Browsing by Author "Du Plessis, Stefan"

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    10Kin1day : a bottom-up neuroimaging initiative
    (Frontiers Media, 2019) Van den Heuvel, Martijn P.; Scholtens, Lianne H.; Van der Burgh, Hannelore K.; Agosta, Federica; Alloza, Clara; Arango, Celso; Auyeung, Bonnie; Baron-Cohen, Simon; Basaia, Silvia; Benders, Manon J. N. L.; Beyer, Frauke; Booij, Linda; Braun, Kees P. J.; Filho, Geraldo Busatto; Cahn, Wiepke; Cannon, Dara M.; Chaim-Avancini, Tiffany M.; Chan, Sandra S. M.; Chen, Eric Y. H.; Crespo-Facorro, Benedicto; Crone, Eveline A.; Dannlowski, Udo; De Zwarte, Sonja M. C.; Dietsche, Bruno; Donohoe, Gary; Du Plessis, Stefan; Durston, Sarah; Diaz-Caneja, Covadonga M.; Díaz-Zuluaga, Ana M.; Emsley, Robin; Filippi, Massimo; Frodl, Thomas; Gorges, Martin; Graff, Beata; Grotegerd, Dominik; Gąsecki, Dariusz; Hall, Julie M.; Holleran, Laurena; Holt, Rosemary; Hopman, Helene J.; Jansen, Andreas; Janssen, Joost; Jodzio, Krzysztof; Jancke, Lutz; Kaleda, Vasiliy G.; Kassubek, Jan; Masouleh, Shahrzad Kharabian; Kircher, Tilo; Koevoets, Martijn G. J. C.; Kostic, Vladimir S.; Krug, Axel; Lawrie, Stephen M.; Lebedeva, Irina S.; Lee, Edwin H. M.; Lett, Tristram A.; Lewis, Simon J. G.; Liem, Franziskus; Lombardo, Michael V.; Lopez-Jaramillo, Carlos; Margulies, Daniel S.; Markett, Sebastian; Marques, Paulo; Martinez-Zalacaín, Ignacio; McDonald, Colm; McIntosh, Andrew M.; McPhilemy, Genevieve; Meinert, Susanne L.; Menchon, Jose M.; Montag, Christian; Moreira, Pedro S.; Morgado, Pedro; Mothersill, David O.; Merillat, Susan; Muller, Hans-Peter; Nabulsi, Leila; Najt, Pablo; Narkiewicz, Krzysztof; Naumczyk, Patrycja; Oranje, Bob; De la Foz, Victor Ortiz-Garcia; Peper, Jiska S.; Pineda, Julian A.; Rasser, Paul E.; Redlich, Ronny; Repple, Jonathan; Reuter, Martin; Rosa, Pedro G. P.; Ruigrok, Amber N. V.; Sabisz, Agnieszka; Schall, Ulrich; Seedat, Soraya, 1966-; Serpa, Mauricio H.; Skouras, Stavros; Soriano-Mas, Carles; Sousa, Nuno; Szurowska, Edyta; Tomyshev, Alexander S.; Tordesillas-Gutierrez, Diana; Valk, Sofie L.; Van den Berg, Leonard H.; Van Erp, Theo G. M.; Van Haren, Neeltje E. M.; Van Leeuwen, Judith M. C.; Villringer, Arno; Vinkers, Christiaan H.; Vollmar, Christian; Waller, Lea; Walter, Henrik; Villringer, Arno; Vinkers, Christiaan H.; Vollmar, Christian; Waller, Lea; Walter, Henrik; Whalley, Heather C.; Witkowska, Marta; Witte, A. Veronica; Zanetti, Marcus V.; Zhang, Rui; De Lange, Siemon C.
    Parkinson’s disease (PD) is a well-known neurodegenerative disease with a strong association established with systemic inflammation. Recently, the role of the gingipain protease group from Porphyromonas gingivalis was implicated in Alzheimer’s disease and here we present evidence, using a fluorescent antibody to detect gingipain R1 (RgpA), of its presence in a PD population. To further elucidate the action of this gingipain, as well as the action of the lipopolysaccharide (LPS) from P. gingivalis, low concentrations of recombinant RgpA and LPS were added to purified fluorescent fibrinogen. We also substantiate previous findings regarding PD by emphasizing the presence of systemic inflammation via multiplex cytokine analysis, and demonstrate hypercoagulation using thromboelastography (TEG), confocal and electron microscopy. Biomarker analysis confirmed significantly increased levels of circulating proinflammatory cytokines. In our PD and control blood analysis, our results show increased hypercoagulation, the presence of amyloid formation in plasma, and profound ultrastructural changes to platelets. Our laboratory analysis of purified fibrinogen with added RgpA, and/or LPS, showed preliminary data with regards to the actions of the protease and the bacterial membrane inflammagen on plasma proteins, to better understand the nature of established PD.
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    Measuring the impact of HIV on the fronto-striatal system
    (Stellenbosch : Stellenbosch University, 2016-12) Du Plessis, Stefan; Emsley, Robin Alexander; Vink, Matthijs; Stellenbosch University. Faculty of Medicine and Health Science. Dept. of Psychiatry.
