Kainate receptors in the CA2 region of the hippocampus

<正>The hippocampus is involved in important brain functions such as learning and memory,spatial navigation,fear processing,and social behavior(Dudek et al,2016).The most prominent areas of the hippocampus are typically denoted as the dentate gyrus and the three areas of the cornu ammonis(CA1,CA2,and CA3).Discovered by Lorente de Nó(1934),the CA2 region of the hippocampus is a relatively small area interposed between CA3 and CA1 that forms the nexus linking the input of the entorhinal corte...     

α2-Adrenoceptor antagonists potentiate the anticonflict and the rotarod impairing effects of benzodiazepines

Summary Putative interactions between the specific ₂-adrenoceptor antagonist idazoxan and benzodiazepines (BDZs) were examined in two different rat conflict models; Vogel's drinking conflict test (VT) and Montgomery's conflict test (MT) (the elevated +-maze). In the MT, idazoxan (0.031mg/kg) produced anxiogenic-like effects, which were counteracted both by the triazolo-BDZ alprazolam (APZ; 0.2mg/kg) and the conventional BDZ diazepam (DIZ; 0.2mg/ kg). In fact, the anxiolytic-like effects of APZ were significantly potentiated when co-administering idazoxan. A tendency to such a phenomenon was seen also in rats treated with DIZ and idazoxan. In the VT, the anxiolytic-like effects both of APZ (1.0 mg/kg) and DIZ (4.0 mg/kg) were significantly enhanced when co-administering idazoxan (1.0 mg/kg) in a dose not affecting the behaviorper se. Similar potentiating phenomena by behaviorally inert doses of ₂-adrenoceptor antagonists (idazoxan 1.0 mg/kg; yohimbine 2.0 mg/kg) were seen with regard to the ataxic/sedative effects of the BDZs (APZ 0.25 mg/kg; DIZ 1.5 mg/ kg). The present results provide further support for the notion that the anxiolytic-like effects of BDZs are not related to attenuation of Locus Coeruleus activity. In addition, it is suggested that the potentiation caused by the ₂-adrenoceptor antagonist is mediated via a noradrenaline induced increase in signal-to-noise ratio in target neurons of the brain noradrenergic system.     

Does the severity of the LGMD2A phenotype in compound heterozygotes depend on the combination of mutations?

Introduction: Limb‐girdle muscular dystrophy type 2A (LGMD2A) is caused by a deficiency of calpain‐3/p94. Although the symptoms in most LGMD2A patients are generally homogeneous, some variation in the severity and progression of the disease has been reported. Methods: We describe 2 patients who carry the same combination of compound heterozygous mutations (pG222R/pR748Q) and whose symptoms are exceptionally benign compared to homozygotes with each missense mutation. Results: The benign phenotype observed in association with the combined pG222R and pR748Q mutations suggested that it may result from a compensatory effect of compound heterozygosity rather than the individual mutations themselves. Our analyses revealed that these two mutations exert different effects on the protease activity of calpain‐3, suggesting “molecular complementation” in these patients. Conclusion: We propose several hypotheses to explain how this specific combination of mutations may rescue the normal proteolytic activity of calpain‐3, resulting in an exceptionally benign phenotype. Muscle Nerve, 2011     

Spongiform encephalopathy in transgenic mice expressing a point mutation in the β2-α2 loop of the prion protein

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases attributed to misfolding of the cellular prion protein, PrP(C), into a β-sheet-rich, aggregated isoform, PrP(Sc). We previously found that expression of mouse PrP with the two amino acid substitutions S170N and N174T, which result in high structural order of the β2-α2 loop in the NMR structure at pH 4.5 and 20°C, caused transmissible de novo prion disease in transgenic mice. Here we report that expression of mouse PrP with the single-residue substitution D167S, which also results in a structurally well ordered β2-α2 loop at 20°C, elicits spontaneous PrP aggregation in vivo. Transgenic mice expressing PrP(D167S) developed a progressive encephalopathy characterized by abundant PrP plaque formation, spongiform change, and gliosis. These results add to the evidence that the β2-α2 loop has an important role in intermolecular interactions, including that it may be a key determinant of prion protein aggregation.     

