Browsing by Subject "Thalamus"

Now showing 1 - 6 of 6
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    Astrocytic GABA transporter 1 deficit in novel SLC6A1 variants mediated epilepsy: Connected from protein destabilization to seizures in mice and humans
    (Elsevier, 2022) Mermer, Felicia; Poliquin, Sarah; Zhou, Shuizhen; Wang, Xiaodong; Ding, Yifeng; Yin, Fei; Shen, Wangzhen; Wang, Juexin; Rigsby, Kathryn; Xu, Dong; Mack, Taralynn; Nwosu, Gerald; Flamm, Carson; Stein, Matthew; Kang, Jing-Qiong; Biomedical Engineering and Informatics, Luddy School of Informatics, Computing, and Engineering
    Objective: Mutations in γ-aminobutyric acid (GABA) transporter 1 (GAT-1)-encoding SLC6A1 have been associated with myoclonic atonic epilepsy and other phenotypes. We determined the patho-mechanisms of the mutant GAT-1, in order to identify treatment targets. Methods: We conducted whole-exome sequencing of patients with myoclonic atonic epilepsy (MAE) and characterized the seizure phenotypes and EEG patterns. We studied the protein stability and structural changes with homology modeling and machine learning tools. We characterized the function and trafficking of the mutant GAT-1 with 3H radioactive GABA uptake assay and confocal microscopy. We utilized different models including a knockin mouse and human astrocytes derived from induced pluripotent stem cells (iPSCs). We focused on astrocytes because of their direct impact of astrocytic GAT-1 in seizures. Results: We identified four novel SLC6A1 variants associated with MAE and 2 to 4 Hz spike-wave discharges as a common EEG feature. Machine learning tools predicted that the variant proteins are destabilized. The variant protein had reduced expression and reduced GABA uptake due to endoplasmic reticular retention. The consistent observation was made in cortical and thalamic astrocytes from variant-knockin mice and human iPSC-derived astrocytes. The Slc6a+/A288V mouse, representative of MAE, had increased 5-7 Hz spike-wave discharges and absence seizures. Interpretation: SLC6A1 variants in various locations of the protein peptides can cause MAE with similar seizure phenotypes and EEG features. Reduced GABA uptake is due to decreased functional GAT-1, which, in thalamic astrocytes, could result in increased extracellular GABA accumulation and enhanced tonic inhibition, leading to seizures and abnormal EEGs.
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    Causal effects of psychostimulants on neural connectivity: a mechanistic, randomized clinical trial
    (Wiley, 2022) Wang, Yun; Kessel, Ellen; Lee, Seonjoo; Hong, Susie; Raffanello, Elizabeth; Hulvershorn, Leslie A.; Margolis, Amy; Peterson, Bradley S.; Posner, Jonathan; Psychiatry, School of Medicine
    Background: Psychostimulants are frequently used to treat attention-deficit/hyperactivity disorder (ADHD), but side effects are common leading to many patients discontinuing treatment. Identifying neural mechanisms by which psychostimulants attenuate symptoms may guide the development of more refined and tolerable therapeutics. Methods: We conducted a 12-week, randomized, placebo-controlled trial (RCT) of a long-acting amphetamine, lisdexamfetamine (LDEX), in patients with ADHD, ages 6-25 years old. Of the 58 participants who participated in the RCT, 49 completed pre- and post-RCT magnetic resonance imaging scanning with adequate data quality. Healthy controls (HCs; n = 46) were included for comparison. Treatment effects on striatal and thalamic functional connectivity (FC) were identified using static (time-averaged) and dynamic (time-varying) measures and then correlated with symptom improvement. Analyses were repeated in independent samples from the Adolescent Brain Cognitive Development study (n = 103) and the ADHD-200 Consortium (n = 213). Results: In 49 participants (25 LDEX; 24 Placebo), LDEX increased static and decreased dynamic FC (DFC). However, only DFC was associated with the therapeutic effects of LDEX. Additionally, at baseline, DFC was elevated in unmedicated-ADHD participants relative to HCs. Independent samples yielded similar findings - ADHD was associated with increased DFC, and psychostimulants with reduced DFC. Static FC findings were inconsistent across samples. Conclusions: Changes in dynamic, but not static, FC were associated with the therapeutic effects of psychostimulants. While prior research has focused on static FC, DFC may offer a more reliable target for new ADHD interventions aimed at stabilizing network dynamics, though this needs confirmation with subsequent investigations.
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    Extension of retinofugal projections in an assembled model of human pluripotent stem cell-derived organoids
    (Cell Press, 2021-09-14) Fligor, Clarisse M.; Lavekar, Sailee S.; Harkin, Jade; Shields, Priya K.; VanderWall, Kirstin B.; Huang, Kang-Chieh; Gomes, Cátia; Meyer, Jason S.; Biology, School of Science
    The development of the visual system involves the coordination of spatial and temporal events to specify the organization of varied cell types, including the elongation of axons from retinal ganglion cells (RGCs) to post-synaptic targets in the brain. Retinal organoids recapitulate many features of retinal development, yet have lacked downstream targets into which RGC axons extend, limiting the ability to model projections of the human visual system. To address these issues, retinal organoids were generated and organized into an in vitro assembloid model of the visual system with cortical and thalamic organoids. RGCs responded to environmental cues and extended axons deep into assembloids, modeling the projections of the visual system. In addition, RGC survival was enhanced in long-term assembloids, overcoming prior limitations of retinal organoids in which RGCs are lost. Overall, these approaches will facilitate studies of human visual system development, as well as diseases or injuries to this critical pathway.
