Retinal Gangliosides in RCS Mutant Rats

Abstract: The distribution of retinal gangliosides was studied in normal and mutant rats with retinal dystrophy at 30 and 180 days of age. The loss of photoreceptor cells in the retinal dystrophic RCS rats was not associated with a significant reduction in the relative distribution of any of the major retinal gangliosides. The loss of photoreceptors, however, caused a marked increase in total retinal ganglioside concentration. These findings suggest that photoreceptor cells contain a low concentration of gangliosides and that no major retinal ganglioside is localized or concentrated in these cells. The cellular localization and function of the most abundant retinal ganglioside, G_D3, is discussed.     

Effect of Obtusifolin Administration on Retinal Capillary Cell Death and the Development of Retinopathy in Diabetic Rats

Oxidative stress is increased in the retina in diabetes, and it is considered to play an important role in the development of retinopathy. Findings indicate that obtusifolin has antioxidant properties. The purpose of this study was to examine the effect of obtusifolin on retinal capillary cell apoptosis and the development of pathology in diabetes. Retina was used from streptozotocin-induced diabetic rats receiving diets supplemented with or without obtusifolin (100, 200, and 400 mg/kg) for 11 months of diabetes. Capillary cell apoptosis (by terminal transferase-mediated dUTP nick-end labeling) and formation of acellular capillaries were investigated in the trypsin-digested retinal microvessels. The effect of obtusifolin administration on retinal 8-hydroxy-2′deoxyguanosine (8-OHdG) and nitrotyrosine levels was determined by enzyme-linked immunosorbent assay. Obtusifolin administration for the entire duration of diabetes inhibited capillary cell apoptosis and the number of acellular capillaries in the retina, despite similar severity of hyperglycemia in the four diabetic groups (with and without obtusifolin). Retinal 8-OHdG and nitrotyrosine levels were significantly increased, respectively, in diabetes, and obtusifolin administration inhibited these increases. Our results demonstrate that the long-term administration of obtusifolin has beneficial effects on the development of diabetic retinopathy via inhibition of accumulation of oxidatively modified DNA and nitrotyrosine in the retina. Obtusifolin represents an achievable adjunct therapy to help prevent vision loss in diabetic patients.     

Combined Oral Administration of Bovine Collagen Peptides with Calcium Citrate Inhibits Bone Loss in Ovariectomized Rats

Purpose

Collagen peptides (CPs) and calcium citrate are commonly used as bone health supplements for treating osteoporosis. However, it remains unknown whether the combination of oral bovine CPs with calcium citrate is more effective than administration of either agent alone.

Methods

Forty 12-week-old Sprague-Dawley rats were randomly divided into five groups (n = 8) for once-daily intragastric administration of different treatments for 3 months at 3 months after ovariectomy (OVX) as follows: sham + vehicle; OVX + vehicle; OVX + 750 mg/kg CP; OVX + CP-calcium citrate (75 mg/kg); OVX + calcium citrate (75 mg/kg). After euthanasia, the femurs were removed and analyzed by dual energy X-ray absorptiometry and micro-computed tomography, and serum samples were analyzed for bone metabolic markers.

Results

OVX rats supplemented with CPs or CP-calcium citrate showed osteoprotective effects, with reductions in the OVX-induced decreases in their femoral bone mineral density. Moreover, CP-calcium citrate prevented trabecular bone loss, improved the microarchitecture of the distal femur, and significantly inhibited bone loss with increased bone volume, connectivity density, and trabecular number compared with OVX control rats. CP or CP-calcium citrate administration significantly increased serum procollagen type I N-terminal propeptide levels and reduced serum bone-specific alkaline phosphatase, osteocalcin, and C-telopeptide of type I collagen levels.

Conclusions

Our data indicate that combined oral administration of bovine CPs with calcium citrate inhibits bone loss in OVX rats. The present findings suggest that combined oral administration of bovine CPs with calcium citrate is a promising alternative for reducing bone loss in osteopenic postmenopausal women.     

