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González-González MA, Conde SV, Latorre R, Thébault SC, Pratelli M, Spitzer NC, Verkhratsky A, Tremblay MÈ, Akcora CG, Hernández-Reynoso AG, Ecker M, Coates J, Vincent KL, Ma B. Bioelectronic Medicine: a multidisciplinary roadmap from biophysics to precision therapies. Front Integr Neurosci 2024; 18:1321872. [PMID: 38440417 PMCID: PMC10911101 DOI: 10.3389/fnint.2024.1321872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Accepted: 01/10/2024] [Indexed: 03/06/2024] Open
Abstract
Bioelectronic Medicine stands as an emerging field that rapidly evolves and offers distinctive clinical benefits, alongside unique challenges. It consists of the modulation of the nervous system by precise delivery of electrical current for the treatment of clinical conditions, such as post-stroke movement recovery or drug-resistant disorders. The unquestionable clinical impact of Bioelectronic Medicine is underscored by the successful translation to humans in the last decades, and the long list of preclinical studies. Given the emergency of accelerating the progress in new neuromodulation treatments (i.e., drug-resistant hypertension, autoimmune and degenerative diseases), collaboration between multiple fields is imperative. This work intends to foster multidisciplinary work and bring together different fields to provide the fundamental basis underlying Bioelectronic Medicine. In this review we will go from the biophysics of the cell membrane, which we consider the inner core of neuromodulation, to patient care. We will discuss the recently discovered mechanism of neurotransmission switching and how it will impact neuromodulation design, and we will provide an update on neuronal and glial basis in health and disease. The advances in biomedical technology have facilitated the collection of large amounts of data, thereby introducing new challenges in data analysis. We will discuss the current approaches and challenges in high throughput data analysis, encompassing big data, networks, artificial intelligence, and internet of things. Emphasis will be placed on understanding the electrochemical properties of neural interfaces, along with the integration of biocompatible and reliable materials and compliance with biomedical regulations for translational applications. Preclinical validation is foundational to the translational process, and we will discuss the critical aspects of such animal studies. Finally, we will focus on the patient point-of-care and challenges in neuromodulation as the ultimate goal of bioelectronic medicine. This review is a call to scientists from different fields to work together with a common endeavor: accelerate the decoding and modulation of the nervous system in a new era of therapeutic possibilities.
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Affiliation(s)
- María Alejandra González-González
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Department of Pediatric Neurology, Baylor College of Medicine, Houston, TX, United States
| | - Silvia V. Conde
- iNOVA4Health, NOVA Medical School, Faculdade de Ciências Médicas, NOVA University, Lisbon, Portugal
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Stéphanie C. Thébault
- Laboratorio de Investigación Traslacional en salud visual (D-13), Instituto de Neurobiología, Universidad Nacional Autónoma de México (UNAM), Querétaro, Mexico
| | - Marta Pratelli
- Neurobiology Department, Kavli Institute for Brain and Mind, UC San Diego, La Jolla, CA, United States
| | - Nicholas C. Spitzer
- Neurobiology Department, Kavli Institute for Brain and Mind, UC San Diego, La Jolla, CA, United States
| | - Alexei Verkhratsky
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Achucarro Centre for Neuroscience, IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- International Collaborative Center on Big Science Plan for Purinergic Signaling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- Department of Stem Cell Biology, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania
| | - Marie-Ève Tremblay
- Division of Medical Sciences, University of Victoria, Victoria, BC, Canada
- Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada
- Department of Molecular Medicine, Université Laval, Québec City, QC, Canada
- Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, BC, Canada
| | - Cuneyt G. Akcora
- Department of Computer Science, University of Central Florida, Orlando, FL, United States
| | | | - Melanie Ecker
- Department of Biomedical Engineering, University of North Texas, Denton, TX, United States
| | | | - Kathleen L. Vincent
- Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, TX, United States
| | - Brandy Ma
- Stanley H. Appel Department of Neurology, Houston Methodist Hospital, Houston, TX, United States
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Nigrostriatal dopamine depletion promoted an increase in inhibitory markers (parvalbumin, GAD67, VGAT) and cold allodynia. Neurosci Lett 2021; 762:136135. [PMID: 34311052 DOI: 10.1016/j.neulet.2021.136135] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Revised: 07/21/2021] [Accepted: 07/21/2021] [Indexed: 01/13/2023]
Abstract
Pain constitutes the major non-motor symptom in Parkinson's disease (PD). Its mechanism is still poorly understood although an increase in excitation or a decrease in inhibition have been reported in preclinical studies. The aim of this study was to investigate gamma aminobutyric acid (GABA) inhibition in the 6-hydroxydopamine (6-OHDA) PD rat model. Therefore, the expression of three inhibitory markers parvalbumin, glutamate decarboxylase 67 (GAD67) and vesicular GABA transporter (VGAT) was evaluated, besides cold allodynia, in bilateral 6-OHDA lesioned rat. There was a significant increase in the expression of the three markers labeling within the spinal dorsal horn (SDH) of 6-OHDA lesioned rats. In parallel, there was also an increase of the excitatory marker protein kinase C gamma (PKCγ) . PKCγ cells have a crucial role in pain chronicity and are regulated by GABAergic influences. Central dopamine depletion induced an increase in excitation as reveled by an increase in cFOS expression upon acetone stimulus and the presence of cold allodynia. In addition, dopamine depletion induced increased expression in inhibitory markers, which may reflect a disinhibition or a decreased inhibition in 6-OHDA lesioned rats.
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Griego E, Galván EJ. Metabotropic Glutamate Receptors at the Aged Mossy Fiber - CA3 Synapse of the Hippocampus. Neuroscience 2020; 456:95-105. [PMID: 31917351 DOI: 10.1016/j.neuroscience.2019.12.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 12/06/2019] [Accepted: 12/09/2019] [Indexed: 12/28/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) are a group of G-protein-coupled receptors that exert a broad array of modulatory actions at excitatory synapses of the central nervous system. In the hippocampus, the selective activation of the different mGluRs modulates the intrinsic excitability, the strength of synaptic transmission, and induces multiple forms of long-term plasticity. Despite the relevance of mGluRs in the normal function of the hippocampus, we know very little about the changes that mGluRs functionality undergoes during the non-pathological aging. Here, we review data concerning the physiological actions of mGluRs, with particular emphasis on hippocampal area CA3. Later, we examine changes in the expression and functionality of mGluRs during the aging process. We complement this review with original data showing an array of electrophysiological modifications observed in the synaptic transmission and intrinsic excitability of aged CA3 pyramidal cells in response to the pharmacological stimulation of the different mGluRs.
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Affiliation(s)
- Ernesto Griego
- Departamento de Farmacobiología, Cinvestav Sede Sur, México City, Mexico
| | - Emilio J Galván
- Departamento de Farmacobiología, Cinvestav Sede Sur, México City, Mexico.
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Jones GL, Wittmann G, Yokosawa EB, Yu H, Mercer AJ, Lechan RM, Low MJ. Selective Restoration of Pomc Expression in Glutamatergic POMC Neurons: Evidence for a Dynamic Hypothalamic Neurotransmitter Network. eNeuro 2019; 6:ENEURO.0400-18.2019. [PMID: 30957016 PMCID: PMC6449166 DOI: 10.1523/eneuro.0400-18.2019] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 02/15/2019] [Accepted: 02/17/2019] [Indexed: 01/19/2023] Open
Abstract
Hypothalamic POMC deficiency leads to obesity and metabolic deficiencies, largely due to the loss of melanocortin peptides. However, POMC neurons in the arcuate nucleus (ARC) are comprised of glutamatergic and GABAergic subpopulations. The developmental program, relative proportion and function of these two subpopulations are unresolved. To test whether glutamatergic POMC neurons serve a distinct role in maintaining energy homeostasis, we activated Pomc expression Cre- dependently in Vglut2-expressing neurons of mice with conditionally silenced Pomc alleles. The Vglut2-Pomc restored mice had normal ARC Pomc mRNA levels, POMC immunoreactivity, as well as body weight and body composition at age 12 weeks. Unexpectedly, the cumulative total of Vglut2+ glutamatergic- and Gad67+ GABAergic-Pomc neurons detected by in situ hybridization (ISH) exceeded 100% in both Vglut2- Pomc restored and control mice, indicating that a subpopulation of Pomc neurons must express both neuronal markers. Consistent with this hypothesis, triple ISH of C57BL/6J hypothalami revealed that 35% of ARC Pomc neurons were selectively Gad67+, 21% were selectively Vglut2+, and 38% expressed both Gad67 and Vglut2. The single Gad67+ and Vglut2+Pomc neurons were most prevalent in the rostral ARC, while the Vglut2/Gad67+ dual-phenotype cells predominated in the caudal ARC. A lineage trace using Ai9-tdTomato reporter mice to label fluorescently all Vglut2-expressing neurons showed equal numbers of tdTomato+ and tdTomato- POMC immunoreactive neurons. Together, these data suggest that POMC neurons exhibit developmental plasticity in their expression of glutamatergic and GABAergic markers, enabling re-establishment of normal energy homeostasis in the Vglut2-Pomc restored mice.
