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Cachope R, Pereda AE. Regulatory Roles of Metabotropic Glutamate Receptors on Synaptic Communication Mediated by Gap Junctions. Neuroscience 2020; 456:85-94. [PMID: 32619474 DOI: 10.1016/j.neuroscience.2020.06.034] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Revised: 06/19/2020] [Accepted: 06/22/2020] [Indexed: 12/18/2022]
Abstract
Variations of synaptic strength are thought to underlie forms of learning and can functionally reshape neural circuits. Metabotropic glutamate receptors play key roles in regulating the strength of chemical synapses. However, information within neural circuits is also conveyed via a second modality of transmission: gap junction-mediated synapses. We review here evidence indicating that metabotropic glutamate receptors also play important roles in the regulation of synaptic communication mediated by neuronal gap junctions, also known as 'electrical synapses'. Activity-driven interactions between metabotropic glutamate receptors and neuronal gap junctions can lead to long-term changes in the strength of electrical synapses. Further, the regulatory action of metabotropic glutamate receptors on neuronal gap junctions is not restricted to adulthood but is also of critical relevance during brain development and contributes to the pathological mechanisms that follow brain injury.
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Affiliation(s)
- Roger Cachope
- CHDI Foundation, USA; Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Alberto E Pereda
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA.
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2
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Castellano P, Nwagbo C, Martinez LR, Eugenin EA. Methamphetamine compromises gap junctional communication in astrocytes and neurons. J Neurochem 2016; 137:561-75. [PMID: 26953131 DOI: 10.1111/jnc.13603] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Revised: 02/22/2016] [Accepted: 02/26/2016] [Indexed: 12/18/2022]
Abstract
Methamphetamine (meth) is a central nervous system (CNS) stimulant that results in psychological and physical dependency. The long-term effects of meth within the CNS include neuronal plasticity changes, blood-brain barrier compromise, inflammation, electrical dysfunction, neuronal/glial toxicity, and an increased risk to infectious diseases including HIV. Most of the reported meth effects in the CNS are related to dysregulation of chemical synapses by altering the release and uptake of neurotransmitters, especially dopamine, norepinephrine, and epinephrine. However, little is known about the effects of meth on connexin (Cx) containing channels, such as gap junctions (GJ) and hemichannels (HC). We examined the effects of meth on Cx expression, function, and its role in NeuroAIDS. We found that meth altered Cx expression and localization, decreased GJ communication between neurons and astrocytes, and induced the opening of Cx43/Cx36 HC. Furthermore, we found that these changes in GJ and HC induced by meth treatment were mediated by activation of dopamine receptors, suggesting that dysregulation of dopamine signaling induced by meth is essential for GJ and HC compromise. Meth-induced changes in GJ and HC contributed to amplified CNS toxicity by dysregulating glutamate metabolism and increasing the susceptibility of neurons and astrocytes to bystander apoptosis induced by HIV. Together, our results indicate that connexin containing channels, GJ and HC, are essential in the pathogenesis of meth and increase the sensitivity of the CNS to HIV CNS disease. Methamphetamine (meth) is an extremely addictive central nervous system stimulant. Meth reduced gap junctional (GJ) communication by inducing internalization of connexin-43 (Cx43) in astrocytes and reducing expression of Cx36 in neurons by a mechanism involving activation of dopamine receptors (see cartoon). Meth-induced changes in Cx containing channels increased extracellular levels of glutamate and resulted in higher sensitivity of neurons and astrocytes to apoptosis in response to HIV infection.
