NMDA受体在海马CA_3区习得性LTP保持中的作用

在大鼠明暗分辨学习的建立和巩固过程中,通过与记录电极一起慢性埋植于海马CA_3区的注药管微量注射NMDA受体的特异性拮抗剂2-amino-5-phosphonovaleric acid(APV),观察对海马CA_3区突触效应及与之相关的习得性行为的影响。结果如下:(1)在动物经训练PS峰幅值刚增大至最高水平后,即在习得性LTP刚好形成后,每实验单元先于CA_3区注射AFV 1μl(2mmol/L),然后在药物有效作用时间内再进行训练,则PS峰值不能随训练而保持在最高水平,相反经8个实验单元,PS峰值降至实验前水平;相应地动物的正确反应率不能随训练而巩固,反而下降至10％以下。(2)在动物习得性LTP已形成并经一单元训练PS保持在最高水平后,于每实验单元训练前注射APV 1μl(2mmol/L),PS峰值同样不会随训练而保持在最高水平,经14个实验单元注药和训练,PS峰值逐渐降至实验前水平,相应地动物行为的正确反应率也降至10％以下,习得性行为消退,不过其消退速度比前一情况的动物为慢,说明习得性LTP发展情况不同,APV的作用效率有差别。结果表明:NMDA受体在习得性LTP的巩固中起着重要作用。     

Studies on the biological activity of an insulin-stimulating peptide from a tryptic digest of bovine serum albumin

Summary A two-chain polypeptide, which corresponds to amino acid residues 115–143 and 144–184(185) of bovine serum albumin, connected to each other by a disulfide bridge, potentiated the effects of insulin on glucose transport and glucose metabolism in isolated rat adipocytes. Although the peptide alone had little activity, it shifted the concentration-response curves of insulin-stimulated D-[I-¹⁴C]glucose oxidation, 2-deoxyglucose transport, and lipid synthesis from D-[U-¹⁴C]glucose to lower insulin concentrations. It also increased the maximal responses of these parameters to insulin. However, it did not affect insulin binding to adipocytes. The peptide protected insulin considerably from degradation, but this effect alone cannot account for its effect in increasing the maximal responses to the hormone, and even when degradation of a submaximal concentration of insulin was suppressed by bacitracin, the peptide still had an enhancing effect. These results suggest not only that the peptide influences a step distal to receptor-mediated insulin binding but also that inhibition of insulin degradation alone cannot explain its total effect.The peptide lost its insulin-stimulating activity completely when it was further digested with V8 or lysinespecific endopeptidase, or when it was reduced and then carboxamidomethylated or oxidized with performic acid. Similar active tryptic fragments were obtained from human and rat albumins.Insulin-stimulating peptides should be useful in studies on the mechanisms of insulin action including both the sensitivities and responsiveness of target cells to the hormone.Abbreviations ISP insulin-stimulating peptide - HEPES N-(2-hydroxyethyl)piperazine-N-2-ethanesulfonic acid - HPLC high-performance liquid chromatography - SDS sodium dodecyl sulfate     

N-Methyl-d-Aspartate Receptor Proteins NR2A and NR2B Are Differentially Distributed in the Developing Rat Central Nervous System as Revealed by Subunit-Specific Antibodies

Abstract: We have identified the regional distributions and developmental expression of NMDA-receptor proteins NR2A and NR2B in rat CNS, using two subunit-specific affinity-purified polyclonal antibodies that recognize NR2A and NR2B. In western blots of cells transfected with NR2A or NR2B cDNAs, and of brain homogenates, each antibody detects a single predominant 172-kDa protein corresponding to its homologous subunit. Both subunits are glycoproteins that are enriched in synaptic membranes. In adult rat CNS, NR2A and NR2B are enriched in cortex and hippocampus but are present in other forebrain regions. In hindbrain, NR2A is present at low levels but NR2B is barely detectable. These subunits are differentially expressed in postnatal CNS development. In cortex and striatum, NR2A is absent at birth but expression increases thereafter, whereas NR2B is expressed at nearly adult levels during forebrain development. In hindbrain, low levels of NR2A are present throughout development, whereas NR2B is expressed only transiently in the first postnatal weeks. These results suggest that native NMDA receptors are modulated by NR2A and NR2B in adult forebrain but not appreciably in hindbrain. In contrast, during early postnatal development, NR2B may have a more dominant role than NR2A in modulating NMDA receptors throughout the CNS. Thus, transient changes in NMDA-receptor function may occur during maturation of certain neuronal and/or glial populations via differential expression of NR2A and NR2B subunits.     

