51
|
Mitchell EA, Gentet LJ, Dempster J, Belelli D. GABAA and glycine receptor-mediated transmission in rat lamina II neurones: relevance to the analgesic actions of neuroactive steroids. J Physiol 2007; 583:1021-40. [PMID: 17656439 PMCID: PMC2277187 DOI: 10.1113/jphysiol.2007.134445] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Analgesic neurosteroids such as 5alpha-pregnan-3alpha-ol-20-one (5alpha3alpha) are potent selective endogenous modulators of the GABA(A) receptor (GABA(A)R) while certain synthetic derivatives (i.e. minaxolone) additionally enhance the function of recombinant glycine receptors (GlyR). Inhibitory transmission within the superficial dorsal horn has been implicated in mediating the analgesic actions of neurosteroids. However, the relative contribution played by synaptic and extrasynaptic receptors is unknown. In this study, we have compared the actions of 5alpha3alpha and minaxolone upon inhibitory transmission mediated by both GABA(A) and strychnine-sensitive GlyRs in lamina II neurones of juvenile (P15-21) rats. At the near physiological temperature of 35 degrees C and at a holding potential of -60 mV we recorded three kinetically distinct populations of miniature IPSCs (mIPSCs): GlyR-mediated, GABA(A)R-mediated and mixed GABA(A)R-GlyR mIPSCs, arising from the corelease of both inhibitory neurotransmitters. In addition, sequential application of strychnine and bicuculline revealed a small (5.2 +/- 1.0 pA) GlyR- but not a GABA(A)R-mediated tonic conductance. 5alpha3alpha (1-10 microm) prolonged GABA(A)R and mixed mIPSCs in a concentration-dependent manner but was without effect upon GlyR mIPSCs. In contrast, minaxolone (1-10 microm) prolonged the decay of GlyR mIPSCs and, additionally, was approximately 10-fold more potent than 5alpha3alpha upon GABA(A)R mIPSCs. However, 5alpha3alpha and minaxolone (1 microm) evoked a similar bicuculline-sensitive inhibitory conductance, indicating that the extrasynaptic GABA(A)Rs do not discriminate between these two steroids. Furthermore, approximately 92% of the effect of 1 microm 5alpha3alpha upon GABAergic inhibition could be accounted for by its action upon the extrasynaptic conductance. These findings are relevant to modulation of inhibitory circuits within spinally mediated pain pathways and suggest that extrasynaptic GABA(A)Rs may represent a relevant molecular target for the analgesic actions of neurosteroids.
Collapse
Affiliation(s)
- Elizabeth A Mitchell
- Neurosciences Institute, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
| | | | | | | |
Collapse
|
52
|
Picton AJ, Fisher JL. Effect of the alpha subunit subtype on the macroscopic kinetic properties of recombinant GABA(A) receptors. Brain Res 2007; 1165:40-9. [PMID: 17658489 PMCID: PMC2084258 DOI: 10.1016/j.brainres.2007.06.050] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Revised: 06/12/2007] [Accepted: 06/20/2007] [Indexed: 12/26/2022]
Abstract
The GABA(A) receptors (GABARs) are chloride-permeable ligand-gated ion channels responsible for fast inhibitory neurotransmission. These receptors are structurally heterogeneous, and in mammals can be formed from a combination of sixteen different subunit subtypes. Much of this variety comes from the six different alpha subunit subtypes. All neuronal GABARs contain an alpha subunit, and the identity of the alpha subtype affects the pharmacological properties of the receptors. The expression of each of the different alpha subtypes is regulated developmentally and regionally and changes with both normal physiological processes such development and synaptic plasticity, and pathological conditions such as epilepsy. In order to understand the functional significance of this structural heterogeneity, we examined the effect of the alpha subtype on the receptor's response to GABA. Each of the six alpha subtypes was transiently co-expressed with the beta3 and gamma2L subunits in mammalian cells. The sensitivity to GABA was measured with whole-cell recordings. We also determined the activation, deactivation, desensitization, and recovery kinetics for the six isoforms using rapid application recordings from excised macropatches. We found unique characteristics associated with each alpha subunit subtype. These properties would be expected to influence the post-synaptic response to GABA, creating functional diversity among neurons expressing different alpha subunits.
