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Somogyi J, Szabo A, Somogyi P, Lamsa K. Molecular analysis of ivy cells of the hippocampal CA1 stratum radiatum using spectral identification of immunofluorophores. Front Neural Circuits 2012; 6:35. [PMID: 22666191 PMCID: PMC3364487 DOI: 10.3389/fncir.2012.00035] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 05/18/2012] [Indexed: 11/13/2022] Open
Abstract
Neuronal nitric oxide synthase-expressing (nNOS+) GABAergic interneurons are common in hippocampal stratum (str.) radiatum. However, these cells are less well characterized than nNOS+ ivy cells in str. pyramidale or neurogliaform cells (NGC) in str. lacunosum-moleculare. Here we have studied the laminar distribution of the axons and dendrites, and the immunoreactivity of these neurons recorded in rat hippocampal slices. We have used spectral analysis of antibody- or streptavidin-conjugated fluorophores to improve recognition of genuine signals in reactions for molecules such as nNOS and neuropeptide-Y (NPY). We found that most nNOS+ cells with soma in the CA1 area str. radiatum exhibit characteristic properties of ivy cells, and were positive for NPY and negative for reelin. However, laminar distributions of their neurites differ from original characterization of ivy cells with the soma in or close to str. pyramidale. Both their dendrites and axon are mainly in str. radiatum and to a lesser extent in str. oriens, and in addition often extend to str. lacunosum-moleculare. We conclude that ivy cells in str. radiatum may predominantly be feedforward inhibitory interneurons in the CA1 area, and their axonal output delivering GABA, NPY, and NO can influence both the entorhinal cortex innervated and the CA3 innervated zones pre- and post-synaptically. Spectral analysis of fluorophores provides an objective algorithm to analyze signals in immunoreactions for neurochemical markers.
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Affiliation(s)
- Jozsef Somogyi
- Medical Research Council Anatomical Neuropharmacology Unit, Department of Pharmacology, Oxford University Oxford, UK
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52
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Tang ZQ, Lu Y. Two GABAA responses with distinct kinetics in a sound localization circuit. J Physiol 2012; 590:3787-805. [PMID: 22615438 DOI: 10.1113/jphysiol.2012.230136] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The temporal characteristics and functional diversity of GABAergic inhibition are determined by the spatiotemporal neurotransmitter profile, intrinsic properties of GABAA receptors, and other factors. Here, we report two distinct GABAA responses and the underlying mechanisms in neurons of the chicken nucleus laminaris (NL), the first encoder of interaural time difference for sound localization in birds. The time course of the postsynaptic GABAA currents in NL neurons, recorded with whole-cell voltage clamp, differed between different characteristic frequency (CF) regions. Compared to low-CF (LF) neurons, middle/high-CF (MF/HF) neurons had significantly slower IPSCs, with a 2.6-fold difference in the decay time constants of spontaneous IPSCs and a 5.3-fold difference in the decay of IPSCs elicited by single-pulse stimulus. Such differences were especially dramatic when IPSCs were elicited by train stimulations at physiologically relevant frequencies, and at high stimulus intensities. To account for these distinct GABAA responses, we showed that MF/HF neurons exhibited more prominent asynchronous release of GABA. Supporting this observation, replacement of extracellular Ca2+ with Sr2+ increased the decay of IPSCs in LF neurons, and EGTA-AM reduced the decay of IPSCs in MF/HF neurons. Furthermore, pharmacological evidence suggests that GABA spillover plays a greater role in prolonging the IPSCs of MF/HF neurons. Consequently, under whole-cell current clamp, synaptically released GABA produced short- and long-lasting suppression of the neuronal excitability of LF and MF/HF neurons, respectively. Taken together, these results suggest that the GABAergic inputs to NL neurons may exert a dynamic modulation of interaural time difference (ITD) coding in a CF-dependent manner.
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Affiliation(s)
- Zheng-Quan Tang
- Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH 44272, USA.
