N-acetylaspartylglutamate acts as an agonist upon homomeric NMDA receptor (NMDAR1) expressed in Xenopus oocytes.

The electrophysiological effects of N-acetylaspartylglutamate (NAAG), an endogenous peptide restrictively distributed in the central nervous system, were studied using Xenopus oocytes injected with RNAs transcribed from cloned glutamate receptor cDNAs. NAAG induced an inward current, dose dependently, in oocytes injected with RNA for an N-methyl-D-aspartate receptor subunit (NMDAR1). In contrast, the oocytes injected with RNAs for AMPA-selective glutamate receptors (GluR1, GluR3, GluR1+GluR2 and GluR2+GluR3) scarcely responded to NAAG, and the oocytes injected with RNA for kainate receptor (GluR6) did not respond to NAAG. The half-maximal response (ED50) value of NAAG on expressed NMDAR1 was 185 microM, which shows that NAAG is about 115-times less potent than L-glutamate (Glu), the ED50 of which value was 1.6 microM. The maximal current amplitude induced by NAAG was about 70% of that by Glu. NAAG-induced current in NMDAR1-injected oocytes was potentiated by glycine, dose-dependently antagonized by DL-2-amino-5-phosphonovaleric acid, and blocked by magnesium ions in a voltage-dependent fashion. These results suggest that NAAG is one of the endogenous agonists selective for NMDAR1.     

Effect of N-acetylaspartylglutamate (NAAG) on non-quantal and spontaneous quantal release of acetylcholine at the neuromuscular synapse of rat

N-Acetylaspartylglutamate (NAAG), known to be present in rat motor neurons, may participate in neuronal modulation of non-quantal secretion of acetylcholine (ACh) from motor nerve terminals. Non-quantal release of ACh was estimated by the amplitude of the endplate membrane hyperpolarization (H-effect) caused by inhibition of nicotinic receptors by (+)-tubocurarine and acetylcholinesterase by armin (diethoxy-p-nitrophenyl phosphate). Application of exogenous NAAG decreased the H-effect in a dose-dependent manner. The reduction of the H-effect by NAAG was completely removed when N-acetyl-beta-aspartylglutamate (betaNAAG) or 2-(phosphonomethyl)-pentanedioic acid (2-PMPA) was used to inhibit glutamate carboxypeptidase II (GCP II), a presynaptic Schwann cell membrane-associated ectoenzyme that hydrolyzes NAAG to glutamate and N-acetylaspartate. Bath application of glutamate decreased the H-effect similarly to the action of NAAG but N-acetylaspartate was without effect. Inhibition of NMDA receptors by dl-2-amino-5-phosphopentanoic acid, (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine (MK801), and 7-chlorokynurenic acid or inhibition of muscle nitric oxide synthase (NO synthase) by N(G)-nitro-l-arginine methyl ester and 3-bromo-7-nitroindazole completely prevented the decrease of the H-effect by NAAG. These results suggest that glutamate, produced by enzymatic hydrolysis of bath-applied NAAG, can modulate non-quantal secretion of ACh from the presynaptic terminal of the neuromuscular synapse via activation of postsynaptic NMDA receptors and synthesis of nitric oxide (NO) in muscle fibers. NAAG also increased the frequency of miniature endplate potentials (mEPPs) generated by spontaneous quantal secretion of ACh, whereas the mean amplitude and time constants for rise time and for decay of mEPPs did not change.     

Protease‐activated receptor‐1 modulates hippocampal memory formation and synaptic plasticity

Protease‐activated receptor‐1 (PAR1) is an unusual G‐protein coupled receptor (GPCR) that is activated through proteolytic cleavage by extracellular serine proteases. Although previous work has shown that inhibiting PAR1 activation is neuroprotective in models of ischemia, traumatic injury, and neurotoxicity, surprisingly little is known about PAR1's contribution to normal brain function. Here, we used PAR1?/? mice to investigate the contribution of PAR1 function to memory formation and synaptic function. We demonstrate that PAR1?/? mice have deficits in hippocampus‐dependent memory. We also show that while PAR1?/? mice have normal baseline synaptic transmission at Schaffer collateral‐CA1 synapses, they exhibit severe deficits in N‐methyl‐d ‐aspartate receptor (NMDAR)‐dependent long‐term potentiation (LTP). Mounting evidence indicates that activation of PAR1 leads to potentiation of NMDAR‐mediated responses in CA1 pyramidal cells. Taken together, this evidence and our data suggest an important role for PAR1 function in NMDAR‐dependent processes subserving memory formation and synaptic plasticity.     