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Affiliation(s)
- Paul Castellano
- Public Health Research Institute (PHRI), New Jersey Medical School, Rutgers University, Newark, New Jersey, USA.,Department of Microbiology and Molecular Genetics, New Jersey Medical School, Rutgers University, Newark, New Jersey, USA
| | - Chisom Nwagbo
- Public Health Research Institute (PHRI), New Jersey Medical School, Rutgers University, Newark, New Jersey, USA.,Department of Microbiology and Molecular Genetics, New Jersey Medical School, Rutgers University, Newark, New Jersey, USA
| | - Luis R Martinez
- New York Institute of Technology College of Osteopathic Medicine, Old Westbury, New York, USA
| | - Eliseo A Eugenin
- Public Health Research Institute (PHRI), New Jersey Medical School, Rutgers University, Newark, New Jersey, USA.,Department of Microbiology and Molecular Genetics, New Jersey Medical School, Rutgers University, Newark, New Jersey, USA
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3
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Miller AC, Voelker LH, Shah AN, Moens CB. Neurobeachin is required postsynaptically for electrical and chemical synapse formation. Curr Biol 2014; 25:16-28. [PMID: 25484298 DOI: 10.1016/j.cub.2014.10.071] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Revised: 10/27/2014] [Accepted: 10/28/2014] [Indexed: 02/03/2023]
Abstract
BACKGROUND Neural networks and their function are defined by synapses, which are adhesions specialized for intercellular communication that can be either chemical or electrical. At chemical synapses, transmission between neurons is mediated by neurotransmitters, whereas at electrical synapses, direct ionic and metabolic coupling occur via gap junctions between neurons. The molecular pathways required for electrical synaptogenesis are not well understood, and whether they share mechanisms of formation with chemical synapses is not clear. RESULTS Here, using a forward genetic screen in zebrafish, we find that the autism-associated gene neurobeachin (nbea), which encodes a BEACH-domain-containing protein implicated in endomembrane trafficking, is required for both electrical and chemical synapse formation. Additionally, we find that nbea is dispensable for axonal formation and early dendritic outgrowth but is required to maintain dendritic complexity. These synaptic and morphological defects correlate with deficiencies in behavioral performance. Using chimeric animals in which individually identifiable neurons are either mutant or wild-type, we find that Nbea is necessary and sufficient autonomously in the postsynaptic neuron for both synapse formation and dendritic arborization. CONCLUSIONS Our data identify a surprising link between electrical and chemical synapse formation and show that Nbea acts as a critical regulator in the postsynaptic neuron for the coordination of dendritic morphology with synaptogenesis.
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Affiliation(s)
- Adam C Miller
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, Seattle, WA 98109, USA.
| | - Lisa H Voelker
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, Seattle, WA 98109, USA; Molecular and Cellular Biology, University of Washington, 1959 NE Pacific Street, Seattle, WA 98195, USA
| | - Arish N Shah
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, Seattle, WA 98109, USA
| | - Cecilia B Moens
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, Seattle, WA 98109, USA
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Cachope R, Pereda AE. Two independent forms of activity-dependent potentiation regulate electrical transmission at mixed synapses on the Mauthner cell. Brain Res 2012; 1487:173-82. [PMID: 22771708 DOI: 10.1016/j.brainres.2012.05.059] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2012] [Revised: 04/24/2012] [Accepted: 05/09/2012] [Indexed: 10/28/2022]
Abstract
Mixed (electrical and chemical) synaptic contacts on the Mauthner cells, known as Club endings, constitute a valuable model for the study of vertebrate electrical transmission. While electrical synapses are still perceived by many as passive intercellular channels that lack modifiability, a wealth of experimental evidence shows that gap junctions at Club endings are subject to dynamic regulatory control by two independent activity-dependent mechanisms that lead to potentiation of electrical transmission. One of those mechanisms relies on activation of NMDA receptors and postsynaptic CaMKII. A second mechanism relies on mGluR activation and endocannabinoid production and is indirectly mediated via the release of dopamine from nearby varicosities, which in turn leads to potentiation of the synaptic response via a PKA-mediated postsynaptic mechanism. We review here these two forms of potentiation and their signaling mechanisms, which include the activation of two kinases with well-established roles as regulators of synaptic strength, as well as the functional implications of these two forms of potentiation. Special Issue entitled Electrical Synapses.
