1
|
GABAρ subunits confer a bicuculline-insensitive component to GFAP+ cells of cerebellum. Proc Natl Acad Sci U S A 2014; 111:17522-7. [PMID: 25422464 DOI: 10.1073/pnas.1419632111] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
GABA-A receptors mediating synaptic or extrasynaptic transmission are molecularly and functionally distinct, and glial cells are known to express a plethora of GABA-A subunits. Here we demonstrate that GFAP(+) cells of the granular layer of cerebellum express GABAρ subunits during early postnatal development, thereby conferring peculiar pharmacologic characteristics to GABA responses. Electron microscopy revealed the presence of GABAρ in the plasma membrane of GFAP(+) cells. In contrast, expression in the adult was restricted to Purkinje neurons and a subset of ependymal cells. Electrophysiological studies in vitro revealed that astrocytes express functional receptors with an EC50 of 52.2 ± 11.8 μM for GABA. The evoked currents were inhibited by bicuculline (100 μM) and TPMPA (IC50, 5.9 ± 0.6 μM), indicating the presence of a GABAρ component. Coimmunoprecipitation demonstrated protein-protein interactions between GABAρ1 and GABAα1, and double immunofluorescence showed that these subunits colocalize in the plasma membrane. Three populations of GABA-A receptors in astrocytes were identified: classic GABA-A, bicuculline-insensitive GABAρ, and GABA-A-GABAρ hybrids. Clusters of GABA-A receptors were distributed in the perinuclear space and along the processes of GFAP(+) cells. Time-lapse microscopy showed GABAρ2-GFP accumulation in clusters located in the soma and along the processes. The clusters were relatively immobile, with mean displacement of 9.4 ± 0.9 μm and a net distance traveled of 1-2 μm, owing mainly to directional movement or simple diffusion. Modulation of GABAρ dynamics may be a novel mechanism of extrasynaptic transmission regulating GABAergic control of GFAP(+) cells during early postnatal development.
Collapse
|
2
|
Eaton MM, Lim YB, Covey DF, Akk G. Modulation of the human ρ1 GABAA receptor by inhibitory steroids. Psychopharmacology (Berl) 2014; 231:3467-78. [PMID: 24317445 PMCID: PMC4048647 DOI: 10.1007/s00213-013-3379-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 11/25/2013] [Indexed: 11/28/2022]
Abstract
RATIONALE Modulators of the ρ1 GABAA receptor may be useful in the treatment of visual, sleep, and cognitive disorders. Neuroactive steroids and analogues have been shown to modulate ρ1 receptor function, but the molecular mechanisms are poorly understood. OBJECTIVES We employed electrophysiology and voltage-clamp fluorometry to compare the actions of several neuroactive steroids and analogues on the human ρ1 GABAA receptor. RESULTS Results confirmed that P294S and T298F mutations affect modulation by steroids. The P294S mutation abolished inhibition by (3α,5β)-3-hydroxypregnan-20-one (3α5βP) while the T298F mutation eliminated inhibition by 17β-estradiol. Voltage-clamp fluorometry demonstrated that steroids differing in the presence of a charged group on C3 or nature of substituent on C17 uniquely modified fluorescence changes elicited by GABA in the extracellular domain. The I307Q mutation reversed the inhibitory effect of 3α5βP but was without effect on modulation by (3α,5β)-3-hydroxypregnan-20-one sulfate or 17β-estradiol. The effect of 3α5βP on the fluorescence change generated at Y241C was dependent on whether the steroid acted as an inhibitor or a potentiator. Further, the effect was limited to uncharged 5β-reduced steroids containing an acetyl group on C17. CONCLUSIONS The data demonstrate that steroids and analogues differ with respect to conformational changes elicited by these drugs as well as sensitivity to the effects of mutations. Steroids and analogues could be provisionally divided into three major groups based on their actions on the ρ1 GABAA receptor: 5β-reduced uncharged steroids, sulfated and carboxylated steroids, and 17β-estradiol. Further division among 5β-reduced uncharged steroids was based on substituent at position C17.