大鼠视网膜变性相关组织形态及功能研究

目的　探讨视网膜变性RCS (RoyalCollegeSurgeon)大鼠的视网膜形态及功能特点。 方法　应用HE染色、免疫组化染色和眼电生理技术 ,对比研究正常和变性两组大鼠视网膜特点。结果　 1 RCS大鼠在 3月龄时 ,视网膜外核层和感光细胞内外节完全消失 ;突触素免疫组化染色显示外丛状层不着色 ;视紫红质免疫组化染色显示原视网膜外层部位有阳性反应 ;胶质纤维酸性蛋白染色显示原视网膜外层部位有强阳性反应。 2 RCS大鼠的闪光视网膜电图 (flashelectronicretinogram ,FERG)a、b波振幅较正常Wistar大鼠明显降低 (P <0 0 1)。结论　在形态和功能上 ,3月龄RCS大鼠视网膜与人类晚期视网膜色素变性极为相似 ,因此可用于视网膜联合移植研究。     

热习服对大鼠肾脏促红细胞生成素的影响

目的:探讨热习服对大鼠肾脏促红细胞生成素的影响.方法:雄性SD大鼠21只,按体重配对随机分为对照组、单次高温暴露组(高温组)和热习服组,每组7只,各组在各自的实验条件下进行10天,对照组大鼠第11天留取肾脏组织标本;高温组和热习服组第11天进行相同条件的标准热负荷实验后留取肾脏组织标本.采用用酶联免疫吸附法(ELISA)定量测定肾脏组织中促红细胞生成素(Epo)含量,采用实时荧光定量PCR(RT-PCR)方法检测肾脏促红细胞生成素mRNA的表达,Western blot技术检测肾脏组织中促红细胞生成素蛋白表达水平的变化.结果:高温组与热习服大鼠肾脏促红细胞生成素水平明显高于对照大鼠(p＜0.05).热习服与高温组大鼠肾脏促红细胞生成素水平无明显差别.经RT-PCR检测,与对照组相比,高温组肾组织Epo mRNA表达显著增强(P＜0.05),而热习服组较高温组明显降低(P＜0.05),但仍然明显高于对照组的水平.Western blot实验中对照大鼠、高温组与热习服大鼠肾脏组织均有明显的Epo蛋白表达.与对照组相比,高温组Epo表达显著增强(P＜0.01),而热习服组较高温组明显降低(P＜0.05),但高于对照组的水平.结论:热习服后大鼠肾脏组织中促红细胞生成素含量明显升高,大鼠肾脏组织中促红细胞生成素mRNA与蛋白的表达均明显增强.提示热习服能显著提高肾脏Epo的表达水平,热习服后红细胞代谢变化可能与Epo水平提高有关.     

Neuroprotective Effect of Erythropoietin on Phenylhydrazine-Induced Hemolytic Hyperbilirubinemia in Neonatal Rats

Neonatal unconjugated hyperbilirubinemia might cause severe bilirubin neurotoxicity in especially hemolytic conditions. The study aimed to elucidate the potential neuroprotective effects of erythropoietin (EPO) in hemolysis-induced hyperbilirubinemia. In newborn rats, hyperbilirubinemia secondary to hemolysis was induced by injecting with phenylhydrazine hydrochloride (PHZ) and rats were injected with either vehicle or EPO. At 54th hour of the PHZ injection, rats were decapitated. Serum levels of TNF-α, IL-1β, IL-10, brain-derived neurotrophic factor (BDNF) and S100-B and brain malondialdehyde, glutathione levels and myeloperoxidase activities were measured. TUNEL staining and NF-κB expression were evaluated. As compared to control pups, in vehicle-treated PHZ group, TNF-α and IL-1β levels, malondialdehyde level and myeloperoxidase activity were increased with concomitant decreases in IL-10 and glutathione. All EPO regimens reversed PHZ-induced alterations in IL-10, TNF-α, malondialdehyde and glutathione levels. Three-day-treatment abolished increases in myeloperoxidase activity and IL-1β levels, while BDNF and S100-B were elevated. Increased TUNEL (+) cells and NF-κB expressions in the brain of PHZ group were reduced in the 3-day-treated group. EPO exerted anti-inflammatory effects on PHZ-induced neural damage in newborn rats, while the neuroprotection was more obvious when the treatments were repeated successively. The results suggest that EPO treatment may have a therapeutic potential in supporting neuroplasticity in the hyperbilirubinemic neonates.     