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Affiliation(s)
- Roger Cachope
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY 10461, USA
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5
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Zhang C. Expression of connexin 57 in the olfactory epithelium and olfactory bulb. Neurosci Res 2011; 71:226-34. [PMID: 21840349 DOI: 10.1016/j.neures.2011.07.1832] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 07/16/2011] [Accepted: 07/26/2011] [Indexed: 01/20/2023]
Abstract
In the visual system, deletion of connexin 57 (Cx57) reduces gap junction coupling among horizontal cells and results in smaller receptive fields. To explore potential functions of Cx57 in olfaction, in situ hybridization and immunohistochemistry methods were used to investigate expression of Cx57 in the olfactory epithelium and olfactory bulb. Hybridization signal was stronger in the olfactory epithelial layer compared to the connective tissue underneath. Within the sensory epithelial layer, hybridization signal was visible in sublayers containing cell bodies of basal cells and olfactory neurons but not evident at the apical sublayer comprising cell bodies of sustentacular cells. These Cx57 positive cells were clustered into small groups to form different patterns in the olfactory epithelium. However, individual patterns did not associate with specific regions of olfactory turbinates or specific olfactory receptor zones. Patched distribution of hybridization positive cells was also observed in the olfactory bulb and accessory olfactory bulb in layers where granule cells, mitral cells, and juxtaglomerular cells reside. Immunostaining was observed in the cell types described above but the intensity was weaker than that in the retina. This study has provided anatomical basis for future studies on the function of Cx57 in the olfactory system.
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Affiliation(s)
- Chunbo Zhang
- Department of Biological and Chemical Sciences, Illinois Institute of Technology, Chicago, IL 60616, USA.
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6
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Hoge GJ, Davidson KGV, Yasumura T, Castillo PE, Rash JE, Pereda AE. The extent and strength of electrical coupling between inferior olivary neurons is heterogeneous. J Neurophysiol 2010; 105:1089-101. [PMID: 21177999 DOI: 10.1152/jn.00789.2010] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gap junctions constitute the only form of synaptic communication between neurons in the inferior olive (IO), which gives rise to the climbing fibers innervating the cerebellar cortex. Although its exact functional role remains undetermined, electrical coupling was shown to be necessary for the transient formation of functional compartments of IO neurons and to underlie the precise timing of climbing fibers required for cerebellar learning. So far, most functional considerations assume the existence of a network of permanently and homogeneously coupled IO neurons. Contrasting this notion, our results indicate that coupling within the IO is highly variable. By combining tracer-coupling analysis and paired electrophysiological recordings, we found that individual IO neurons could be coupled to a highly variable number of neighboring neurons. Furthermore, a given neuron could be coupled at remarkably different strengths with each of its partners. Freeze-fracture analysis of IO glomeruli revealed the close proximity of glutamatergic postsynaptic densities to connexin 36-containing gap junctions, at distances comparable to separations between chemical transmitting domains and gap junctions in goldfish mixed contacts, where electrical coupling was shown to be modulated by the activity of glutamatergic synapses. On the basis of structural and molecular similarities with goldfish mixed synapses, we speculate that, rather than being hardwired, variations in coupling could result from glomerulus-specific long-term modulation of gap junctions. This striking heterogeneity of coupling might act to finely influence the synchronization of IO neurons, adding an unexpected degree of complexity to olivary networks.
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Affiliation(s)
- Gregory J Hoge
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA.
