Electron tomography on γ‐aminobutyric acid‐ergic synapses reveals a discontinuous postsynaptic network of filaments

The regulation of synaptic strength at γ‐aminobutyric acid (GABA)‐ergic synapses is dependent on the dynamic capture, retention, and modulation of GABA A‐type receptors by cytoplasmic proteins at GABAergic postsynaptic sites. How these proteins are oriented and organized in the postsynaptic cytoplasm is not yet established. To better understand these structures and gain further insight into the mechanisms by which they regulate receptor populations at postsynaptic sites, we utilized electron tomography to examine GABAergic synapses in dissociated rat hippocampal cultures. GABAergic synapses were identified and selected for tomography by using a set of criteria derived from the structure of immunogold‐labeled GABAergic synapses. Tomography revealed a complex postsynaptic network composed of filaments that extend ～100 nm into the cytoplasm from the postsynaptic membrane. The distribution of these postsynaptic filaments was strikingly similar to that of the immunogold label for gephyrin. Filaments were interconnected through uniform patterns of contact, forming complexes composed of 2–12 filaments each. Complexes did not link to form an integrated, continuous scaffold, suggesting that GABAergic postsynaptic specializations are less rigidly organized than glutamatergic postsynaptic densities. J. Comp. Neurol. 522:921–936, 2014. © 2013 Wiley Periodicals, Inc.     

Characterization of the novel GlyT1 PET tracer [18F]MK‐6577 in humans

Decreased glutamatergic neurotransmission is hypothesized to be involved in the pathophysiology of schizophrenia. Inhibition of glycine transporter Type‐1 (GlyT1) reuptake is expected to increase the glutamatergic neurotransmission and may serve as treatment for cognitive and negative symptoms of schizophrenia. In this article, we present human data from a novel GlyT1 PET tracer, [¹⁸F]MK‐6577. In the process of developing a GlyT1 inhibitor therapeutic, a PET tracer can assist in determining the dose with a high probability of sufficiently testing the mechanism of action. This article reports the human PET studies with [¹⁸F]MK‐6577 for measuring GlyT1 receptor availability at baseline in normal human subjects and occupancy with a GlyT1 inhibitor, MK‐2637. Studies were also performed to measure radiation burden and the baseline test‐retest (T‐RT) variability of the tracer. The effective dose from sequential whole‐body dosimetry scans in three male subjects was estimated to be 24.5 ± 2.9 µSV/MBq (mean ± SD). The time–activity curves from T‐RT scans modeled satisfactorily using a two tissue compartmental model. The tracer uptake was highest in the pons (V_T = 6.7 ± 0.9, BP_ND = 4.1 ± 0.43) and lowest in the cortex (V_T = 2.1 ± 0.5, BP_ND = 0.60 ± 0.23). V_T T‐RT variability measured in three subjects was <12% on average. The occupancy scans performed in a cohort of 15 subjects indicated absence of a reference region. The in vivo potency (Occ₅₀) of MK‐2637 was determined using two methods: A: Lassen plot with a population input function (Occ₅₀ = 106 nM, SE = 20 nM) and B: pseudo reference tissue model using cortex as the pseudo reference region (Occ₅₀ = 141 nM, SE = 21 nM). Synapse 69:33–40, 2015. © 2014 Wiley Periodicals, Inc.     

不同冻干保护剂对利巴韦林冻干粉针的影响研究

目的研究Emprove低内毒素蔗糖、无水乳糖、Emprove低内毒素葡萄糖、Emprove低内毒素甘露醇、Emprove低内毒素山梨醇、Emprove低内毒素氯化钾、Emprove低内毒素甘氨酸7种不同类型常用冻干保护剂对利巴韦林冻干粉针性能的影响。方法以外观和复溶效果为指标,考察了预冻时间、冻干保护剂用量、冻干时间的影响。测定了空白粉针剂和利巴韦林粉针剂冻干后含水量、p H值和利巴韦林质量分数。结果以无水乳糖为冻干保护剂,预冻时间6 h,冻干时间9 h,保护剂用量4%;以Emprove低内毒素氯化钾为冻干保护剂,预冻时间9 h,冻干时间9 h,保护剂用量4%;以Emprove低内毒素甘露醇为冻干保护剂,预冻时间6 h,冻干时间6 h,保护剂用量4%;以Emprove低内毒素甘氨酸为冻干保护剂,预冻时间12 h,冻干时间9 h,保护剂用量4%。所得冻干粉针外观饱满、平整,迅速、完全复溶。结论无水乳糖、Emprove低内毒素氯化钾、Emprove低内毒素甘露醇、Emprove低内毒素甘氨酸4种冻干保护剂更适合制备利巴韦林冻干粉针,可为水溶性药物冻干粉针剂的制备提供了参考。     