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53
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Armstrong C, Krook-Magnuson E, Soltesz I. Neurogliaform and Ivy Cells: A Major Family of nNOS Expressing GABAergic Neurons. Front Neural Circuits 2012; 6:23. [PMID: 22623913 PMCID: PMC3353154 DOI: 10.3389/fncir.2012.00023] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Accepted: 04/13/2012] [Indexed: 12/05/2022] Open
Abstract
Neurogliaform and Ivy cells are members of an abundant family of neuronal nitric oxide synthase (nNOS) expressing GABAergic interneurons found in diverse brain regions. These cells have a defining dense local axonal plexus, and display unique synaptic properties including a biphasic postsynaptic response with both a slow GABA(A) component and a GABA(B) component following even a single action potential. The type of transmission displayed by these cells has been termed "volume transmission," distinct from both tonic and classical synaptic transmission. Electrical connections are also notable in that, unlike other GABAergic cell types, neurogliaform family cells will form gap junctions not only with other neurogliaform cells, but also with non-neurogliaform family GABAergic cells. In this review, we focus on neurogliaform and Ivy cells throughout the hippocampal formation, where recent studies highlight their role in feedforward inhibition, uncover their ability to display a phenomenon called persistent firing, and reveal their modulation by opioids. The unique properties of this family of cells, their abundance, rich connectivity, and modulation by clinically relevant drugs make them an attractive target for future studies in vivo during different behavioral and pharmacological conditions.
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Affiliation(s)
- Caren Armstrong
- Department of Anatomy and Neurobiology, University of California IrvineIrvine, CA, USA
| | - Esther Krook-Magnuson
- Department of Anatomy and Neurobiology, University of California IrvineIrvine, CA, USA
| | - Ivan Soltesz
- Department of Anatomy and Neurobiology, University of California IrvineIrvine, CA, USA
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54
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Microcircuits mediating feedforward and feedback synaptic inhibition in the piriform cortex. J Neurosci 2012; 32:919-31. [PMID: 22262890 DOI: 10.1523/jneurosci.4112-11.2012] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Local inhibition by GABA-releasing neurons is important for the operation of sensory cortices, but the details of these inhibitory circuits remain unclear. We addressed this question in the olfactory system by making targeted recordings from identified classes of inhibitory and glutamatergic neurons in the piriform cortex (PC) of mice. First, we looked for feedforward synaptic inhibition provided by interneurons located in the outermost layer of the PC, layer Ia, which is the unique recipient of afferent fibers from the olfactory bulb. We found two types of feedforward inhibition: a fast-rising, spatially restricted kind that was generated by horizontal cells, and a slow-rising, more diffuse kind generated by neurogliaform cells. Both cell types targeted the distal apical dendrites of layer II principal neurons. Next, we studied feedback synaptic inhibition in isolation by making a tissue cut across layer I to selectively remove feedforward inhibitory connections. We identified a powerful type of feedback inhibition of layer II neurons, mostly generated by soma-targeting fast-spiking multipolar cells in layer III, which in turn were driven by feedforward excitation from layer II semilunar cells. Dynamic clamp simulation of feedback inhibition revealed differential effects of this inhibition on the two main types of layer II principal neurons. Thus, our results articulate the connectivity and functions of two important classes of inhibitory microcircuits in the PC. Feedforward and feedback inhibition generated by these circuits is likely to be required for the operation of this sensory paleocortex during the processing of olfactory information.
