Researcher: Özyurt, Mustafa Görkem
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Özyurt, Mustafa Görkem
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Publication Metadata only Exploring the receptor origin of vibration-induced reflexes(Nature Publishing Group, 2020) Yıldırım, Mustafa A.; Aydın, Tuğba; Paker, Nurdan; Soy, Derya; Coşkun, Evrim; Ones, Kadriye; Bardak, Ayşenur; Kesiktaş, Nur; Çelik, Berna; Önder, Burcu; Kılıc, Ayşeguü; Küçük, Habib C.; Karacan, İlhan; N/A; N/A; N/A; Topkara, Betilay; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; PhD Student; PhD Student; Faculty Member; Graduate School of Health Sciences; Graduate School of Sciences and Engineering; School of Medicine; 353320; N/A; 6741Study Design: An experimental design. Objectives: The aim of this study was to determine the latencies of vibration-induced reflexes in individuals with and without spinal cord injury (SCI), and to compare these latencies to identify differences in reflex circuitries. Setting: A tertiary rehabilitation center in Istanbul. Methods: Seventeen individuals with chronic SCI (SCI group) and 23 participants without SCI (Control group) were included in this study. Latency of tonic vibration reflex (TVR) and whole-body vibration-induced muscular reflex (WBV-IMR) of the left soleus muscle was tested for estimating the reflex origins. The local tendon vibration was applied at six different vibration frequencies (50, 85, 140, 185, 235, and 265 Hz), each lasting for 15 s with 3-s rest intervals. The WBV was applied at six different vibration frequencies (35, 37, 39, 41, 43, and 45 Hz), each lasting for 15 s with 3-s rest intervals. Results: Mean (SD) TVR latency was 39.7 (5.3) ms in the SCI group and 35.9 (2.7) ms in the Control group with a mean (95% CI) difference of -3.8 (-6.7 to -0.9) ms. Mean (SD) WBV-IMR latency was 45.8 (7.4) ms in the SCI group and 43.3 (3.0) ms in the Control group with a mean (95% CI) difference of -2.5 (-6.5 to 1.4) ms. There were significant differences between TVR latency and WBV-IMR latency in both the groups (mean (95% CI) difference; -6.2 (-9.3 to -3.0) ms, p = 0.0001 for the SCI group and -7.4 (-9.3 to -5.6) ms, p = 0.011 for Control group). Conclusions: The results suggest that the receptor of origin of TVR and WBV-IMR may be different.Publication Metadata only Optimal location for eliciting the tibial H-reflex and motor response(Wiley, 2018) N/A; N/A; Özyurt, Mustafa Görkem; Shabsog, Mohammed Kamal Yahya; Dursun, Merve; Türker, Kemal Sıtkı; PhD Student; Undergraduate Student; Undergraduate Student; Faculty Member; Graduate School of Sciences and Engineering; School of Medicine; School of Medicine; School of Medicine; School of Medicine; N/A; N/A; N/A; 6741Introduction: Although there are numerous protocols to adjust the amplitude of the Hoffmann reflex (H-reflex) relative to the size of the direct motor response (M-response), the optimal stimulating location has not been described. We sought to determine the optimal positioning of the stimulating cathode when evoking the tibial nerve H-reflex and M-response. Methods: A small cathode was placed on defined points in the popliteal fossa while an anode was fixed on the patella. The tibial nerve was stimulated electrically, and the response of the soleus muscle was recorded using intramuscular and surface electromyography. Results: We found that more-lateral points along a line drawn across the popliteal fossa were the best locations to obtain only the M-response, whereas stimulating the midpoint was optimal for obtaining only the H-reflex. Discussion: By using specified locations for electrical stimulation to evoke H-reflex and M-response, the functionality of the tibial nerve can be assessed.Publication Metadata only Effect of aging on H-reflex response to fatigue(Springer, 2020) Lavender, Andrew Philip; Balkozak, Sadik; Karacan, Ilhan; Bilici, Idil; Hill, Anne-Marie; N/A; Özyurt, Mustafa Görkem; Topkara, Betilay; Türker, Kemal Sıtkı; PhD Student; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; School of Medicine; Graduate School of Health Sciences; School of Medicine; N/A; 353320; 6741Injury as a result of tripping is relatively common among older people. The risk of falling increases with fatigue and of importance is the ability to dorsiflex the foot through timely activation of the tibialis anterior (TA) muscle to ensure the foot clears the ground, or an obstacle, during the swing phase of walking. We, therefore, questioned whether the muscle spindle input to the motoneurons alters with ongoing fatigue in older people. We electrically stimulated the common peroneal nerve to assess the TA primary afferent efficacy using H-reflex before, immediately following and after