    ENGLISH SUMMARY : HIV infection remains a major contributor to the global health burden despite the introduction of effective prevention strategies and the effectiveness of combined antiretroviral therapy (cART). Of particular importance is the impact of HIV on the brain. While cART has been successful in treating the more severe forms HIV induced cognitive impairment, the minor forms of impairment are now more prevalent. There remains some controversy with regard to the latter. Being diagnosed in the absence of other symptoms, there is some doubt that this category of cognitive impairment is valid at all. As such, investigating HIV induced functional brain changes may be helpful in the study of these forms of impairment. Although functional magnetic resonance imaging (fMRI) studies have thus far shown various forms of functional impairment in the brain, how these impairments relate to one another is unclear. Many key aspects of HIV’s potential impact on the frontostriatal system remain unexplored. Our overall objective was therefore to investigate the early impact of HIV on the brain using fMRI as an objective measurement tool. First, we investigated the effects of HIV on the brain by performing a quantitative meta analysis of all suitable fMRI data. Next, we proceeded to investigate the fronto-striatal network based on the results of the meta-analysis by performing fMRI imaging in a sample of HIV+ participants and matched HIV negative controls. Participants performed a stop-signal anticipation and a monetary incentive delay task to investigate the impact of HIV on important sub-networks of the fronto-striatal system. Finally, we investigated the relationship between striatal dysfunction with structural brain changes. The results from the meta-analysis showed that HIV consistently affects the fronto-striatal system based on past fMRI studies. In subsequent studies, we demonstrated diminished functioning of the fronto-striatal networks involved in inhibition of voluntary movement as well as reward processing. Furthermore, this fronto-striatal dysfunction was also related to cortical atrophy often seen in HIV. Based on these findings, I therefore conclude that fronto-striatal dysfunction is a core component of HIV infection and needs to be considered in the assessment and management of all patients afflicted by this still very prevalent illness.
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    Proteomic analysis of human spermatozoa proteins with oxidative stress
    (BioMed Central, 2013-05) Sharma, Rakesh; Agarwal, Ashok; Mohanty, Gayatri; Hamada, Alaa J.; Gopalan, Banu; Willard, Belinda; Yadav, Satya; Du Plessis, Stefan
    Background: Oxidative stress plays a key role in the etiology of male infertility. Significant alterations in the sperm proteome are associated with poor semen quality. The aim of the present study was to examine if elevated levels of reactive oxygen species cause an alteration in the proteomic profile of spermatozoa. Methods This prospective study consisted of 52 subjects: 32 infertile men and 20 normal donors. Seminal ejaculates were classified as ROS+ or ROS- and evaluated for their proteomic profile. Samples were pooled and subjected to LC-MS/MS analysis through in-solution digestion of proteins for peptide characterization. The expression profile of proteins present in human spermatozoa was examined using proteomic and bioinformatic analysis to elucidate the regulatory pathways of oxidative stress. Results Of the 74 proteins identified, 10 proteins with a 2-fold difference were overexpressed and 5 were underexpressed in the ROS+ group; energy metabolism and regulation, carbohydrate metabolic processes such as gluconeogenesis and glycolysis, protein modifications and oxidative stress regulation were some of the metabolic processes affected in ROS+ group. Conclusions We have identified proteins involved in a variety of functions associated with response and management of oxidative stress. In the present study we focused on proteins that showed a high degree of differential expression and thus, have a greater impact on the fertilizing potential of the spermatozoa. While proteomic analyses identified the potential biomarkers, further studies through Western Blot are necessary to validate the biomarker status of the proteins in pathological conditions.
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    Utilizing virtual reality as a therapeutic tool psychiatry
    (Stellenbosch : Stellenbosch University, 2022-04) Du Plessis, Stefan; Van den Heever, D. J.; Schreve, K.; Rosenstein, D.; Stellenbosch University. Faculty of Engineering. Institute of Biomedical Engineering.
    ENGLISH ABSTRACT: The mass production of modern cellphone technology has resulted in a dra matic cost reduction of producing Virtual Reality (VR) head-mounted dis plays. Although VR has been effective in the treatment of phobias, uptake is still far from mainstream. Fear of heights (i.e. acrophobia) is one of the more common forms of phobias in the general population. Up to 28% of people have distress and anxiety when exposed to heights (i.e. visual heights intoler ance (VHI)), with up to 6% of people meeting clinical criteria for the specific phobia. Virtual Reality Exposure Therapy (VRET) for acrophobia has been shown to be effective as early as the 1990s. There are, however, still relatively few randomized controlled studies that have looked at its effectiveness . Even fewer studies look at physiological responses associated with fear cessation. Biofeedback is the process of presenting participants with their physiological responses allowing them to gain a measure of control over them. Biofeedback shows promise as a treatment adjunct for specific phobias. We therefore aim to create a VR height exposure platform, that offers a graduated exposure, is optimized to avoid excessive motion sickness, is cost-effective for widespread use, and is validated by participant reports collected during the exposure. Here we developed and tested a cost effective VR acrophobia environment with biofeedback in a sample of 22 participants, 4 of whom had clinically measurable acrophobia. We constructed an Electrodermal Activity (EDA) biofeedback prototype using two Arduino boards, one being electrically isolated (Nano) to reduce noise and increase safety. The second Arduino (UNO R3) was con nected via USB to a VR workstation running the Unreal Engine 4.24.2. USB connectivity was established via the UE4duino plugin. All participants un derwent clinical screening, excluding for confounding psychopathology except acrophobia. Acrophobia symptoms were evaluated using the Visual Height Intolerance Severity Scale (vHISS) questionnaire. Participants were placed on a VR platform which ascended to 28 meters. Subjective stress responses were recorded during the task as well as VR related motion sickness. Data was en tered into a repeated measures ANOVA to check for within-subject differences in levels of stress, comparing when the platform was on the ground as well as in the air. Afterwards participants experiences were evaluated via a brief questionnaire. Biofeedback based on the mean of the signal consistently informed participants that they were stressed while the platform was elevated. Participants showed a significant increase in mean skin conductance signal while the platform was elevated. Continuous decomposition analysis as well as subjective responses confirmed the accuracy of the biofeedback provided. All participants reported a positive experience using the biofeedback, most perceiving it to be accurate. The present work indicates that biofeedback in VRET is a promising treatment adjunct, which should be explored in further clinical trials.