突触前α7烟碱受体对海马神经元兴奋性突触传递的调控

采用盲法膜片钳技术观察突触前烟碱受体(nicotinic acetylcholinel receptors,nAChRs)对海马脑片CAl区锥体神经元兴奋性突触传递的调控作用。结果显示,nAChRs激动剂碘化二甲基苯基哌嗪(dimethylphenyl—piperazinium iodide,DMPP)不能在CAl区锥体神经元上诱发出烟碱电流。DMPP对CAl区锥体神经元自发兴奋性突触后电流(spontaneous excitatory postsynaptic current,sEPSC)具有明显的增频和增幅作用,并呈现明显的浓度依赖关系。DMPP对微小兴奋性突触后电流(miniature excitatory postsynaptic current,mEPSC)具有增频作用,但不具有增幅作用。上述DMPP增强突触传递的作用不能被nAChRs拮抗剂美加明、六烃季铵和双氢-β-刺桐丁所阻断,但可被α-银环蛇毒素阻断。上述结果提示,海马脑片CAl区锥体神经元兴奋性突触前nAChRs含有对α-银环蛇毒素敏感的胡亚单位,其激活可增强海马CAl区锥体神经元突触前递质谷氨酸的释放,从而对兴奋性突触传递发挥调控作用。     

Bioanalysis of N-acetyl-aspartyl-glutamate as a marker of glutamate carboxypeptidase II inhibition

We report the characterization of two methods for the analysis of N-acetyl-aspartyl-glutamate (NAAG) in biological fluids. In the first method, NAAG concentrations were calculated based on differences between glutamate concentrations before and after NAAG hydrolysis with exogenous glutamate carboxypeptidase II (GCP II) using high-performance liquid chromatography (HPLC) followed by fluorescence detection. In the second method, NAAG levels were quantified directly using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Analyses of NAAG levels in human cerebrospinal fluid samples using either method gave similar results within experimental error, confirming the validity of the two independent measurements. These methods will be useful in future clinical trials to assess drug-induced GCP II inhibition in biological matrices.     

Inhibition of NAALADase by 2‐PMPA attenuates cocaine‐induced relapse in rats: a NAAG‐mGluR2/3‐mediated mechanism

Pharmacological activation of group II metabotropic glutamate receptors (mGluR2/3) inhibits cocaine self‐administration and reinstatement of drug‐seeking behavior, suggesting a possible use of mGluR2/3 agonists in the treatment of cocaine dependence. In this study, we investigated whether elevation of the endogenous mGluR2/3 ligand N‐acetyl‐aspartatylglutamate (NAAG) levels by the N‐acetylated‐alpha‐linked‐acidic dipeptidase inhibitor 2‐(phosphonomethyl)pentanedioic acid (2‐PMPA) attenuates cocaine self‐administration and cocaine‐induced reinstatement of drug seeking. N‐acetylated‐alpha‐linked‐acidic dipeptidase is a NAAG degradation enzyme that hydrolyzes NAAG to N‐acetylaspartate and glutamate. Systemic administration of 2‐PMPA (10‐100 mg/kg, i.p.) inhibited intravenous self‐administration maintained by low unit doses of cocaine and cocaine (but not sucrose)‐induced reinstatement of drug‐seeking behavior. Microinjections of 2‐PMPA (3–5 μg/side) or NAAG (3–5 μg/side) into the nucleus accumbens (NAc), but not into the dorsal striatum, also inhibited cocaine‐induced reinstatement, an effect that was blocked by intra‐NAc injection of LY341495, a selective mGluR2/3 antagonist. In vivo microdialysis demonstrated that 2‐PMPA (10‐100 mg/kg, i.p.) produced a dose‐dependent reduction in both extracellular dopamine (DA) and glutamate, an effect that was also blocked by LY341495. Finally, pre‐treatment with 2‐PMPA partially attenuated cocaine‐enhanced extracellular NAc DA, while completely blocking cocaine‐enhanced extracellular NAc glutamate in rats during reinstatement testing. Intra‐NAc perfusion of LY341495 blocked 2‐PMPA‐induced reductions in cocaine‐enhanced extracellular NAc glutamate, but not DA. These findings suggest that 2‐PMPA is effective in attenuating cocaine‐induced reinstatement of drug‐seeking behavior, likely by attenuating cocaine‐induced increases in NAc DA and glutamate via pre‐synaptic mGluR2/3s.     

