,4-D. The PIN-FORMED auxin efflux carriers PIN1, PIN2 and the ATP-binding cassette-B auxin transporters ABCB1 and ABCB19 were shown to be partially responsible for the efflux of natural auxins during SE induction. Importantly, all somatic embryos induced in Arabidopsis by IAA in the presence of NPA showed a normal embryo to seedling conversion and subsequent plant development, whereas for the 2,4-D system this was limited to 50-60% of the embryos. We showed that the auxin transport inhibition promotes de novo shoot regeneration capacity from callus induced by 4-Cl-IAA in Brassica napus. In addition, we observed a obvious acceleration in shoot bud emerging from callus induced by 4-Cl-IAA than 2,4-D. Based on our data we conclude, that the efficiency of plant propagation can be significantly improved by applying the natural auxins in the presence of the auxin transport inhibitor NPA.

plant biology↗

bioRxiv2021

A hybrid boundary element-finite element method to solve the EEG forward problem

This article presents a hybrid boundary element-finite element (BE-FE) method to solve the EEG forward problem and take advantages of both the boundary element method (BEM) and finite element method (FEM). Although realistic EEG forward problems with heterogeneous and anisotropic regions can be solved by FEM accurately, the FEM modeling of the brain with dipolar sources may lead to singularity. In contrast, the BEM can solve EEG forward problems with isotropic tissue regions and dipolar sources using a suitable integral formulation. This work utilizes both FEM and BEM strengths attained by dividing the regions into some homogeneous BE regions with sources and some heterogeneous and anisotropic FE regions. Furthermore, the BEM is applied for modeling the brain, including dipole sources and the FEM for other head layers. To validate the proposed method, inhomogeneous isotropic/anisotropic three- and four-layer spherical head models are studied. Moreover, a four-layer realistic head model is investigated. Results for six different dipole eccentricities and two different dipole orientations are computed using the BEM, FEM, and hybrid BE-FE method together with statistical analysis and the related error criteria are compared. The proposed method is a promising new approach for solving realistic EEG forward problems.

neuroscience↗

bioRxiv2021

Normal development of the brain: a survey of joint structural-functional brain studies

Joint structural-functional (S-F) developmental studies present a novel approach to address the complex neuroscience questions on how the human brain works and how it matures. Joint S-F biomarkers have the inherent potential to model effectively the brains maturation, fill the information gap in temporal brain atlases, and demonstrate how the brains performance matures during the lifespan. This review presents the current state of knowledge on heterochronous and heterogeneous development of S-F links during the maturation period. The S-F relationship has been investigated in early-matured unimodal and prolonged-matured transmodal regions of the brain using a variety of structural and functional biomarkers and data acquisition modalities. Joint S-F unimodal studies have employed auditory and visual stimuli, while the main focus of joint S-F transmodal studies has been resting-state networks and working memory. However, non-significant associations between some structural and functional biomarkers and their maturation show that designing and developing effective S-F biomarkers is still a challenge in the field. Maturational characteristics of brain asymmetries have been poorly investigated by the joint S-F studies, and the results were inconsistent with previous non-joint ones. The inherent complexity of the brain performance can be modeled using multifactorial and nonlinear techniques as promising methods to simulate the impact of age on S-F relations considering their analysis challenges.

neuroscience↗

bioRxiv2020

Impaired dynamic profile of brain recurring functional connectivity states in Alzheimers disease

Up to now, disrupted functional organization of the brain in Alzheimers disease (AD) has mostly been examined by assessing "static" functional connectivity (FC). However, recent studies have provided clear evidence that brain FC exhibits intrinsic spatiotemporal "dynamic" organization also being significantly affected in AD. However, inconsistency in former studies is a motivation for further investigation of impaired dynamic profile of brain FC networks in Alzheimers disease._In this work, we identified recurring FC states during rest (eyes-open) in 24 AD patients and 37 healthy controls (HC) by combining sliding window-based method (examining dynamic FC) and k-means clustering algorithm (identifying recurring FC states over time). To define the optimum number of recurring FC states in k-means algorithm, we employed non-supervised validity criteria such as silhouette value and Dunn index over bootstrap samples. Then, we examined differences in dynamic properties of recurring FC states including probability of occurrence, lifetime and switching profile between groups. Afterward, association between impaired dynamic profile of recurring FC states and cognitive performance was assessed in AD patients. Our findings revealed three recurring FC states and among them, FC state with the most significant differences in probability of occurrence (corrected p-value < 0.0001) included brain regions involved in default mode, frontoparietal and salience networks. This recurring FC state occurred significantly less and lasted shorter in patients with AD than in the HC. Further, the probability of occurrence in this recurring FC state significantly correlated positively with cognitive decline in patients with AD. Our findings suggest more decreased in cognitive performance in patients with AD associated with more reduced ability of AD patients to access clinically relevant impaired brain FC networks. Impaired dynamic profile of recurring FC states in AD provide greater understanding of ADs pathophysiology.

neuroscience↗