a fatiguing maximal isometric contraction. M-response was kept unchanged throughout the experiment to ensure a similar stimulus intensity was delivered across time points. H-reflex increased significantly while the TA muscle was in a state of fatigue for the younger participants but tended to decrease with increasing age. The main contributor to the tonicity of TA muscle, i.e., excitatory synapses of spindle primary endings of motoneurons that innervate TA muscle, tend to lose their efficacy during fatigue in the older individuals but increased efficiency in the majority of the younger people. Since TA muscle is the main dorsiflexor of the foot and it needs to be active during the swing phase of stepping to prevent tripping, older individuals become more susceptible to falling when their muscles are fatigued. This finding may help improve devices/treatments to overcome the problem of tripping among older individuals.Publication Metadata only Assessment of the corticospinal fiber integrity in mirror movement disorder(Elsevier, 2018) Solmaz, Bilgehan; Akçimen, Fulya; Dalçık, Hakkı; Algın, Oktay; Başak, Ayşe Nazlı; Çavdar, Safiye; Özyurt, Mustafa Görkem; Shabsog, Mohammed Kamal Yahya; Türker, Kemal Sıtkı; Demir, Ata Berk; Özgür, Merve; Faculty Member; PhD Student; Undergraduate Student; Faculty Member; PhD Student; PhD Student; School of Medicine; Graduate School of Sciences and Engineering; School of Medicine; School of Medicine; Graduate School of Health Sciences; Graduate School of Health Sciences; 1995; N/A; N/A; 6741; N/A; 197462Mirror movements are unintended movements occurring on one side of the body that mirror the contralateral voluntary ones. It has been proposed that mirror movements occur due to abnormal decussation of the corticospinal pathways. Using detailed multidisciplinary approach, we aimed to enlighten the detailed mechanism underlying the mirror movements in a case subject who is diagnosed with mirror movements of the hands and we compared the findings with the unaffected control subjects. To evaluate the characteristics of mirror movements, we used several techniques including whole exome sequencing, computed tomography, diffusion tensor imaging and transcranial magnetic stimulation. Computed tomography showed the absence of a spinous process of C5, fusion of the body of C5-C6 vertebrae, hypoplastic dens and platybasia of the posterior cranial fossa. A syrinx cavity was present between levels C3-C4 of the spinal cord. Diffusion tensor imaging of the corticospinal fibers showed disorganization and minimal decussations at the lower medulla oblongata. Transcranial magnetic stimulation showed that motor commands were distributed to the motor neuron pools on the left and right sides of the spinal cord via fast-conducting corticospinal tract fibers. Moreover, a heterozygous missense variation in the deleted in colorectal carcinoma gene has been observed. Developmental absence of the axonal guidance molecules or their receptors may result in abnormalities in the leading of the corticospinal fibers. Clinical evaluations and basic neuroscience techniques, in this case, provide information for this rare disease and contribute to our understanding of the normal physiology of bimanual coordination. (C) 2018 Elsevier Ltd. All rights reserved.Publication Metadata only Comparison of the temporal properties of medium latency responses induced by cortical and peripheral stimulation(Elsevier Sci Ltd, 2020) Göztepe, Mehmet Berke; Uysal, Hilmi; N/A; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; School of Medicine; School of Medicine; N/A; 6741Sudden foot dorsiflexion lengthens soleus muscle and activates stretch-based spinal reflexes. Dorsiflexion can be triggered by activating tibialis anterior (TA) muscle through peroneal nerve stimulation or transcranial magnetic stimulation (TMS) which evokes a response in the soleus muscle referred to as Medium Latency Reflex (MLR) or motor-evoked potential-80 (Soleus MEP80), respectively. This study aimed to examine the relationship between these responses in humans. Therefore, latency characteristics and correlation of responses between soleus MEP80 and MLR were investigated. We have also calculated the latencies from the onset of tibialis activity, i.e., subtracting of TA-MEP from MEP80 and TA direct motor response from MLR. We referred to these calculations as Stretch Loop Latency Central (SLLc) for MEP80 and Stretch Loop Latency Peripheral (SLLp) for MLR. The latency of SLLc was found to be 61.4 +/- 5.6 ms which was significantly shorter (P = 0.0259) than SLLp (64.0 +/- 4.2 ms) and these latencies were correlated (P = 0.0045, r = 0.689). The latency of both responses was also found to be inversely related to