Role of protein kinase A in GABAA receptor dysfunction in CA1 pyramidal cells following chronic benzodiazepine treatment

One-week treatment with the benzodiazepine (BZ) flurazepam (FZP), results in anticonvulsant tolerance, associated with reduced GABAA receptor (GABAR) subunit protein and miniature inhibitory post-synaptic current (mIPSC) amplitude in CA1 neurons of rat hippocampus. Because protein kinase A (PKA) has been shown to modulate GABAR function in CA1 pyramidal cells, the present study assessed whether GABAR dysfunction is associated with changes in PKA activity. Two days after 1-week FZP treatment, there were significant decreases in basal (- 30%) and total (- 25%) PKA activity, and a 40% reduction in PKA RIIbeta protein in the insoluble fraction of CA1 hippocampus. The soluble component of CA1 showed a significant increase in basal (100%) but not total PKA activity. Whole-cell recording in vitro showed a 50% reduction in mIPSC amplitude in CA1 pyramidal cells, with altered sensitivity to PKA modulators. Neurons from FZP-treated rats responded to 8-bromo-cAMP with a significant increase (31%) in mIPSC amplitude. Likewise, vasoactive intestinal polypeptide (VIP), an endogenous PKA activator, caused a significant 36% increase in mIPSC amplitude in FZP-treated cells. Neither agent had a significant effect on mIPSC amplitude in control cells. This study supports a role for PKA in GABAR dysfunction after chronic FZP treatment.     

Mice lacking glutamate carboxypeptidase II are protected from peripheral neuropathy and ischemic brain injury

Excessive glutamate release is associated with neuronal damage. A new strategy for the treatment of neuronal injury involves inhibition of the neuropeptidase glutamate carboxypeptidase II (GCP II), also known as N-acetylated alpha-linked acidic dipeptidase. GCP II is believed to mediate the hydrolysis of N-acetyl-aspartyl-glutamate (NAAG) to glutamate and N-acetyl-aspartate, and inhibition of NAAG peptidase activity (by GCP II and other peptidases) is neuroprotective. Mice were generated in which the Folh1 gene encoding GCP II was disrupted (Folh1-/- mice). No overt behavioral differences were apparent between Folh1-/- mice and wild-type littermates, with respect to their overall performance in locomotion, coordination, pain threshold, cognition and psychiatric behavioral paradigms. Morphological analysis of peripheral nerves, however, showed significantly smaller axons (reduced myelin sheaths and axon diameters) in sciatic nerves from Folh1-/- mice. Following sciatic nerve crush, Folh1-/- mice suffered less injury and recovered faster than wild-type littermates. In a model of ischemic injury, the Folh1-/- mice exhibited a significant reduction (p < 0.05) in infarct volume compared with their wild-type littermates when subjected to middle cerebral artery occlusion, a model of stroke. These findings support the hypothesis that GCP II inhibitors may represent a novel treatment for peripheral neuropathies as well as stroke.     