Collapse
Affiliation(s)
- Megan M Eaton
- Department of Anesthesiology, Washington University School of Medicine, Campus Box 8054, 660 S. Euclid Ave, St. Louis, MO, 63110, USA
| | | | | | | |
Collapse
|
3
|
Rosas-Arellano A, Machuca-Parra AI, Reyes-Haro D, Miledi R, Martínez-Torres A. Expression of GABAρ receptors in the neostriatum: localization in aspiny, medium spiny neurons and GFAP-positive cells. J Neurochem 2012; 122:900-10. [PMID: 22168837 DOI: 10.1111/j.1471-4159.2011.07621.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
GABAergic transmission in the neostriatum plays a central role in motor coordination, in which a plethora of GABA-A receptor subunits combine to modulate neural inhibition. GABAρ receptors were originally described in the mammalian retina. These receptors possess special electrophysiological and pharmacological properties, forming a characteristic class of ionotropic receptors. In previous studies, we suggested that GABAρ receptors are expressed in the neostriatum, and in this report we show that they are indeed present in all the calretinin-positive interneurons of the neostriatum. In addition, they are located in calbindin-positive interneurons and projection neurons that express the dopamine D(2) receptor. GABAρ receptors were also located in 30% of the glial fibrillary acidic protein-positive cells, and may therefore also contribute to gliotransmission. Quantitative reverse transcription-PCR suggested that the mRNAs of this receptor do not express as much as in the retina, and that GABAρ2 is more abundant than GABAρ1. Electrophysiological recordings in brain slices provided evidence of neurons expressing a cis-4-aminocrotonic acid-activated, 1,2,5,6-tetrahydropyridine-4-yl methylphosphinic acid-sensitive ionotropic GABA receptor, indicating the presence of functional GABAρ receptors in the neostriatum. Finally, electron-microscopy and immunogold located the receptors mainly in perisynaptic as well as in extrasynaptic sites. All these observations reinforce the importance of GABAρ receptors in the neostriatum and contribute to the diversity of inhibitory regulation in this area.
Collapse
Affiliation(s)
- Abraham Rosas-Arellano
- Departamento de Neurobiología Celular y Molecular, Universidad Nacional Autónoma de México, Instituto de Neurobiología, Campus Juriquilla, Querétaro, Mexico
| | | | | | | | | |
Collapse
|
4
|
Martínez-Delgado G, Estrada-Mondragón A, Miledi R, Martínez-Torres A. An Update on GABAρ Receptors. Curr Neuropharmacol 2011; 8:422-33. [PMID: 21629448 PMCID: PMC3080597 DOI: 10.2174/157015910793358141] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Revised: 04/08/2010] [Accepted: 06/21/2010] [Indexed: 01/29/2023] Open
Abstract
The present review discusses the functional and molecular diversity of GABAρ receptors. These receptors were originally described in the mammalian retina, and their functional role in the visual pathway has been recently elucidated; however new studies on their distribution in the brain and spinal cord have revealed that they are more spread than originally thought, and thus it will be important to determine their physiological contribution to the GABAergic transmission in other areas of the central nervous system. In addition, molecular modeling has revealed peculiar traits of these receptors that have impacted on the interpretations of the latest pharmacolgical and biophysical findings. Finally, sequencing of several vertebrate genomes has permitted a comparative analysis of the organization of the GABAρ genes.
Collapse
Affiliation(s)
- Gustavo Martínez-Delgado
- Instituto de Neurbiología, Departamento de Neurobiología Celular y Molecular, Laboratorio D15, Campus UNAM Juriquilla. Querétaro 76230, México
| | | | | | | |
Collapse
|
5
|
Rosas-Arellano A, Parodi J, Machuca-Parra AI, Sánchez-Gutiérrez A, Inestrosa NC, Miledi R, Martínez-Torres A. The GABA(A)ρ receptors in hippocampal spontaneous activity and their distribution in hippocampus, amygdala and visual cortex. Neurosci Lett 2011; 500:20-5. [PMID: 21683123 DOI: 10.1016/j.neulet.2011.05.235] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 05/13/2011] [Accepted: 05/31/2011] [Indexed: 10/18/2022]
Abstract
A bicuculline-resistant and TPMPA-sensitive GABAergic component was identified in hippocampal neurons in culture and in acute isolated brain slices. In both preparations, total GABAergic activity showed two inactivation kinetics: fast and slow. RT-PCR, in situ hybridization (ISH) and immunohistochemistry detected expression of GABAρ subunits. Immunogold and electron microscopy indicated that the receptors are mostly extrasynaptic. In addition, by RT-PCR and immunofluorescence we found GABAρ present in amygdala and visual cortex.