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Horowitz SS, Stamper SA, Simmons JA. Neuronal connexin expression in the cochlear nucleus of big brown bats. Brain Res 2008; 1197:76-84. [PMID: 18241843 DOI: 10.1016/j.brainres.2007.12.048] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2007] [Revised: 12/12/2007] [Accepted: 12/13/2007] [Indexed: 11/26/2022]
Abstract
We present immunohistochemical data describing the presence and distribution of connexins, structural component of gap junctions, in the cochlear nuclei of adult big brown bats (Eptesicus fuscus). Echolocating big brown bats show microsecond scale echo-delay sensitivity that requires accurate synchronization of neuronal responses to the timing of echoes. Midbrain and auditory cortical neuronal response timing is similar to that observed in other non-echolocating mammals, suggesting that lower auditory processing nuclei may have specialized mechanisms for obtaining the required temporal hyperacuity. Our data shows that connexin 36, a gap junction protein specific to neurons, is most densely expressed in the bat's cochlear nuclear complex, the medullary region that receives and processes first-order afferents from the auditory nerve. Cx36 expression is absent in the cochlear nucleus of normal mice, which have high-frequency hearing sensitivity similar to big brown bats. Glial connexins, Cx26 and Cx43, expressed in astrocytes and several inner ear structures, are also found in the bat cochlear nucleus complex, associated with major fiber tracts in and around the cochlear nuclei. The extensive presence of neuronally-associated Cx36 in brainstem auditory structures of adult bats suggests a possible role for gap junctions in mediating echo-delay hyperacuity.
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Affiliation(s)
- Seth S Horowitz
- Psychology Department, Brown University, Box 1853, Providence RI 02912, USA.
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Chanson M, Kotsias BA, Peracchia C, O’Grady SM. Interactions of connexins with other membrane channels and transporters. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2007; 94:233-44. [PMID: 17475311 PMCID: PMC2692730 DOI: 10.1016/j.pbiomolbio.2007.03.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Cell-to-cell communication through gap junctions exists in most animal cells and is essential for many important biological processes including rapid transmission of electric signals to coordinate contraction of cardiac and smooth muscle, the intercellular propagation of Ca(2+) waves and synchronization of physiological processes between adjacent cells within a tissue. Recent studies have shown that connexins (Cx) can have either direct or indirect interactions with other plasma membrane ion channels or membrane transport proteins with important functional consequences. For example, in tissues most severely affected by cystic fibrosis (CF), activation of the CF Transmembrane Conductance Regulator (CFTR) has been shown to influence connexin function. Moreover, a direct interaction between Cx45.6 and the Major Intrinsic Protein/AQP0 in lens appears to influence the process of cell differentiation whereas interactions between aquaporin 4 (AQP4) and Cx43 in mouse astrocytes may coordinate the intercellular movement of ions and water between astrocytes. In this review, we discuss evidence supporting interactions between Cx and membrane channels/transporters including CFTR, aquaporins, ionotropic glutamate receptors, and between pannexin1, another class of putative gap-junction-forming proteins, and Kvbeta3, a regulatory beta-subunit of voltage gated potassium channels. Although the precise molecular nature of these interactions has yet to be defined, their consequences may be critical for normal tissue homeostasis.
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Affiliation(s)
- Marc Chanson
- Dept. of Pediatrics, Geneva University Hospitals, Geneva, Switzerland
| | - Basilio A. Kotsias
- Instituto de Investigaciones Médicas Alfredo Lanari, Universidad de Buenos Aires, Argentina
| | - Camillo Peracchia
- Dept. of Pharmacology and Physiology, University of Rochester, School of Medicine, Rochester, NY, USA
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9
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KAMASAWA N, FURMAN CS, DAVIDSON KGV, SAMPSON JA, MAGNIE AR, GEBHARDT BR, KAMASAWA M, YASUMURA T, ZUMBRUNNEN JR, PICKARD GE, NAGY JI, RASH JE. Abundance and ultrastructural diversity of neuronal gap junctions in the OFF and ON sublaminae of the inner plexiform layer of rat and mouse retina. Neuroscience 2006; 142:1093-117. [PMID: 17010526 PMCID: PMC1847771 DOI: 10.1016/j.neuroscience.2006.08.020] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2006] [Revised: 07/28/2006] [Accepted: 08/01/2006] [Indexed: 11/17/2022]
Abstract