Collapse
Affiliation(s)
- Amber J Picton
- Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, South Carolina 29208, USA
| | | |
Collapse
|
53
|
Fedi M, Berkovic SF, Macdonell RAL, Curatolo JM, Marini C, Reutens DC. Intracortical hyperexcitability in humans with a GABAA receptor mutation. Cereb Cortex 2007; 18:664-9. [PMID: 17615250 DOI: 10.1093/cercor/bhm100] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A missense mutation of the gamma2 subunit of the gamma-aminobutyric acid A (GABA(A)) receptor has been linked to an inherited human generalized epilepsy. As synaptic inhibition in the human brain is largely mediated by the GABA(A) receptor, we tested the hypothesis that the GABRG2(R43Q) mutation alters cortical excitability. Fourteen subjects affected by the GABRG2(R43Q) mutation (5 males, mean age: 44 +/- 15 years) and 24 controls (11 males, mean age: 38 +/- 11 years) were studied with transcranial magnetic stimulation (TMS). To assess the specificity of the effect of the mutation, 4 additional family members unaffected by the GABRG2(R43Q) mutation (2 males, mean age: 41 +/- 16 years) were included. Subjects affected by the GABRG2(R43Q) mutation demonstrated reduced net short-interval intracortical inhibition and increased intracortical facilitation assessed with paired-pulse stimulation. Subjects with the mutation had similar motor thresholds to controls both at rest and with weak voluntary activation. No significant differences were noted between groups in the cortical silent period. Our findings provide in vivo evidence for increased intracortical excitability in subjects affected by the GABRG2(R43Q) mutation. These findings are also likely to represent an important clue to the mechanisms linking this gene defect and the epilepsy phenotype.
Collapse
Affiliation(s)
- Marco Fedi
- Department of Medicine, The University of Melbourne, Heidelberg, Victoria, Australia
| | | | | | | | | | | |
Collapse
|
54
|
Lagier S, Panzanelli P, Russo RE, Nissant A, Bathellier B, Sassoè-Pognetto M, Fritschy JM, Lledo PM. GABAergic inhibition at dendrodendritic synapses tunes gamma oscillations in the olfactory bulb. Proc Natl Acad Sci U S A 2007; 104:7259-64. [PMID: 17428916 PMCID: PMC1855399 DOI: 10.1073/pnas.0701846104] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
In the olfactory bulb (OB), odorants induce oscillations in the gamma range (20-80 Hz) that play an important role in the processing of sensory information. Synaptic transmission between dendrites is a major contributor to this processing. Glutamate released from mitral cell dendrites excites the dendrites of granule cells, which in turn mediate GABAergic inhibition back onto mitral cells. Although this reciprocal synapse is thought to be a key element supporting oscillatory activity, the mechanisms by which dendrodendritic inhibition induces and maintains gamma oscillations remain unknown. Here, we assessed the role of the dendrodendritic inhibition, using mice lacking the GABA(A) receptor alpha1-subunit, which is specifically expressed in mitral cells but not in granule cells. The spontaneous inhibitory postsynaptic current frequency in these mutants was low and was consistent with the reduction of GABA(A) receptor clusters detected by immunohistochemistry. The remaining GABA(A) receptors in mitral cells contained the alpha3-subunit and supported slower decaying currents of unchanged amplitude. Overall, inhibitory-mediated interactions between mitral cells were smaller and slower in mutant than in WT mice, although the strength of sensory afferent inputs remained unchanged. Consequently, both experimental and theoretical approaches revealed slower gamma oscillations in the OB network of mutant mice. We conclude, therefore, that fast oscillations in the OB circuit are strongly constrained by the precise location, subunit composition and kinetics of GABA(A) receptors expressed in mitral cells.