NAAG peptidase inhibitor increases dialysate NAAG and reduces glutamate, aspartate and GABA levels in the dorsal hippocampus following fluid percussion injury in the rat

Traumatic brain injury (TBI) produces a rapid and excessive elevation in extracellular glutamate that induces excitotoxic brain cell death. The peptide neurotransmitter N-acetylaspartylglutamate (NAAG) is reported to suppress neurotransmitter release through selective activation of presynaptic group II metabotropic glutamate receptors. Therefore, strategies to elevate levels of NAAG following brain injury could reduce excessive glutamate release associated with TBI. We hypothesized that the NAAG peptidase inhibitor, ZJ-43 would elevate extracellular NAAG levels and reduce extracellular levels of amino acid neurotransmitters following TBI by a group II metabotropic glutamate receptor (mGluR)-mediated mechanism. Dialysate levels of NAAG, glutamate, aspartate and GABA from the dorsal hippocampus were elevated after TBI as measured by in vivo microdialysis. Dialysate levels of NAAG were higher and remained elevated in the ZJ-43 treated group (50 mg/kg, i.p.) compared with control. ZJ-43 treatment also reduced the rise of dialysate glutamate, aspartate, and GABA levels. Co-administration of the group II mGluR antagonist, LY341495 (1 mg/kg, i.p.) partially blocked the effects of ZJ-43 on dialysate glutamate and GABA, suggesting that NAAG effects are mediated through mGluR activation. The results are consistent with the hypothesis that inhibition of NAAG peptidase may reduce excitotoxic events associated with TBI.     

Protection against glucose-induced neuronal death by NAAG and GCP II inhibition is regulated by mGluR3

Glutamate carboxypeptidase II (GCP II) inhibition has previously been shown to be protective against long-term neuropathy in diabetic animals. In the current study, we have determined that the GCP II inhibitor 2-(phosphonomethyl) pentanedioic acid (2-PMPA) is protective against glucose-induced programmed cell death (PCD) and neurite degeneration in dorsal root ganglion (DRG) neurons in a cell culture model of diabetic neuropathy. In this model, inhibition of caspase activation is mediated through the group II metabotropic glutamate receptor, mGluR3. 2-PMPA neuroprotection is completely reversed by the mGluR3 antagonist (S)-alpha-ethylglutamic acid (EGLU). In contrast, group I and III mGluR inhibitors have no effect on 2-PMPA neuroprotection. Furthermore, we show that two mGluR3 agonists, the direct agonist (2R,4R)-4-aminopyrrolidine-2, 4-dicarboxylate (APDC) and N-acetyl-aspartyl-glutamate (NAAG) provide protection to neurons exposed to high glucose conditions, consistent with the concept that 2-PMPA neuroprotection is mediated by increased NAAG activity. Inhibition of GCP II or mGluR3 may represent a novel mechanism to treat neuronal degeneration under high-glucose conditions.     

Learning-dependent plasticity of hippocampal CA1 pyramidal neuron postburst afterhyperpolarizations and increased excitability after inhibitory avoidance learning depend upon basolateral amygdala inputs

Hippocampal pyramidal neurons in vitro exhibit transient learning-dependent reductions in the amplitude and duration of calcium-dependent postburst afterhyperpolarizations (AHPs), accompanied by other increases in excitability (i.e., increased firing rate, or reduced spike-frequency accommodation) after trace eyeblink conditioning or spatial learning, with a time-course appropriate to support consolidation of the learned tasks. Both these tasks require multiple days of training for acquisition. The hippocampus also plays a role in acquisition of single trial inhibitory avoidance learning. The current study assessed AHP plasticity in this single-trial learning task using in vitro tissue slices prepared at varying intervals posttrial using intracellular current-clamp recordings. Reduced AHPs and reduced accommodation were seen in ventral CA1 pyramidal neurons within 1 h posttraining, plasticity which persisted 24 h but was extinguished >72 h posttrial. There was also a reduction in ventral CA1 AHPs and accommodation 1 h following simple exposure to the IA apparatus (a novel context) but this change was extinguished by 24 h postexposure. Reductions in AHPs and accommodation were also seen in dorsal CA1 pyramidal neurons, but were delayed until 24 h posttrial and extinguished at >72 h posttrial. Finally, transient inactivation of the basolateral complex of the amygdala (with the local anesthetics lidocaine or bupivacaine) either immediately before or immediately posttrial blocked both learning and learning-dependent changes in excitability in the hippocampus assessed 24 h posttrial. CA3 pyramidal neurons showed no reductions in AHP peak amplitude or accommodation following IA training or context exposure.     