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Affiliation(s)
- Graham L. Jones
- Neuroscience Graduate Program
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105
| | - Gábor Wittmann
- Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, Tufts Medical Center, Boston, MA 02111
| | - Eva B. Yokosawa
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105
| | - Hui Yu
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105
| | - Aaron J. Mercer
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105
| | - Ronald M. Lechan
- Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, Tufts Medical Center, Boston, MA 02111
| | - Malcolm J. Low
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105
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Ortiz-Pérez A, Limón-Morales O, Rojas-Castañeda J, Cerbón M, Picazo O. Prolactin prevents the kainic acid-induced neuronal loss in the rat hippocampus by inducing prolactin receptor and putatively increasing the VGLUT1 overexpression. Neurosci Lett 2019; 694:116-123. [DOI: 10.1016/j.neulet.2018.11.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 11/24/2018] [Accepted: 11/26/2018] [Indexed: 01/08/2023]
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Target-Dependent Compartmentalization of the Corelease of Glutamate and GABA from the Mossy Fibers. J Neurosci 2017; 37:701-714. [PMID: 28100750 DOI: 10.1523/jneurosci.1915-16.2016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Revised: 12/01/2016] [Accepted: 12/04/2016] [Indexed: 01/27/2023] Open
Abstract
The mossy fibers (MFs) corelease glutamate and GABA onto pyramidal cells of CA3 during development, until the end of the third postnatal week. However, the major target cells of the MF are the interneurons of CA3. Therefore, it has been shown that the interneurons of the hilus and stratum lucidum receive this dual monosynaptic input on MF stimulation. Because the plasticity of glutamatergic transmission from the different terminals of the MF is target specific, we here asked whether the corelease of glutamate and GABA was also subjected to a target-dependent compartmentalization. We analyzed the occurrence and plasticity of MF simultaneous glutamatergic-GABAergic signaling onto interneurons of the different strata of CA3 in rats during the third postnatal week. We show the coexistence of time-locked, glutamate receptor and GABA receptor-mediated mono synaptic responses evoked by MF stimulation in interneurons from stratum lucidum and stratum radiatum, but not in interneurons from stratum lacunosum-moleculare. As expected from the transmission of MF origin, MF GABAergic responses were depressed by the activation of metabotropic glutamate receptors. Strikingly, while MF glutamatergic responses underwent LTD, the simultaneous MF GABAergic responses of stratum lucidum interneurons, but not of stratum radiatum interneurons, displayed a Hebbian form of LTP that was mimicked by PKC activation. PKA activation potentiated MF glutamatergic responses of stratum radiatum interneurons, whereas in stratum lucidum interneurons only GABAergic responses were potentiated. We here disclose that the corelease of glutamate and GABA, as well as their plasticity are compartmentalized in a target-dependent manner, showing counterbalanced compensatory plasticity of two neurotransmitters released by different terminals of the same pathway. SIGNIFICANCE STATEMENT The mossy fibers transiently corelease glutamate and GABA onto pyramidal cells of CA3. We here describe that they can also corelease these amino acids onto interneurons, in a target-dependent manner. Many interneurons in stratum lucidum and stratum radiatum receive both signals, while those in stratum lacunosum-moleculare exclusively receive a glutamatergic signal. It is noteworthy that glutamatergic LTD, which is known to exist on stratum lucidum interneurons, coexists in the same pathway with a presynaptic form of GABAergic LTP, while interneurons of stratum radiatum, despite receiving this dual signaling, do not display such plasticity. The GABAergic LTP is mimicked with PKA or PKC activation. We disclose compartmentalized corelease of glutamate and GABA and its differential plasticity from a single pathway onto different interneuron sets.
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Abstract
Neurotransmitter switching is the gain of one neurotransmitter and the loss of another in the same neuron in response to chronic stimulation. Neurotransmitter receptors on postsynaptic cells change to match the identity of the newly expressed neurotransmitter. Neurotransmitter switching often appears to change the sign of the synapse from excitatory to inhibitory or from inhibitory to excitatory. In these cases, neurotransmitter switching and receptor matching thus change the polarity of the circuit in which they take place. Neurotransmitter switching produces up or down reversals of behavior. It is also observed in response to disease. These findings raise the possibility that neurotransmitter switching contributes to depression, schizophrenia, and other illnesses. Many early discoveries of the single gain or loss of a neurotransmitter may have been harbingers of neurotransmitter switching.
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Affiliation(s)
- Nicholas C Spitzer
- Neurobiology Section, Division of Biological Sciences, Kavli Institute for Brain and Mind, University of California, San Diego, La Jolla, California 92093-0357;
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The plastic neurotransmitter phenotype of the hippocampal granule cells and of the moss in their messy fibers. J Chem Neuroanat 2015; 73:9-20. [PMID: 26703784 DOI: 10.1016/j.jchemneu.2015.11.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 10/29/2015] [Accepted: 11/03/2015] [Indexed: 01/09/2023]
Abstract
The granule cells (GCs) and their axons, the mossy fibers (MFs), make synapses with interneurons in the hilus and CA3 area of the hippocampus and with pyramidal cells of CA3, each with distinct anatomical and functional characteristics. Many features of synaptic communication observed at the MF synapses are not usually observed in most cortical synapses, and thus have drawn the attention of many groups studying different aspects of the transmission of information. One particular aspect of the GCs, that makes their study unique, is that they express a dual glutamatergic-GABAergic phenotype and several groups have contributed to the understanding of how two neurotransmitters of opposing actions can act on a single target when simultaneously released. Indeed, the GCs somata and their mossy fibers express in a regulated manner glutamate and GABA, GAD, VGlut and VGAT, all markers of both phenotypes. Finally, their activation provokes both glutamate-R-mediated and GABA-R-mediated synaptic responses in the postsynaptic cell targets and even in the MFs themselves. The developmental and activity-dependent expression of these phenotypes seems to follow a "logical" way to maintain an excitation-inhibition balance of the dentate gyrus-to-CA3 communication.
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Ortiz F, Gutiérrez R. Entorhinal cortex lesions result in adenosine-sensitive high frequency oscillations in the hippocampus. Exp Neurol 2015; 271:319-28. [DOI: 10.1016/j.expneurol.2015.06.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 05/19/2015] [Accepted: 06/07/2015] [Indexed: 12/17/2022]
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Abstract
Among the many forms of brain plasticity, changes in synaptic strength and changes in synapse number are particularly prominent. However, evidence for neurotransmitter respecification or switching has been accumulating steadily, both in the developing nervous system and in the adult brain, with observations of transmitter addition, loss, or replacement of one transmitter with another. Natural stimuli can drive these changes in transmitter identity, with matching changes in postsynaptic transmitter receptors. Strikingly, they often convert the synapse from excitatory to inhibitory or vice versa, providing a basis for changes in behavior in those cases in which it has been examined. Progress has been made in identifying the factors that induce transmitter switching and in understanding the molecular mechanisms by which it is achieved. There are many intriguing questions to be addressed.
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Affiliation(s)
- Nicholas C Spitzer
- Neurobiology Section, Division of Biological Sciences & Kavli Institute for Brain and Mind, UCSD, La Jolla, CA 92093, USA.
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11
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Non-cell-autonomous mechanism of activity-dependent neurotransmitter switching. Neuron 2014; 82:1004-16. [PMID: 24908484 DOI: 10.1016/j.neuron.2014.04.029] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/14/2014] [Indexed: 11/21/2022]
Abstract
Activity-dependent neurotransmitter switching engages genetic programs regulating transmitter synthesis, but the mechanism by which activity is transduced is unknown. We suppressed activity in single neurons in the embryonic spinal cord to determine whether glutamate-gamma-aminobutyric acid (GABA) switching is cell autonomous. Transmitter respecification did not occur, suggesting that it is homeostatically regulated by the level of activity in surrounding neurons. Graded increase in the number of silenced neurons in cultures led to graded decrease in the number of neurons expressing GABA, supporting non-cell-autonomous transmitter switching. We found that brain-derived neurotrophic factor (BDNF) is expressed in the spinal cord during the period of transmitter respecification and that spike activity causes release of BDNF. Activation of TrkB receptors triggers a signaling cascade involving JNK-mediated activation of cJun that regulates tlx3, a glutamate/GABA selector gene, accounting for calcium-spike BDNF-dependent transmitter switching. Our findings identify a molecular mechanism for activity-dependent respecification of neurotransmitter phenotype in developing spinal neurons.
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Lewis BB, Miller LE, Herbst WA, Saha MS. The role of voltage-gated calcium channels in neurotransmitter phenotype specification: Coexpression and functional analysis in Xenopus laevis. J Comp Neurol 2014; 522:2518-31. [PMID: 24477801 PMCID: PMC4043876 DOI: 10.1002/cne.23547] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Revised: 01/22/2014] [Accepted: 01/22/2014] [Indexed: 12/20/2022]
Abstract
Calcium activity has been implicated in many neurodevelopmental events, including the specification of neurotransmitter phenotypes. Higher levels of calcium activity lead to an increased number of inhibitory neural phenotypes, whereas lower levels of calcium activity lead to excitatory neural phenotypes. Voltage-gated calcium channels (VGCCs) allow for rapid calcium entry and are expressed during early neural stages, making them likely regulators of activity-dependent neurotransmitter phenotype specification. To test this hypothesis, multiplex fluorescent in situ hybridization was used to characterize the coexpression of eight VGCC α1 subunits with the excitatory and inhibitory neural markers xVGlut1 and xVIAAT in Xenopus laevis embryos. VGCC coexpression was higher with xVGlut1 than xVIAAT, especially in the hindbrain, spinal cord, and cranial nerves. Calcium activity was also analyzed on a single-cell level, and spike frequency was correlated with the expression of VGCC α1 subunits in cell culture. Cells expressing Cav2.1 and Cav2.2 displayed increased calcium spiking compared with cells not expressing this marker. The VGCC antagonist diltiazem and agonist (−)BayK 8644 were used to manipulate calcium activity. Diltiazem exposure increased the number of glutamatergic cells and decreased the number of γ-aminobutyric acid (GABA)ergic cells, whereas (−)BayK 8644 exposure decreased the number of glutamatergic cells without having an effect on the number of GABAergic cells. Given that the expression and functional manipulation of VGCCs are correlated with neurotransmitter phenotype in some, but not all, experiments, VGCCs likely act in combination with a variety of other signaling factors to determine neuronal phenotype specification. J. Comp. Neurol. 522:2518–2531, 2014.