甘氨酸通过PTEN/Akt通路减轻脑出血大鼠神经损伤

探讨甘氨酸对脑出血大鼠神经损伤的保护作用及其机制。将48只大鼠随机分为假手术组、模型组、甘氨酸组(分别给予0.5 mg/kg或2 mg/kg甘氨酸)。采用侧脑室注射自体血建立大鼠脑出血模型;干湿重法检测脑组织含水量,甲酰胺法检测血脑屏障通透性,原位末端标记法(TUNEL)法检测脑组织细胞凋亡的情况,实时聚合酶链反应(Real-time PCR)检测蛋白激酶B(Akt)、磷酸酶与张力蛋白同源物基因(PTEN)mRNA的表达,免疫印迹(Western blot)法检测脑组织中Akt、PTEN蛋白的表达水平。结果显示,与模型组比较,2 mg/kg甘氨酸组大鼠脑组织含水量、EB含量、血肿块体积、凋亡细胞数量显著降低,Akt mRNA和蛋白的表达显著升高,PTEN mRNA和蛋白的表达水平显著降低(P＜0.05)。结果表明甘氨酸对大鼠脑出血造成的大鼠脑神经的损伤有一定的保护作用,这可能与甘氨酸干预的PTEN/Akt通路有关。     

ON-OFF Interactions in the Retina: Role of Glycine and GABA

In the vertebrate retina, visual signals are segregated into parallel ON and OFF pathways, which provide information for light increments and decrements. The segregation is first evident at the level of the ON and OFF bipolar cells and it apparently remains as signals propagate to higher brain visual centers. A fundamental question in visual neuroscience is how these two parallel pathways function: are they independent from each other or do they interact somehow? In the latter case, what kinds of mechanisms are involved and what are the consequences from this cross-talk? This review summarizes current knowledge about the types of interactions between the ON and OFF channels in nonmammalian and mammalian retina. Data concerning the ON-OFF interactions in distal retina revealed by recording of single bipolar cell activity and electroretinographic ON (b-wave) and OFF (d-wave) responses are presented. Special emphasis is put on the ON-OFF interactions in proximal retina and their dependence on the state of light adaptation in mammalian retina. The involvement of the GABAergic and glycinergic systems in the ON-OFF crosstalk is also discussed.     

Novel nootropic drug sunifiram enhances hippocampal synaptic efficacy via glycine‐binding site of N‐methyl‐D‐aspartate receptor