Sustained saturating level of glycine induces changes in NR2B-containing-NMDA receptor localization in the CA1 region of the hippocampus

Post-synaptic actions of glycine are terminated by specialized transporters. There are two genes encoding glycine transporters, GlyT1 and GlyT2. Glycine acts as a co-agonist at N -methyl- d -aspartate glutamatergic receptors (NMDARs). Blockage of GlyT1 enhances NMDAR function by controlling ambient glycine concentrations. Using whole-cell patch-clamp recordings of acute hippocampal slices, we investigated NMDAR kinetics of CA1 pyramidal neurons of mice expressing 50% of GlyT1 (GlyT1+/−). In this study, we report that the glycine modulatory site of the NMDAR at CA1 synapses is saturated in GlyT1+/− but not in wild-type (WT) mice. We also found that the effect of ifenprodil, a highly selective NR2B-containing-NMDAR antagonist, is significantly reduced at CA1 synapses in GlyT1+/− compared to WT mice while immunoblotting experiments do not show significant differences for NR1, NR2A-B-C-D subunits in both types of mice, suggesting alteration in NR2B-containing-NMDAR localization under a state of chronic saturating level of endogenous glycine. Using a pharmacological approach with MK-801 and DL-TBOA, we discriminated synaptic vis-à-vis extra-synaptic NMDARs. We found that NR2B-containing-NMDARs are expressed at a higher level in the extra-synaptic area of CA1 pyramidal neurons from GlyT1+/− compared to WT mice. Our results demonstrate that chronic saturating level of glycine induces significant changes in NMDAR localization and kinetic. Therefore, results from our study should help to gain a better understanding of the role of glycine in pathological conditions.     

Chronic opioid potentiates presynaptic but impairs postsynaptic N-methyl-D-aspartic acid receptor activity in spinal cords: implications for opioid hyperalgesia and tolerance

Opioids are the most effective analgesics for the treatment of moderate to severe pain. However, chronic opioid treatment can cause both hyperalgesia and analgesic tolerance, which limit their clinical efficacy. In this study, we determined the role of pre- and postsynaptic NMDA receptors (NMDARs) in controlling increased glutamatergic input in the spinal cord induced by chronic systemic morphine administration. Whole-cell voltage clamp recordings of excitatory postsynaptic currents (EPSCs) were performed on dorsal horn neurons in rat spinal cord slices. Chronic morphine significantly increased the amplitude of monosynaptic EPSCs evoked from the dorsal root and the frequency of spontaneous EPSCs, and these changes were largely attenuated by blocking NMDARs and by inhibiting PKC, but not PKA. Also, blocking NR2A- or NR2B-containing NMDARs significantly reduced the frequency of spontaneous EPSCs and the amplitude of evoked EPSCs in morphine-treated rats. Strikingly, morphine treatment largely decreased the amplitude of evoked NMDAR-EPSCs and NMDAR currents of dorsal horn neurons elicited by puff NMDA application. The reduction in postsynaptic NMDAR currents caused by morphine was prevented by resiniferatoxin pretreatment to ablate TRPV1-expressing primary afferents. Furthermore, intrathecal injection of the NMDAR antagonist significantly attenuated the development of analgesic tolerance and the reduction in nociceptive thresholds induced by chronic morphine. Collectively, our findings indicate that chronic opioid treatment potentiates presynaptic, but impairs postsynaptic, NMDAR activity in the spinal cord. PKC-mediated increases in NMDAR activity at nociceptive primary afferent terminals in the spinal cord contribute critically to the development of opioid hyperalgesia and analgesic tolerance.     