Collapse
Affiliation(s)
- Samuel Lagier
- Laboratory of Perception and Memory, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2182, Institut Pasteur, 25 Rue du Dr. Roux, F-75724 Paris Cedex 15, France
| | | | - Raúl E. Russo
- Laboratory of Perception and Memory, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2182, Institut Pasteur, 25 Rue du Dr. Roux, F-75724 Paris Cedex 15, France
- Neurofisiolgía Celulary Molecular, Instituto de Investigaciones Biológicas, Clemente Estable, Avenida Italia 3318, CP 11600 Montevideo, Uruguay
| | - Antoine Nissant
- Laboratory of Perception and Memory, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2182, Institut Pasteur, 25 Rue du Dr. Roux, F-75724 Paris Cedex 15, France
| | - Brice Bathellier
- Laboratory of Perception and Memory, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2182, Institut Pasteur, 25 Rue du Dr. Roux, F-75724 Paris Cedex 15, France
- Laboratory of Computational Neuroscience, Brain and Mind Institute, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Marco Sassoè-Pognetto
- Department of Anatomy, Pharmacology, and Forensic Medicine and
- Istituto Nazionale di Neuroscienze, University of Turin, I-10126 Turin, Italy
| | - Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland; and
| | - Pierre-Marie Lledo
- Laboratory of Perception and Memory, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2182, Institut Pasteur, 25 Rue du Dr. Roux, F-75724 Paris Cedex 15, France
- To whom correspondence should be addressed. E-mail:
| |
Collapse
|
55
|
Valdés-Sánchez L, Escámez T, Echevarria D, Ballesta JJ, Tabarés-Seisdedos R, Reiner O, Martinez S, Geijo-Barrientos E. Postnatal alterations of the inhibitory synaptic responses recorded from cortical pyramidal neurons in the Lis1/sLis1 mutant mouse. Mol Cell Neurosci 2007; 35:220-9. [PMID: 17433713 DOI: 10.1016/j.mcn.2007.02.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Revised: 02/17/2007] [Accepted: 02/22/2007] [Indexed: 12/17/2022] Open
Abstract
Mutations in the mouse Lis1 gene produce severe alterations in the developing cortex. We have examined some electrophysiological responses of cortical pyramidal neurons during the early postnatal development of Lis/sLis1 mutant mice. In P7 and P30 Lis1/sLis1 neurons we detected a lower frequency and slower decay phase of mIPSCs, and at P30 the mIPSCs amplitude and the action potential duration were reduced. Zolpidem (an agonist of GABAA receptors containing the alpha1 subunit) neither modified the amplitude nor the decay time of mIPSCs at P7 in Lis1/sLis1 neurons, whereas it increased the decay time at P30. The levels of GABAA receptor alpha1 subunit mRNA were reduced in the Lis1/sLis1 brain at P7 and P30, whereas reduced levels of the corresponding protein were only found at P7. These results demonstrate the presence of functional alterations in the postnatal Lis1/sLis1 cortex and point to abnormalities in GABAA receptor subunit switching processes during postnatal development.
Collapse
Affiliation(s)
- Lourdes Valdés-Sánchez
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Campus de San Juan, Apartado 18, San Juan, 03550 Alicante, Spain
| | | | | | | | | | | | | | | |
Collapse
|
56
|
Fritschy JM, Panzanelli P. Molecular and synaptic organization of GABAA receptors in the cerebellum: Effects of targeted subunit gene deletions. THE CEREBELLUM 2007; 5:275-85. [PMID: 17134990 DOI: 10.1080/14734220600962805] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
GABAA receptors form heteromeric GABA-gated chloride channels assembled from a large family of subunit genes. In cerebellum, distinct GABAA receptor subtypes, differing in subunit composition, are segregated between cell types and synaptic circuits. The cerebellum therefore represents a useful system to investigate the significance of GABAA receptor heterogeneity. For instance, studies of mice carrying targeted deletion of major GABAA receptor subunit genes revealed the role of alpha subunit variants for receptor assembly, synaptic targeting, and functional properties. In addition, these studies unraveled mandatory association between certain subunits and demonstrated distinct pharmacology of receptors mediating phasic and tonic inhibition. Although some of these mutants have a profound loss of GABAA receptors, they exhibit only minor impairment of motor function, suggesting activation of compensatory mechanisms to preserve inhibitory networks in the cerebellum. These adaptations include an altered balance between phasic and tonic inhibition, activation of voltage-independent K+ conductances, and upregulation of GABAA receptors in interneurons that are not affected directly by the mutation. Deletion of the alpha1 subunit gene leads to complete loss of GABAA receptors in Purkinje cells. A striking alteration occurs in these mice, whereby presynaptic GABAergic terminals are preserved in the molecular layer but make heterologous synapses with spines, characterized by a glutamatergic-like postsynaptic density. During development of alpha1(0/0) mice, GABAergic synapses are initially formed but are replaced upon spine maturation. These findings suggest that functional GABAA receptors are required for long-term maintenance of GABAergic synapses in Purkinje cells.