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Affiliation(s)
- Brittany B Lewis
- Department of Biology, College of William and Mary, Williamsburg, Virginia, 23185
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Münster-Wandowski A, Gómez-Lira G, Gutiérrez R. Mixed neurotransmission in the hippocampal mossy fibers. Front Cell Neurosci 2013; 7:210. [PMID: 24319410 PMCID: PMC3837298 DOI: 10.3389/fncel.2013.00210] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2013] [Accepted: 10/23/2013] [Indexed: 01/14/2023] Open
Abstract
The hippocampal mossy fibers (MFs), the axons of the granule cells (GCs) of the dentate gyrus, innervate mossy cells and interneurons in the hilus on their way to CA3 where they innervate interneurons and pyramidal cells. Synapses on each target cell have distinct anatomical and functional characteristics. In recent years, the paradigmatic view of the MF synapses being only glutamatergic and, thus, excitatory has been questioned. Several laboratories have provided data supporting the hypothesis that the MFs can transiently release GABA during development and, in the adult, after periods of enhanced excitability. This transient glutamate-GABA co-transmission coincides with the transient up-regulation of the machinery for the synthesis and release of GABA in the glutamatergic GCs. Although some investigators have deemed this evidence controversial, new data has appeared with direct evidence of co-release of glutamate and GABA from single, identified MF boutons. However, this must still be confirmed by other groups and with other methodologies. A second, intriguing observation is that MF activation produced fast spikelets followed by excitatory postsynaptic potentials in a number of pyramidal cells, which, unlike the spikelets, underwent frequency potentiation and were strongly depressed by activation of metabotropic glutamate receptors. The spikelets persisted during blockade of chemical transmission and were suppressed by the gap junction blocker carbenoxolone. These data are consistent with the hypothesis of mixed electrical-chemical synapses between MFs and some pyramidal cells. Dye coupling between these types of principal cells and ultrastructural studies showing the co-existence of AMPA receptors and connexin 36 in this synapse corroborate their presence. A deeper consideration of mixed neurotransmission taking place in this synapse may expand our search and understanding of communication channels between different regions of the mammalian CNS.
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Dulcis D, Spitzer NC. Reserve pool neuron transmitter respecification: Novel neuroplasticity. Dev Neurobiol 2012; 72:465-74. [PMID: 21595049 DOI: 10.1002/dneu.20920] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The identity of the neurotransmitters expressed by neurons has been thought to be fixed and immutable, but recent studies demonstrate that changes in electrical activity can rapidly and reversibly reconfigure the transmitters and corresponding transmitter receptors that neurons express. Induction of transmitter expression can be achieved by selective activation of afferents recruited by a physiological range of sensory input. Strikingly, neurons acquiring an additional transmitter project to appropriate targets prior to transmitter respecification in some cases, indicating the presence of reserve pools of neurons that can boost circuit function. We discuss the evidence for such reserve pools, their likely locations and ways to test for their existence, and the potential clinical value of such circuit-specific neurotransmitter respecification for treatments of neurological disorders.
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Affiliation(s)
- Davide Dulcis
- Neurobiology Section, Division of Biological Sciences and Center for Neural Circuits and Behavior, Kavli Institute for Brain and Mind, University of California-San Diego, La Jolla, CA 92093, USA.
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15
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Heldt SA, Mou L, Ressler KJ. In vivo knockdown of GAD67 in the amygdala disrupts fear extinction and the anxiolytic-like effect of diazepam in mice. Transl Psychiatry 2012; 2:e181. [PMID: 23149445 PMCID: PMC3565763 DOI: 10.1038/tp.2012.101] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In mammals, γ-aminobutyric acid (GABA) transmission in the amygdala is particularly important for controlling levels of fear and anxiety. Most GABA synthesis in the brain is catalyzed in inhibitory neurons from L-glutamic acid by the enzyme glutamic acid decarboxylase 67 (GAD67). In the current study, we sought to examine the acquisition and extinction of conditioned fear in mice with knocked down expression of the GABA synthesizing enzyme GAD67 in the amygdala using a lentiviral-based (LV) RNA interference strategy to locally induce loss-of-function. In vitro experiments revealed that our LV-siRNA-GAD67 construct diminished the expression of GAD67 as determined with western blot and fluorescent immunocytochemical analyses. In vivo experiments, in which male C57BL/6J mice received bilateral amygdala microinjections, revealed that LV-siRNA-GAD67 injections produce significant inhibition of endogenous GAD67 when compared with control injections. In contrast, no significant changes in GAD65 expression were detected in the amygdala, validating the specificity of LV knockdown. Behavioral experiments showed that LV knockdown of GAD67 results in a deficit in the extinction, but not the acquisition or retention, of fear as measured by conditioned freezing. GAD67 knockdown did not affect baseline locomotion or basal measures of anxiety as measured in open field apparatus. However, diminished GAD67 in the amygdala blunted the anxiolytic-like effect of diazepam (1.5 mg kg(-1)) as measured in the elevated plus maze. Together, these studies suggest that of GABAergic transmission in amygdala mediates the inhibition of conditioned fear and the anxiolytic-like effect of diazepam in adult mice.
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Affiliation(s)
- S A Heldt
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, USA.
| | - L Mou
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - K J Ressler
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA,Howard Hughes Medical Institute, Bethesda, MD, USA
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Demarque M, Spitzer NC. Neurotransmitter phenotype plasticity: an unexpected mechanism in the toolbox of network activity homeostasis. Dev Neurobiol 2012; 72:22-32. [PMID: 21557513 DOI: 10.1002/dneu.20909] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The transmitter phenotype of a neuron has long been thought to be stable for the lifespan. Much as eyes have one color and do not change it over time, neurons have been thought to have one neurotransmitter and retain it for their lifetime. Both principles, exclusivity and stability, are challenged by recent data. More and more neurons in different regions of the brain appear to coexpress two or more neurotransmitters. Moreover, the profile of neurotransmitter expression of a given neuron has been shown to change over time, both during development and in response to changes in activity. The present review summarizes recent studies of this neurotransmitter phenotype plasticity (NPP). Homeostatic mechanisms of plasticity are aimed at maintaining the system within a functional range. They appear to be critical for optimal network operations and have been thought to operate largely by regulating intrinsic excitability, synapse number and synaptic strength. NPP provides a new and unexpected level of regulation of network homeostasis. We propose that it provides the basis for NT coexpression and discuss emerging issues and new questions for further studies in coming years.
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Affiliation(s)
- Michaël Demarque
- Neurobiology Section, Division of Biological Sciences, Kavli Institute for Brain and Mind, University of California San Diego, La Jolla, California 92093, USA.
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17
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Abstract
For many years it has been assumed that the identity of the transmitters expressed by neurons is stable and unchanging. Recent work, however, shows that electrical activity can respecify neurotransmitter expression during development and in the mature nervous system, and an understanding is emerging of the molecular mechanisms underlying activity-dependent transmitter respecification. Changes in postsynaptic neurotransmitter receptor expression accompany and match changes in transmitter specification, thus enabling synaptic transmission. The functional roles of neurotransmitter respecification are beginning to be understood and appear to involve homeostatic synaptic regulation, which in turn influences behaviour. Activation of this novel form of plasticity by sensorimotor stimuli may provide clinical benefits.
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Treviño M, Vivar C, Gutiérrez R. Excitation-inhibition balance in the CA3 network--neuronal specificity and activity-dependent plasticity. Eur J Neurosci 2011; 33:1771-85. [PMID: 21501253 DOI: 10.1111/j.1460-9568.2011.07670.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Activation of the axons of the granule cells, the mossy fibers, excites pyramidal cells and interneurons in the CA3 area, which, in turn, inhibit pyramidal cells. The integration of the various inputs that converge onto CA3 cells has been studied by pharmacological dissection of either the excitatory or inhibitory components. This strategy has the disadvantage of partially isolating the recorded cell from the network, ignoring the sources and the impact of concurrent inputs. To overcome this limitation, we dissociated excitatory and inhibitory synaptic conductances by mathematical extraction techniques, and analysed the dynamics of the integration of excitatory and inhibitory inputs in pyramidal cells and stratum lucidum interneurons (Sl-Ints) of CA3. We have uncovered a shunting mechanism that decreases the responsiveness of CA3 output cells to mossy fiber input after a period of enhanced excitability. The activation of the dentate gyrus (DG) after applying a kindling-like protocol in vitro, or after producing one or several seizures in vivo, results in a graded and reversible increase of inhibitory conductances in pyramidal cells, while in Sl-Ints, an increase of excitatory conductances occurs. Thus, interneurons reach more depolarized membrane potentials on DG activation yielding a high excitatory postsynaptic potential-spike coupling, while the contrary occurs in pyramidal cells. This effective activation of feedforward inhibition is synergized by the emergence of direct DG-mediated inhibition on pyramidal cells. These factors force the synaptic conductance to peak at a potential value close to resting membrane potential, thus producing shunt inhibition and decreasing the responsiveness of CA3 output cells to mossy fiber input.