Specificity and actions of an arylaspartate inhibitor of glutamate transport at the Schaffer collateral-CA1 pyramidal cell synapse

In this study we characterized the pharmacological selectivity and physiological actions of a new arylaspartate glutamate transporter blocker, L-threo-ß-benzylaspartate (L-TBA). At concentrations up to 100 µM, L-TBA did not act as an AMPA receptor (AMPAR) or NMDA receptor (NMDAR) agonist or antagonist when applied to outside-out patches from mouse hippocampal CA1 pyramidal neurons. L-TBA had no effect on the amplitude of field excitatory postsynaptic potentials (fEPSPs) recorded at the Schaffer collateral-CA1 pyramidal cell synapse. Excitatory postsynaptic currents (EPSCs) in CA1 pyramidal neurons were unaffected by L-TBA in the presence of physiological extracellular Mg²⁺ concentrations, but in Mg²⁺-free solution, EPSCs were significantly prolonged as a consequence of increased NMDAR activity. Although L-TBA exhibited approximately four-fold selectivity for neuronal EAAT3 over glial EAAT1/EAAT2 transporter subtypes expressed in Xenopus oocytes, the L-TBA concentration-dependence of the EPSC charge transfer increase in the absence of Mg²⁺ was the same in hippocampal slices from EAAT3 +/+ and EAAT3 −/− mice, suggesting that TBA effects were primarily due to block of glial transporters. Consistent with this, L-TBA blocked synaptically evoked transporter currents in CA1 astrocytes with a potency in accord with its block of heterologously expressed glial transporters. Extracellular recording in the presence of physiological Mg²⁺ revealed that L-TBA prolonged fEPSPs in a frequency-dependent manner by selectively increasing the NMDAR-mediated component of the fEPSP during short bursts of activity. The data indicate that glial glutamate transporters play a dominant role in limiting extrasynaptic transmitter diffusion and binding to NMDARs. Furthermore, NMDAR signaling is primarily limited by voltage-dependent Mg²⁺ block during low-frequency activity, while the relative contribution of transport increases during short bursts of higher frequency signaling.     

产前应激对子代大鼠海马CA3区神经元Ca2+和K+通道的影响

本研究的目的在于探讨产前应激对子代大鼠海马CA3神经元高电压激活(HVA)钙通道、延迟整流钾电流(delayedrectifierpotassiumcurrents,IKD)的影响。产前应激(prenatalstress,PNS)组孕鼠孕晚期给予束缚应激,应用全细胞膜片钳技术进行研究。结果显示产前应激增加了子代海马CA3神经元HVA钙通道峰电流幅值,对照组和产前应激组子代CA3神经元平均最大HVA钙电流峰值分别为-576.52±7.03pA和-702.05±6.82pA(P<0.01)。同时未改变其电导-电压关系,也未改变延迟整流钾通道电流-电压关系、电导-电压关系。结果提示,在胎儿发育的关键时期,给予母体产前应激,引起子代海马神经元HVA钙电流增加,其机制一方面PNS导致皮质酮升高,从而可能增加HVA钙通道mRNA表达;另一方面PNS所致反应性氧化产物(reactiveoxygenspecies,ROS)增多,后者可能通过磷酸化HVACa2 通道亚单位,从而提高HVA钙电流幅值。     

Plasmin potentiates synaptic N-methyl-D-aspartate receptor function in hippocampal neurons through activation of protease-activated receptor-1

Protease-activated receptor-1 (PAR1) is activated by a number of serine proteases, including plasmin. Both PAR1 and plasminogen, the precursor of plasmin, are expressed in the central nervous system. In this study we examined the effects of plasmin in astrocyte and neuronal cultures as well as in hippocampal slices. We find that plasmin evokes an increase in both phosphoinositide hydrolysis (EC(50) 64 nm) and Fura-2/AM fluorescence (195 +/- 6.7% above base line, EC(50) 65 nm) in cortical cultured murine astrocytes. Plasmin also activates extracellular signal-regulated kinase (ERK1/2) within cultured astrocytes. The plasmin-induced rise in intracellular Ca(2+) concentration ([Ca(2+)](i)) and the increase in phospho-ERK1/2 levels were diminished in PAR1(-/-) astrocytes and were blocked by 1 microm BMS-200261, a selective PAR1 antagonist. However, plasmin had no detectable effect on ERK1/2 or [Ca(2+)](i) signaling in primary cultured hippocampal neurons or in CA1 pyramidal cells in hippocampal slices. Plasmin (100-200 nm) application potentiated the N-methyl-D-aspartate (NMDA) receptor-dependent component of miniature excitatory postsynaptic currents recorded from CA1 pyramidal neurons but had no effect on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate- or gamma-aminobutyric acid receptor-mediated synaptic currents. Plasmin also increased NMDA-induced whole cell receptor currents recorded from CA1 pyramidal cells (2.5 +/- 0.3-fold potentiation over control). This effect was blocked by BMS-200261 (1 microm; 1.02 +/- 0.09-fold potentiation over control). These data suggest that plasmin may serve as an endogenous PAR1 activator that can increase [Ca(2+)](i) in astrocytes and potentiate NMDA receptor synaptic currents in CA1 pyramidal neurons.     