Cationic Liposome-Mediated Gene Delivery Via Systemic Administration

Abstract

Cationic liposomes have been studied as a potential carrier for delivering genes to cells for the purpose of gene therapy. This report summarizes our efforts to characterize the in vivo expression of transgene delivered by cationic liposomes via intravenous administrtion. Using a CMV driven gene expression system containing cDNA of luciferase or green fluorescence protein gene as a reporter and two commonly used cationic lipids, 2, 3-dioleoyloxypropyl-1-trimethyl ammonium chloride (DOTMA) and 2, 3-dioleoyloxyl-1-trimethylammonium propanyl chloride (DOTAP), we demonstrate that a significant level of gene expression can be obtained in different organs including the lung, heart, spleen, liver and kidneys following intravenous administration in the mouse. Our finding show that the transfection efficiency of cationic liposomes is determined by the structure of the cationic lipids, the lipid composition of liposomes and cationic lipid to DNA ratio. Furthermore, gene expression was short in duration, peaked between 4-24 hours post injection, and dropped to less than 1% of the peak level within a 4 day period. Experiments with repeated injections revealed that cells initially transfected by the first transfection were not fully responsive to the subsequent second transfection for approximately 14 days.     

A Biomathematical Model of Human Erythropoiesis under Erythropoietin and Chemotherapy Administration

Anaemia is a common haematologic side effect of dose-dense multi-cycle cytotoxic polychemotherapy requiring erythrocyte transfusions or erythropoietin (EPO) administration. To simulate the effectiveness of different EPO application schedules, we performed both modelling of erythropoiesis under chemotherapy and pharmacokinetic and dynamic modelling of EPO applications in the framework of a single comprehensive biomathematical model. For this purpose, a cell kinetic model of bone marrow erythropoiesis was developed that is based on a set of differential compartment equations describing proliferation and maturation of erythropoietic cell stages. The system is regulated by several feedback loops comprising those mediated by EPO. We added a model of EPO absorption after injection at different sites and a pharmacokinetic model of EPO derivatives to account for the effects of external EPO applications. Chemotherapy is modelled by a transient depletion of bone marrow cell stages. Unknown model parameters were determined by fitting the predictions of the model to data sets of circulating erythrocytes, haemoglobin, haematocrit, percentage of reticulocytes or EPO serum concentrations derived from the literature or cooperating clinical study groups. Parameter fittings resulted in a good agreement of model and data. Depending on site of injection and derivative (Alfa, Beta, Delta, Darbepoetin), nine groups of EPO applications were distinguished differing in either absorption kinetics or pharmacokinetics. Finally, eight different chemotherapy protocols were modelled. The model was validated on the basis of scenarios not used for parameter fitting. Simulations were performed to analyze the impact of EPO applications on the risk of anaemia during chemotherapy. We conclude that we established a model of erythropoiesis under chemotherapy that explains a large set of time series data under EPO and chemotherapy applications. It allows predictions regarding yet untested EPO schedules. Prospective clinical studies are needed to validate model predictions and to explore the feasibility and effectiveness of the proposed schedules.     

Erythropoietin Inhibits Gluconeogenesis and Inflammation in the Liver and Improves Glucose Intolerance in High-Fat Diet-Fed Mice

Erythropoietin (EPO) has multiple biological functions, including the modulation of glucose metabolism. However, the mechanisms underlying the action of EPO are still obscure. This study is aimed at investigating the potential mechanisms by which EPO improves glucose tolerance in an animal model of type 2 diabetes. Male C57BL/6 mice were fed with high-fat diet (HFD) for 12 weeks and then treated with EPO (HFD-EPO) or vehicle saline (HFD-Con) for two week. The levels of fasting blood glucose, serum insulin and glucose tolerance were measured and the relative levels of insulin-related phosphatidylinositol 3-kinase (PI3K)/Akt, insulin receptor (IR) and IR substrate 1 (IRS1) phosphorylation were determined. The levels of phosphoenolpyruvate carboxykinase (PEPCK), glucose-6- phosphatase (G6Pase), toll like receptor 4 (TLR4), tumor necrosis factor (TNF)-α and IL-6 expression and nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK), extracellular-signal-regulated kinase (ERK) and p38 MAPK activation in the liver were examined. EPO treatment significantly reduced the body weights and the levels of fasting blood glucose and serum insulin and improved the HFD-induced glucose intolerance in mice. EPO treatment significantly enhanced the levels of Akt, but not IR and IRS1, phosphorylation, accompanied by inhibiting the PEPCK and G6Pase expression in the liver. Furthermore, EPO treatment mitigated the HFD-induced inflammatory TNF-α and IL-6 production, TLR4 expression, NF-κB and JNK, but not ERK and p38 MAPK, phosphorylation in the liver. Therefore, our data indicated that EPO treatment improved glucose intolerance by inhibiting gluconeogenesis and inflammation in the livers of HFD-fed mice.     

