| 1. |
- Michaëlsson, Henrik, et al.
(författare)
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The novel antidepressant ketamine enhances dentate gyrus proliferation with no effects on synaptic plasticity or hippocampal function in depressive-like rats
- 2019
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 225:4
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Tidskriftsartikel (refereegranskat)abstract
- Aim Major depressive disorder is a common and debilitating condition with substantial economic impact. Treatment options, although effective, are aimed at relieving the symptoms with limited disease modification. Ketamine, a commonly used anaesthetic, has received substantial attention as it shows rapid antidepressant effects clinically. We studied the effects of ketamine on hippocampal function and dentate gyrus proliferation in rats showing a depressive-like phenotype. Methods Adolescent and adult animals were pre-natally exposed to the glucocorticoid analog dexamethasone, and we verified a depressive-like phenotype using behavioural tests, such as the sucrose preference. We subsequently studied the effects of ketamine on hippocampal synaptic transmission, plasticity and dentate gyrus proliferation. In addition, we measured hippocampal glutamate receptor expression. We also tested the ketamine metabolite hydroxynorketamine for NMDA-receptor independent effects. Results Surprisingly, our extensive experimental survey revealed limited effects of ketamine or its metabolite on hippocampal function in control as well as depressive-like animals. We found no effects on synaptic efficacy or induction of long-term potentiation in adolescent and adult animals. Also there was no difference when comparing the dorsal and ventral hippocampus. Importantly, however, ketamine 24 hours prior to experimentation significantly increased the dentate gyrus proliferation, as revealed by Ki-67 immunostaining, in the depressive-like phenotype. Conclusion We find limited effects of ketamine on hippocampal glutamatergic transmission. Instead, alterations in dentate gyrus proliferation could explain the antidepressant effects of ketamine.
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| 2. |
- Perez-Alcazar, Marta, et al.
(författare)
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Human Cerebrospinal Fluid Promotes Neuronal Viability and Activity of Hippocampal Neuronal Circuits In Vitro
- 2016
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Ingår i: Frontiers in Cellular Neuroscience. - : Frontiers Media SA. - 1662-5102. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- For decades it has been hypothesized that molecules within the cerebrospinal fluid (CSF) diffuse into the brain parenchyma and influence the function of neurons. However, the functional consequences of CSF on neuronal circuits are largely unexplored and unknown. A major reason for this is the absence of appropriate neuronal in vitro model systems, and it is uncertain if neurons cultured in pure CSF survive and preserve electrophysiological functionality in vitro. In this article, we present an approach to address how human CSF (hCSF) influences neuronal circuits in vitro. We validate our approach by comparing the morphology, viability, and electrophysiological function of single neurons and at the network level in rat organotypic slice and primary neuronal cultures cultivated either in hCSF or in defined standard culture media. Our results demonstrate that rodent hippocampal slices and primary neurons cultured in hCSF maintain neuronal morphology and preserve synaptic transmission. Importantly, we show that hCSF increases neuronal viability and the number of electrophysiologically active neurons in comparison to the culture media. In summary, our data indicate that hCSF represents a physiological environment for neurons in vitro and a superior culture condition compared to the defined standard media. Moreover, this experimental approach paves the way to assess the functional consequences of CSF on neuronal circuits as well as suggesting a novel strategy for central nervous system (CNS) disease modeling.
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| 3. |
- Riebe, Ilse, 1978, et al.
(författare)
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Tonically active NMDA receptors - a signalling mechanism critical for interneuronal excitability in the CA1 stratum radiatum.
- 2016
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Ingår i: The European journal of neuroscience. - : Wiley. - 1460-9568 .- 0953-816X. ; 43:2, s. 169-178
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Tidskriftsartikel (refereegranskat)abstract
- In contrast to tonic extrasynaptic GABAA receptor-mediated signalling, the physiological significance of tonic extrasynaptic NMDA receptor-mediated (NMDAR) signalling remains uncertain. In this study we used reversible open-channel blockers of NMDARs, memantine and phencyclidine (PCP), as tools to examine tonic NMDAR-mediated signalling in rat hippocampal slices. Memantine in concentrations up to 10 μM had no effect on synaptically evoked NMDAR-mediated responses in pyramidal neurons or GABAergic interneurons. On the other hand, 10 μM memantine reduced tonic NMDAR-mediated currents in GABAergic interneurons by approximately 50%. These tonic NMDAR-mediated currents in interneurons contributed significantly to the excitability of the interneurons since 10 μM memantine reduced the disynaptic IPSC in pyramidal cells by about 50%. Moreover, 10 μM memantine, but also PCP in concentrations ≤ 1 μM, increased the magnitude of the population spike, likely because of disinhibition. The relatively higher impact of tonic NMDAR-mediated signalling in interneurons was at least partly explained by the expression of GluN2D-containing NMDARs, which was not observed in mature pyramidal cells. Our results are consistent with the idea that low doses of readily reversible NMDA receptor open-channel blockers preferentially inhibits tonically active extrasynaptic NMDARs, and they suggest that tonically active NMDARs contribute more prominently to the intrinsic excitation in GABAergic interneurons than in pyramidal cells. We propose that this specific difference between interneurons and pyramidal cells can explain the disinhibition caused by the Alzheimer's disease medication memantine. This article is protected by copyright. All rights reserved.
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| 4. |
- Sapkota, K., et al.
(författare)
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Mechanism and properties of positive allosteric modulation of N-methyl-D-aspartate receptors by 6-alkyl 2-naphthoic acid derivatives
- 2017
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Ingår i: Neuropharmacology. - : Elsevier BV. - 0028-3908. ; 125, s. 64-79
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Tidskriftsartikel (refereegranskat)abstract
- The theory that N-methyl-D-aspartate receptor (NMDAR) hypofunction is responsible for the symptoms of schizophrenia is well supported by many pharmacological and genetic studies. Accordingly, positive allosteric modulators (PAMs) that augment NMDAR signaling may be useful for treating schizophrenia. Previously we have identified several NMDAR PAMs containing a carboxylic acid attached to naphthalene, phenanthrene, or coumarin ring systems. In this study, we describe several functional and mechanistic properties of UBP684, a 2-naphthoic acid derivative, which robustly potentiates agonist responses at each of the four GluN1a/GluN2 receptors and at neuronal NMDARs. UBP684 increases the maximal L-glutamate/glycine response while having minor subunit-specific effects on agonist potency. PAM binding is independent of agonist binding, and PAM activity is independent of membrane voltage, redox state, and the GIuN1 exon 5 N-terminal insert. UBP684 activity is, however, markedly pH-dependent, with greater potentiation occurring at lower pHs and inhibitory activity at pH 8.4. UBP684 increases channel open probability (P-o) and slows receptor deactivation time upon removal of L-glutamate, but not glycine. The structurally related PAM, UBP753, reproduced most of these findings, but did not prolong agonist removal deactivation time. Studies using cysteine mutants to lock the GluN1 and GluN2 ligand-binding domains (LBDs) in the agonist-bound states indicate that PAM potentiation requires GluN2 LBD conformational flexibility. Together, these findings suggest that UBP684 and UBP753 stabilize the GluN2 LBD in an active conformation and thereby increase P-o. Thus, UBP684 and UBP753 may serve as lead compounds for developing agents to enhance NMDAR activity in disorders associated with NMDAR hypofunction. (C) 2017 Elsevier Ltd. All rights reserved.
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