Collapse
Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.
| | | |
Collapse
|
57
|
Pangratz-Fuehrer S, Rudolph U, Huguenard JR. Giant spontaneous depolarizing potentials in the developing thalamic reticular nucleus. J Neurophysiol 2007; 97:2364-72. [PMID: 17251370 DOI: 10.1152/jn.00646.2006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The thalamic reticular nucleus (nRt) provides a major source of inhibition in the thalamo-cortical circuit and is critically involved in the generation of spindle oscillations. Here we describe the properties of thalamic giant depolarizing potentials (tGDPs) that were observed in nRt during early development. tGDPs persisted in presence of ionotropic glutamate antagonists but were completely abolished by GABA(A)R antagonist SR 35591. tGDPs occurred primarily between p3 and p8 (in 30-50% of cells) and occasionally up until p15. tGDPs lasted 0.4-3 s with peak conductances of 2-13 nS and occurred at frequencies between 0.02 and 0.06 Hz. We used mice with a benzodiazepine-insensitive alpha3 subunit [alpha3(H126R)] to probe for the identity of the GABA receptors responsible for tGDP generation. Benzodiazepine enhancement of tGDP amplitude and duration persisted in nRt neurons in alpha3(H126R) mice, indicating that the GABA(A)Rs containing alpha3 are not critical for tGDP generation and suggesting that tGDPs are mediated by GABA(A)Rs containing the alpha5 subunit, which is transiently expressed in nRt neurons in early postnatal development. Furthermore we found that exogenous GABA application depolarized nRt neurons younger than p8, indicating elevated [Cl(-)](i) at this developmental stage. Taken together, these data suggest that in immature nRt, long-lasting depolarizing responses mediated by GABA receptors could trigger Ca(2+) entry and play a role in functional development of the spindle-generating circuitry.
Collapse
Affiliation(s)
- Susanne Pangratz-Fuehrer
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA 94305, USA
| | | | | |
Collapse
|
58
|
Reddy TE, Shakhnovich BE, Roberts DS, Russek SJ, DeLisi C. Positional clustering improves computational binding site detection and identifies novel cis-regulatory sites in mammalian GABAA receptor subunit genes. Nucleic Acids Res 2007; 35:e20. [PMID: 17204484 PMCID: PMC1807961 DOI: 10.1093/nar/gkl1062] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2006] [Revised: 10/18/2006] [Accepted: 11/20/2006] [Indexed: 11/12/2022] Open
Abstract
Understanding transcription factor (TF) mediated control of gene expression remains a major challenge at the interface of computational and experimental biology. Computational techniques predicting TF-binding site specificity are frequently unreliable. On the other hand, comprehensive experimental validation is difficult and time consuming. We introduce a simple strategy that dramatically improves robustness and accuracy of computational binding site prediction. First, we evaluate the rate of recurrence of computational TFBS predictions by commonly used sampling procedures. We find that the vast majority of results are biologically meaningless. However clustering results based on nucleotide position improves predictive power. Additionally, we find that positional clustering increases robustness to long or imperfectly selected input sequences. Positional clustering can also be used as a mechanism to integrate results from multiple sampling approaches for improvements in accuracy over each one alone. Finally, we predict and validate regulatory sequences partially responsible for transcriptional control of the mammalian type A gamma-aminobutyric acid receptor (GABA(A)R) subunit genes. Positional clustering is useful for improving computational binding site predictions, with potential application to improving our understanding of mammalian gene expression. In particular, predicted regulatory mechanisms in the mammalian GABA(A)R subunit gene family may open new avenues of research towards understanding this pharmacologically important neurotransmitter receptor system.
