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Biomedical subjects

A Colak

Publications and source records attributed to A Colak.

At least 37 records · Page 2Linked to original sources
PubMed1997

A new model for tethered cord syndrome: a biochemical, electrophysiological, and electron microscopic study.

In order to investigate the pathophysiology of the tethered cord syndrome, a few experimental models have been developed and used previously. In this study, the authors present a new experimental model to investigate the biochemical, electrophysiological, and histopathological changes in the tethered spinal cord syndrome. A model was produced in guinea pigs using an application of cyanoacrylate to fixate the filum terminale and the surrounding tissue to the dorsal aspect of the sacrum following 5-gram stretching of the spinal cord. The experiments were performed on 40 animals divided into two groups. The responses to tethering were evaluated with hypoxanthine and lipid peroxidation, somatosensory and motor evoked potentials, and transmission electron microscope examination. The hypoxanthine and lipid peroxidation levels significantly increased, indicating an ischemic injury (p < 0.01). The average hypoxanthine level in the control group was 478.8 +/- 68.8 nmol/g wet tissue, while it was 651.2 +/- 71.5 nmol/g in the tethered cord group. The lipid peroxidation level in group I was 64.0 +/- 5.7 nmol/g wet tissue, whereas it was 84.0 +/- 4.7 nmol/g in group II. In the tethered cord group, the latencies of the somatosensory and motor evoked potentials significantly increased, and the amplitudes decreased. These changes indicated a defective conduction in the motor and sensorial nerve fibers. In the transmission electron microscopic examinations, besides the reversible changes like edema and destruction in the gray-white matter junction, irreversible changes like scarcity of neurofilaments and destruction in axons and damage in myelin sheaths were observed. We consider that this work can be used as an experimental model for tethered cord syndrome.

Animals↗
PubMed1997

Follow-up of children with shunted hydrocephalus.

In order to determine if routine yearly evaluations of children with shunted hydrocephalus were likely to diagnose shunt malfunction, we reviewed the medical records of the last 100 children who had such routine evaluations. Only 4 children had symptoms that were potentially referable to malfunction; none were subsequently found to have malfunction and no child had signs of malfunction. We also reviewed the medical records of the last 100 children who had shunt revisions to determine if any of them were diagnosed during routine follow-up examinations. Four were: 2 with clinical signs of malfunction and 2 with evidence of malfunction on routine scans. Only 1 child in either group had signs or symptoms of malfunction if they had a functioning shunt in place for longer than 1 year. Although yearly follow-up visits are common practice, we conclude that such examinations are unlikely to detect shunt malfunction. Follow-up at intervals of 2 years is probably appropriate after 2 years of age if the child has had a functional shunt for 1 year and has had a scan that indicates a functioning shunt.

Child↗
PubMed1996

Effect of divalent metal ions on the microsomal aniline hydroxylase system of rainbow trout.

The ability of trout to metabolize aniline in vitro in the presence of some divalent metal ions was investigated in the liver microsomes of rainbow trout, Salmo gairdneri. Trout liver microsomes were highly capable of catalyzing aniline hydroxylation to p-aminophenol with a specific activity of 0.068 nmoles/ min per mg of microsomal protein in potassium phosphate buffer, pH 7.4 at 25 degrees C. The activity of the aniline hydroxylase system was competitively inhibited by Hg+2, Ni+2, Cd+2, and Zn+2, while Cu+2 and Fe+3 seemed to inhibit the activity noncompetitively at 1 mM aniline concentrations. IC50 values at fixed aniline concentration were estimated to be 0.45 mM for Hg+2, Ni+2, and Cd+2, 1.8 mM for Zn+2 and Fe+3, and 1.3 mM for Cu+2. Eadie-Hofstee plots gave identical Vmax values of approximately 0.046 nmol/min per mg of protein while K(m) values were increased in the presence of Hg+2, Ni+2, Cd+2, and Zn+2, indicating competitive inhibition. Both K(m) and Vmax values were affected by Fe+3 and Cu+2, suggesting noncompetitive inhibition. Ki values extracted from the Dixon plots were determined to be 0.23, 0.43, and 0.65 mM for Hg+2, Ni+2, and Cd+2, respectively, providing the most effective inhibition on the aniline hydroxylase system among studied metal ions. The Ki values were much higher in the presence of others. The results indicate a selective inhibition of the aniline hydroxylase system of trout liver microsomes by divalent metal ions.

Aniline Hydroxylase↗
PubMed1996

CNS involvement of Langerhans cell histiocytosis. Report of 23 surgically treated cases.