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55
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Microcircuits mediating feedforward and feedback synaptic inhibition in the piriform cortex. J Neurosci 2012. [PMID: 22262890 DOI: 10.1523/jneurosci.4112‐11.2012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Local inhibition by GABA-releasing neurons is important for the operation of sensory cortices, but the details of these inhibitory circuits remain unclear. We addressed this question in the olfactory system by making targeted recordings from identified classes of inhibitory and glutamatergic neurons in the piriform cortex (PC) of mice. First, we looked for feedforward synaptic inhibition provided by interneurons located in the outermost layer of the PC, layer Ia, which is the unique recipient of afferent fibers from the olfactory bulb. We found two types of feedforward inhibition: a fast-rising, spatially restricted kind that was generated by horizontal cells, and a slow-rising, more diffuse kind generated by neurogliaform cells. Both cell types targeted the distal apical dendrites of layer II principal neurons. Next, we studied feedback synaptic inhibition in isolation by making a tissue cut across layer I to selectively remove feedforward inhibitory connections. We identified a powerful type of feedback inhibition of layer II neurons, mostly generated by soma-targeting fast-spiking multipolar cells in layer III, which in turn were driven by feedforward excitation from layer II semilunar cells. Dynamic clamp simulation of feedback inhibition revealed differential effects of this inhibition on the two main types of layer II principal neurons. Thus, our results articulate the connectivity and functions of two important classes of inhibitory microcircuits in the PC. Feedforward and feedback inhibition generated by these circuits is likely to be required for the operation of this sensory paleocortex during the processing of olfactory information.
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56
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A novel functionally distinct subtype of striatal neuropeptide Y interneuron. J Neurosci 2012; 31:16757-69. [PMID: 22090502 DOI: 10.1523/jneurosci.2628-11.2011] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We investigated the properties of neostriatal neuropeptide Y (NPY)-expressing interneurons in transgenic GFP (green fluorescent protein)-NPY reporter mice. In vitro whole-cell recordings and biocytin staining demonstrated the existence of a novel class of neostriatal NPY-expressing GABAergic interneurons that exhibit electrophysiological, neurochemical, and morphological properties strikingly different from those of previously described NPY-containing, plateau-depolarization low-threshold spike (NPY-PLTS) interneurons. The novel NPY interneuron type (NPY-neurogliaform) differed from previously described NPY-PLTS interneurons by exhibiting a significantly lower input resistance and hyperpolarized membrane potential, regular, nonaccommodating spiking in response to depolarizing current injections, and an absence of plateau depolarizations or low-threshold spikes. NPY-neurogliaform interneurons were also easily distinguished morphologically by their dense, compact, and highly branched dendritic and local axonal arborizations that contrasted sharply with the sparse and extended axonal and dendritic arborizations of NPY-PLTS interneurons. Furthermore, NPY-neurogliaform interneurons did not express immunofluorescence for somatostatin or nitric oxide synthase that was ubiquitous in NPY-PLTS interneurons. IPSP/Cs could only rarely be elicited in spiny projection neurons (SPNs) in paired recordings with NPY-PLTS interneurons. In contrast, the probability of SPN innervation by NPY-neurogliaform interneurons was extremely high, the synapse very reliable (no failures were observed), and the resulting postsynaptic response was a slow, GABA(A) receptor-mediated IPSC that has not been previously described in striatum but that has been elicited from NPY-GABAergic neurogliaform interneurons in cortex and hippocampus. These properties suggest unique and distinctive roles for NPY-PLTS and NPY-neurogliaform interneurons in the integrative properties of the neostriatum.
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57
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GABAergic circuits mediate the reinforcement-related signals of striatal cholinergic interneurons. Nat Neurosci 2011; 15:123-30. [PMID: 22158514 PMCID: PMC3245803 DOI: 10.1038/nn.2984] [Citation(s) in RCA: 228] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 10/17/2011] [Indexed: 11/08/2022]
Abstract
Neostriatal cholinergic interneurons are believed to be important for reinforcement-mediated learning and response selection by signaling the occurrence and motivational value of behaviorally relevant stimuli through precisely timed multiphasic population responses. An important problem is to understand how these signals regulate the functioning of the neostriatum. Here we describe the synaptic organization of a previously unknown circuit that involves direct nicotinic excitation of several classes of GABAergic interneurons, including neuroptide Y-expressing neurogilaform neurons, and enables cholinergic interneurons to exert rapid inhibitory control of the activity of projection neurons. We also found that, in vivo, the dominant effect of an optogenetically reproduced pause-excitation population response of cholinergic interneurons was powerful and rapid inhibition of the firing of projection neurons that is coincident with synchronous cholinergic activation. These results reveal a previously unknown circuit mechanism that transmits reinforcement-related information of ChAT interneurons in the mouse neostriatal network.