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Affiliation(s)
- Mario Treviño
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional Apartado Postal 14-740, México D.F. 07000, Mexico
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Stanić D, Mulder J, Watanabe M, Hökfelt T. Characterization of NPY Y2 receptor protein expression in the mouse brain. II. Coexistence with NPY, the Y1 receptor, and other neurotransmitter-related molecules. J Comp Neurol 2011; 519:1219-57. [DOI: 10.1002/cne.22608] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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20
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Vivash L, Tostevin A, Liu D, Dalic L, Dedeurwaerdere S, Hicks R, Williams D, Myers D, O'Brien T. Changes in hippocampal GABAA/cBZR density during limbic epileptogenesis: Relationship to cell loss and mossy fibre sprouting. Neurobiol Dis 2011; 41:227-36. [DOI: 10.1016/j.nbd.2010.08.021] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 08/10/2010] [Accepted: 08/25/2010] [Indexed: 12/12/2022] Open
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21
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Galván EJ, Cosgrove KE, Barrionuevo G. Multiple forms of long-term synaptic plasticity at hippocampal mossy fiber synapses on interneurons. Neuropharmacology 2010; 60:740-7. [PMID: 21093459 DOI: 10.1016/j.neuropharm.2010.11.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Revised: 10/29/2010] [Accepted: 11/10/2010] [Indexed: 11/24/2022]
Abstract
The hippocampal mossy fiber (MF) pathway originates from the dentate gyrus granule cells and provides a powerful excitatory synaptic drive to neurons in the dentate gyrus hilus and area CA3. Much of the early work on the MF pathway focused on its electrophysiological properties, and ability to drive CA3 pyramidal cell activity. Over the last ten years, however, a new focus on the synaptic interaction between granule cells and inhibitory interneurons has emerged. These data have revealed an immense heterogeneity of long-term plasticity at MF synapses on various interneuron targets. Interestingly, these studies also indicate that the mechanisms of MF long-term plasticity in some interneuron subtypes may be more similar to pyramidal cells than previously appreciated. In this review, we first define the synapse types at each of the interneuron targets based on the receptors present. We then describe the different forms of long-term plasticity observed, and the mechanisms underlying each form as they are currently understood. Finally we highlight various open questions surrounding MF long-term plasticity in interneurons, focusing specifically on the induction and maintenance of LTP, and what the functional impact of persistent changes in efficacy at MF-interneuron synapses might be on the emergent properties of the inhibitory network dynamics in area CA3. This article is part of a Special Issue entitled 'Synaptic Plasticity & Interneurons'.
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Affiliation(s)
- Emilio J Galván
- Dept. of Pharmacobiology, CINVESTAV-Sur, Mexico City, Mexico.
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22
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Liu DS, O'Brien TJ, Williams DA, Hicks RJ, Myers DE. Lamina-specific changes in hippocampal GABAA/cBZR and mossy fibre sprouting during and following amygdala kindling in the rat. Neurobiol Dis 2009; 35:337-47. [DOI: 10.1016/j.nbd.2009.05.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Revised: 05/13/2009] [Accepted: 05/15/2009] [Indexed: 10/20/2022] Open
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Transmitter-receptor mismatch in GABAergic synapses in the absence of activity. Proc Natl Acad Sci U S A 2008; 105:18988-93. [PMID: 19020084 DOI: 10.1073/pnas.0806979105] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Competition among different axons to reach the somatodendritic region of the target neuron is an important event during development to achieve the final architecture typical of the mature brain. Trasmitter-receptor matching is a critical step for the signaling between neurons. In the cerebellar cortex, there is a persistent competition between the two glutamatergic inputs, the parallel fibers and the climbing fibers, for the innervation of the Purkinje cells. The activity of the latter input is necessary to maintain its own synaptic contacts on the proximal dendritic domain and to confine the parallel fibers in the distal one. Here, we show that climbing fiber activity also limits the distribution of the GABAergic input in the proximal domain. In addition, blocking the activity by tetrodotoxin infusion in Wistar rat cerebellum, a synapse made by GABAergic terminals onto the recently formed Purkinje cell spines appear in the proximal dendrites. The density of GABAergic terminals is increased, and unexpected double symmetric/asymmetric postsynaptic densities add to the typical symmetric phenotype of the GABAergic shaft synapses. Moreover, glutamate receptors appear in these ectopic synapses even in the absence of glutamate transmitter inside the presynaptic terminal and close to GABA receptors. These results suggest that the Purkinje cell has an intrinsic tendency to develop postsynaptic assemblies of excitatory types, including glutamate receptors, over the entire dendritic territory. GABA receptors are induced in these assemblies when contacted by GABAergic terminals, thus leading to the formation of hybrid synapses.
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Abstract
OBJECTIVES To review the understanding about co-localisation of amino acid transmitters in the brain. RESULTS The idea that neurons release the same transmitter at all their synapses is associated with Henry Dale and formulated as Dale's principle by John Eccles. This idea has been modified during the last years based on several studies showing that transmitters can co-exist at the same synapse. First, a large body of evidence was presented showing that a classical transmitter can be co-localized with different types of neuropeptides. Then, several studies showed that a synapse could co-release two classical transmitters. CONCLUSION This review presents and discusses data from our laboratory showing co-release of glutamate/gamma-aminobutyric acid (GABA), aspartate/glutamate and aspartate/GABA from different types of hippocampal synapses.
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Affiliation(s)
- V Gundersen
- Department of Anatomy and the CMBN, University of Oslo, Norway.
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Romo-Parra H, Treviño M, Heinemann U, Gutiérrez R. GABA Actions in Hippocampal Area CA3 During Postnatal Development: Differential Shift From Depolarizing to Hyperpolarizing in Somatic and Dendritic Compartments. J Neurophysiol 2008; 99:1523-34. [DOI: 10.1152/jn.01074.2007] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
γ-Aminobutyric acid type A receptor (GABAA-R) activation leads to depolarization of pyramidal cells during the first postnatal week and produces hyperpolarization from the second week. However, immunohistochemical evidence has suggested that during the second and third postnatal weeks the NKCC1 cotransporter relocates from the soma to the dendrites of CA3 pyramidal cells. We hypothesized that this leads to depolarizing responses in apical dendrites. Here we show that the activation of GABAA-R in the distal dendrites of CA3 pyramidal cells at P15 by restricted application of muscimol or synaptic activation by stimulation of interneurons in stratum radiatum (SR) causes depolarizing postsynaptic potentials (PSPs), which are blocked by NKCC1 cotransporter antagonists. By contrast, activation of proximal GABAA-R by muscimol application or by stimulation of interneurons in s. oriens (SO) leads to hyperpolarizing PSPs. Activation of the dentate gyrus (DG) in the presence of glutamatergic blockers evokes hyperpolarizing responses during the second postnatal week; however, the reversal potential of the DG-evoked inhibitory (I)PSPs is more depolarized than that of IPSPs evoked by activation of SO interneurons. Despite the shift of GABA action from depolarizing to hyperpolarizing, DG-evoked field potentials (f-PSPs) recorded in s. lucidum/radiatum (SL/R) do not change in polarity until the third week. Current source density analysis yielded results consistent with depolarizing actions of GABA in the dendritic compartment. Our data suggest that GABAergic input to apical dendrites of pyramidal cells of CA3 evokes depolarizing PSPs long after synaptic inhibition has become hyperpolarizing in the somata, in the axon initial segments and in basal dendrites.
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Uchigashima M, Fukaya M, Watanabe M, Kamiya H. Evidence against GABA release from glutamatergic mossy fiber terminals in the developing hippocampus. J Neurosci 2007; 27:8088-100. [PMID: 17652600 PMCID: PMC6672728 DOI: 10.1523/jneurosci.0702-07.2007] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Hippocampal mossy fibers of young rodents have been reported to corelease inhibitory neurotransmitter GABA in addition to excitatory transmitter glutamate. In this study, we aimed at re-evaluating this corelease hypothesis of both inhibitory and excitatory transmitters in the hippocampus. Electrophysiological examination revealed that, in juvenile mice and rats of the two to 3 weeks old, stimulation at the granule cell layer of the dentate gyrus elicited monosynaptic GABAergic IPSCs in CA3 neurons in the presence of ionotropic glutamate receptor (iGluR) blockers, only when rather strong stimuli were given. The group II mGluR agonist (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclo-propyl)glycine (DCG-IV), which selectively suppresses transmission at the mossy fiber-CA3 synapse, abolished almost all postsynaptic responses elicited by the weak stimuli, whereas those by strong stimuli were inhibited only slightly. In addition, the minimal stimulation elicited GABAergic IPSCs in neonatal mice of the first postnatal week, whereas these responses are not sensitive to DCG-IV. Immunohistochemical examination revealed that mossy fiber terminals expressed GABA and the GABA-synthesizing enzyme GAD67, although the expression levels were much weaker than those in the inhibitory interneurons. Notably, the expression levels of the vesicular GABA transporter were much lower than those of GABA and GAD67, and almost below detection threshold. These results suggest that mossy fiber synapses are purely glutamatergic and apparent monosynaptic IPSCs so far reported are evoked by costimulation of inhibitory interneurons, at least in young mice and rats. Hippocampal mossy fiber terminals synthesize and store GABA, but have limited ability in vesicular release for GABA in the developing rodents.