Enhanced Synaptic Inhibition in the Cerebellar Cortex of the Ataxic PMCA2−/− Knockout Mouse

Mice with genetic deletion of a calcium extrusion pump, the plasma membrane calcium ATPase isoform 2, PMCA2, exhibit overt cerebellar ataxia, but the cellular mechanisms are only partially understood. Here, we report an enhanced synaptic GABAergic inhibition within the molecular layer of cerebellar cortex slices from PMCA2 knockout (PMCA2^?/?) mice, a finding that could contribute to the observed ataxia. Purkinje neurons from PMCA2^?/? mice exhibited an increased frequency and amplitude of spontaneous inhibitory post-synaptic currents that was accompanied by an enhanced spontaneous firing frequency of molecular layer interneurons (both basket cells and stellate cells). The elevated inhibition was sufficient to reduce the frequency and regularity of spike firing by PMCA2^?/? Purkinje neurons. Acute pharmacological inhibition of PMCA recapitulated some of these features in wild-type mice indicating that the changes were in part a direct result of PMCA2 removal. However, additional compensatory mechanisms within the PMCA2^?/? mouse were also a major factor. Indeed, morphological studies revealed an abnormally large number of molecular layer interneurons (basket cells and stellate cells) and GABAergic synapses within the PMCA2^?/? cerebellar cortex. We conclude that loss of PMCA2 adversely influences the function and organisation of Purkinje neuron synaptic inhibition as a major contributory mechanism to the ataxic phenotype of the PMCA2^?/? mouse.     

Potential involvement of GRIN2B encoding the NMDA receptor subunit NR2B in the spectrum of Alzheimer’s disease

Increasing evidence links dysregulation of NR2B-containing N-methyl-d-aspartate receptor remodelling and trafficking to Alzheimer’s disease (AD). This theme offers the possibility that the GRIN2B gene, encoding this selective NR2B subunit, represents a potential molecular modulating factor for this disease. Based on this hypothesis, we carried out a mutation scanning of exons and flanking regions of GRIN2B in a well-characterized cohort of AD patients, recruited from Southern Italy. A “de novo” p.K1293R mutation, affecting a highly conserved residue of the protein in the C-terminal domain, was observed for the first time in a woman with familial AD, as the only genetic alteration of relevance. Moreover, an association study between the other detected sequence variants and AD was performed. In particular, the study was focused on five identified single nucleotide polymorphisms: rs7301328, rs1805482, rs3026160, rs1806191 and rs1806201, highlighting a significant contribution from the GRIN2B rs1806201 T allele towards disease susceptibility [adjusted odds ratio (OR) = 1.92, 95% confidence interval (CI) 1.40–2.63, p < 0.001, after correction for sex, age, and APOE ε4 genotype]. This was confirmed by haplotype analysis that identified a specific haplotype, carrying the rs1806201 T allele (CCCTC), over-represented in patients versus controls (adjusted OR = 6.03; p < 0.0001). Although the pathogenic role of the GRIN2B-K1293R mutation in AD is not clear, our data advocate that genetic variability in the GRIN2B gene, involved in synaptic functioning, might provide valuable insights into disease pathogenesis, continuing to attract significant attention in biomedical research on its genetic and functional role.     

Immunohistochemical Localization of α2-Adrenergic Receptors in the Neonatal Rat Cochlea and the Vestibular Labyrinth

The α₂-adrenergic receptors (α₂-ARs), which mediate physiological responses to noradrenaline and adrenaline, are encoded by three different genes but all are coupled to the G_i/G_o subfamily of G proteins. The present study investigated the localization of three subtypes, i.e., α_2a-, α_2b-, and α_2c-ARs, in cochlea and vestibular labyrinth in rat in the early postnatal period by immunohistochemistry. The results showed that α₂-ARs were widely distributed in regions, including the organ of Corti, spiral ganglion neurons, stria vascularis, crista ampullaris, Scarpa's ganglion, utricle, and Reissner's membrane. Furthermore, the cellular locations of α₂-ARs between different cell subtypes as well as receptor subtypes and different observed time points also had diversity. α_2a-AR mainly targeted to nuclei at postnatal ages (P)3. While at P(8), only ganglion neurons maintained this character whereas other cell types expressed α_2a-AR mainly in plasma membrane. The α_2b- and α_2c-ARs exhibited predominantly in plasma membrane. Compared with P(8), α_2c-AR was not present at stria vascularis at P(3). Overall, our observations indicated that there was region-specific regulation of α₂-ARs development in cochlea and vestibular labyrinth. In addition, the extensive expressions of α₂-ARs established a significant foundation for the exploration of the function of α₂-ARs in cochlea and vestibular labyrinth.     

Is the central inspiratory activity responsible for pCO2-dependent drive of the sympathetic discharge?