Sunifiram is a novel pyrrolidone nootropic drug structurally related to piracetam, which was developed for neurodegenerative disorder like Alzheimer's disease. Sunifiram is known to enhance cognitive function in some behavioral experiments such as Morris water maze task. To address question whether sunifiram affects N‐methyl‐D ‐aspartate receptor (NMDAR)‐dependent synaptic function in the hippocampal CA1 region, we assessed the effects of sunifiram on NMDAR‐dependent long‐term potentiation (LTP) by electrophysiology and on phosphorylation of synaptic proteins by immunoblotting analysis. In mouse hippocampal slices, sunifiram at 10–100 nM significantly enhanced LTP in a bell‐shaped dose‐response relationship which peaked at 10 nM. The enhancement of LTP by sunifiram treatment was inhibited by 7‐chloro‐kynurenic acid (7‐ClKN), an antagonist for glycine‐binding site of NMDAR, but not by ifenprodil, an inhibitor for polyamine site of NMDAR. The enhancement of LTP by sunifilam was associated with an increase in phosphorylation of α‐amino‐3‐hydroxy‐5‐methylisozazole‐4‐propionate receptor (AMPAR) through activation of calcium/calmodulin‐dependent protein kinase II (CaMKII) and an increase in phosphorylation of NMDAR through activation of protein kinase Cα (PKCα). Sunifiram treatments at 1–1000 nM increased the slope of field excitatory postsynaptic potentials (fEPSPs) in a dose‐dependent manner. The enhancement was associated with an increase in phosphorylation of AMPAR receptor through activation of CaMKII. Interestingly, under the basal condition, sunifiram treatments increased PKCα (Ser‐657) and Src family (Tyr‐416) activities with the same bell‐shaped dose‐response curve as that of LTP peaking at 10 nM. The increase in phosphorylation of PKCα (Ser‐657) and Src (Tyr‐416) induced by sunifiram was inhibited by 7‐ClKN treatment. The LTP enhancement by sunifiram was significantly inhibited by PP2, a Src family inhibitor. Finally, when pretreated with a high concentration of glycine (300 μM), sunifiram treatments failed to potentiate LTP in the CA1 region. Taken together, sunifiram stimulates the glycine‐binding site of NMDAR with concomitant PKCα activation through Src kinase. Enhancement of PKCα activity triggers to potentiate hippocampal LTP through CaMKII activation. © 2013 Wiley Periodicals, Inc.     

Inborn errors of creatine metabolism and epilepsy

Creatine metabolism disorders include guanidinoacetate methyltransferase (GAMT) deficiency, arginine:glycine amidinotransferase (AGAT) deficiency, and the creatine transporter (CT1‐encoded by SLC6A8 gene) deficiency. Epilepsy is one of the main symptoms in GAMT and CT1 deficiency, whereas the occurrence of febrile convulsions in infancy is a relatively common presenting symptom in all the three above‐mentioned diseases. GAMT deficiency results in a severe early onset epileptic encephalopathy with development arrest, neurologic deterioration, drug‐resistant seizures, movement disorders, mental disability, and autistic‐like behavior. In this disorder, epilepsy and associated abnormalities on electroencephalography (EEG) are more responsive to substitutive treatment with creatine monohydrate than to conventional antiepileptic drugs. AGAT deficiency is mainly characterized by mental retardation and severe language disorder without epilepsy. In CT1 deficiency epilepsy is generally less severe than in GAMT deficiency. All creatine disorders can be investigated through measurement of creatine metabolites in body fluids, brain proton magnetic resonance spectroscopy (¹H‐MRS), and molecular genetic techniques. Blood guanidinoacetic acid (GAA) assessment and brain H‐MRS examination should be part of diagnostic workup for all patients presenting with epileptic encephalopathy of unknown origin. In girls with learning and/or intellectual disabilities with or without epilepsy, SLC6A8 gene assessment should be part of the diagnostic procedures. The aims of this review are the following: (1) to describe the electroclinical features of epilepsy occurring in inborn errors of creatine metabolism; and (2) to delineate the metabolic alterations associated with GAMT, AGAT, and CT1 deficiency and the role of a substitutive therapeutic approach on their clinical and electroencephalographic epileptic patterns.     

Inhibitory neuromodulators do not alter the course of experimental hepatic encephalopathy

The neuromodulators, adenosine, serotonin, and glycine, did not alter the course of hepatic encephalopathy (HE) that followed a portacaval shunt and hepatic artery ligation in rats. The substances were instilled into the brain ventricle through an intraventricular cannula in doses that affect other aspects of behavior in the normal rat (adenosine, suppression of food intake; serotonin, loss of muscle strength and ataxia; glycine, leaning and circling). A subconvulsive dose of the glycine antagonist, strychnine, also had no effect on the course of HE. A large dose of the adenosine antagonist, caffeine, had a depressive rather than excitatory effect and shortened the time taken to induction of coma. These studies and a similar previous one with -aminobutyric acid (GABA) suggest that the inhibitory neuromodulators do not have a prominent role in the pathogenesis of hepatic coma.