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58
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Markwardt SJ, Dieni CV, Wadiche JI, Overstreet-Wadiche L. Ivy/neurogliaform interneurons coordinate activity in the neurogenic niche. Nat Neurosci 2011; 14:1407-9. [PMID: 21983681 PMCID: PMC3203322 DOI: 10.1038/nn.2935] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Accepted: 08/15/2011] [Indexed: 11/09/2022]
Abstract
Depolarization by the neurotransmitter GABA regulates adult neurogenesis. We found interneurons of the neurogliaform cell family to be a primary source of GABA for newborn neurons in mouse dentate gyrus. GABAergic depolarization occurred in concert with reduced synaptic inhibition of mature neurons, suggesting that the local circuitry coordinates the activation of new and pre-existing cells.
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Affiliation(s)
- Sean J Markwardt
- Department of Neurobiology, McKnight Brain Institute, University of Alabama at Birmingham, Birmingham, Alabama, USA
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59
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Interneuron networks in the hippocampus. Curr Opin Neurobiol 2011; 21:709-16. [DOI: 10.1016/j.conb.2011.05.006] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2011] [Revised: 05/04/2011] [Accepted: 05/10/2011] [Indexed: 10/18/2022]
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60
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Armstrong C, Szabadics J, Tamás G, Soltesz I. Neurogliaform cells in the molecular layer of the dentate gyrus as feed-forward γ-aminobutyric acidergic modulators of entorhinal-hippocampal interplay. J Comp Neurol 2011; 519:1476-91. [PMID: 21452204 DOI: 10.1002/cne.22577] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Feed-forward inhibition from molecular layer interneurons onto granule cells (GCs) in the dentate gyrus is thought to have major effects regulating entorhinal-hippocampal interactions, but the precise identity, properties, and functional connectivity of the GABAergic cells in the molecular layer are not well understood. We used single and paired intracellular patch clamp recordings from post-hoc-identified cells in acute rat hippocampal slices and identified a subpopulation of molecular layer interneurons that expressed immunocytochemical markers present in members of the neurogliaform cell (NGFC) class. Single NGFCs displayed small dendritic trees, and their characteristically dense axonal arborizations covered significant portions of the outer and middle one-thirds of the molecular layer, with frequent axonal projections across the fissure into the CA1 and subicular regions. Typical NGFCs exhibited a late firing pattern with a ramp in membrane potential prior to firing action potentials, and single spikes in NGFCs evoked biphasic, prolonged GABA(A) and GABA(B) postsynaptic responses in GCs. In addition to providing dendritic GABAergic inputs to GCs, NGFCs also formed chemical synapses and gap junctions with various molecular layer interneurons, including other NGFCs. NGFCs received low-frequency spontaneous synaptic events, and stimulation of perforant path fibers revealed direct, facilitating synaptic inputs from the entorhinal cortex. Taken together, these results indicate that NGFCs form an integral part of the local molecular layer microcircuitry generating feed-forward inhibition and provide a direct GABAergic pathway linking the dentate gyrus to the CA1 and subicular regions through the hippocampal fissure.
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Affiliation(s)
- Caren Armstrong
- Department of Anatomy and Neurobiology, University of California, Irvine, School of Medicine, Irvine, California 92697, USA.
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61
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Méndez P, Bacci A. Assortment of GABAergic plasticity in the cortical interneuron melting pot. Neural Plast 2011; 2011:976856. [PMID: 21785736 PMCID: PMC3139185 DOI: 10.1155/2011/976856] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Accepted: 05/01/2011] [Indexed: 12/30/2022] Open
Abstract
Cortical structures of the adult mammalian brain are characterized by a spectacular diversity of inhibitory interneurons, which use GABA as neurotransmitter. GABAergic neurotransmission is fundamental for integrating and filtering incoming information and dictating postsynaptic neuronal spike timing, therefore providing a tight temporal code used by each neuron, or ensemble of neurons, to perform sophisticated computational operations. However, the heterogeneity of cortical GABAergic cells is associated to equally diverse properties governing intrinsic excitability as well as strength, dynamic range, spatial extent, anatomical localization, and molecular components of inhibitory synaptic connections that they form with pyramidal neurons. Recent studies showed that similarly to their excitatory (glutamatergic) counterparts, also inhibitory synapses can undergo activity-dependent changes in their strength. Here, some aspects related to plasticity and modulation of adult cortical and hippocampal GABAergic synaptic transmission will be reviewed, aiming at providing a fresh perspective towards the elucidation of the role played by specific cellular elements of cortical microcircuits during both physiological and pathological operations.