Neuronal gap junctions are abundant in both outer and inner plexiform layers of the mammalian retina. In the inner plexiform layer (IPL), ultrastructurally-identified gap junctions were reported primarily in the functionally-defined and anatomically-distinct ON sublamina, with few reported in the OFF sublamina. We used freeze-fracture replica immunogold labeling and confocal microscopy to quantitatively analyze the morphologies and distributions of neuronal gap junctions in the IPL of adult rat and mouse retina. Under "baseline" conditions (photopic illumination/general anesthesia), 649 neuronal gap junctions immunogold-labeled for connexin36 were identified in rat IPL, of which 375 were photomapped to OFF vs. ON sublaminae. In contrast to previous reports, the volume-density of gap junctions was equally abundant in both sublaminae. Five distinctive morphologies of gap junctions were identified: conventional crystalline and non-crystalline "plaques" (71% and 3%), plus unusual "string" (14%), "ribbon" (7%) and "reticular" (2%) forms. Plaque and reticular gap junctions were distributed throughout the IPL. However, string and ribbon gap junctions were restricted to the OFF sublamina, where they represented 48% of gap junctions in that layer. In string and ribbon junctions, curvilinear strands of connexons were dispersed over 5 to 20 times the area of conventional plaques having equal numbers of connexons. To define morphologies of gap junctions under different light-adaptation conditions, we examined an additional 1150 gap junctions from rats and mice prepared after 30 min of photopic, mesopic and scotopic illumination, with and without general anesthesia. Under these conditions, string and ribbon gap junctions remained abundant in the OFF sublamina and absent in the ON sublamina. Abundant gap junctions in the OFF sublamina of these two rodents with rod-dominant retinas revealed previously-undescribed but extensive pathways for inter-neuronal communication; and the wide dispersion of connexons in string and ribbon gap junctions suggests unique structural features of gap junctional coupling in the OFF vs. ON sublamina.
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Affiliation(s)
- N. KAMASAWA
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - C. S. FURMAN
- Department of Physiology, Southern Illinois University School of Medicine, Southern Illinois University at Carbondale, Carbondale, IL 62901, USA
| | - K. G. V. DAVIDSON
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - J. A. SAMPSON
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - A. R. MAGNIE
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - B. R. GEBHARDT
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - M. KAMASAWA
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - T. YASUMURA
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
| | - J. R. ZUMBRUNNEN
- Department of Statistics, Colorado State University, Fort Collins, CO 80523, USA
| | - G. E. PICKARD
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
- Program in Molecular, Cellular and Integrative Neurosciences, Colorado State University, Fort Collins, CO 80523, USA
| | - J. I. NAGY
- Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada R3E 3J7
| | - J. E. RASH
- Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA
- Program in Molecular, Cellular and Integrative Neurosciences, Colorado State University, Fort Collins, CO 80523, USA
- *Correspondence to: J. E. Rash, Department of Biomedical Sciences, Colorado State University, Campus Delivery 1617, Fort Collins, CO 80523, USA. Tel: +1-970-491-5606; fax: +1-970-491-7907. E-mail address: (J. E. Rash)
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10
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Garner CC, Waites CL, Ziv NE. Synapse development: still looking for the forest, still lost in the trees. Cell Tissue Res 2006; 326:249-62. [PMID: 16909256 DOI: 10.1007/s00441-006-0278-1] [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] [Received: 06/07/2006] [Accepted: 06/08/2006] [Indexed: 01/23/2023]
Abstract
Synapse development in the vertebrate central nervous system is a highly orchestrated process occurring not only during early stages of brain development, but also (to a lesser extent) in the mature nervous system. During development, the formation of synapses is intimately linked to the differentiation of neuronal cells, the extension of their axons and dendrites, and the course wiring of the nervous system. Subsequently, the stabilization, elimination, and strengthening of synaptic contacts is coupled to the refinement of axonal and dendritic arbors, to the establishment of functionally meaningful connections, and probably also to the day-to-day acquisition, storage, and retrieval of memories, higher order thought processes, and behavioral patterns.
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Affiliation(s)
- Craig C Garner
- Department of Psychiatry and Behavioral Science, Nancy Pritzer Laboratory, Stanford University, Palo Alto, CA 94304-5485, USA.