the response amplitude (P = 0.0121, r = 0.451) probably due to the activation of large motor units. When amplitude differences were corrected, i.e. investigating the responses with similar amplitudes, SLLp, and SLLc latencies found to be similar (P = 0.1317). Due to the identical features of the soleus MEP80 and MLR, we propose that they may both have spinal origins.Publication Metadata only Chiropractic spinal manipulation alters TMS induced i-wave excitability and shortens the cortical silent period(2018) Haavik, Heidi; Niazi, Imran Khan; Jochumsen, Mads; Ugincius, Paulius; Navid, Muhammad Samran; Department of Physics; N/A; N/A; N/A; Sebik, Oğuz; Yılmaz, Gizem; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; Researcher; PhD Student; PhD Student; Faculty Member; Department of Physics; College of Sciences; Graduate School of Health Sciences; Graduate School of Sciences and Engineering; School of Medicine; Koc University Hospital; N/A; N/A; N/A; 6741The objective of this study was to construct peristimulus time histogram (PSTH) and peristimulus frequencygram (PSF) using single motor unit recordings to further characterize the previously documented immediate sensorimotor effects of spinal manipulation. Single pulse transcranial magnetic stimulation (TMS) via a double cone coil over the tibialis anterior (TA) motor area during weak isometric dorsiflexion of the foot was used on two different days in random order; pre/post spinal manipulation (in eighteen subjects) and pre/post a control (in twelve subjects) condition. TA electromyography (EMG) was recorded with surface and intramuscular fine wire electrodes. Three subjects also received sham double cone coil TMS pre and post a spinal manipulation intervention. From the averaged surface EMG data cortical silent periods (CSP) were constructed and analysed. Twenty-one single motor units were identified for the spinal manipulation intervention and twelve single motor units were identified for the control intervention. Following spinal manipulations there was a shortening of the silent period and an increase in the single unit I-wave amplitude. No changes were observed following the control condition. The results provide evidence that spinal manipulation reduces the TMS-induced cortical silent period and increases low threshold motoneurone excitability in the lower limb muscle. These finding may have important clinical implications as they provide support that spinal manipulation can be used to strengthen muscles. This could be followed up on populations that have reduced muscle strength, such as stroke victims.Publication Metadata only Periodontal mechanoreceptors and bruxism at low bite forces(Pergamon-Elsevier Science Ltd, 2019) Laine, Christopher M.; Tinastepe, Neslihan; N/A; N/A; N/A; Yılmaz, Gizem; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; PhD Student; PhD Student; Faculty Member; Graduate School of Health Sciences; Graduate School of Sciences and Engineering; School of Medicine; Koç University Hospital; N/A; N/A; 6741Objective: In this study, we examined if 6-9 Hz jaw tremor, an indirect indicator of Periodontal Mechanoreceptor (PMR) activity, is different in bruxists compared to healthy participants during production of a low-level constant bite force. Methods: Bite force and surface EMG from the masseter muscle were recorded simultaneously as participants (13 patients, 15 controls) held a force transducer between the upper and lower incisors very gently. Results: Tremor in 6-9 Hz band for bruxists was greater on average compared to controls, but the difference was not significant, both for force recordings and EMG activity. Conclusions: The low effect sizes measured with the current protocol contrast highly with those of our previous study, where larger, dynamic bite forces were used, and where jaw tremor was markedly different in bruxists compared with controls. Significance: We have now gained important insight into the conditions under which abnormal jaw tremor can be elicited in bruxism. From a scientific standpoint, this is critical for understanding the 'abnormality' of PMR feedback in bruxism. Prom a clinical perspective, our results represent progress towards the development of an optimal protocol in which jaw tremor can serve as a biological marker of bruxism.Publication Metadata only Coculture model of blood-brain barrier on electrospun nanofibers(TUBITAKScientific and Technical Research Council Turkey, 2020) Bayir, Ece; Dogan, Sule; Öztürk, Şükrü; Sendemir, Aylin; N/A; Özyurt, Mustafa Görkem; PhD Student; Graduate School of Sciences and Engineering; School of Medicine; N/AThe blood-brain barrier (BBB) is a control mechanism that limits the diffusion of many substances to the central