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    On the Origin of Tremor in Parkinson’s Disease
    (Public Library of Science, 2012) Dovzhenok, Andrey; Rubchinsky, Leonid L.; Mathematical Sciences, School of Science
    The exact origin of tremor in Parkinson's disease remains unknown. We explain why the existing data converge on the basal ganglia-thalamo-cortical loop as a tremor generator and consider a conductance-based model of subthalamo-pallidal circuits embedded into a simplified representation of the basal ganglia-thalamo-cortical circuit to investigate the dynamics of this loop. We show how variation of the strength of dopamine-modulated connections in the basal ganglia-thalamo-cortical loop (representing the decreasing dopamine level in Parkinson's disease) leads to the occurrence of tremor-like burst firing. These tremor-like oscillations are suppressed when the connections are modulated back to represent a higher dopamine level (as it would be the case in dopaminergic therapy), as well as when the basal ganglia-thalamo-cortical loop is broken (as would be the case for ablative anti-parkinsonian surgeries). Thus, the proposed model provides an explanation for the basal ganglia-thalamo-cortical loop mechanism of tremor generation. The strengthening of the loop leads to tremor oscillations, while the weakening or disconnection of the loop suppresses them. The loop origin of parkinsonian tremor also suggests that new tremor-suppression therapies may have anatomical targets in different cortical and subcortical areas as long as they are within the basal ganglia-thalamo-cortical loop.
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    Striatal and thalamic GABA level concentrations play differential roles for the modulation of response selection processes by proprioceptive information.
    (Elsevier, 2015-10-15) Dharmadhikari, Shalmali; Ma, Ruoyun; Yeh, Chien-Lin; Stock, Ann-Kathrin; Snyder, Sandy; Zauber, S. Elizabeth; Dydak, Ulrike; Beste, Christian; Department of Radiology and Imaging Sciences, IU School of Medicine
    The selection of appropriate responses is a complex endeavor requiring the integration of many different sources of information in fronto-striatal-thalamic circuits. An often neglected but relevant piece of information is provided by proprioceptive inputs about the current position of our limbs. This study examines the importance of striatal and thalamic GABA levels in these processes using GABA-edited magnetic resonance spectroscopy (GABAMRS) and a Simon task featuring proprioception-induced interference in healthy subjects. As a possible model of deficits in the processing of proprioceptive information, we also included Parkinson's disease (PD) patients in this study.The results show that proprioceptive information about unusual postures complicates response selection processes in controls, but not in PD patients. The well-known deficits of PD patients in processing proprioceptive information can turn into a benefit when altered proprioceptive information would normally complicate response selection processes. Striatal and thalamic GABA levels play dissociable roles in the modulation of response selection processes by proprioceptive information: Striatal GABA levels seem to be important for the general speed of responding, most likely because striatal GABA promotes response selection. In contrast, the modulation of response conflict by proprioceptive information is closely related to thalamic GABA concentrations with higher concentration being related to a smaller response conflict effect. The most likely explanation for this finding is that the thalamus is involved in the integration of sensorimotor, attentional, and cognitive information for the purpose of response formation. Yet, this effect in the thalamus vanishes when controls and PD patients were analyzed separately.
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    Thalamic GABA Predicts Fine Motor Performance in Manganese-Exposed Smelter Workers
    (Public Library of Science, 2014-02-04) Long, Zaiyang; Li, Xiang-Rong; Xu, Jun; Edden, Richard A. E.; Qin, Wei-Ping; Long, Li-Ling; Murdoch, James B.; Zheng, Wei; Jiang, Yue-Ming; Dydak, Ulrike; Radiology and Imaging Sciences, School of Medicine
    Overexposure to manganese (Mn) may lead to parkinsonian symptoms including motor deficits. The main inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is known to play a pivotal role in the regulation and performance of movement. Therefore this study was aimed at testing the hypothesis that an alteration of GABA following Mn exposure may be associated with fine motor performance in occupationally exposed workers and may underlie the mechanism of Mn-induced motor deficits. A cohort of nine Mn-exposed male smelter workers from an Mn-iron alloy factory and 23 gender- and age-matched controls were recruited and underwent neurological exams, magnetic resonance spectroscopy (MRS) measurements, and Purdue pegboard motor testing. Short-echo-time MRS was used to measure N-Acetyl-aspartate (NAA) and myo-inositol (mI). GABA was detected with a MEGA-PRESS J-editing MRS sequence. The mean thalamic GABA level was significantly increased in smelter workers compared to controls (p = 0.009). Multiple linear regression analysis reveals (1) a significant association between the increase in GABA level and the duration of exposure (R(2) = 0.660, p = 0.039), and (2) significant inverse associations between GABA levels and all Purdue pegboard test scores (for summation of all scores R(2) = 0.902, p = 0.001) in the smelter workers. In addition, levels of mI were reduced significantly in the thalamus and PCC of smelter workers compared to controls (p = 0.030 and p = 0.009, respectively). In conclusion, our results show clear associations between thalamic GABA levels and fine motor performance. Thus in Mn-exposed subjects, increased thalamic GABA levels may serve as a biomarker for subtle deficits in motor control and may become valuable for early diagnosis of Mn poisoning.