Collapse
Affiliation(s)
- Timothy E. Reddy
- Bioinformatics Program, Boston University24 Cummington Street, Boston, MA 02215, USA
| | - Boris E. Shakhnovich
- Bioinformatics Program, Boston University24 Cummington Street, Boston, MA 02215, USA
| | - Daniel S. Roberts
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine715 Albany St., Boston, MA 02118, USA
- Program in BioMedical Neuroscience, Boston University44 Cummington Street, Boston, MA 02215, USA
| | - Shelley J. Russek
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine715 Albany St., Boston, MA 02118, USA
| | - Charles DeLisi
- Bioinformatics Program, Boston University24 Cummington Street, Boston, MA 02215, USA
- Laboratory of Molecular Neurobiology, Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine715 Albany St., Boston, MA 02118, USA
- Biomedical Engineering, Boston University44 Cummington Street, Boston, MA 02215, USA
| |
Collapse
|
59
|
Prenosil GA, Schneider Gasser EM, Rudolph U, Keist R, Fritschy JM, Vogt KE. Specific subtypes of GABAA receptors mediate phasic and tonic forms of inhibition in hippocampal pyramidal neurons. J Neurophysiol 2006; 96:846-57. [PMID: 16835366 DOI: 10.1152/jn.01199.2005] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The main inhibitory neurotransmitter in the mammalian brain, GABA, mediates multiple forms of inhibitory signals, such as fast and slow inhibitory postsynaptic currents and tonic inhibition, by activating a diverse family of ionotropic GABA(A) receptors (GABA(A)Rs). Here, we studied whether distinct GABA(A)R subtypes mediate these various forms of inhibition using as approach mice carrying a point mutation in the alpha-subunit rendering individual GABA(A)R subtypes insensitive to diazepam without altering their GABA sensitivity and expression of receptors. Whole cell patch-clamp recordings were performed in hippocampal pyramidal cells from single, double, and triple mutant mice. Comparing diazepam effects in knock-in and wild-type mice allowed determining the contribution of alpha1, alpha2, alpha3, and alpha5 subunits containing GABA(A)Rs to phasic and tonic forms of inhibition. Fast phasic currents were mediated by synaptic alpha2-GABA(A)Rs on the soma and by synaptic alpha1-GABA(A)Rs on the dendrites. No contribution of alpha3- or alpha5-GABA(A)Rs was detectable. Slow phasic currents were produced by both synaptic and perisynaptic GABA(A)Rs, judged by their strong sensitivity to blockade of GABA reuptake. In the CA1 area, but not in the subiculum, perisynaptic alpha5-GABA(A)Rs contributed to slow phasic currents. In the CA1 area, the diazepam-sensitive component of tonic inhibition also involved activation of alpha5-GABA(A)Rs and slow phasic and tonic signals shared overlapping pools of receptors. These results show that the major forms of inhibitory neurotransmission in hippocampal pyramidal cells are mediated by distinct GABA(A)Rs subtypes.
Collapse
Affiliation(s)
- George A Prenosil
- University of Zurich, Institute of Pharmacology and Toxicology, Zurich, Switzerland
| | | | | | | | | | | |
Collapse
|
60
|
Jiao Y, Zhang C, Yanagawa Y, Sun QQ. Major effects of sensory experiences on the neocortical inhibitory circuits. J Neurosci 2006; 26:8691-701. [PMID: 16928857 PMCID: PMC6674381 DOI: 10.1523/jneurosci.2478-06.2006] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
During postnatal development, sensory experiences play critical roles in the refinement of cortical connections. However, both the process of postnatal experience-dependent maturation of neocortical inhibitory networks and its underlying mechanisms remain elusive. Here, we examined the differential properties of intracortical inhibitory networks of layer IV in "sensory-spared" and "sensory-deprived" cortices of glutamate acid decarboxylase 67 (GAD67)-green fluorescent protein (GFP) (delta neo) and wild-type mouse. Our results showed that row D whisker trimming (WT) begun at postnatal day 7 (P7), but not after P15, induced a robust reduction of parvalbumin (PV) expression, measured by the PV/GFP ratio and PV cell densities, in the deprived barrels. WT also induced a robust reduction in the number of inhibitory perisomatic varicosities and synaptic GAD65/67 immunoreactivities in spiny neurons of the deprived barrels. Although the GAD65/67 expressions in interneurons were also downregulated in the deprived barrels, the GFP expression remained unchanged. Patch-clamp recording from spiny cells showed a 1.5-fold reduction of intracortical evoked IPSCs (eIPSCs) in deprived versus spared cortices. The reduction in eIPSCs occurred via changes in presynaptic properties and unitary IPSC amplitudes. Miniature IPSCs showed subtle but significant differences between the two experimental conditions. In addition, properties of the IPSCs in deprived barrels resemble those of IPSCs recorded in immature brains (P7). Together, these results suggest that the properties of local intracortical inhibitory networks are modified by sensory experiences. Perisomatic inhibition mediated by PV-positive basket cells is pruned by sensory deprivation.