nervous system (CNS). In this study, we designed an in-vitro 3-dimensional BBB system to obtain a fast and reliable model to mimic drug delivery characteristics of the CNS. A support membrane of polycaprolactone nanofiber surfaces was prepared using electrospinning. After confirming the fiber morphology and size, endothelial cells (HUVEC) and glial cells were cultured on either side of this membrane. The model's similarity to in vivo physiology was tested with a home-designed transmembrane resistance (TR) device, with positive and negative control molecules. Finally, 2 doses of methotrexate (MTX), a chemotherapy agent, were applied to the model, and its permeability through the model was determined indirectly by a vitality test on the MCF-7 cell line. Nicotine, the positive control, completed its penetration through the model almost instantly, while albumin, the negative control, was blocked significantly even after 2 days. MTX reached a deadly threshold 24 h after application. The TR value of the model was promising, being around 260 ohm.cm2. The provided model proposes a disposable and reliable tool for investigating drug permeability through the BBB and has the potential to reduce the number of animal experiments.Publication Metadata only Medium latency excitatory reflex of soleus re-examined(Springer, 2019) Uysal, Hilmi; Göztepe, Mehmet Berke; N/A; N/A; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; School of Medicine; N/A; 6741We aimed to study the receptor origin and postsynaptic potential profile of the medium latency reflex (MLR) response that develops in the soleus muscle when common peroneal nerve of antagonist tibialis anterior (TA) muscle is electrically stimulated. To achieve this aim, we electrically stimulated common peroneal nerve and recorded surface electromyography (SEMG) responses of soleus and TA muscles of informed volunteers. Additionally, we recorded intramuscular EMG from the soleus muscle. Stimulation of common peroneal nerve induced a direct motor response (M-response) in the TA and MLR in SEMG of the soleus. Using voluntarily-activated single motor units (SMUs) from the soleus muscle we noted that there were two distinct responses following the stimulus. The first response was a reciprocal inhibitory reflex probably originating from the antagonist muscle spindle primary (Ia) afferents. This was followed by an indirect reflex response activated by the contraction of the TA muscle during the M-response. This contraction generated a rapid acceleration in the direction of dorsiflexion hence inducing a stretch stimulus on soleus muscle. The response of soleus to this stimulus was a stretch reflex. We suggest that this stretch reflex is the main contributor to the so-called soleus MLR in the literature. This study illustrated the importance of using SMUs and also using discharge-rate based analysis for closely examining previously established' reflexes.Publication Metadata only Amyotrophic lateral sclerosis weakens spinal recurrent inhibition and post-activation depression(Elsevier Ireland Ltd, 2020) İsak, Barış; N/A; Özyurt, Mustafa Görkem; Topkara, Betilay; Türker, Kemal Sıtkı; PhD Student; PhD Student; Faculty Member; Graduate School of Sciences and Engineering; Graduate School of Health Sciences; School of Medicine; N/A; 353320; 6741Objectives: Amyotrophic lateral sclerosis (ALS) disrupts motoneurons that control movement and some vital functions, however, exact details of the neuronal circuits involved in ALS have yet to be fully endorsed. To contribute to our understanding of the responsible neuronal circuits, we aimed to investigate the spinal recurrent inhibition (RI) and post-activation depression (P-AD) in ALS patients. Methods: In two groups of ALS patients, i.e. lumbar-affected (clinical signs in leg muscles) and nonlumbar-affected (clinical signs in arms or bulbar region but not in the legs), RI and P-AD on the soleus muscle were investigated using single motor units and amplitude changes of H-reflex in surface electromyography, respectively. The data were compared with healthy subjects. Results: Compared to controls, P-AD of H-reflex was reduced severely in lumbar-affected patients and reduced to a certain degree in nonlumbar-affected patients. Similarly, a significant reduction in the duration of RI on firing motoneurons was found in lumbar-affected patients (11.5 +/- 2.6 ms) but not in nonlumbar-affected patients (29.7 +/- 12.4 ms, P < 0.0001) compared to controls (30.8 +/- 7.2 ms, P < 0.0001). Conclusion: The current study revealed that spinal inhibitory circuits are impaired in ALS. Significance: These findings may provide insight for proposing new therapeutic approaches and following disease progression in humans.