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Affiliation(s)
| | | | | | - Haruyuki Kamiya
- Neurobiology, Hokkaido University School of Medicine, Sapporo 060-8638, Japan
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27
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Raedt R, Boon P, Persson A, Alborn AM, Boterberg T, Van Dycke A, Linder B, De Smedt T, Wadman WJ, Ben-Menachem E, Eriksson PS. Radiation of the rat brain suppresses seizure-induced neurogenesis and transiently enhances excitability during kindling acquisition. Epilepsia 2007; 48:1952-63. [PMID: 17555527 DOI: 10.1111/j.1528-1167.2007.01146.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
PURPOSE Adult hippocampal neurogenesis is enhanced in several models for temporal lobe epilepsy (TLE). In this study, we used low-dose whole brain radiation to suppress hippocampal neurogenesis and then studied the effect of this treatment on epileptogenesis in a kindling model for TLE. METHODS Half of the rats were exposed to a radiation dose of 8 Gy one day before the initiation of a rapid kindling protocol. Afterdischarge threshold (ADT), afterdischarge duration (ADD), clinical seizure severity, and inflammation were compared between groups. On the first and third day after radiation, rats were injected with 5'-bromo-2'-deoxyuridine (BrdU) to evaluate neurogenesis. Seven and 21 days after radiation, numbers of doublecortin (DCX) positive neuroblasts in subgranular zone and granule cell layer were compared between groups. RESULTS We showed that radiation significantly suppressed neurogenesis and neuroblast production during kindling acquisition. Radiation prevented an increase in ADT that became significantly lower in radiated rats. On the third and fourth kindling acquisition day radiated rats developed more severe seizures more rapidly, which resulted in a significantly higher mean severity score on these days. Differences in ADD could not be demonstrated. DISCUSSION Our results demonstrate that brain radiation with a relatively low dose effectively suppressed the generation of new granule cells and transiently enhanced excitability during kindling acquisition. Although seizure-induced neurogenesis was lower in the radiated rats we could not detect a strong effect on the final establishment of the permanent fully kindled state, which argues against a prominent role of seizure-induced neurogenesis in epileptogenesis.
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Affiliation(s)
- Robrecht Raedt
- Laboratory for Clinical and Experimental Neurophysiology, Department of Neurology, Ghent University Hospital, Ghent, Belgium.
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28
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Ulrich D, Bettler B. GABA(B) receptors: synaptic functions and mechanisms of diversity. Curr Opin Neurobiol 2007; 17:298-303. [PMID: 17433877 DOI: 10.1016/j.conb.2007.04.001] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2007] [Accepted: 04/05/2007] [Indexed: 12/20/2022]
Abstract
GABA(B) receptors are the G-protein-coupled receptors for GABA, the main inhibitory neurotransmitter in the mammalian central nervous system. They are implicated in a variety of neurological and psychiatric disorders. With the cloning of GABA(B) receptors ten years ago, substantial progress was made in our understanding of this receptor system. Here, we review current concepts of synaptic GABA(B) functions and present the evidence that points to specific roles for receptor subtypes. We discuss ultrastructural studies revealing that most GABA(B) receptors are located remote from GABAergic terminals, which raises questions as to when such receptors become activated. Finally, we provide possible explanations for the perplexing situation that GABA(B) receptor subtypes that have indistinguishable properties in vitro generate distinct GABA(B) responses in vivo.
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Affiliation(s)
- Daniel Ulrich
- Pharmazentrum, Institute of Physiology, University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
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29
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Treviño M, Vivar C, Gutiérrez R. Beta/gamma oscillatory activity in the CA3 hippocampal area is depressed by aberrant GABAergic transmission from the dentate gyrus after seizures. J Neurosci 2007; 27:251-9. [PMID: 17202493 PMCID: PMC6672272 DOI: 10.1523/jneurosci.3815-06.2007] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Oscillatory activity in the CA3 region is thought to be involved in the encoding and retrieval of information. These oscillations originate from the recurrent excitation between pyramidal cells that are entrained by the synchronous rhythmic inhibition of local interneurons. We show here that, after seizures, the dentate gyrus (DG) tonically inhibits beta/gamma (20-24 Hz) field oscillations in the CA3 area through GABA-mediated signaling. These oscillations originate in the interneuron network because they are maintained in the presence of ionotropic glutamate receptor antagonists, and they can be blocked by GABA(A) receptor antagonists or by perfusion of a calcium-free extracellular medium. Inhibition of this oscillatory activity requires intact DG-to-CA3 connections, and it is suppressed by the activation of metabotropic glutamate receptors (mGluR). The influence of mGluR activation was reflected in the spontaneous subthreshold membrane oscillations of CA3 interneurons after one seizure but could also be observed in pyramidal cells after several seizures. Coincident stimulation of the DG at and beta/gamma frequencies produced a frequency-dependent excitation of interneurons and the inhibition of pyramidal cells. Indeed, these effects were maximal at the frequency that matched the mGluR-sensitive spontaneous field oscillations, suggesting a resonance phenomenon. Our results shed light on the mechanisms that may underlie the deficits in memory and cognition observed after epileptic seizures.
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Affiliation(s)
- Mario Treviño
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, México DF 07000, México
| | - Carmen Vivar
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, México DF 07000, México
| | - Rafael Gutiérrez
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, México DF 07000, México
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30
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Jaffe DB, Gutiérrez R. Mossy fiber synaptic transmission: communication from the dentate gyrus to area CA3. PROGRESS IN BRAIN RESEARCH 2007; 163:109-32. [PMID: 17765714 DOI: 10.1016/s0079-6123(07)63006-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Communication between the dentate gyrus (DG) and area CA3 of the hippocampus proper is transmitted via axons of granule cells--the mossy fiber (MF) pathway. In this review we discuss and compare the properties of transmitter release from the MFs onto pyramidal neurons and interneurons. An examination of the anatomical connectivity from DG to CA3 reveals a surprising interplay between excitation and inhibition for this circuit. In this respect it is particularly relevant that the major targets of the MFs are interneurons and that the consequence of MF input into CA3 may be inhibitory or excitatory, conditionally dependent on the frequency of input and modulatory regulation. This is further complicated by the properties of transmitter release from the MFs where a large number of co-localized transmitters, including GABAergic inhibitory transmitter release, and the effects of presynaptic modulation finely tune transmitter release. A picture emerges that extends beyond the hypothesis that the MFs are simply "detonators" of CA3 pyramidal neurons; the properties of synaptic information flow from the DG have more subtle and complex influences on the CA3 network.
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Affiliation(s)
- David B Jaffe
- Department of Biology, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA.
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31
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Villalba RM, Raju DV, Hall RA, Smith Y. GABA(B) receptors in the centromedian/parafascicular thalamic nuclear complex: an ultrastructural analysis of GABA(B)R1 and GABA(B)R2 in the monkey thalamus. J Comp Neurol 2006; 496:269-87. [PMID: 16538684 DOI: 10.1002/cne.20950] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Strong gamma-aminobutyric acid type B (GABA(B)) receptor binding has been shown throughout the thalamus, but the distribution of the two GABA(B) receptor subunits, GABA(B) receptor subunit 1 (GABA(B)R1) and GABA(B) receptor subunit 2 (GABA(B)R2), remains poorly characterized. In primates, the caudal intralaminar nuclei, centromedian and parafascicular (CM/PF), are an integral part of basal ganglia circuits and a main source of inputs to the striatum. In this study, we analyzed the subcellular and subsynaptic distribution of GABA(B) receptor subunits by using light and electron microscopic immunocytochemical techniques. Quantitative immunoperoxidase and immunogold analysis showed that both subunits display a similar pattern of distribution in CM/PF, being expressed largely at extrasynaptic and perisynaptic sites in neuronal cell bodies, dendrites, and axon-like processes and less abundantly in axon terminals. Postsynaptic GABA(B)R1 labeling was found mostly on the plasma membrane (70-80%), whereas GABA(B)R2 was more evenly distributed between the plasma membrane and intracellular compartments of CM/PF neurons. A few axon terminals forming symmetric and asymmetric synapses were also labeled for GABA(B)R1 and GABA(B)R2, but the bulk of presynaptic labeling was expressed in small axon-like processes. About 20% of presynaptic vesicle-containing dendrites of local circuit neurons displayed GABA(B)R1/R2 immunoreactivity. Vesicular glutamate transporters (vGluT1)-containing terminals forming asymmetric synapses expressed GABA(B)R1 and/or displayed postsynaptic GABA(B)R1 at the edges of their asymmetric specialization. Overall, these findings provide evidence for multiple sites where GABA(B) receptors could modulate GABAergic and glutamatergic transmission in the primate CM/PF complex.
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Affiliation(s)
- Rosa M Villalba
- Yerkes National Primate Research Center, Emory University, Atlanta, Georgia 30322, USA.
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32
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Ikegaya Y. [Potential roles for mossy fiber sprouting in temporal lobe epilepsy]. Nihon Yakurigaku Zasshi 2006; 127:355-61. [PMID: 16819240 DOI: 10.1254/fpj.127.355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
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Gómez-Lira G, Lamas M, Romo-Parra H, Gutiérrez R. Programmed and induced phenotype of the hippocampal granule cells. J Neurosci 2006; 25:6939-46. [PMID: 16049169 PMCID: PMC6724843 DOI: 10.1523/jneurosci.1674-05.2005] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Certain neurons choose the neurotransmitter they use in an activity-dependent manner, and trophic factors are involved in this phenotypic differentiation during development. Developing hippocampal granule cells (GCs) constitutively express the markers of the glutamatergic and GABAergic phenotypes, but when development is completed, the GABAergic phenotype shuts off. With electrophysiological, single-cell reverse transcription-PCR and immunohistological techniques, we show here that short-term (24 h) cultures of fully differentiated adult glutamatergic GCs, which express glutamate, VGlut-1 (vesicular glutamate transporter) mRNA, calbindin, and dynorphin mRNA, can be induced to reexpress the GABAergic markers GABA, GAD67 (glutamate decarboxylase 67 kDa isoform), and VGAT (vesicular GABA transporter) mRNA, by sustained synaptic or direct activation of glutamate receptors and by activation of TrkB (tyrosine receptor kinase B) receptors, with brain-derived neurotrophic factor (BDNF) (30 min). The expression of the GABAergic markers was prevented by the blockade of glutamate receptors and sodium or calcium channels, and by inhibitors of protein kinases and protein synthesis. In hippocampal slices of epileptic rats and in BDNF-treated slices from naive rats, we confirmed the appearance of monosynaptic GABAA receptor-mediated responses to GC stimulation, in the presence of glutamate receptors blockers. Accordingly, GC cultures prepared from these slices showed the coexpression of the glutamatergic and GABAergic markers. Our results demonstrate that the neurotransmitter choice of the GCs, which are unique in terms of their continuing birth and death throughout life, depends on programmed and environmental factors, and this process is neither limited by a critical developmental period nor restricted by their insertion in their natural network.