Collapse
Affiliation(s)
- Abraham Rosas-Arellano
- Departamento de Neurobiología Celular y Molecular, Laboratorio de Neurobiología Molecular y Celular, Instituto de Neurobiología, Campus UNAM-Juriquilla, Querétaro, QRO 76230, Mexico
| | | | | | | | | | | | | |
Collapse
|
6
|
Abstract
The activity of many receptors and ion channels in the nervous system can be regulated by redox-dependent mechanisms. Native and recombinant GABA(A) receptors are modulated by endogenous and pharmacological redox agents. However, the sensitivity of GABA(C) receptors to redox modulation has not been demonstrated. We studied the actions of different reducing and oxidizing agents on human homomeric GABArho(1) receptors expressed in Xenopus laevis oocytes. The reducing agents dithiothreitol (2 mM) and N-acetyl-L-cysteine (1 mM) potentiated GABA-evoked Cl(-) currents recorded by two-electrode voltage-clamp, while the oxidants 5-5'-dithiobis-2-nitrobenzoic acid (500 microM) and oxidized dithiothreitol (2 mM) caused inhibition. The endogenous antioxidant glutathione (5 mM) also enhanced GABArho(1) receptor-mediated currents while its oxidized form GSSG (3 mM) had inhibitory effects. All the effects were rapid and easily reversible. Redox modulation of GABArho(1) receptors was strongly dependent on the GABA concentration; dose-response curves for GABA were shifted to the left in the presence of reducing agents, whereas oxidizing agents produced the opposite effect, without changes in the maximal response to GABA and in the Hill coefficient. Our results demonstrate that, similarly to GABA(A) receptors and other members of the cys-loop receptor superfamily, GABA(C) receptors are subjected to redox modulation.
Collapse
Affiliation(s)
- Cecilia I Calero
- Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina
| | | |
Collapse
|
7
|
Wahle P, Schmidt M. GABAC receptors are expressed in GABAergic and non-GABAergic neurons of the rat superior colliculus and visual cortex. Exp Brain Res 2009; 199:245-52. [DOI: 10.1007/s00221-009-1710-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Accepted: 01/09/2009] [Indexed: 10/21/2022]
|
8
|
Inhibitory interaction between P2X4 and GABA(C) rho1 receptors. Biochem Biophys Res Commun 2008; 375:38-43. [PMID: 18675255 DOI: 10.1016/j.bbrc.2008.07.096] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 07/18/2008] [Indexed: 01/16/2023]
Abstract
Reciprocal functional inhibition between P2X and GABA(A/C) receptors represents a novel mechanism fine-tuning neuronal excitability. However, the participating receptors and underlying mechanisms are not fully understood. P2X(4) receptor is widely found in neurons that express GABA(C) rho1 receptor. Thus, we co-expressed P2X(4) and rho1 receptors in HEK293 cells and, using patch-clamp recording, examined whether they have mutual functional inhibition. Currents evoked by simultaneous application of ATP and GABA (I(ATP+GABA)) were significantly smaller compared to the addition of I(ATP) and I(GABA). Furthermore, I(ATP) were strongly suppressed during rho1 receptor activation. Similarly, I(GABA) were greatly attenuated during P2X(4) receptor activation. Such mutual inhibition was absent in cells only expressing P2X(4) or rho1 receptor. Taken together, these functional data support negative cross-talk between P2X(4) and rho1 receptors.
Collapse
|
9
|
Mejía C, García-Alcocer G, Berumen LC, Rosas-Arellano A, Miledi R, Martínez-Torres A. Expression of GABAρ subunits during rat cerebellum development. Neurosci Lett 2008; 432:1-6. [DOI: 10.1016/j.neulet.2007.11.062] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2007] [Revised: 11/02/2007] [Accepted: 11/29/2007] [Indexed: 11/15/2022]
|
10
|
Abstract
The expression of GABA(C) receptors has long been regarded as a specific property of bipolar cells in the inner retina where they control the information transfer from bipolar to retinal ganglion cells. A number of recent anatomical and physiological studies, however, have provided evidence that GABA(C) receptors are also expressed in many brain structures apart from the retina. The presence of GABA(C) receptors in many GABAergic neurons suggests that this receptor type may be involved in the regulation of local inhibition. This chapter focuses on the distribution of GABA(C) receptors and their possible function in various brain areas.