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Affiliation(s)
- Pablo Méndez
- European Brain Research Institute (EBRI), Via del Fosso di Fiorano 64, 00143 Rome, Italy
| | - Alberto Bacci
- European Brain Research Institute (EBRI), Via del Fosso di Fiorano 64, 00143 Rome, Italy
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62
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Barberis A, Petrini EM, Mozrzymas JW. Impact of synaptic neurotransmitter concentration time course on the kinetics and pharmacological modulation of inhibitory synaptic currents. Front Cell Neurosci 2011; 5:6. [PMID: 21734864 PMCID: PMC3123770 DOI: 10.3389/fncel.2011.00006] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Accepted: 06/05/2011] [Indexed: 12/26/2022] Open
Abstract
The time course of synaptic currents is a crucial determinant of rapid signaling between neurons. Traditionally, the mechanisms underlying the shape of synaptic signals are classified as pre- and post-synaptic. Over the last two decades, an extensive body of evidence indicated that synaptic signals are critically shaped by the neurotransmitter time course which encompasses several phenomena including pre- and post-synaptic ones. The agonist transient depends on neurotransmitter release mechanisms, diffusion within the synaptic cleft, spill-over to the extra-synaptic space, uptake, and binding to post-synaptic receptors. Most estimates indicate that the neurotransmitter transient is very brief, lasting between one hundred up to several hundreds of microseconds, implying that post-synaptic activation is characterized by a high degree of non-equilibrium. Moreover, pharmacological studies provide evidence that the kinetics of agonist transient plays a crucial role in setting the susceptibility of synaptic currents to modulation by a variety of compounds of physiological or clinical relevance. More recently, the role of the neurotransmitter time course has been emphasized by studies carried out on brain slice models that revealed a striking, cell-dependent variability of synaptic agonist waveforms ranging from rapid pulses to slow volume transmission. In the present paper we review the advances on studies addressing the impact of synaptic neurotransmitter transient on kinetics and pharmacological modulation of synaptic currents at inhibitory synapses.
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Affiliation(s)
- Andrea Barberis
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology Genova, Italy
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63
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Juszczak GR. Desensitization of GABAergic receptors as a mechanism of zolpidem-induced somnambulism. Med Hypotheses 2011; 77:230-3. [PMID: 21565448 DOI: 10.1016/j.mehy.2011.04.019] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Accepted: 04/06/2011] [Indexed: 11/25/2022]
Abstract
Sleepwalking is a frequently reported side effect of zolpidem which is a short-acting hypnotic drug potentiating activity of GABA(A) receptors. Paradoxically, the most commonly used medications for somnambulism are benzodiazepines, especially clonazepam, which also potentiate activity of GABA(A) receptors. It is proposed that zolpidem-induced sleepwalking can be explained by the desensitization of GABAergic receptors located on serotonergic neurons. According to the proposed model, the delay between desensitization of GABA receptors and a compensatory decrease in serotonin release constitutes the time window for parasomnias. The occurrence of sleepwalking depends on individual differences in receptor desensitization, autoregulation of serotonin release and drug pharmacokinetics. The proposed mechanism of interaction between GABAergic and serotonergic systems can be also relevant for zolpidem abuse and zolpidem-induced hallucinations. It is therefore suggested that special care should be taken when zolpidem is used in patients taking at the same time selective serotonin reuptake inhibitors.