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Affiliation(s)
- Gisela Gómez-Lira
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, 07000 Distrito Federal, Mexico
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Meltzer LA, Yabaluri R, Deisseroth K. A role for circuit homeostasis in adult neurogenesis. Trends Neurosci 2005; 28:653-60. [PMID: 16271403 DOI: 10.1016/j.tins.2005.09.007] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2005] [Revised: 08/25/2005] [Accepted: 09/20/2005] [Indexed: 11/24/2022]
Abstract
Insertion of new neurons into adult neural circuits could either promote or impair circuit function, depending on whether homeostatic mechanisms are in place to regulate the resulting changes in neural activity. In the hippocampus (a mammalian forebrain structure important in aspects of memory and mood) several lines of behavioral evidence suggest important adaptive roles for adult-generated neurons, indicating that there could be mechanisms to control the potentially adverse increase in excitation associated with new cells. Here, we delineate behavioral and computational models for the role of circuit homeostasis in enabling neuron insertion to modulate hippocampal function adaptively, and we describe molecular and cellular mechanisms for implementing this circuit-level adaptive regulation of hippocampal activity.
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Affiliation(s)
- Leslie A Meltzer
- Department of Bioengineering, Neuroscience Program, Stanford University, W083 Clark Center, 318 Campus Drive West, Stanford, CA 94305, USA
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Sirvanci S, Meshul CK, Onat F, San T. Glutamate and GABA immunocytochemical electron microscopy in the hippocampal dentate gyrus of normal and genetic absence epilepsy rats. Brain Res 2005; 1053:108-15. [PMID: 16038886 DOI: 10.1016/j.brainres.2005.06.024] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2004] [Revised: 06/07/2005] [Accepted: 06/10/2005] [Indexed: 11/22/2022]
Abstract
It is generally accepted that absence epilepsy results from the impairment of GABAergic and glutamatergic neurotransmission. In particular, besides excessive GABA mediation within the thalamo-cortico-thalamic circuit in absence epilepsy, neuronal networks of the hippocampus have recently received attention. In the present study, we examined the density of glutamate and GABA neurotransmitter immunolabeling in the dentate gyrus of the hippocampus of genetic absence epilepsy rats from Strasbourg (GAERS) compared to the control group. GABA and glutamate were found to exist in synaptic vesicles of the mossy fiber terminals of the control and GAERS groups. The density of glutamate immunolabeling within the mossy fiber terminals in the hilar region of GAERS hippocampus was found to be significantly decreased compared to the control group. There was no difference in the density of immunolabeling within GABA nerve terminals between GAERS and control group. The findings of this study suggest that mechanisms underlying absence seizures in GAERS may also manifest themselves in other brain regions such as the hippocampus. The presence of GABA within synaptic vesicles of mossy fiber terminals, as revealed by high resolution ultrastructural immunocytochemistry, has provided additional evidence to the possible modulatory role of GABA on synaptic transmission between the mossy fiber and the target cell.
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Affiliation(s)
- Serap Sirvanci
- Marmara University School of Medicine, Department of Histology and Embryology, Istanbul, Turkey
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36
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Treviño M, Gutiérrez R. The GABAergic projection of the dentate gyrus to hippocampal area CA3 of the rat: pre- and postsynaptic actions after seizures. J Physiol 2005; 567:939-49. [PMID: 16002442 PMCID: PMC1474233 DOI: 10.1113/jphysiol.2005.092064] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The glutamatergic granule cells of the dentate gyrus transiently express GABAergic markers after seizures. Here we show that when this occurs, their activation produces (i) GABA(A) receptor-mediated synaptic field responses in CA3, with the physiological and pharmacological characteristics of mossy fibre transmission, and (ii) GABA(A) receptor-mediated collateral inhibition. Control hippocampal slices present, on stimulation of the dentate gyrus, population responses in stratum lucidum, which are blocked by ionotropic glutamate receptor antagonists. By contrast, in slices from rats subjected to seizures in vivo, dentate activation additionally produces GABA(A) receptor-mediated field synaptic responses in the presence of glutamate receptor antagonists. One-dimensional current source density analysis confirmed the spatial coincidence of the glutamatergic and GABAergic dendritic currents. The GABA(A) receptor-mediated field responses show frequency-dependent facilitation and strong inhibition during activation of metabotropic glutamate receptors. In the presence of glutamate receptor blockers, a conditioning pulse delivered to one site of the dentate gyrus inhibits the population synaptic response and the afferent volley provoked by the activation of a second site, in a bicuculline-sensitive manner. In accordance with this, antidromic responses evoked by mossy fibre activation were enhanced by perfusion of bicuculline. Our results suggest that, for GABA receptor-dependent field potentials to be detected, a considerable number of boutons of a well-defined GABAergic pathway should simultaneously release GABA to act on a large number of receptors. Therefore, putative GABA release from the mossy fibres acts on pre- and postsynaptic sites to affect hippocampal activity at the network level after seizures.
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Affiliation(s)
- Mario Treviño
- Department of Physiology, Biophysics and Neuroscience, Centro de Investigación y Estudios Avanzados, Mexico
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37
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Gutiérrez R. The dual glutamatergic–GABAergic phenotype of hippocampal granule cells. Trends Neurosci 2005; 28:297-303. [PMID: 15927685 DOI: 10.1016/j.tins.2005.04.005] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Revised: 03/14/2005] [Accepted: 04/19/2005] [Indexed: 12/01/2022]
Abstract
Markers of the glutamatergic and GABAergic phenotypes coexist in developing hippocampal granule cells, and activation of these neurons produces simultaneous glutamate-receptor-mediated and GABA-receptor-mediated responses in their postsynaptic cells. In the adult, markers of the GABAergic phenotype and the consequent GABAergic transmission disappear but can be transiently expressed in an activity-dependent manner. Coexistence of glutamate and GABA in neurons from other regions of the brain is being discovered, and the possibility of these neurotransmitters being co-released gives the CNS a powerful computational tool. Although waiting to be confirmed by paired recordings, the hypothesis that glutamate and GABA are co-released from single cells is a valuable heuristic proposal in understanding the plasticity inherent to neuronal communication.
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Affiliation(s)
- Rafael Gutiérrez
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, Apartado Postal 14-740, México City, DF 07000, México.
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38
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Ottem EN, Godwin JG, Krishnan S, Petersen SL. Dual-phenotype GABA/glutamate neurons in adult preoptic area: sexual dimorphism and function. J Neurosci 2005; 24:8097-105. [PMID: 15371511 PMCID: PMC6729791 DOI: 10.1523/jneurosci.2267-04.2004] [Citation(s) in RCA: 161] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
It is generally assumed that the inhibitory neurotransmitter GABA and the stimulatory neurotransmitter glutamate are released from different neurons in adults. However, this tenet has made it difficult to explain how the same afferent signals can cause opposite changes in GABA and glutamate release. Such reciprocal release is a central mechanism in the neural control of many physiological processes including activation of gonadotropin-releasing hormone (GnRH) neurons, the neural signal for ovulation. Activation of GnRH neurons requires simultaneous suppression of GABA and stimulation of glutamate release, each of which occurs in response to a daily photoperiodic signal, but only in the presence of estradiol (E2). In rodents, E2 and photoperiodic signals converge in the anteroventral periventricular nucleus (AVPV), but it is unclear how these signals differentially regulate GABA and glutamate secretion. We now report that nearly all neurons in the AVPV of female rats express both vesicular glutamate transporter 2 (VGLUT2), a marker of hypothalamic glutamatergic neurons, as well as glutamic acid decarboxylase and vesicular GABA transporter (VGAT), markers of GABAergic neurons. These dual-phenotype neurons are the main targets of E2 in the region and are more than twice as numerous in females as in males. Moreover, dual-phenotype synaptic terminals contact GnRH neurons, and at the time of the surge, VGAT-containing vesicles decrease and VGLUT2-containing vesicles increase in these terminals. Thus, we propose a new model for ovulation that includes dual-phenotype GABA/glutamate neurons as central transducers of hormonal and neural signals to GnRH neurons.
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Affiliation(s)
- Erich N Ottem
- Department of Biology, Center for Neuroendocrine Studies, University of Massachusetts-Amherst, Amherst, Massachusetts 01002, USA
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39
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Spitzer NC, Borodinsky LN, Root CM. Homeostatic activity-dependent paradigm for neurotransmitter specification. Cell Calcium 2005; 37:417-23. [PMID: 15820389 DOI: 10.1016/j.ceca.2005.01.021] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2004] [Accepted: 01/06/2005] [Indexed: 01/21/2023]
Abstract
Calcium-signaling plays a central role in specification of the chemical transmitters neurons express, adjusting the numbers of cells that express excitatory and inhibitory transmitters as if to achieve homeostatic regulation of excitability. Here we review the extent to which this activity-dependent regulation is observed for a range of different transmitters. Strikingly the homeostatic paradigm is observed both for classical and for peptide transmitters and in mature as well as in embryonic nervous systems. Transmitter homeostasis adds another dimension to homeostatic regulation of function in the nervous system that includes regulation of levels of voltage-gated ion channels, densities of neurotransmitter receptors, and synapse numbers and strength.
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Affiliation(s)
- Nicholas C Spitzer
- Neurobiology Section, Division of Biological Sciences and Center for Molecular Genetics, UCSD, La Jolla, CA 92093-0357, USA.