Collapse
Affiliation(s)
- Matthias Schmidt
- Allgemeine Zoologie and Neurobiologie, Ruhr-Universität Bochum, 44780 Bochum, Germany.
| |
Collapse
|
11
|
Klein OD, Cotter PD, Moore MW, Zanko A, Gilats M, Epstein CJ, Conte F, Rauen KA. Interstitial deletions of chromosome 6q: genotype-phenotype correlation utilizing array CGH. Clin Genet 2007; 71:260-6. [PMID: 17309649 DOI: 10.1111/j.1399-0004.2007.00757.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Interstitial deletions of the long arm of chromosome 6 are relatively rare, with fewer than 100 cases reported. Phenotypic variation is in large part due to differences in size and location of the segmental aneuploidy. We report three new patients with interstitial deletions of chromosome 6q defined at the molecular level by array comparative genomic hybridization (array CGH). In two of three cases, the molecular breakpoints differed from those indicated by conventional karyotyping, demonstrating the enhanced resolution of array CGH. Two patients had minimal deletions of 6 and 8.8 Mb involving 6q16.2-->q21, and the third patient had a deletion of 11.3 Mb spanning 6q15-->q21. All three had developmental delay, craniofacial dysmorphology, and functional eye disorders, suggesting that genes affecting brain and craniofacial development are located in 6q16.2-->q21, the deleted region common to all three patients. Furthermore, gene(s) for discordant phenotypic features, such as central diabetes insipidus, may reside at 6q15, the monosomic region unique to patient 3. All three cases described here showed loss of paternal alleles within the deleted segment, providing further evidence of the predominantly paternal origin for 6q deletions and rearrangements.
Collapse
Affiliation(s)
- O D Klein
- Department of Pediatrics, University of California San Francisco, San Francisco, CA 94115, USA
| | | | | | | | | | | | | | | |
Collapse
|
12
|
Harvey VL, Duguid IC, Krasel C, Stephens GJ. Evidence that GABA rho subunits contribute to functional ionotropic GABA receptors in mouse cerebellar Purkinje cells. J Physiol 2006; 577:127-39. [PMID: 16945976 PMCID: PMC2000691 DOI: 10.1113/jphysiol.2006.112482] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Ionotropic gamma-amino butyric acid (GABA) receptors composed of heterogeneous molecular subunits are major mediators of inhibitory responses in the adult CNS. Here, we describe a novel ionotropic GABA receptor in mouse cerebellar Purkinje cells (PCs) using agents reported to have increased affinity for rho subunit-containing GABA(C) over other GABA receptors. Exogenous application of the GABA(C)-preferring agonist cis-4-aminocrotonic acid (CACA) evoked whole-cell currents in PCs, whilst equimolar concentrations of GABA evoked larger currents. CACA-evoked currents had a greater sensitivity to the selective GABA(C) antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) than GABA-evoked currents. Focal application of agonists produced a differential response profile; CACA-evoked currents displayed a much more pronounced attenuation with increasing distance from the PC soma, displayed a slower time-to-peak and exhibited less desensitization than GABA-evoked currents. However, CACA-evoked currents were also completely blocked by bicuculline, a selective agent for GABA(A) receptors. Thus, we describe a population of ionotropic GABA receptors with a mixed GABA(A)/GABA(C) pharmacology. TPMPA reduced inhibitory synaptic transmission at interneurone-Purkinje cell (IN-PC) synapses, causing clear reductions in miniature inhibitory postsynaptic current (mIPSC) amplitude and frequency. Combined application of NO-711 (a selective GABA transporter subtype 1 (GAT-1) antagonist) and SNAP-5114 (a GAT-(2)/3/4 antagonist) induced a tonic GABA conductance in PCs; however, TPMPA had no effect on this current. Immunohistochemical studies suggest that rho subunits are expressed predominantly in PC soma and proximal dendritic compartments with a lower level of expression in more distal dendrites; this selective immunoreactivity contrasted with a more uniform distribution of GABA(A) alpha1 subunits in PCs. Finally, co-immunoprecipitation studies suggest that rho subunits can form complexes with GABA(A) receptor alpha1 subunits in the cerebellar cortex. Overall, these data suggest that rho subunits contribute to functional ionotropic receptors that mediate a component of phasic inhibitory GABAergic transmission at IN-PC synapses in the cerebellum.