Nitric oxide and carbon monoxide as possible retrograde messengers in hgippocampal long-term potentiation

We have been investigating the hypothesis that the membrane-permeant molecules nitric oxide (NO) and carbon monoxide(CO) may act as retrograde messengers during long-term potentiation (LTP). Inhibitors of either NO synthase or heme oxygenase, the enzyme that produces CO, blocked induction of LTP in the CA1 region of hippocampal slices. Brief application of either NO or CO to slices produced a rapid and long-lasting increase in the size of synaptic potentials if, and only if, the application occurred at the same time as weak tetanic stimulation of the presynaptic fibers. The long-term enhancement by NO or CO was spatially restricted to synapses from active presynaptic fibers and appeared to involve mechanisms utilized by LTP, occluding the subsequent induction of LTP by strong tetanic stimulation. The enhancement by No or CO was not blocked by the NMDA receptor blocker APV, suggesting that NO and CO act downstream for the NMDA receptor. In other systems, both NO and CO produce many of their effects by activation of soluble guanylyl cyclase nd cGMP-dependent protein kinase. An inhibitor of soluble guabylyl cyclase blocked the induction of normal LTP. Conversely, membrane-permeabel analog 8-Br-cGMP produced a rapid onset and long-lasting synaptic enhancement if, and only if, it was applied at the same time as weak presynaptic stimulation. Similarly, two inhibitors of cGMP-dependent protein kinase blocked the induction of normal LTP, and a selective activator of cGMP-dependent protein kinase produced activity-dependent long-lasting synaptic enhancement. 8-Br-cGMP also produced and activity-dependent, long-lasting increase in the amplitude of evoked synaptic current between pairs of hippocampal neurons in dissociated cell culture. In addition, 8-Br-cGMP, like NO, produced a long-lasting increase in the frequency of spontaneous miniature synaptic currents. These results are consistent with the hypothesis that NO and CO, either alone or in combination, serve as retrograde messengers that produce activity-dependent presynaptic enhancement, perhaps by stimulating soluble guanbylyl cyclase and cGMP-dependent protein kinase, during LTP in hippocampus. 1994 John Wiley & Sons, Inc.     

Enhancement of Endogenous Release of Glutamate and γ-Aminobutyric Acid from Hippocampus CA1 Slices After In Vivo Long-Term Potentiation

The effect of long-term potentiation (LTP) on endogenous amino acid release from rat hippocampus slices was studied. LTP was induced in vivo by application of a tetanus (200 Hz, 200 ms) to the Schaffer collateral fibers in unanesthetized rats. Endogenous release of glutamate and gamma-aminobutyric acid (GABA) was investigated 60 min after tetanization in CA1 subslices of potentiated and control rats. No significant effects of LTP were observed in basal and K(+)-induced Ca(2+)-independent release components of these amino acids. In contrast, K(+)-induced Ca(2+)-dependent release of both glutamate and GABA increased approximately 100% in slices from potentiated rats. No differences were observed in total content of glutamate and GABA between the subslices from control and LTP animals. These results suggest a persistent increase in the recruitment of the presynaptic vesicular pool of glutamate and GABA during LTP.     

The identification of dysfunctional crosstalk of pathways in Parkinson disease

Parkinson disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease, affecting 1–2% of the population over the age of 65. Both genetic and environmental factors trigger risks of and protection from PD. However, the molecular mechanism of PD is far from being clear. In this study, we downloaded the gene expression profile of PD from Gene Expression Omnibus and identified differentially expressed genes (DEGs) and dysfunctional pathways in PD patients compared with controls. To further understand how these pathways act together to account for the initiation of PD, we constructed a pathway crosstalk network by calculating the Jaccard index among pathways. A total of 873 DEGs and 16 dysfunctional pathways between PD patients and controls were identified. Through constructing a network of pathways, the relationships among PD pathways were visually presented by their interactions. Our results demonstrate the existence of crosstalk between different pathways in PD pathogenesis. These results not only may explain the causes of PD, but could also open the door to new therapeutic approaches for this disease.     

Multisensory learning: from experimental psychology to animal training

Abstract

Stimuli and events that animals have to learn about in both their natural environments and in modern environments, such as our homes and farms, are often “multisensory,” i.e., they usually occur in more than one sensory modality. There are studies in humans and animals showing that stimuli that are multisensory are learned more quickly than stimuli presented in just a single sensory modality. My aim is to highlight how animals can combine information from several sensory modalities simultaneously, and show how using multisensory stimuli in training can enhance an animal's ability to learn new behaviors.