Systemic Evaluation of Hypoxic-Ischemic Brain Injury in Neonatal Rats

The objective of the study was to evaluate the systematically rat model of neonatal hypoxic-ischemic brain damage. The right carotid arteries of 7-day-old healthy Wistar rats were ligated, and then, the rats were subjected to an environment with 8 % of oxygen. Four weeks after the birth, neurobehavioral test, water maze test, and motor-evoked potential and neuropathologic examinations were performed. The footprint analysis showed significantly larger and instable paces in the hypoxic-ischemic group (P < 0.05); the time that rats crossed the balance beam in the hypoxic-ischemic group was longer than the control group (P < 0.05). The water maze test showed that the escape latency of hypoxic-ischemic group was significantly longer than that of control group (P < 0.05). The hindlimb quadriceps compound muscle-evoked potential CMEP of rats in hypoxic-ischemic group showed that the wave amplitude was lower than that of control group (P < 0.05). HE staining showed visible periventricular leukomalacia in hypoxic-ischemic groups; disrupted nuclear membrane was detected in the IH group with transelectronmicroscopy; Immunohistochemistry: compared with control group, MBP-positive neurocytes decreased, glial fibrillary acidic protein positive neurocytes increased in the periventricular zone (P < 0.05). Carotid artery ligation combining the hypoxic chamber created a reliable and stable rat model of neonatal hypoxic-ischemic brain damage and can be used for experimental research related to management of cerebral palsy.     

Expression of Erythropoietin mRNA in the Brainstem of Rats Adapted to Intermittent Hypoxia

We studied the content of mRNA of a glycoprotein, erythropoietin, in structures of the rat brainstem; the animals were adapted to intermittent hypoxia at different contents of oxygen in hypoxic gas mixtures (12 or 7% О₂, a 2-week-long course with five sessions per day). Under conditions of such adaptation, the content of erythropoietin in the brainstem demonstrated a clear trend toward a decrease after a course of moderate hypoxic trainings (12% О₂), and a more than twofold drop after a “stronger” course (7% О₂). We suppose that the decrease in the intensity of synthesis of this glycoprotein     

Systemic Treatment with Erythropoietin Protects the Neurovascular Unit in a Rat Model of Retinal Neurodegeneration

Rats expressing a transgenic polycystic kidney disease (PKD) gene develop photoreceptor degeneration and subsequent vasoregression, as well as activation of retinal microglia and macroglia. To target the whole neuroglialvascular unit, neuro- and vasoprotective Erythropoietin (EPO) was intraperitoneally injected into four –week old male heterozygous PKD rats three times a week at a dose of 256 IU/kg body weight. For comparison EPO-like peptide, lacking unwanted side effects of EPO treatment, was given five times a week at a dose of 10 µg/kg body weight. Matched EPO treated Sprague Dawley and water-injected PKD rats were held as controls. After four weeks of treatment the animals were sacrificed and analysis of the neurovascular morphology, glial cell activity and pAkt localization was performed. The number of endothelial cells and pericytes did not change after treatment with EPO or EPO-like peptide. There was a nonsignificant reduction of migrating pericytes by 23% and 49%, respectively. Formation of acellular capillaries was significantly reduced by 49% (p<0.001) or 40% (p<0.05). EPO-treatment protected against thinning of the central retina by 10% (p<0.05), a composite of an increase of the outer nuclear layer by 12% (p<0.01) and in the outer segments of photoreceptors by 26% (p<0.001). Quantification of cell nuclei revealed no difference. Microglial activity, shown by gene expression of CD74, decreased by 67% (p<0.01) after EPO and 36% (n.s.) after EPO-like peptide treatment. In conclusion, EPO safeguards the neuroglialvascular unit in a model of retinal neurodegeneration and secondary vasoregression. This finding strengthens EPO in its protective capability for the whole neuroglialvascular unit.     