Collapse
Affiliation(s)
- Victoria L Harvey
- School of Pharmacy, University of Reading, Whiteknights, PO Box 228, Reading RG6 6AJ, UK
| | | | | | | |
Collapse
|
13
|
Alakuijala A, Alakuijala J, Pasternack M. Evidence for a functional role of GABAC receptors in the rat mature hippocampus. Eur J Neurosci 2006; 23:514-20. [PMID: 16420458 DOI: 10.1111/j.1460-9568.2005.04572.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: 11/29/2022]
Abstract
Both gamma-aminobutyric acid (GABA)(C) receptor subunit mRNA and protein are expressed in the stratum pyramidale in the CA1 area of the adult rat hippocampus, but so far no conclusive evidence about functional hippocampal GABA(C) receptors has been presented. Here, the contribution of GABA(C) receptors to stimulus-evoked postsynaptic potentials was studied in the hippocampal CA1 area with extracellular and intracellular recordings at the age range of 21-47 postnatal days. Activation of GABA(C) receptors with the specific agonist cis-4-aminocrotonic acid (CACA) suppressed postsynaptic excitability and increased the membrane conductance. The GABA(C) receptor antagonist 1,2,5,6-tetrahydropyridine-4-ylmethylphosphinic acid (TPMPA), but not the GABA(A) receptor antagonist bicuculline, inhibited the effects of CACA. GABA-mediated long-lasting depolarizing responses evoked by high-frequency stimulation of local inhibitory interneurons in the CA1 area in the presence of ionotropic glutamate receptor and GABA(B) receptor blockers were prolonged by TPMPA, indicating that GABA(C) receptors are activated under these conditions. For weaker stimulation, the effect of TPMPA was enhanced after GABA uptake was inhibited. Our data demonstrate that GABA(C) receptors can be activated by endogenous synaptic transmitter release following strong stimulation or under conditions of reduced GABA uptake. The lack of GABA(C) receptor activation by less intensive stimulation under control conditions suggests that these receptors are extrasynaptic and activated via spillover of synaptically released GABA.
Collapse
Affiliation(s)
- Anniina Alakuijala
- Institute of Biotechnology, PO Box 56, FI-00014 University of Helsinki, Finland
| | | | | |
Collapse
|
14
|
López-Chávez A, Miledi R, Martínez-Torres A. Cloning and functional expression of the bovine GABA(C) rho2 subunit. Molecular evidence of a widespread distribution in the CNS. Neurosci Res 2005; 53:421-7. [PMID: 16213047 DOI: 10.1016/j.neures.2005.08.014] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2005] [Revised: 08/30/2005] [Accepted: 08/31/2005] [Indexed: 11/17/2022]
Abstract
GABA(C) receptors were first described as a non-desensitizing, bicuculline- and baclofen-insensitive component in Xenopus oocytes expressing bovine retina mRNA. However, the expression, tissue distribution and functional properties of GABA(C) receptors from other areas of the CNS still remain controversial. In previous experiments, the injection of rat cerebellum mRNA into Xenopus oocytes induced the expression of receptors that generated currents with both GABA(A) and GABA(C) characteristics; the latter component apparently being given by the rho2 subunit, suggesting the expression of GABA(C) receptors in the CNS and the formation of homooligomeric receptors. In this study, using RT-PCR, we found that the rho1 and rho2 subunits are widely expressed in the CNS including areas where they have not been previously described such as the bulb, pons and the caudate nucleus. To determine if the GABA(C) component of the GABA-currents elicited by oocytes expressing cerebellum mRNA was caused by activation of homomeric GABA rho2 receptors, we cloned the corresponding cDNA and expressed it in Xenopus oocytes. It was found that oocytes injected with rho2 cDNA, efficiently formed GABA-gated homooligomeric receptors. The GABA-dose-current response gave an EC50=1.19muM and the currents were resistant to bicuculline and reversibly antagonized by the specific GABA(C) receptor antagonist TPMPA. Altogether, our results indicate a widespread distribution of both rho1 and rho2 subunits in the bovine CNS and show further that the rho2 subunit cDNA isolated from cerebellum, forms fully functional receptors when expressed in Xenopus oocytes.