Out of 27 cats anesthetized with chloralose—urethane mixture, paralyzed, vagotomized and artificially ventilated, phrenic nerve response to systemic hypercapnia (7–8 vol.% CO₂/O₂ mixture) was accompanied by an increase in pressure and sympathetic discharge in 19 cats. Out of these 19 cats, 12 were totally debuffered and in the remaining 7 cats one carotid sinus nerve was left intact. Single unit activity in the sympathetic cervical nerve and spontaneous mass activity in the cervical, splanchnic, renal sympathetic and phrenic nerves were recorded. Evoked response in the phrenic nerve was produced by electrical stimulation of the descending bulbospinal inspiratory pathways in the midplane area of the medulla or in the ventrolateral cervical spinal cord. Starting from the control mean end-tidal CO₂ concentration of 4.7 vol.% (±1.0 S.D.) a progressing hypocapnia was induced by hyperventilation up to the end-tidal CO₂ concentration of 1.3—3.2 vol.% (mean 2.4 vol.% ± 0.5 S.D.) significantly below p_aCO₂ apneic threshold. In chemo- and baroreceptor denervated cats with a pressor and excitatory sympathetic response to hypercapnia, a hypocapnia resulted in a fall of the arterial blood pressure (mean 16.9 mm Hg ± 7.5 S.D., 2.2 kp_a ± S.D.). With the increasing p_aCO₂ over the period of hypocapnic apnea a pressor and excitatory sympathetic response preceded, in all experiments, the onset of the phrenic nerve rhythmic activity. The difference between p_aCO₂ threshold for the pressor and sympathetic response (35.7 mm Hg ± 3.6 S.D., 4.7 kp_a ± 0.5 S.D.) and p_aCO₂ threshold for the reappearance of the phrenic nerve rhythmic activity (43.6 mm Hg ± 2.6 S.D., 5.8 kp_a ± 0.3 S.D.) was highly significant. If apneic hypocapnia was combined with the continuous stimulation of the afferent fibers of the superior laryngeal nerve the CO₂ threshold for phrenic rhythmic activity was significantly increased whereas CO₂ threshold for the pressor and sympathetic excitatory response remained unchanged. CO₂ administration during hypocapnic apnea caused a progressing reduction of the magnitude of the evoked phrenic nerve response.From these findings it is concluded that the central excitatory effect of CO₂ on the sympathetic activity may be accomplished in the absence of the rhythmic respiratory activity and independently of the subthreshold tonic inspiratory activity. Pressor and sympathetic excitatory response to CO₂ observed during hypocapnic apnea is presumably caused by a neuronal pool different from that responsible for the central inspiratory activity. It is suggested that this CO₂ sensitive neuronal mechanism might be involved in the central generation of sympathetic tone.     

TGF-β signaling through SMAD2/3 induces the quiescent microglial phenotype within the CNS environment

Microglia are myeloid-derived cells that colonize the central nervous system (CNS) at early stages of development and constitute up to 20% of the glial populations throughout life. While extensive progress has been recently made in identifying the cellular origin of microglia, the mechanism whereby the cells acquire the unique ramified and quiescent phenotype within the CNS milieu remains unknown. Here, we show that upon co-culturing of either CD117(+) /Lin(-) hematopoietic progenitors or CD11c(+) bone marrow derived cells with organotypic hippocampal slices or primary glia, the cells acquire a ramified morphology concomitant with reduced levels of CD86, MHCII, and CD11c and up-regulation of the microglial cell-surface proteins CX(3) CR1 and Iba-1. We further demonstrate that the transforming growth factor beta (TGF-β) signaling pathway via SMAD2/3 phosphorylation is essential for both primary microglia and myeloid-derived cells in order to acquire their quiescent phenotype. Our study suggests that the abundant expression of TGF-β within the CNS during development and various inflammatory processes plays a key role in promoting the quiescent phenotype of microglia and may thus serve as a target for therapeutic strategies aimed at modulating the function of microglia in neurodegenerative diseases such as Alzheimer's and prion.     

Can we relate MeCP2 deficiency to the structural and chemical abnormalities in the Rett brain?

The mutated gene for Rett syndrome, MECP2, has now been identified in ninety percent of cases. Molecular biologists are immersed in the study of this gene's biology determining how its mutation could be responsible for such an enigmatic phenotype. In this paper the same question is considered, re-examining the structural phenotype of the Rett brain and asking; is MeCP2 present at the appropriate time and place in brain development to influence the structural and chemical abnormalities which characterize the Rett brain? Data from the literature and previous research suggest that MeCP2 is expressed during critical periods of brain development at several sites and in different neurons. It supports the idea that inadequate functioning of MeCP2 alters trophic factors and raises the possibility that replacement of these factors might improve brain function. The availability of mouse models now makes it possible to test such ideas.     