Collapse
Affiliation(s)
- Yuanyuan Jiao
- Department of Zoology and Physiology and
- Neuroscience Program, University of Wyoming, Laramie, Wyoming 82071, and
| | | | - Yuchio Yanagawa
- Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine and Solution-Oriented Research for Science and Technology, Japan Science and Technology Corporation, Maebashi 371-8511, Japan
| | - Qian-Quan Sun
- Department of Zoology and Physiology and
- Neuroscience Program, University of Wyoming, Laramie, Wyoming 82071, and
| |
Collapse
|
61
|
Abstract
During postnatal development, sensory experiences play critical roles in the refinement of cortical connections. However, both the process of postnatal experience-dependent maturation of neocortical inhibitory networks and its underlying mechanisms remain elusive. Here, we examined the differential properties of intracortical inhibitory networks of layer IV in "sensory-spared" and "sensory-deprived" cortices of glutamate acid decarboxylase 67 (GAD67)-green fluorescent protein (GFP) (delta neo) and wild-type mouse. Our results showed that row D whisker trimming (WT) begun at postnatal day 7 (P7), but not after P15, induced a robust reduction of parvalbumin (PV) expression, measured by the PV/GFP ratio and PV cell densities, in the deprived barrels. WT also induced a robust reduction in the number of inhibitory perisomatic varicosities and synaptic GAD65/67 immunoreactivities in spiny neurons of the deprived barrels. Although the GAD65/67 expressions in interneurons were also downregulated in the deprived barrels, the GFP expression remained unchanged. Patch-clamp recording from spiny cells showed a 1.5-fold reduction of intracortical evoked IPSCs (eIPSCs) in deprived versus spared cortices. The reduction in eIPSCs occurred via changes in presynaptic properties and unitary IPSC amplitudes. Miniature IPSCs showed subtle but significant differences between the two experimental conditions. In addition, properties of the IPSCs in deprived barrels resemble those of IPSCs recorded in immature brains (P7). Together, these results suggest that the properties of local intracortical inhibitory networks are modified by sensory experiences. Perisomatic inhibition mediated by PV-positive basket cells is pruned by sensory deprivation.
Collapse
|
62
|
Ponomarev I, Maiya R, Harnett MT, Schafer GL, Ryabinin AE, Blednov YA, Morikawa H, Boehm SL, Homanics GE, Berman AE, Berman A, Lodowski KH, Bergeson SE, Harris RA. Transcriptional signatures of cellular plasticity in mice lacking the alpha1 subunit of GABAA receptors. J Neurosci 2006; 26:5673-83. [PMID: 16723524 PMCID: PMC1894896 DOI: 10.1523/jneurosci.0860-06.2006] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
GABAA receptors mediate the majority of inhibitory neurotransmission in the CNS. Genetic deletion of the alpha1 subunit of GABAA receptors results in a loss of alpha1-mediated fast inhibitory currents and a marked reduction in density of GABAA receptors. A grossly normal phenotype of alpha1-deficient mice suggests the presence of neuronal adaptation to these drastic changes at the GABA synapse. We used cDNA microarrays to identify transcriptional fingerprints of cellular plasticity in response to altered GABAergic inhibition in the cerebral cortex and cerebellum of alpha1 mutants. In silico analysis of 982 mutation-regulated transcripts highlighted genes and functional groups involved in regulation of neuronal excitability and synaptic transmission, suggesting an adaptive response of the brain to an altered inhibitory tone. Public gene expression databases permitted identification of subsets of transcripts enriched in excitatory and inhibitory neurons as well as some glial cells, providing evidence for cellular plasticity in individual cell types. Additional analysis linked some transcriptional changes to cellular phenotypes observed in the knock-out mice and suggested several genes, such as the early growth response 1 (Egr1), small GTP binding protein Rac1 (Rac1), neurogranin (Nrgn), sodium channel beta4 subunit (Scn4b), and potassium voltage-gated Kv4.2 channel (Kcnd2) as cell type-specific markers of neuronal plasticity. Furthermore, transcriptional activation of genes enriched in Bergman glia suggests an active role of these astrocytes in synaptic plasticity. Overall, our results suggest that the loss of alpha1-mediated fast inhibition produces diverse transcriptional responses that act to regulate neuronal excitability of individual neurons and stabilize neuronal networks, which may account for the lack of severe abnormalities in alpha1 null mutants.
