Browsing by Author "Ozturk, Gurkan"

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Active Shrinkage Protects Neurons Following Axonal Transection
(Cell Press, 2023) Aydin, Mehmet Sxerif; Bay, Sadik; Yigit, Esra Nur; Ozgul, Cemil; Oguz, Elif Kaval; Konuk, Elcin Yenidunya; Ozturk, Gurkan
Trauma, vascular events, or neurodegenerative processes can lead to axonal injury and eventual transec(axotomy). Neurons can survive axotomy, yet the underlying mechanisms are not fully understood. Excessive water entry into injured neurons poses a particular risk due to swelling and subsequent death. Using in vitro and in vivo neurotrauma model systems based on laser transection and surgical nerve cut, demonstrated that axotomy triggers actomyosin contraction coupled with calpain activity. As a consequence, neurons shrink acutely to force water out through aquaporin channels preventing swelling and bursting. Inhibiting shrinkage increased the probability of neuronal cell death by about 3-fold. These studies reveal a previously unrecognized cytoprotective response mechanism to neurotrauma and offer fresh perspective on pathophysiological processes in the nervous system.
Comparison of Techniques for Long-Term Storage of Fat Grafts: an Experimental Study
(Lippincott Williams & Wilkins, 2006) Atik, Bekir; Ozturk, Gurkan; Erdogan, Ender; Tan, Onder
Background: Absorption of autologous fat graft in the recipient area necessitates recurrent fat transplantation. Harvesting extra tissue during the first operation and storing it for future use is considered a solution to this problem. Methods: Fat tissue was removed from the inguinal region of 40 Swiss albino mice, which were arranged into four equal groups, and treated as follows: immediately transplanted to the donor animal; dry frozen; immersed in glycerol; or frozen in liquid nitrogen. The grafts that were frozen or immersed in glycerol were stored at -35 degrees C for 6 months and then transplanted to their original donors. Transplantations were performed by injecting the fat under the scalp. Viability of the fat tissue was evaluated with the MTT reduction test before transplantation, and histology of the transplanted tissue was examined at the end of the study. Results: The viability and histology of grafts frozen in liquid nitrogen were similar to those of fresh tissue, whereas with other methods the grafts had a considerable loss of viability during storage that was reflected in the low number of adipocytes and high proportion of vacuolar and fibrotic areas. Conclusion: Freezing fat grafts in liquid nitrogen and storing them at -35 degrees C is an effective way of preserving tissue for future use, with clear superiority over other methods.
Consequences of Neurite Transection in Vitro
(Mary Ann Liebert inc, 2012) Cengiz, Nurettin; Ozturk, Gurkan; Erdogan, Ender; Him, Aydin; Oguz, Elif Kaval
In order to quantify degenerative and regenerative changes and analyze the contribution of multiple factors to the outcome after neurite transection, we cultured adult mouse dorsal root ganglion neurons, and with a precise laser beam, we transected the nerve fibers they extended. Cell preparations were continuously visualized for 24 h with time-lapse microscopy. More distal cuts caused a more elongated field of degeneration, while thicker neurites degenerated faster than thinner ones. Transected neurites degenerated more if the uncut neurites of the same neuron simultaneously degenerated. If any of these uncut processes regenerated, the transected neurites underwent less degeneration. Regeneration of neurites was limited to distal cuts. Unipolar neurons had shorter regeneration than multipolar ones. Branching slowed the regenerative process, while simultaneous degeneration of uncut neurites increased it. Proximal lesions, small neuronal size, and extensive and rapid neurite degeneration were predictive of death of an injured neuron, which typically displayed necrotic rather than apoptotic form. In conclusion, this in vitro model proved useful in unmasking many new aspects and correlates of mechanically-induced neurite injury.
The Effect of Non-Enzymatic Glycation of Extracellular Matrix Proteins on Axonal Regeneration in Vitro
(Springer, 2006) Ozturk, Gurkan; Sekeroglu, Mehmet Ramazan; Erdogan, Ender; Ozturk, Mustafa
Non-enzymatic glycation of peripheral nerve extracellular matrix (ECM) may contribute to the development of diabetic distal sensory neuropathy (DNP). We investigated the relative importance of glycation of collagen types I and IV, laminin and fibronectin in DNP-related impairment in peripheral nerve regeneration. Dorsal root ganglia (DRGs) from young adult mice were embedded in collagen type I modified by 10% substitution with normal or glycated forms of the proteins and incubated for 3 days. Outgrowth of axons and migration of cells into the ECM were quantified. Mean length of growing axons was significantly reduced by glycation of laminin and collagen type IV. The sum of lengths of all axons from each DRG was greatly reduced with glycated laminin, collagen types IV and I. Glycation of fibronectin had no effect on axonal growth. The number of migrating cells was not affected by glycation. We conclude that non-enzymatic glycation of laminin and collagen types IV and I (in decreasing order) impairs peripheral nerve regeneration in vitro.