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Affiliation(s)
- Grzegorz R Juszczak
- Department of Animal Behavior, Institute of Genetics and Animal Breeding, Jastrzebiec, Poland.
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64
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Grothe B, Koch U. Dynamics of binaural processing in the mammalian sound localization pathway--the role of GABA(B) receptors. Hear Res 2011; 279:43-50. [PMID: 21447375 DOI: 10.1016/j.heares.2011.03.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2010] [Revised: 03/14/2011] [Accepted: 03/21/2011] [Indexed: 01/01/2023]
Abstract
The initial binaural processing in the superior olive represents the fastest computation known in the entire mammalian brain. Although the binaural system has to perform under very different and often highly dynamic acoustic conditions, the integration of binaural information in the superior olivary complex (SOC) has not been considered to be adaptive or dynamic itself. Recent evidence, however, shows that the initial processing of interaural level and interaural time differences relies on well-adjusted interactions of both the excitatory and the inhibitory projections, respectively. Under static conditions, these inputs seem to be tightly balanced, but may also require dynamic adjustment for proper function when the acoustic environment changes. GABA(B) receptors are at least one mechanism rendering the system more dynamic than considered so far. A comprehensive description of how binaural processing in the SOC is dynamically regulated by GABA(B) receptors in adults and in early development is important for understanding how spatial auditory processing changes with acoustic context.
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Affiliation(s)
- Benedikt Grothe
- Division of Neurobiology, Department Biology II, Ludwig-Maximilians-Universitaet Munich, Großhaderner Str. 2-4, D-82152 Martinsried-Planegg, Germany.
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65
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Dityatev A, Rusakov DA. Molecular signals of plasticity at the tetrapartite synapse. Curr Opin Neurobiol 2011; 21:353-9. [PMID: 21277196 DOI: 10.1016/j.conb.2010.12.006] [Citation(s) in RCA: 180] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 12/24/2010] [Accepted: 12/27/2010] [Indexed: 01/19/2023]
Abstract
The emergence of astroglia as an important participant of the synaptic machinery has led to the 'tripartite synapse' hypothesis. Recent findings suggest that synaptic signaling also involves the surrounding extracellular matrix (ECM). The ECM can incorporate and store molecular traces of both neuronal and glial activities. It can also modulate function of local receptors or ion channels and send diffuse molecular signals using products of its use-dependent proteolytic cleavage. Recent experimental findings implicate the ECM in mechanisms of synaptic plasticity and glial remodeling, thus lending support to the 'tetrapartite synapse' concept. This inclusive view might help to understand better the mechanisms underlying signal integration and novel forms of long-term homeostatic regulation in the brain.
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Affiliation(s)
- Alexander Dityatev
- Department of Neuroscience and Brain Technologies, Italian Institute of Technology, via Morego 30, Genova 16163, Italy.
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66
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Jang HJ, Cho KH, Park SW, Kim MJ, Yoon SH, Rhie DJ. The development of phasic and tonic inhibition in the rat visual cortex. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2010; 14:399-405. [PMID: 21311681 DOI: 10.4196/kjpp.2010.14.6.399] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2010] [Revised: 11/08/2010] [Accepted: 11/09/2010] [Indexed: 11/15/2022]
Abstract
Gamma-aminobutyric acid (GABA)-ergic inhibition is important in the function of the visual cortex. In a previous study, we reported a developmental increase in GABA(A) receptor-mediated inhibition in the rat visual cortex from 3 to 5 weeks of age. Because this developmental increase is crucial to the regulation of the induction of long-term synaptic plasticity, in the present study we investigated in detail the postnatal development of phasic and tonic inhibition. The amplitude of phasic inhibition evoked by electrical stimulation increased during development from 3 to 8 weeks of age, and the peak time and decay kinetics of inhibitory postsynaptic potential (IPSP) and current (IPSC) slowed progressively. Since the membrane time constant decreased during this period, passive membrane properties might not be involved in the kinetic changes of IPSP and IPSC. Tonic inhibition, another mode of GABA(A) receptor-mediated inhibition, also increased developmentally and reached a plateau at 5 weeks of age. These results indicate that the time course of the postnatal development of GABAergic inhibition matched well that of the functional maturation of the visual cortex. Thus, the present study provides significant insight into the roles of inhibitory development in the functional maturation of the visual cortical circuits.