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Vivar C, Gutiérrez R. Blockade of the membranal GABA transporter potentiates GABAergic responses evoked in pyramidal cells by mossy fiber activation after seizures. Hippocampus 2005; 15:281-4. [PMID: 15668946 DOI: 10.1002/hipo.20063] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The presence of a neurotransmitter within a synaptic terminal is normally due to its local synthesis. However, uptake of the neurotransmitter from the extracellular milieu by a specific membranal transporter can also explain its intraterminal accumulation. A specific vesicular transporter carries the neurotransmitter into synaptic vesicles, enabling it to be released in a calcium-dependent manner when the terminal is invaded by an action potential. Under certain circumstances, a neurotransmitter can also be released by the reversal in the direction of its membranal transporter, in a calcium-independent manner. Interestingly, gamma-aminobutyric acid (GABA) can be released in this manner after epileptic activity. With intracellular recordings, in this work we show that in rats subjected to seizures, but not in naive rats, mossy fiber stimulation in the presence of glutamate receptor blockers produces bicuculline-sensitive inhibitory postsynaptic potentials (IPSPs) in pyramidal cells. The blockade of the membranal GABA transporter (GAT-1) strongly enhances the amplitude and decay time of the IPSPs in both high and low extracellular calcium concentrations. This electrophysiological evidence, together with previous neurochemical and immunohistological data, show that GAT-1 contributes to the termination of the synaptic action of mossy fiber-released GABA and rules out its involvement in depolarization-dependent GABA release.
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Affiliation(s)
- Carmen Vivar
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y Estudios Avanzados del IPN, México DF, México
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41
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Kahn L, Alonso G, Normand E, Manzoni OJ. Repeated morphine treatment alters polysialylated neural cell adhesion molecule, glutamate decarboxylase-67 expression and cell proliferation in the adult rat hippocampus. Eur J Neurosci 2005; 21:493-500. [PMID: 15673448 DOI: 10.1111/j.1460-9568.2005.03883.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Altered synaptic transmission and plasticity in brain areas involved in reward and learning are thought to underlie the long-lasting effects of addictive drugs. In support of this idea, opiates reduce neurogenesis [A.J. Eisch et al. (2000) Proceedings of the National Academy of Sciences USA, 97, 7579-7584] and enhance long-term potentiation in adult rodent hippocampus [J.M. Harrison et al. (2002) Journal of Neurophysiology, 87, 2464-2470], a key structure of learning and memory processes. Here we studied how repeated morphine treatment and withdrawal affect cell proliferation and neuronal phenotypes in the dentate gyrus-CA3 region of the adult rat hippocampus. Our data showed a strong reduction of cellular proliferation in morphine-dependent animals (54% of control) that was followed by a rebound increase after 1 week withdrawal and a return to normal after 2 weeks withdrawal. Morphine dependence was also associated with a drastic reduction in the expression levels of the polysialylated form of neural cell adhesion molecule (68% of control), an adhesion molecule expressed by newly generated neurons and involved in cell migration and structural plasticity. Polysialylated neural cell adhesion molecule levels quickly returned to normal following withdrawal. In morphine-dependent rats, we found a significant increase of glutamate decarboxylase-67 mRNA transcription (170% of control) in dentate gyrus granular cells which was followed by a marked rebound decrease after 1 week withdrawal and a return to normal after 4 weeks withdrawal. Together, the results show, for the first time, that, in addition to reducing cell proliferation and neurogenesis, chronic exposure to morphine dramatically alters neuronal phenotypes in the dentate gyrus-CA3 region of the adult rat hippocampus.
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Affiliation(s)
- Laëtitia Kahn
- INSERM Equipe Avenir 'Plasticité synaptique: Maturation & Addiction', Bordeaux Cedex, France
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Santhakumar V, Aradi I, Soltesz I. Role of mossy fiber sprouting and mossy cell loss in hyperexcitability: a network model of the dentate gyrus incorporating cell types and axonal topography. J Neurophysiol 2004; 93:437-53. [PMID: 15342722 DOI: 10.1152/jn.00777.2004] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mossy cell loss and mossy fiber sprouting are two characteristic consequences of repeated seizures and head trauma. However, their precise contributions to the hyperexcitable state are not well understood. Because it is difficult, and frequently impossible, to independently examine using experimental techniques whether it is the loss of mossy cells or the sprouting of mossy fibers that leads to dentate hyperexcitability, we built a biophysically realistic and anatomically representative computational model of the dentate gyrus to examine this question. The 527-cell model, containing granule, mossy, basket, and hilar cells with axonal projections to the perforant-path termination zone, showed that even weak mossy fiber sprouting (10-15% of the strong sprouting observed in the pilocarpine model of epilepsy) resulted in the spread of seizure-like activity to the adjacent model hippocampal laminae after focal stimulation of the perforant path. The simulations also indicated that the spatially restricted, lamellar distribution of the sprouted mossy fiber contacts reported in in vivo studies was an important factor in sustaining seizure-like activity in the network. In contrast to the robust hyperexcitability-inducing effects of mossy fiber sprouting, removal of mossy cells resulted in decreased granule cell responses to perforant-path activation in agreement with recent experimental data. These results indicate the crucial role of mossy fiber sprouting even in situations where there is only relatively weak mossy fiber sprouting as is the case after moderate concussive experimental head injury.
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Morimoto K, Fahnestock M, Racine RJ. Kindling and status epilepticus models of epilepsy: rewiring the brain. Prog Neurobiol 2004; 73:1-60. [PMID: 15193778 DOI: 10.1016/j.pneurobio.2004.03.009] [Citation(s) in RCA: 613] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2003] [Accepted: 03/24/2004] [Indexed: 01/09/2023]
Abstract
This review focuses on the remodeling of brain circuitry associated with epilepsy, particularly in excitatory glutamate and inhibitory GABA systems, including alterations in synaptic efficacy, growth of new connections, and loss of existing connections. From recent studies on the kindling and status epilepticus models, which have been used most extensively to investigate temporal lobe epilepsy, it is now clear that the brain reorganizes itself in response to excess neural activation, such as seizure activity. The contributing factors to this reorganization include activation of glutamate receptors, second messengers, immediate early genes, transcription factors, neurotrophic factors, axon guidance molecules, protein synthesis, neurogenesis, and synaptogenesis. Some of the resulting changes may, in turn, contribute to the permanent alterations in seizure susceptibility. There is increasing evidence that neurogenesis and synaptogenesis can appear not only in the mossy fiber pathway in the hippocampus but also in other limbic structures. Neuronal loss, induced by prolonged seizure activity, may also contribute to circuit restructuring, particularly in the status epilepticus model. However, it is unlikely that any one structure, plastic system, neurotrophin, or downstream effector pathway is uniquely critical for epileptogenesis. The sensitivity of neural systems to the modulation of inhibition makes a disinhibition hypothesis compelling for both the triggering stage of the epileptic response and the long-term changes that promote the epileptic state. Loss of selective types of interneurons, alteration of GABA receptor configuration, and/or decrease in dendritic inhibition could contribute to the development of spontaneous seizures.
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Affiliation(s)
- Kiyoshi Morimoto
- Department of Neuropsychiatry, Faculty of Medicine, Kagawa University, Kagawa 761-0793, Japan
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Bough KJ, Mott DD, Dingledine RJ. Medial perforant path inhibition mediated by mGluR7 is reduced after status epilepticus. J Neurophysiol 2004; 92:1549-57. [PMID: 15152022 DOI: 10.1152/jn.00315.2004] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Metabotropic glutamate receptor (mGluR)-mediated inhibition within the dentate gyrus is altered after epilepsy. Whether these changes occur during the developmental period of the disease (i.e., the latent period) has not yet been investigated. Field excitatory postsynaptic potentials (fEPSPs) were recorded in the lateral (LPP) and medial perforant path (MPP) simultaneously in adult mouse hippocampal slices 3-9 days after pilocarpine (PILO)-induced status epilepticus. Genetically manipulated mice (mGluR8 knockout and mGluR4/8 double knockout) and pharmacologically selective agonists were used to identify specific mGluR subtypes affected after PILO. Pharmacological activation of mGluR7 by L-AP4 in both wild-type and mGluR4/8 double knockout mice selectively reduced fEPSPs in the MPP, but not LPP, and this level of inhibition was significantly reduced 3-9 days after PILO-induced SE. Activation of mGluR2/3 reversibly depressed the fEPSP slopes in both the MPP and LPP, but no alterations were noted after PILO. mGluR8 activation selectively inhibited evoked responses in the LPP, but not in the MPP, and this level of inhibition did not change after PILO treatment. These data suggest that reduced presynaptic inhibition mediated by mGluR7, but not mGluR2/3 or mGluR8, may play a role during the latent period in generating hyperexcitability in the dentate and thereby contribute to epileptogenesis.
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Affiliation(s)
- Kristopher J Bough
- School of Medicine, Dept. of Pharmacology, Emory University, Rollins Research Center, Rm. 5002, 1510 Clifton Road, Atlanta, GA 30322-3090, USA.