Enhancement of Cultured Adult Motor Neuron Survival With Cold Pre-Incubation
(Elsevier Ireland Ltd, 2013) Bektas, Serap; Ozturk, Gurkan
The aim of the study was to extend the survival of adult spinal motor neurons in serum free culture. Anterior half of the spinal cord was removed from young adult mice and dissociated. Cultured cells attempted to extend neurites within hours of incubation at 37 degrees C and died within 24 h. To prevent this early regenerative activity, thus to decrease the metabolic requirements of the neurons, cultures were transferred to 4 degrees C immediately after they were set and kept there for 3 days. Preparations were then taken to 37 degrees C where they lived up to 8 days. Some neurons continued to extend neurites until the day they died. To understand whether the enhancement of survival involves new protein synthesis, transcription and translation were blocked during cold pre-incubation, which shortened the half life of neurons but not changed the maximum survival period. In conclusion this study has shown that, in the serum-free cultures, the survival of adult spinal motor neurons can be significantly enhanced by cold pre-incubation whose effect seems to depend largely on a reduction in the metabolic activity and less on new protein synthesis. (c) 2012 Elsevier Ireland Ltd. All rights reserved.
Ets-Domain Transcription Factor Elk-1 Mediates Neuronal Survival: Smn as a Potential Target
(Elsevier Science Bv, 2011) Demir, Ozlem; Aysit, Nese; Onder, Zeynep; Turkel, Nezaket; Ozturk, Gurkan; Sharrocks, Andrew D.; Kurnaz, Isil Aksan
Elk-1 belongs to the ternary complex factors (TCFs) subfamily of the ETS domain proteins, and plays a critical role in the expression of immediate-early genes (IEGs) upon mitogen stimulation and activation of the mitogen-activated protein kinase (MAPK) cascade. The association of TCFs with serum response elements (SREs) on IEG promoters has been widely studied and a role for Elk-1 in promoting cell cycle entry has been determined. However, the presence of the ETS domain transcription factor Elk-1 in axons and dendrites of post-mitotic adult brain neurons has implications for an alternative function for Elk-1 in neurons other than controlling proliferation. In this study, possible alternative roles for Elk-1 in neurons were investigated, and it was demonstrated that blocking TCF-mediated transactivation in neuronal cells leads to apoptosis through a caspase-dependent mechanism. Indeed RNAi-mediated depletion of endogenous Elk-1 results in increased caspase activity. Conversely, overexpression of either Elk-1 or Elk-VP16 fusion proteins was shown to rescue PC12 cells from chemically-induced apoptosis, and that higher levels of endogenous Elk-1 correlated with longer survival of DRGs in culture. It was shown that Elk-1 regulated the Mcl-1 gene expression required for survival, and that RNAi-mediated degradation of endogenous Elk-1 resulted in elimination of the mcl-1 message. We have further identified the survival-of-motor neuron-1 (SMN1) gene as a novel target of Elk-1, and show that the ets motifs in the SMN1 promoter are involved in this regulation. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
Glutamate Responsiveness of Medial Vestibular Nucleus Neurons in Aged Rats
(Pergamon-elsevier Science Ltd, 2010) Him, Aydin; Guneser, Ramazan; Cengiz, Nureddin; Ozturk, Gurkan
Disequilibrium, dizziness, vertigo and falls are vestibular system-related problems which are very common especially in older people. In order to clarify these age-related disorders one must understand first the age-related changes in the properties of vestibular neurons that are responsible for equilibrium. The responsiveness of medial vestibular nucleus (MVN) neurons to the NMDA and AMPA/kainate receptor agonists was investigated in slices prepared from young and aged rats using extracellular single cell recording techniques. In both young and aged rats bath application of NMDA and AMPA caused a reversible, dose dependant increase in the spontaneous discharge of the MVN neurons. The excitatory effects of both NMDA and AMPA on the spontaneous activity of aged MVN neurons were similar to those of young MVN neurons. The spontaneous firing rates of the MVN cells were also similar in young and aged rats. These results suggest that the responsiveness of the NMDA and AMPA/kainate receptors and the excitability of the MVN neurons do not change with age. (C) 2009 Elsevier Inc. All rights reserved.