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Affiliation(s)
- Hyun-Jong Jang
- Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea
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67
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Capogna M. Neurogliaform cells and other interneurons of stratum lacunosum-moleculare gate entorhinal-hippocampal dialogue. J Physiol 2010; 589:1875-83. [PMID: 21135049 DOI: 10.1113/jphysiol.2010.201004] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The stratum lacunosum-moleculare of the hippocampus is an area of integration that receives inputs from extrinsic excitatory fibres including those from the entorhinal cortex, and is under the control of several neuromodulators. A critical aspect is the presence in this hippocampal layer of specific interneurons that are likely to influence the strength and the temporal structure of entorhinal-CA1 hippocampal dynamics. I review here recent data on the physiological role of these interneurons. Special focus is devoted to one interneuron type, the so-called neurogliaform cell, because recent studies have defined its unusual mode of cell-to-cell communication. Neurogliaform cells mediate feedforward inhibition of CA1 pyramidal cells, form a network of cells connected via chemical and electrical synapses, and evoke slow inhibitory synaptic currents mediated by GABA(A) and GABA(B) receptors. The modulation of entorhinal input by neurogliaform cells and their contribution to network theta rhythm are also discussed. I hope that novel information on neurogliaform cells will contribute to the ever-growing appreciation of GABAergic cell type diversity, and will inspire neuroscientists interested not only in synaptic physiology but also in the brain's spatial representation system.
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Affiliation(s)
- Marco Capogna
- MRC Anatomical Neuropharmacology Unit, Mansfield Road, Oxford OX1 3TH, UK.
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68
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Zhan RZ, Timofeeva O, Nadler JV. High ratio of synaptic excitation to synaptic inhibition in hilar ectopic granule cells of pilocarpine-treated rats. J Neurophysiol 2010; 104:3293-304. [PMID: 20881195 DOI: 10.1152/jn.00663.2010] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
After experimental status epilepticus, many dentate granule cells born into the postseizure environment migrate aberrantly into the dentate hilus. Hilar ectopic granule cells (HEGCs) have also been found in persons with epilepsy. These cells exhibit a high rate of spontaneous activity, which may enhance seizure propagation. Electron microscopic studies indicated that HEGCs receive more recurrent mossy fiber innervation than normotopic granule cells in the same animals but receive much less inhibitory innervation. This study used hippocampal slices prepared from rats that had experienced pilocarpine-induced status epilepticus to test the hypothesis that an imbalance of synaptic excitation and inhibition contributes to the hyperexcitability of HEGCs. Mossy fiber stimulation evoked a much smaller GABA(A) receptor-mediated inhibitory postsynaptic currents (IPSC) in HEGCs than in normotopic granule cells from either control rats or rats that had experienced status epilepticus. However, recurrent mossy fiber-evoked excitatory postsynaptic currents (EPSCs) of similar size were recorded from HEGCs and normotopic granule cells in status epilepticus-experienced rats. HEGCs exhibited the highest frequency of miniature excitatory postsynaptic currents (mEPSCs) and the lowest frequency of miniature inhibitory postsynaptic currents (mIPSCs) of any granule cell group. On average, both mEPSCs and mIPSCs were of higher amplitude, transferred more charge per event, and exhibited slower kinetics in HEGCs than in granule cells from control rats. Charge transfer per unit time in HEGCs was greater for mEPSCs and much less for mIPSCs than in the normotopic granule cell groups. A high ratio of excitatory to inhibitory synaptic function probably accounts, in part, for the hyperexcitability of HEGCs.
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Affiliation(s)
- Ren-Zhi Zhan
- Dept. of Pharmacology and Cancer Biology, Box 3813, Duke Univ. Medical Center, Durham, NC 27710, USA
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