Collapse
Affiliation(s)
- Ariel López-Chávez
- Instituto de Neurobiología, Universidad Nacional Autónoma de México-Campus Juriquilla, AP1-1141 Querétaro, Mexico
| | | | | |
Collapse
|
15
|
Alakuijala A, TalviOja K, Pasternack A, Pasternack M. Functional characterization of rat ρ2 subunits expressed in HEK 293 cells. Eur J Neurosci 2005; 21:692-700. [PMID: 15733087 DOI: 10.1111/j.1460-9568.2005.03880.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
GABA(C) receptors are thought to be homo- or heteropentamers composed of rho1, rho2 and rho3 subunits. Previous work on rat rho2 subunits expressed in Xenopus oocytes has suggested that they do not form functional homo-oligomeric GABA(C) receptors, but do combine with rho1 or rho3 subunits to form hetero-oligomers. These findings are difficult to interpret because both human and mouse rho2 subunits do form functional homo-oligomeric receptors. Also, many regions of the rat brain express solely rho2 subunit transcripts which, according to presently available evidence, would not result in expression of functional GABA(C) receptors. We show here that homomeric rat rho2 receptors can be expressed in HEK 293 cells. Homo-oligomeric rat rho2 receptors expressed in mammalian cells matured slowly and displayed small but detectable GABA-induced currents with slow kinetics. Rat rho2 receptors also had a decreased sensitivity to picrotoxin and a marked sensitivity to the GABA(C) receptor agonist cis-aminocrotonic acid. Our results demonstrate for the first time the expression of functional homomeric rat rho2 receptors, and suggest that rho(2) subunits may contribute to brain function, including in areas not expressing other rho subunits.
Collapse
Affiliation(s)
- Anniina Alakuijala
- Institute of Biotechnology, PO Box 56, FI-00014 University of Helsinki, Finland
| | | | | | | |
Collapse
|
16
|
Alakuijala A, Palgi M, Wegelius K, Schmidt M, Enz R, Paulin L, Saarma M, Pasternack M. GABA receptor rho subunit expression in the developing rat brain. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2005; 154:15-23. [PMID: 15617751 DOI: 10.1016/j.devbrainres.2004.09.010] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/27/2004] [Indexed: 11/29/2022]
Abstract
Ionotropic GABA(C) receptors are composed of rho1, rho2 and rho3 subunits. Although the distribution of rho subunit mRNAs in the adult brain has been studied, information on the developmental regulation of different rho subunits in the brain is scattered and incomplete. Here, GABA(C) receptor rho subunit expression was studied in the developing rat brain. In situ hybridization on postnatal brain slices showed rho2 mRNA expression from newborn in superficial gray layer (SGL) of superior colliculus (SuC), and from the first postnatal week in the hippocampal CA1 region and pretectal nucleus of the optic tract. rho2 mRNA was also expressed in the adult dorsal lateral geniculate nucleus. Quantitative RT-PCR revealed expression of all three rho subunits in the hippocampus and superior colliculus from the first postnatal day. In the hippocampus, rho2 mRNA expression clearly dominated over rho1 and rho3, whereas in the superior colliculus, rho1 mRNA expression levels were similar to rho2. In both areas, a clear up-modulation of rho2 and rho3 mRNA during the first postnatal week was detected. GABA(C) receptor protein expression was confirmed in adult hippocampus, superior colliculus and dorsal lateral geniculate nucleus by immunohistochemistry. Our results demonstrate for the first time the expression of all three rho subunit mRNAs in several regions of the developing and adult rat brain. Our quantitative data allows assessment of putative subunit combinations in the superior colliculus and hippocampus. From the selective distribution of rho subunits, it may be hypothesized that GABA(C) receptors are specifically involved in aspects of visual image motion processing in the rat brain.
Collapse
Affiliation(s)
- Anniina Alakuijala
- Institute of Biotechnology, P.O. Box 56, FI-00014 University of Helsinki, Finland
| | | | | | | | | | | | | | | |
Collapse
|
17
|
Liu B, Hattori N, Jiang B, Nakayama Y, Zhang NY, Wu B, Kitagawa K, Taketo M, Matsuda H, Inagaki C. Single cell RT-PCR demonstrates differential expression of GABAC receptor rho subunits in rat hippocampal pyramidal and granule cells. ACTA ACUST UNITED AC 2004; 123:1-6. [PMID: 15046860 DOI: 10.1016/j.molbrainres.2003.12.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/12/2003] [Indexed: 11/20/2022]
Abstract
Although gamma-aminobutyric acid (GABA)C receptor rho1, rho2 and rho3 subunits are reportedly expressed in pyramidal and granule cells in the hippocampus at various developmental stages, it is not clear whether these three rho subunits are coexpressed in a single neuron. To attempt to answer this question, we performed single-cell RT-PCR for rho subunits from neurons of rat brain hippocampus. In hippocampal cultures, pyramidal cells were positive for rho1 mRNA expression in 89%, rho2 in 94% and rho3 in 94%, while granule cells were positive for rho1 mRNA in only 6%, rho2 in 36% and rho3 in 91%. Intensive amplification of the RT-PCR products by the second PCR revealed that all the three rho subunits were coexpressed in a single pyramidal and granule cells from both of the cultures and the slices. These results suggest that all the three GABAC receptor rho1, rho2 and rho3 subunits are present probably in different compositions in pyramidal and granule cells in the rat hippocampus.