An in Vitro Model for Conditioning Lesion Effect
(Springer/plenum Publishers, 2019) Oguz, Elif Kaval; Ozturk, Gurkan
Axons of a peripheral nerve grow faster after an axotomy if it attains a prior injury a few days earlier. This is called conditioning lesion effect (CLE) and very much valued since it may provide new insights into neuron biology and axonal regeneration. There are established in vivo experimental paradigms to study CLE, however, there is a need to have an in vitro conditioning technique where CLE occurs in a maximally controlled environment. Mouse primary sensory neurons were isolated from lumbar 4-5 dorsal root ganglia and incubated at 37 degrees C on a silicon-coated watch glass that prevents cell attachment. After this conditioning period they were transferred to laminin coated culture dishes. Similar cultures were set up with freshly isolated neurons from control animals and from the animals that received a sciatic nerve cut 3days earlier. All preparations were placed on a live cell imaging microscopy providing physiological conditions and photographed for 48h. Axonal regeneration and neuronal survival was assessed. During the conditioning incubation period neurons remained in suspended aggregates and did not grow axons. The regeneration rate of the in vitro conditioned neurons was much higher than the in vivo conditioned and control preparations during the first day of normal incubation. However, higher regeneration rates were compromised by progressive substantial neuronal death in both types of conditioned cultures but not in the control preparations. By using neutralizing antibodies, we demonstrated that activity of endogenous leukemia inhibitory factor is essential for induction of CLE in this model.
The Levels of Nitrite, Nitrate and Lipid Peroxidation in Diabetic Mouse Brain: the Effect of Melatonin and Pentoxifylline
(Taylor & Francis Ltd, 2022) Yalcinkaya, Ahmet S.; Sekeroglu, Mehmet Ramazan; Huyut, Zubeyir; Cokluk, Erdem; Ozbek, Hanefi; Ozturk, Gurkan; Balahoroglu, Ragip
Objective: This study investigated the relationship between diabetes (DM) and nitrite, nitrate and MDA levels and effect of melatonin and pentoxifylline. Methods: Sixty mice were randomly divided into four groups. Control: no action; Diabetes group (DM): after fasting-blood-glucose (FBG) was measured, 150 mg/kg alloxane was applied intraperitoneally three-times every other day; Diabetes + Melatonin (DM + MLT) and Diabetes + Pentoxifylline groups (DM + PTX): following the same procedures with DM, 10 mg/kg melatonin and 50 mg/kg pentoxifylline were administered subcutaneously six days, respectively. Following FBG analysis, brain tissues were taken under the anaesthesia. Nitrite, nitrate and MDA levels were measured. Results: In the all groups with alloxane, FBG were higher than in before application (p < .05). Also, FBG, nitrite, nitrate and MDA levels in the DM + MLT and DM + PTX groups were lower than in the DM (p < .05). Conclusions: Nitrite and nitrate may be related to etiopathogenesis of DM, and pentoxifylline and especially melatonin relatively decrease nitrite, nitrate and lipid peroxidation.
A New Method in Cns (Central Nervous System) in Vitro Cultures in the Mouse: Study of Effectiveness
(Kafkas Univ, veteriner Fakultesi dergisi, 2010) Erdogan, Ender; Ozturk, Gurkan; Ragbetli, Murat Cetin
In this study: to evaluate the effectiveness of collagen coating method, using in the peripheral nervous system cultures. and its involving factors caused from manipulations in central nervous system (CNS) cultures was aimed. Via frontal approach, brains, transected from young Swiss albino mice, were taken into artificial cerebro-spinal fluid immediately and made blocks in agarose gel. With a vibration microtome, 200 pm thickness horizontally live slices were taken in to the dishes filled with culture medium. Tissue sections were analyzed as two groups. In the group 1 (control): fresh slices were evaluated directly. In the group 2: sections were covered with collagen gel (Type I) and left in the incubator (5% CO(2)) for 3 days. These sections were dyed with calcein and propidium iodide for viability and non-viability and then observed with confocal laser scanning microscope. Images were captured digitally and examined. Since negative effects of high melting temperature of standard agar on the livability, using low melting agar to tissue blocking and high frequency - low speed vibrotome setting to cut were more preferably. In the 3 days cultures, viability/nonviability rates were indicated better values. It is concluded that, in the CNS slicing cultures, collagen coating method was an easier, effective, useful and alternative method to present techniques.