We present 23 cases of Langerhans cell histiocytosis with central nervous system (CNS) involvement. The major complaints were a mass on the cranial vault in fifteen (65%), visual disturbance in four (16%), polyurea-polydipsia in three (13%), and progressive weakness in all extremities in one patient (4%). Neurological examination revealed no abnormality in sixteen patients (70%), cranial nerve palsy, visual field defect and optic atrophy in six (26%) and paraparesis in one (4%). Tumoral mass was found to be located on the cranial vault (65%), in the suprasellar region (21%) and in the spinal column (8%). The cranium and spinal column were both involved in one patient. All patients underwent surgery; craniectomy with grossly total tumor excision plus cranioplasty (65%), craniotomy with subtotal tumor excision (26%), and vertebrectomy with grafting (13%) were performed. The clinical, radiological and histopathological features, as well as therapeutical considerations are discussed and the pertinent literature is reviewed.

Adolescent↗
PubMed1996

A huge cerebral hydatid cyst associated with small liver cyst: a comparison of growth rates and sizes.

There are still some unknown aspects of the natural course of echinococcus infestation, especially in the brain. The growth rate of the cysts in brain and in other tissues is matter of some discussion. In this report, a huge primary cerebral hydatid cyst associated with a small liver cyst is presented and a possible relationship between the growth rates and the sizes of the two cysts is discussed. It is shown that the brain hydatid cyst grew faster than liver hydatid cyst by a ratio of 3:1.

Antinematodal Agents↗
PubMed1996

Effect of CO2 laser on spinal epidural fibrosis.

In this study the effect of CO2 laser on spinal epidural fibrosis was examined in 24 guinea pigs which were divided into two groups. The first group was the control group, the second one the CO2 laser group. All animals had laminectomies at 3 levels. Re-exploration was performed three months after the laminectomy. In the second group the same procedure was performed but at the end of the re-exploration, CO2 laser irradiation of the epidural fibrotic tissue was done. The wounds in both groups were closed again. Four months later all animals were sacrificed. For verification and quantification of scar formation (postoperative fibrosis) light microscopic examinations and determination of hydroxyproline were done, using Bergman's spectrophotometric method. The differences which were observed between the two groups were statistically significant (U : 134, P < 0.05). This study demonstrates the reducing effect of CO2 laser irradiation on epidural scar formation. The findings encourage its use as an alternative method of prevention of epidural fibrosis after spinal surgery.

Animals↗
PubMed1995

Adenovirus-mediated gene therapy for experimental spinal cord tumors: tumoricidal efficacy and functional outcome.

We evaluated the efficacy of adenoviral-mediated gene therapy of experimental spinal cord tumors and the functional outcome after this treatment. Spinal cord tumors were generated in the thoracic region of the spinal cord in Fischer 344 rats by stereotaxic intramedullary injection of 1 x 10(4) 9L gliosarcoma cells. Seven days after tumor cell injection, a replication-defective adenoviral vector carrying the herpes simplex virus thymidine kinase gene (ADV-tk) or a control adenoviral vector carrying the beta-galactosidase gene (ADV-beta gal) was injected into the tumors. Beginning 12 h later the animals were treated with the antiviral drug ganciclovir (GCV; 50 mg/kg) or saline twice a day for 6 days. The neurological performance of the animals was assessed during and following treatment. Eighteen days after tumor cell injection, all of the control animals had paraplegia and large tumors. In contrast, no tumors were detected in animals treated with ADV-tk and GCV. In long-term studies, two of the 5 animals treated with ADV-tk and GCV remained tumor-free and remained neurologically intact at 6 months whereas all animals in the control groups became paraplegic within 18 days.

Animals↗
PubMed1995

Efficacy of high dose amino acid solution on spinal cord injury induced by focal Nd:YAG laser irradiation.

In this experimental study, a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser was used to induce highly reproducible focal spinal cord lesions in anaesthetized guinea pigs. The efficacy of high dose amino acid solution (HDAAS) on this injury is investigated. Experiments were performed on 36 animals divided into three groups; sham operated controls, laser irradiated surgical controls, and amino acid groups. Acute responses to injury were evaluated with somatosensory (SSEP) and motor evoked potentials (MEP) and functional recovery was assessed for 8 weeks using the inclined plane technique. In the laser irradiated surgical control group, MEP disappeared one hour after the laser injury, but SSEP revealed changes of amplitude and latency. In this group, the average value of the inclined plane at 24 hours after the laser application was 45.3 +/- 1.4 degrees. In the amino acid group, at the sixth hour of injury, MEP and SSEP changes improved with infusion of HDAAS for 4 hours. This improvement was statistically significant (for latency of SSEP U = 140 p < 0.05). Inclined plane value at 24 hours after the laser application was 65.5 +/- 1.2 degrees in this group. This study showed that application of Nd:YAG laser irradiation on the spinal cord induced spinal cord injury which presented as paraparesis, HDAAS may provide significant therapeutic protection in secondary damage following this injury and may have a potential role in the treatment of acute spinal cord injury.

Amino Acids↗
PubMed1995

Adenovirus-mediated gene therapy in an experimental model of breast cancer metastatic to the brain.