Collapse
Affiliation(s)
- Bing Liu
- Department of Pharmacology, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi, Osaka 570-8506, Japan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Hartmann K, Stief F, Draguhn A, Frahm C. Ionotropic GABA receptors with mixed pharmacological properties of GABAA and GABAC receptors. Eur J Pharmacol 2004; 497:139-46. [PMID: 15306198 DOI: 10.1016/j.ejphar.2004.06.044] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2004] [Accepted: 06/22/2004] [Indexed: 11/17/2022]
Abstract
Ionotropic gamma-aminobutyric acid (GABA) receptors form a large family of molecular isoforms with distinct properties. We have characterized a distinct new type of GABA receptors in CA1 pyramidal cells in rat hippocampal slices. Somatic application of GABA induced currents which were partially suppressed by (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA), a specific antagonist of GABA(C) receptors. This sensitivity was enhanced when we evoked the currents by the GABA(C) receptor agonist cis-4-aminocrotonic acid (CACA). However, both GABA- and CACA-evoked currents were sensitive towards bicuculline and thus lack the defining feature of GABA(C) receptors, which are insensitive towards this antagonist. Spontaneous miniature post-synaptic currents (mIPSCs) revealed a similar pharmacological behaviour. We conclude that juvenile CA1 pyramidal cells express a fraction of ionotropic GABA receptors with mixed pharmacological properties of both, GABA(A) and GABA(C) receptors.
Collapse
Affiliation(s)
- Kristin Hartmann
- Johannes-Müller-Institut für Physiologie, Universitätsklinikum Charité, Humboldt-Universität Berlin, Tucholskystrasse 2, 10117 Berlin, Germany
| | | | | | | |
Collapse
|
19
|
Yang L, Omori K, Omori K, Otani H, Suzukawa J, Inagaki C. GABAC receptor agonist suppressed ammonia-induced apoptosis in cultured rat hippocampal neurons by restoring phosphorylated BAD level. J Neurochem 2003; 87:791-800. [PMID: 14535961 DOI: 10.1046/j.1471-4159.2003.02069.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ammonia-induced apoptosis and its prevention by GABAC receptor stimulation were examined using primary cultured rat hippocampal neurons. Ammonia (0.5-5 mm NH4Cl) dose-dependently induced apoptosis in pyramidal cell-like neurons as assayed by double staining with Hoechst 33258 and anti-neurofilament antibody. A GABAC receptor agonist, cis-4-aminocrotonic acid (CACA, 200 microm), but not GABAA and GABAB receptor agonists, muscimol (10 micro m) and baclofen (50 microm), respectively, inhibited the ammonia (2 mm)-induced apoptosis, and this inhibition was abolished by a GABAC receptor antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA, 15 microm). Expression of all three GABAC receptor subunits was demonstrated in the cultured neurons by RT-PCR. The ammonia-treatment also activated caspases-3 and -9 as observed in immunocytochemistry for PARP p85 and western blot. Such activation of the caspases was again inhibited by CACA in a TPMPA-sensitive manner. The anti-apoptotic effect of CACA was blocked by inhibitors for MAP kinase kinase and cAMP-dependent protein kinase, PD98059 (20 microm) and KT5720 (1 microm), suggesting possible involvement of an upstream pro-apoptotic protein, BAD. Levels of phospho-BAD (Ser112 and Ser155) were decreased by the ammonia-treatment and restored by coadministration of CACA. These findings suggest that GABAC receptor stimulation protects hippocampal pyramidal neurons from ammonia-induced apoptosis by restoring Ser112- and Ser155-phospho-BAD levels.
Collapse
Affiliation(s)
- Li Yang
- Department of Pharmacology, Kansai Medical University, Moriguchi, Osaka, Japan
| | | | | | | | | | | |
Collapse
|