Neuropeptide Y Stimulates Feeding but Inhibits Sexual Behavior in Rats*

The effects of neuropeptide Y (NPY), a tyrosine-rich peptide found in the rat brain, on feeding and sexual behavior were studied in male and female rats. Intraventricular (ivt) injections of NPY during the final hours of the light period induced feeding in a dose-related manner. While the lowest dose tested (0.02 nM) was without effect, higher doses (0.12, 0.47, 2.3 nM) uniformly elicited feeding with a latency of about 15 min in male rats. With the most effective dose, 0.47 nM, the increased food intake was due to an increased local eating rate. In contrast, the pattern of feeding behavior after a related peptide, rat pancreatic polypeptide (rPP), was quite different and less impressive. During the first hour, only one ivt dose of rPP (0.45 nM) evoked an increase in food intake, due to an increased time spent eating. Further, the effects of NPY on food intake were greater during the nocturnal period. Interestingly, increased food intake in nocturnal tests (4 h) was due solely to augmented intake during the first 60 min after ivt administration. In mating tests, initiated 2 h after the onset of darkness and 10 min after ivt administration of peptide, all but the lowest dose of NPY (0.01 nM) drastically suppressed ejaculatory behavior. Most rats treated with higher doses of NPY (0.02, 0.12, or 0.47 nM) mounted and intromitted only a few times before the cessation of sexual activity, and elongated latencies to the initial mount and intromission were observed. In contrast to the dramatic NPY-induced suppression of ejaculatory behavior, rPP (0.11 and 0.45 nM) was without effect on copulatory behavior. To substantiate further that the impairment of sexual behavior seen in NPY-treated rats was not due to an attenuated sexual ability, an additional experiment was performed. Penile reflexes, including erection, were monitored 10 min after ivt injection of NPY (0.12 nM), rPP (0.11 nM), or saline. No effect of NPY or rPP was observed on the proportion of rats showing erection or latency to initial erection, or in the number of erections per test. In fact, a slight facilitation of penile dorsiflexion responses was seen after NPY. These findings suggest that NPY selectively depresses sexual motivation in the male rat. In ovariectomized female rats responding to estrogen plus progesterone with a good level of sexual receptivity (lordosis quotient > 70), ivt saline and 0.01 nM NPY were without effect on sexual behavior. However, higher doses of NPY (0.12 and 0.47 nM) promptly suppressed sexual behavior in tests initiated 10 min after treatment. A significant 50% decrement in receptivity and a virtual elimination of proceptive behavior were observed. Further, although a low level of mounting (one to five mounts in 15 min) was seen in both the saline (33% mounting) and the 0.01 nM NPY (38% mounting) treated groups, none was observed in animals treated with the higher NPY doses. These observations indicate that NPY may also suppress female sexual behavior.     

Therapeutic Effects of Topical Netrin-4 Inhibits Corneal Neovascularization in Alkali-Burn Rats

Netrins are secreted molecules involved in axon guidance and angiogenesis. However, the role of netrins in the vasculature remains unclear. Netrin-4 and netrin-1 have been found to be either pro- or antiangiogenic factors. Previously, we found that netrin-1 acts as an anti-angiogenic factor in rats by inhibiting alkali burn-induced corneal neovascularization. Here, we further investigate the effects of netrin-4, another member of the same netrin family, on neovascularization in vitro and in vivo. We found that netrin-4 functions similarly as netrin-1 in angiogenesis. In vitro angiogenesis assay shows that netrin-4 affected human umbilical vein endothelial cell (HUVEC) tube formation, viability and proliferation, apoptosis, migration, and invasion in a dose-dependent manner. Netrin-4 was topically applied in vivo to alkali-burned rat corneas on day 0 (immediately after injury) and/or day 10 post-injury. Netrin-4 subsequently suppressed and reversed corneal neovascularization. Netrin-4 inhibited corneal epithelial and stromal cell apoptosis, inhibited vascular endothelial growth factor (VEGF), but promoted pigment epithelium-derived factor (PEDF) expression, decreased NK-KB p65 expression, and inhibits neutrophil and macrophage infiltration. These results indicate that netrin-4 shed new light on its potential roles in treatmenting for angiogenic diseases that affect the ocular surface, as well as other tissues.     

Inhibitory Avoidance Learning Inhibits Ectonucleotidases Activities in Hippocampal Synaptosomes of Adult Rats

Several lines of evidence indicate that ATP may play an important role in Long-Term Potentiation. In this investigation we evaluated the effect of a memory task (step-down inhibitory avoidance) on the synaptosomal ecto-enzymes (ATP diphosphohydrolase and 5-nucleotidase) involved in the degradation of ATP to adenosine. After the training session, a decrease in the ATPase (40%) and ADPase (29%) activities of ATP diphosphohydrolase as well as was a decrease in 5-nucleotidase activity (31%) was observed in hippocampal synaptosomes of rats trained and killed immediately after training. In synaptosomes of rats killed 30 minutes after training, a decrease in ATPase activity (28%) was observed. In the test session, no significant changes were observed in the enzyme activities studied. These results provide new information about the activity of ecto-enzymes involved in nucleotide degradation and their possible participation in mechanisms of acquisition and modulation of memory processing.     