We investigated the therapeutic efficacy of adenovirus-mediated gene therapy to treat malignant mammary tumors in vitro and in vivo in the brain. A mammary adenocarcinoma cell line derived from Fischer rats (13762 MAT B III; MAT-B) was used. In vitro studies demonstrated that the MAT-B cells could be efficiently transduced with a replication-defective adenovirus (ADV) vector that carried the herpes simplex virus gene for thymidine kinase (ADV-tk), and that ADV-tk transduction rendered the MAT-B cells sensitive to killing, in a dose-dependent manner, with ganciclovir (GCV). An animal model of a mammary tumor metastatic to the brain was produced by injecting MAT-B cells into the caudate nucleus of Fischer rats. Seven days after MAT-B cell injection, when the tumors were approximately 5 mm2 in cross-sectional size, the tumors were injected with ADV-tk or a control adenovirus vector containing the beta-galactosidase (beta-Gal) gene (ADV-beta gal). After vector injection the animals were treated with GCV or with saline for 6 days. Sixteen days after tumor cell injection, the brains were examined histologically. The rats that were injected with ADV-beta gal and treated with GCV or saline, and those that were injected with ADV-tk and treated with saline had large tumors, whereas the rats that were injected with ADV-tk and treated with GCV had no visible tumor tissue at the site of tumor cell injection. In survival studies animals treated with ADV-tk+GCV survived a significantly longer time than animals treated with ADV-beta gal+GCV. Our results demonstrate that the recombinant adenoviral vector containing the tk gene confers GCV cytotoxic sensitivity to mammary tumor cells in vitro and in the brain, and suggest that this treatment strategy may be useful in treating somatic tumors that metastasize to the brain.

Adenocarcinoma↗
PubMed1994

Brainstem auditory evoked potentials and blink reflexes in patients with pontocerebellar angle tumors.

Brainstem auditory evoked potentials (BAEP) and blink reflexes (BR) were obtained from 13 patients with pontocerebellar angle (PCA) tumors whose pathological diagnosis was as follows: 7 acoustic neurinoma, 3 meningioma, 1 neurinoma, 1 brain stem epidermoid tumor, 1 arteriovenous malformation. The most prominent abnormality was noted in BAEP generated by stimulating the ear ipsilateral to the lesion and ipsilateral R1 reflexes obtained from ipsilateral stimulation of the supraorbital nerve.

Acoustic Stimulation↗
PubMed1994

A new experimental model: for further investigation of the secondary changes following spinal cord injury.

To investigate the pathophysiology of spinal trauma, several experimental models have been used. In this study, the authors present a new experimental model for further investigation of secondary damage following spinal injury. Nd:YAG laser irradiation was applied to the spinal cord of guinea pigs to produce an injury. A 30 Watt (20 Joule) laser produced paraparesis. The injury was evaluated with evoked potentials, lipid peroxidation values, and histopathological examination.

Animals↗
PubMed1993

Reaction of rabbit lateral periventricular tissue to non-infected and infected (Staphylococcus epidermidis) shunt tubing implants. A light and transmission electron microscope study.

The reactions of periventricular tissue of the lateral ventricle to non-infected and infected (Staphylococcus Epidermidis) silicone shunt tubing were examined by light and transmission electron microscopy. It was shown that reactive changes occurred in periventricular tissue in response to the implant of sterile shunt tubing. On the other hand in infected implanted silicone shunt tubing, proliferation of inflammatory cells within the ventricle and periventricular tissue, loss of integrity of the ependyma, glial cell proliferation, and excessive extracellular oedema were demonstrated. Proliferation of ependymal cells combined with inflammatory responses may be a factor in the pathogenesis of infected shunt obstruction.

Animals↗
PubMed1993

Adult medulloblastoma presenting as a large neck tumor. Case report.

Extension of neuroepithelial tumors outside the neuroaxis is uncommon and usually follows surgical intervention. We report a patient with medulloblastoma of the right cerebellar hemisphere with extracranial extension presenting as a large neck tumor and discuss the clinical and pathological features of this case.

Adult↗
PubMed1993

Efficacy of ampicillin/sulbactam combination in experimental shunt infections caused by Staphylococcus epidermidis. A light and scanning electron microscope study.

In this study, the efficacy of ampicillin/sulbactam combination in reactions of periventricular tissue of the lateral ventricle induced by the presence of infected (Staphylococcus epidermidis) silicone rubber shunt tubing was examined by using light and scanning electron microscopy. It was demonstrated that reactive changes to implants had occurred in periventricular tissue in the control group. In infected shunt tubing without given prophylactic antibiotic group, generalized meningitis and ventriculitis, loss of integrity of ependymal cells, numerous inflammatory cells, bacterial colonies, exuda and even pus were seen. It was also shown that rarely inflammatory reactions, minimal disintegration of ependymal cells, no bacterial colonies, and phagocytes were present in the group which was given prophylactic ampicillin/sulbactam combination per and postoperatively. We think that ampicillin/sulbactam combination is very effective in prevention and treatment of shunt infections.

Ampicillin↗