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Boyes J, Bolam JP. The subcellular localization of GABA(B) receptor subunits in the rat substantia nigra. Eur J Neurosci 2004; 18:3279-93. [PMID: 14686901 DOI: 10.1111/j.1460-9568.2003.03076.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The inhibitory effects of GABA within the substantia nigra (SN) are mediated in part by metabotropic GABA(B) receptors. To better understand the mechanisms underlying these effects, we have examined the subcellular localization of the GABA(B) receptor subunits, GABA(B1) and GABA(B2), in SN neurons and afferents using pre-embedding immunocytochemistry combined with anterograde or retrograde labelling. In both the SN pars compacta (SNc) and pars reticulata (SNr), GABA(B1) and GABA(B2) showed overlapping, but distinct, patterns of immunolabelling. GABA(B1) was more strongly expressed by putative dopaminergic neurons in the SNc than by SNr projection neurons, whereas GABA(B2) was mainly expressed in the neuropil of both regions. Immunogold labelling for GABA(B1) and GABA(B2) was localized in presynaptic and postsynaptic elements throughout the SN. The majority of labelling was intracellular or was associated with extrasynaptic sites on the plasma membrane. In addition, labelling for both subunits was found on the presynaptic and postsynaptic membranes at symmetric, putative GABAergic synapses, including those formed by anterogradely labelled striatonigral and pallidonigral terminals. Labelling was also observed on the presynaptic membrane and at the edge of the postsynaptic density at asymmetric, putative excitatory synapses. Double immunolabelling, using the vesicular glutamate transporter 2, revealed the glutamatergic nature of many of the immunogold-labelled asymmetric synapses. The widespread distribution of GABA(B) subunits in the SNc and SNr suggests that GABA(B)-mediated effects in these regions are likely to be more complex than previously described, involving presynaptic autoreceptors and heteroreceptors, and postsynaptic receptors on different populations of SN neurons.
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Affiliation(s)
- Justin Boyes
- MRC Anatomical Neuropharmacology Unit, University of Oxford, Oxford OX1 3TH, UK
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Abstract
The dentate gyrus is believed to play a key role in the pathogenesis of temporal lobe epilepsy. In normal brain the dentate granule cells serve as a high-resistance gate or filter, inhibiting the propagation of seizures from the entorhinal cortex to the hippocampus. The filtering function of the dentate gyrus depends in part on the near absence of monosynaptic connections among granule cells. In humans with temporal lobe epilepsy and in animal models of temporal lobe epilepsy, dentate granule cells form an interconnected synaptic network associated with loss of hilar interneurons. This recurrent mossy fiber pathway mediates reverberating excitation that can reduce the threshold for granule cell synchronization. Factors that augment activity in this pathway include modest increases in [K+]o; loss of GABA inhibition; short-term, frequency-dependent facilitation (frequencies of 1-2 Hz); feedback activation of kainate autoreceptors; and release of zinc from recurrent mossy fiber boutons. Factors that diminish activity include short-term, frequency-dependent depression (frequencies < 1 Hz); feedback activation of type II metabotropic glutamate receptors; and the potential release of GABA, neuropeptide Y, adenosine, and dynorphin from recurrent mossy fiber boutons. The axon sprouting and reactive synaptogenesis that follow seizure-related brain damage can also create or strengthen recurrent excitation in other brain regions. These changes are expected to facilitate participation of these regions in seizures. Thus, reactive processes that are often considered important for recovery of function after most brain injuries probably contribute to neurological dysfunction in epilepsy.
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Affiliation(s)
- J Victor Nadler
- Department of Pharmacology, Box 3813, Duke University Medical Center, Durham, North Carolina 27710, USA.
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López-Bendito G, Shigemoto R, Kulik A, Vida I, Fairén A, Luján R. Distribution of metabotropic GABA receptor subunits GABAB1a/b and GABAB2 in the rat hippocampus during prenatal and postnatal development. Hippocampus 2004; 14:836-48. [PMID: 15382254 DOI: 10.1002/hipo.10221] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Metabotropic gamma-aminobutyric acid receptors (GABAB) play modulatory roles in central synaptic transmission and are involved in controlling neuronal migration during development. We used immunohistochemical methods to elucidate the expression pattern as well as the cellular and the precise subcellular localization of the GABA(B1a/b) and GABAB2 subunits in the rat hippocampus during prenatal and postnatal development. At the light microscopic level, both GABA(B1a/b) and GABAB2 were expressed in the hippocampal primordium from embryonic day E14. During postnatal development, immunoreactivity for GABA(B1a/b) and GABAB2 was distributed mainly in pyramidal cells, with discrete GABA(B1a/b)-immunopositive cell bodies of interneurons present throughout the hippocampus. Using double immunofluorescence, we demonstrated that during the second week of postnatal development, GABA(B1a/b) but not GABAB2 was expressed in glial cells throughout the hippocampal formation. At the electron microscopic level, GABA(B1a/b) and GABAB2 showed a similar distribution pattern during postnatal development. Thus, at all ages the two receptor subunits were located postsynaptically in dendritic spines and shafts at extrasynaptic and perisynaptic sites in both pyramidal and nonpyramidal cells. We further demonstrated that the two subunits were localized presynaptically along the extrasynaptic plasma membrane of axon terminals and along the presynaptic active zone in both asymmetrical and, to a lesser extent, symmetrical synapses. These results suggest that GABAB receptors are widely expressed in the hippocampus throughout development and that GABA(B1a/b) and GABAB2 form both pre- and postsynaptic receptors.
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Affiliation(s)
- Guillermina López-Bendito
- Centro Regional de Investigaciones Biomédicas, Facultad de Medicina, Universidad de Castilla-La Mancha, Albacete, Spain
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Abstract
The granule cells of the dentate gyrus (DG), origin of the mossy fibers (MFs), have been considered to be glutamatergic. However, data obtained with different experimental approaches in recent years may be calling for a redefinition of their phenotype. Although they indeed release glutamate for fast neurotransmission, immunohistological and molecular biology evidence has revealed that these glutamatergic cells also express GABAergic markers. The granule cell expression of a GABAergic phenotype is developmentally regulated. Electrophysiological studies reveal that during the first 3 weeks of age, mossy fiber stimulation provokes monosynaptic fast inhibitory transmission mediated by GABA, besides the monosynaptic excitatory glutamatergic transmission, onto their targets in CA3. After this age, mossy fiber GABAergic transmission abruptly disappears and the GABAergic markers are undetected. In the adult, the GABAergic markers are upregulated and GABA-mediated transmission emerges after induction of hyperexcitability. The simultaneous glutamate- and GABA-mediated signals share the same plastic and pharmacological characteristics that correspond to neurotransmission of mossy fiber origin. This intriguing evidence gives rise to two fundamental points of discussion. The first is the plausible fact that glutamate and GABA, two neurotransmitters of opposing actions, are coreleased from the mossy fibers. The second relates to its functional implications that can be immediately inferred, as the dentate gyrus can exert direct GABA-mediated excitatory actions early in life and inhibitory actions in young and adult hippocampus. This evidence poses the need to reevaluate and reinterpret some aspects of the physiology of the mossy fiber pathway under normal and pathological conditions. This work reviews the recent evidence that supports the assumption that glutamate and GABA can be coreleased from a single pathway, the mossy fibers, and makes some considerations about its functional implications.
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Affiliation(s)
- Rafael Gutiérrez
- Departamento de Fisiología, Biofísica y Neurociencias, Centro de Investigación y de Estudios Avanzados, Apartado Postal 14-740, Mexico City 07000, D.F., Mexico.
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Maqueda J, Ramírez M, Lamas M, Gutiérrez R. Glutamic acid decarboxylase (GAD)67, but not GAD65, is constitutively expressed during development and transiently overexpressed by activity in the granule cells of the rat. Neurosci Lett 2003; 353:69-71. [PMID: 14642440 DOI: 10.1016/j.neulet.2003.08.077] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
gamma-Aminobutyric acid (GABA)-mediated neurotransmission from the granule cells to CA3 is transiently expressed during the first 3 weeks of age in the rat. In the adult, seizures provoke this inhibitory signaling to reappear. To gain insight into the origin of GABA in these cells, we explored the expression of both isoforms of glutamic acid decarboxylase (GAD, 65 and 67 kDa), during development and after seizures in the adult rat. We found that GAD(67), but not GAD(65), is expressed in the mossy fibers of developing rats. In adults, GAD(67) is no longer detectable, unless seizures are induced. By contrast, GAD(65) is neither expressed in granule cells nor in their mossy fibers at any age nor after seizures, despite the presence of GAD(65) mRNA, confirmed by reverse transcription-polymerase chain reaction in situ.
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Affiliation(s)
- Jasmín Maqueda
- Centro de Investigación y Estudios Avanzados del IPN, Apartado Postal 14-740, 07000, Mexico City, D.F., Mexico
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Abstract
The "glutamatergic" granule cells of the dentate gyrus transiently express a GABAergic phenotype when a state of hyperexcitability is induced in the adult rat. Consequently, granule cell (GC) activation provokes monosynaptic GABAergic responses in their targets of area CA3. Because GABA exerts a trophic action on neonatal CA3 and mossy fibers (MF) constitute its main input, we hypothesized that the GABAergic phenotype of the MF could also be transiently expressed early in life. We addressed this possibility with a multidisciplinary approach. Electrophysiological recordings in developing rats revealed that, until day 22-23 of age, glutamate receptor antagonists block the excitatory response evoked in pyramidal cells by GCs, isolating a fast metabotropic glutamate receptor-sensitive GABAergic response. In a clear-cut manner from day 23-24 of age, GC activation in the presence of glutamatergic antagonists was unable to evoke synaptic responses in CA3. Immunohistological experiments showed the presence of GABA and GAD67 (glutamate decarboxylase 67 kDa isoform) in the developing GCs and their MF, and, using reverse transcription-PCR, we confirmed the expression of vesicular GABA transporter mRNA in the developing dentate gyrus and its downregulation in the adult. The GABAergic markers were upregulated and MF inhibitory transmission reappeared when hyperexcitability was induced in adult rats. Our data evidence for the first time a developmental and activity-dependent regulation of the complex phenotype of the GC. At early ages, the GABAergic input from the MF may add to the interneuronal input to CA3 to foster development, and, in the adult, it can possibly protect the system from enhanced excitability.
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