Systemic Administration of Proteasome Inhibitor Protects Against MPTP Neurotoxicity in Mice

Dysfunction of the proteasome has been suggested to contribute in the degeneration of nigrostriatal dopaminergic neurons. Here, we investigated to determine whether systematic administration of proteasome inhibitor, carbobenzoxy-l-γ-t-butyl-l-glutamyl-l-alanyl-l-leucinal (PSI) protects against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in mice. Three administrations of MPTP at 1-h intervals to mice reduced significantly the concentration of dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) in the striatum after 5 days. In contrast, PSI (0.3 and 1.0 mg/kg) prevented a significant decrease in dopamine, DOPAC and HVA contents of the striatum 5 days after MPTP treatment. In our Western blot analysis study, PSI at a dose of 1.0 mg/kg prevented a significant decrease in TH (tyrosine hydroxylase) protein and a significant increase in glial fibrillary acidic protein 5 days after MPTP treatment. Furthermore, our immunohistochemical study showed that PSI at a dose of 1.0 mg/kg prevented a significant loss in TH immunopositive neurons in the striatum and substantia nigra 5 days after MPTP treatment. In contrast, PSI caused a significant increase in the number of intense ubiquitin immunopositive cells in the striatum and substantia nigra 5 days after MPTP treatment. These results indicate that proteasome inhibitors can protect against MPTP neurotoxicity in mice. The neuroprotective effect of PSI against dopaminergic cell damage may be mediated by the elevation of ubiquitination. Thus, our findings provide further valuable information for the pathogenesis of Parkinson’s disease. Takuya Oshikawa and Hayato Kuroiwa contributed equally to this work.     

Correlation of Cytokine Levels and Microglial Cell Infiltration during Retinal Degeneration in RCS Rats

Microglial cells, which are immunocompetent cells, are involved in all diseases of the central nervous system. During their activation in various diseases, a variety of soluble factors are released. In the present study, the correlation between cytokine levels and microglial cell migration in the course of retinal degeneration of Royal College of Surgeons (RCS) rats was evaluated. MFG-E8 and CD11b were used to confirm the microglial cells. In the retina of RCS rats, the mRNA expression of seven genes (MFG-E8 and its integrins αυ and ß5, CD11b and the cytokines TNF-α, IL-1ß, and MCP-1) formed almost similar bimodal peak distributions, which were centred at P7 and P45 to P60. In contrast, in rdy rats, which comprised the control group, a unimodal peak distribution centred at P14 was observed. The gene expression accompanied the activation and migration of microglial cells from the inner to the outer layer of the retina during the process of degeneration. Principal component analysis and discriminant function analysis revealed that the expression of these seven genes, especially TNF-α and CD11b, positively correlated with retinal degeneration and microglial activity during retinal degeneration in RCS rats, but not in the control rats. Furthermore, linear regression analysis demonstrated a significant correlation between the expression of these genes and the activation of microglial cells in the dystrophic retina. Our findings suggest that the suppression of microglial cells and the blockade of their cytotoxic effects may constitute a novel therapeutic strategy for treating photoreceptor death in various retinal disorders.     

Guanidinoacetate Inhibits Glutamate Uptake in Rat Striatum of Rats at Different Ages

Glutamate plays a central role in the excitatory synaptic transmission and is important for brain development and functioning. Increased glutamate levels in the synaptic cleft are related to neuronal damage associated with excitotoxicity. Guanidinoacetate methyltransferase (GAMT) deficiency is an inherited neurometabolic disorder biochemically characterized by tissue accumulation of guanidinoacetate (GAA) and depletion of creatine. Affected patients present epilepsy and mental retardation whose pathogeny is unclear. In the present study we investigated the in vitro and in vivo (intrastriatal administration) effect of GAA on glutamate uptake by striatum slices of developing and adult rats. Results showed that GAA significantly inhibited in vitro glutamate uptake at 50 μM and 100 μM in all ages tested. We also tested the effect of taurine on the inhibition of glutamate uptake caused by GAA. Taurine significantly attenuated the inhibitory effect caused by 50 μM GAA, but did not alter that provoked by 100 μM GAA. Furthermore, intrastriatal administration of a solution of 30 μM GAA (0.06 nmol/striatum) significantly inhibited glutamate uptake by rat striatum slices. Our results suggest that the inhibition of striatal glutamate uptake caused by GAA might be involved in the neuropathology and especially in the acute neurological features present in patients with GAMT-deficiency.