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11
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Patel LS, Mitchell CK, Dubinsky WP, O’Brien J. Regulation of gap junction coupling through the neuronal connexin Cx35 by nitric oxide and cGMP. ACTA ACUST UNITED AC 2006; 13:41-54. [PMID: 16613779 PMCID: PMC2189984 DOI: 10.1080/15419060600631474] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Gap-junctional coupling among neurons is subject to regulation by a number of neurotransmitters including nitric oxide. We studied the mechanisms by which NO regulates coupling in cells expressing Cx35, a connexin expressed in neurons throughout the central nervous system. NO donors caused potent uncoupling of HeLa cells stably transfected with Cx35. This effect was mimicked by Bay 21-4272, an activator of guanylyl cyclase. A pharmacological analysis indicated that NO-induced uncoupling involved both PKG-dependent and PKG-independent pathways. PKA was involved in both pathways, suggesting that PKG-dependent uncoupling may be indirect. In vitro, PKG phosphorylated Cx35 at three sites: Ser110, Ser276, and Ser289. A mutational analysis indicated that phosphorylation on Ser110 and Ser276, sites previously shown also to be phosphorylated by PKA, had a significant influence on regulation. Ser289 phosphorylation had very limited effects. We conclude that NO can regulate coupling through Cx35 and that regulation is indirect in HeLa cells.
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Affiliation(s)
- Leena S. Patel
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
| | - Cheryl K. Mitchell
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
| | - William P. Dubinsky
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston
- The Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston
| | - John O’Brien
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
- The Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston
- *Corresponding author: John O’Brien, Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, 6431 Fannin St., MSB 7.024, Houston, Texas 77030, Phone: (713) 500-5983, FAX: (713) 500-0682, e-mail:
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12
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Ciolofan C, Li XB, Olson C, Kamasawa N, Gebhardt BR, Yasumura T, Morita M, Rash JE, Nagy JI. Association of connexin36 and zonula occludens-1 with zonula occludens-2 and the transcription factor zonula occludens-1-associated nucleic acid-binding protein at neuronal gap junctions in rodent retina. Neuroscience 2006; 140:433-51. [PMID: 16650609 PMCID: PMC1819557 DOI: 10.1016/j.neuroscience.2006.02.032] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2005] [Revised: 01/21/2006] [Accepted: 02/08/2006] [Indexed: 11/16/2022]
Abstract
Most gap junctions between neurons in mammalian retina contain abundant connexin36, often in association with the scaffolding protein zonula occludens-1. We now investigate co-association of connexin36, zonula occludens-1, zonula occludens-2 and Y-box transcription factor 3 (zonula occludens-1-associated nucleic acid-binding protein) in mouse and rat retina. By immunoblotting, zonula occludens-1-associated nucleic acid-binding protein and zonula occludens-2 were both detected in retina, and zonula occludens-2 in retina was found to co-immunoprecipitate with connexin36. By immunofluorescence, the four proteins appeared as puncta distributed in the plexiform layers. In the inner plexiform layer, most connexin36-puncta were co-localized with zonula occludens-1, and many were co-localized with zonula occludens-1-associated nucleic acid-binding protein. Moreover, zonula occludens-1-associated nucleic acid-binding protein was often co-localized with zonula occludens-1. Nearly all zonula occludens-2-puncta were positive for connexin36, zonula occludens-1 and zonula occludens-1-associated nucleic acid-binding protein. In the outer plexiform layer, connexin36 was also often co-localized with zonula occludens-1-associated nucleic acid-binding protein. In connexin36 knockout mice, labeling of zonula occludens-1 was slightly reduced in the inner plexiform layer, zonula occludens-1-associated nucleic acid-binding protein was decreased in the outer plexiform layer, and both zonula occludens-1-associated nucleic acid-binding protein and zonula occludens-2 were markedly decreased in the inner sublamina of the inner plexiform layer, whereas zonula occludens-1, zonula occludens-2 and zonula occludens-1-associated nucleic acid-binding protein puncta persisted and remained co-localized in the outer sublamina of the inner plexiform layer. By freeze-fracture replica immunogold labeling, connexin36 was found to be co-localized with zonula occludens-2 within individual neuronal gap junctions. In addition, zonula occludens-1-associated nucleic acid-binding protein was abundant in a portion of ultrastructurally-defined gap junctions throughout the inner plexiform layer, and some of these junctions contained both connexin36 and zonula occludens-1-associated nucleic acid-binding protein. These distinct patterns of connexin36 association with zonula occludens-1, zonula occludens-2 and zonula occludens-1-associated nucleic acid-binding protein in different sublaminae of retina, and differential responses of these proteins to connexin36 gene deletion suggest differential regulatory and scaffolding roles of these gap junction accessory proteins. Further, the persistence of a subpopulation of zonula occludens-1/zonula occludens-2/zonula occludens-1-associated nucleic acid-binding protein co-localized puncta in the outer part of the inner plexiform layer of connexin36 knockout mice suggests close association of these proteins with other structures in retina, possibly including gap junctions composed of an as-yet-unidentified connexin.