Pyruvate prevents the inhibition of the long-term potentiation induced by amyloid-β through protein phosphatase 2A inactivation

Amyloid-β (Aβ) oligomers are derived from proteolytic cleavage of amyloid-β protein precursor and can impair memory and hippocampal long-term potentiation (LTP) in vivo and in vitro. They are recognized as the primary neurotoxic agents in Alzheimer's disease. Pyruvate has a protective effect against Aβ-induced neuronal cell death in hippocampal slice cultures. However, whether pyruvate also has a protective effect against the inhibition of neuronal plasticity induced by Aβ remains to be elucidated. This study examined the effect of pyruvate on the Aβ-induced inhibition of LTP in the rat hippocampus. We found that pyruvate prevented the Aβ-induced inhibition of LTP as strong as fostriecin, a specific protein phosphatase 2A (PP2A) inhibitor. Pyruvate prevented the Aβ block of Ca(2+)/calmodulin dependent protein kinase 2 (CaMK2) autophosphorylation and the Aβ-induced PP2A activation. Pyruvate, but not lactate, decreased reactive oxygen species levels in CA1 slices exposed to Aβ. We propose that pyruvate could prevent the Aβ-induced inhibition of LTP by the re-autophosphorylation of CaMK2 through PP2A inactivation. The reduction of reactive oxygen species production is considered to be the upstream mechanism of this observed pyruvate protection.     

Association analysis between the C-1291G polymorphism in the promoter region of the adrenergic α2A receptor gene and polydipsia in schizophrenia

Several lines of studies have shown the existence of an important inhibitory mechanism for the control of water intake involving adrenergic α2A receptors (ADRA2A). A human study using patients with schizophrenia demonstrated an exacerbation of polydipsia by the administration of clonidine, an ADRA2A-agonist, and a relief of polydipsia by mianserin, an ADRA2A-antagonist, suggesting the involvement of the central adrenergic system in the drinking behavior of patients with schizophrenia. Based on these findings we examined a possible association between the C-1291G polymorphism in the promoter region of the ADRA2A gene and polydipsia in schizophrenia using a Japanese case-control sample. Our sample includes 348 patients with schizophrenia (DSM-IV) (84 with polydipsia and 264 without polydipsia). No significant association between the ADRA2A C-1291G polymorphism and polydipsia was found. Our result suggests that the ADRA2A C-1291G polymorphism may not confer susceptibility to polydipsia in schizophrenia in our sample. Further studies with larger samples are warranted.     

Optic nerve degeneration in the DBA/2NNia mouse: is the lamina cribrosa important in the development of glaucomatous optic neuropathy?

To study optic nerve (ON) degeneration in the DBA/2NNia (DBA) mouse, a species lacking a lamina cribrosa and a model for secondary angle-closure glaucoma, serial semi- and ultra-thin sectioning of the myelinated ON and of the ON head was performed and sections evaluated qualitatively and quantitatively by light and electron microscopy. Immunohistochemistry was performed using antibodies against collagen type I, III, VI, laminin, and connexin43. The major finding on the myelinated ON was a significant decrease in cross section area during ON degeneration which was paralleled by a loss of axons and an increase in microglia. The number of astrocytes and blood vessels did not change. The major findings on the ON papilla were that ON heads with only mild degeneration showed a pronounced focal degeneration around the central retinal artery. In more severely degenerated ON, newly formed bundles of collagen type VI were located between astrocyte processes within the ON head. In a species that has no lamina cribrosa, DBA mice can develop typical signs of glaucomatous optic neuropathy. The entrance of the central retinal vessels into the ONH seems to be a preferentially vulnerable region for axon loss in this mouse model. In addition, astrocytes in the ON head form extracellular material similar to that found in human glaucomatous eyes.     

Muse cells decrease the neuroinflammatory response by modulating the proportion of M1 and M2 microglia in vitro

Neuroinflammation hinders repair of the central nervous system(CNS). Stem cell transplantation is a very promising approach for treatment of CNS injuries. However, it is difficult to select seed cells that can both facilitate nerve regeneration and improve the microenvironment in the CNS. In this study, we isolated multilineage-differentiating stress-enduring(Muse) cells from bone marrow mesenchymal stem cells. We explored the anti-inflammatory effect and mechanism of Muse cells in vitro by cocu...     

Involvement of postsynaptic α1- and α2-adrenoceptors in the flexor reflex activity in the spinal Rats

Summary Clonidine (0.2 mg/kg i.v.) and St 587 (1 mg/kg i.v.), selective agonsists of ₂- and ₁-adrenoceptors, respectively, increased the flexor reflex amplitude in the spinal rat. Yohimbine and rauwolscine, ₂-adrenoceptor antagonists, inhibited dose-dependently the effect of clonidine but not of St 587. However, prazosin and clozapine, ₁-adrenoceptor antagonists, diminished the action of both agonists in a dose-dependent manner. After central chemosympathectomy caused by 6-OH-DA or DSP-4 the response to clonidine did not differ from that in the sham-operated animals. In 6-OH-DA treated rats yohimbine (1 mg/kg i.v.) antagonized the effect of clonidine to the same extent as it did in unlesioned animals. It is concluded that the results are functional evidence that ₁- and ₂-adrenoceptors are present in the rat spinal cord, and stimulation of each receptor increases flexor reflex activity.