Collapse
Affiliation(s)
- Igor Ponomarev
- Waggoner Center for Alcohol and Addiction Research, University of Texas, Austin, Texas 78712, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
63
|
Kralic JE, Sidler C, Parpan F, Homanics GE, Morrow AL, Fritschy JM. Compensatory alteration of inhibitory synaptic circuits in cerebellum and thalamus of gamma-aminobutyric acid type A receptor alpha1 subunit knockout mice. J Comp Neurol 2006; 495:408-21. [PMID: 16485284 DOI: 10.1002/cne.20866] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Targeted deletion of the alpha1 subunit gene results in a profound loss of gamma-aminobutyric acid type A (GABA(A)) receptors in adult mouse brain but has only moderate behavioral consequences. Mutant mice exhibit several adaptations in GABA(A) receptor subunit expression, as measured by Western blotting. By using immunohistochemistry, we investigated here whether these adaptations serve to replace the missing alpha1 subunit or represent compensatory changes in neurons that normally express these subunits. We focused on cerebellum and thalamus and distinguished postsynaptic GABA(A) receptor clusters by their colocalization with gephyrin. In the molecular layer of the cerebellum, alpha1 subunit clusters colocalized with gephyrin disappeared from Purkinje cell dendrites of mutant mice, whereas alpha3 subunit/gephyrin clusters, presumably located on dendrites of Golgi interneurons, increased sevenfold, suggesting profound network reorganization in the absence of the alpha1 subunit. In thalamus, a prominent increase in alpha3 and alpha4 subunit immunoreactivity was evident, but without change in regional distribution. In the ventrobasal complex, which contains primarily postsynaptic alpha1- and extrasynaptic alpha4-GABA(A) receptors, the loss of alpha1 subunit was accompanied by disruption of gamma2 subunit and gephyrin clustering, in spite of the increased alpha4 subunit expression. However, in the reticular nucleus, which lacks alpha1-GABA(A) receptors in wild-type mice, postsynaptic alpha3/gamma2/gephyrin clusters were unaffected. These results demonstrate that adaptive responses in the brain of alpha1(0/0) mice involve reorganization of GABAergic circuits and not merely replacement of the missing alpha1 subunit by another receptor subtype. In addition, clustering of gephyrin at synaptic sites in cerebellum and thalamus appears to be dependent on expression of a GABA(A) receptor subtype localized postsynaptically.
Collapse
Affiliation(s)
- Jason E Kralic
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland
| | | | | | | | | | | |
Collapse
|
64
|
Fritschy JM, Panzanelli P, Kralic JE, Vogt KE, Sassoè-Pognetto M. Differential dependence of axo-dendritic and axo-somatic GABAergic synapses on GABAA receptors containing the alpha1 subunit in Purkinje cells. J Neurosci 2006; 26:3245-55. [PMID: 16554475 PMCID: PMC6674111 DOI: 10.1523/jneurosci.5118-05.2006] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Synapse formation and maintenance require extensive transsynaptic interactions involving multiple signal transduction pathways. In the cerebellum, Purkinje cells (PCs) receive GABAergic, axo-dendritic synapses from stellate cells and axo-somatic synapses from basket cells, both with GABAA receptors containing the alpha1 subunit. Here, we investigated the effects of a targeted deletion of the alpha1 subunit gene on GABAergic synaptogenesis in PCs, using electrophysiology and immunoelectron microscopy. Whole-cell patch-clamp recordings in acute slices revealed that PCs from alpha1(0/0) mice lack spontaneous and evoked IPSCs, demonstrating that assembly of functional GABAA receptors requires the alpha1 subunit. Ultrastructurally, stellate cell synapses on PC dendrites were reduced by 75%, whereas basket cell synapses on the soma were not affected, despite the lack of GABAA-mediated synaptic transmission. Most strikingly, GABAergic terminals were retained in the molecular layer of adult alpha1(0/0) mice and formed heterologous synapses with PC spines characterized by a well differentiated asymmetric postsynaptic density. These synapses lacked presynaptic glutamatergic markers and postsynaptic AMPA-type glutamate receptors but contained delta2-glutamate receptors. During postnatal development, initial steps of GABAergic synapse formation were qualitatively normal, and heterologous synapses appeared in parallel with maturation of dendritic spines. These results suggest that synapse formation in the cerebellum is governed by neurotransmitter-independent mechanisms. However, in the absence of GABAA-mediated transmission, GABAergic terminals in the molecular layer apparently become responsive to synaptogenic signals from PC spines and form stable heterologous synapses. In contrast, maintenance of axo-somatic GABAergic synapses does not depend on functional GABAA receptors, suggesting differential regulation in distinct subcellular compartments.
Collapse
Affiliation(s)
- Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland.
| | | | | | | | | |
Collapse
|