Role of AMPA receptor cycling in synaptic transmission and plasticity

Compounds known to disrupt exocytosis or endocytosis were introduced into CA1 pyramidal cells while monitoring excitatory postsynaptic currents (EPSCs). Disrupting exocytosis or the interaction of GluR2 with NSF caused a gradual reduction in the AMPAR EPSC, while inhibition of endocytosis caused a gradual increase in the AMPAR EPSC. These manipulations had no effect on the NMDAR EPSC but prevented the subsequent induction of LTD. These results suggest that AMPARs, but not NMDARs, cycle into and out of the synaptic membrane at a rapid rate and that certain forms of synaptic plasticity may utilize this dynamic process.     

NAAG peptidase inhibition reduces locomotor activity and some stereotypes in the PCP model of schizophrenia via group II mGluR

Phencyclidine (PCP) administration elicits positive and negative symptoms that resemble those of schizophrenia and is widely accepted as a model for the study of this human disorder. Group II metabotropic glutamate receptor (mGluR) agonists have been reported to reduce the behavioral and neurochemical effects of PCP. The peptide neurotransmitter, N-acetylaspartylglutamate (NAAG), is a selective group II agonist. We synthesized and characterized a urea-based NAAG analogue, ZJ43. This novel compound is a potent inhibitor of enzymes, glutamate carboxypeptidase II (K(i) = 0.8 nM) and III (K(i) = 23 nM) that deactivate NAAG following synaptic release. ZJ43 (100 microM) does not directly interact with NMDA receptors or metabotropic glutamate receptors. Administration of ZJ43 significantly reduced PCP-induced motor activation, falling while walking, stereotypic circling behavior, and head movements. To test the hypothesis that this effect of ZJ43 was mediated by increasing the activation of mGluR3 via increased levels of extracellular NAAG, the group II mGluR selective antagonist LY341495 was co-administered with ZJ43 prior to PCP treatment. This antagonist completely reversed the effects of ZJ43. Additionally, LY341495 alone increased PCP-induced motor activity and head movements suggesting that normal levels of NAAG act to moderate the effect of PCP on motor activation via a group II mGluR. These data support the view that NAAG peptidase inhibitors may represent a new therapeutic approach to some of the components of schizophrenia that are modeled by PCP.     

二氧化硫衍生物对大鼠海马CA3区神经元瞬间外向钾电流的影响

为研究二氧化硫(SO2)衍生物——NaHSO3和Na2SO3(二者分子比为1：3)对大鼠海马CA3区神经元瞬间外向钾电流(IA)的影响,利用全细胞膜片钳技术,根据动力学和药理学特性分离鉴定大鼠海马CA3区神经元IA,观察SO2衍生物对IA的效应。发现SO2代谢衍生物可浓度依赖性地增大IA,使IA增大50％的剂量为25μmol/L。此外还与电压呈依赖关系,但不具有频率依赖性。10μmol/L的SO2代谢衍生物不影响IA电流的激活过程,但升高了A-通道稳态失活电压,延长了A-电流失活时间。说明SO2代谢衍生物可增大大鼠海马CA3区神经元IA电流,延长A-电流的失活时间,从而影响海马神经元的膜生理感应,这可能是SO2影响神经细胞功能的机理之一。