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Affiliation(s)
- C Ciolofan
- Department of Physiology, Faculty of Medicine, University of Manitoba, 730 William Avenue, Winnipeg, Manitoba, Canada R3E 3J7
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Burr GS, Mitchell CK, Keflemariam YJ, Heidelberger R, O’Brien J. Calcium-dependent binding of calmodulin to neuronal gap junction proteins. Biochem Biophys Res Commun 2005; 335:1191-8. [PMID: 16112650 PMCID: PMC2222552 DOI: 10.1016/j.bbrc.2005.08.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Accepted: 08/01/2005] [Indexed: 11/29/2022]
Abstract
We examined the interactions of calmodulin with neuronal gap junction proteins connexin35 (Cx35) from perch, its mouse homologue Cx36, and the related perch Cx34.7 using surface plasmon resonance. Calmodulin bound to the C-terminal domains of all three connexins with rapid kinetics in a concentration- and Ca2+-dependent manner. Dissociation was also very rapid. K(d)'s for calmodulin binding at a high-affinity site ranged from 11 to 72 nM, and K(1/2)'s for Ca2+ were between 3 and 5 microM. No binding to the intracellular loops was observed. Binding competition experiments with synthetic peptides mapped the calmodulin binding site to a 10-30 amino acid segment at the beginning of the C-terminal domain of Cx36. The micromolar K(1/2)'s and rapid on and off rates suggest that this interaction may change dynamically in neurons, and may occur transiently when Ca2+ is elevated to a level that would occur in the near vicinity of an activated synapse.
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Affiliation(s)
- Gary S. Burr
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
| | - Cheryl K. Mitchell
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
| | - Yenabi J. Keflemariam
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
| | - Ruth Heidelberger
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston
- The Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston
| | - John O’Brien
- Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston
- The Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston
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14
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Rash JE, Davidson KGV, Kamasawa N, Yasumura T, Kamasawa M, Zhang C, Michaels R, Restrepo D, Ottersen OP, Olson CO, Nagy JI. Ultrastructural localization of connexins (Cx36, Cx43, Cx45), glutamate receptors and aquaporin-4 in rodent olfactory mucosa, olfactory nerve and olfactory bulb. JOURNAL OF NEUROCYTOLOGY 2005; 34:307-41. [PMID: 16841170 PMCID: PMC1525003 DOI: 10.1007/s11068-005-8360-2] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Revised: 01/06/2006] [Accepted: 01/07/2006] [Indexed: 01/21/2023]
Abstract
Odorant/receptor binding and initial olfactory information processing occurs in olfactory receptor neurons (ORNs) within the olfactory epithelium. Subsequent information coding involves high-frequency spike synchronization of paired mitral/tufted cell dendrites within olfactory bulb (OB) glomeruli via positive feedback between glutamate receptors and closely-associated gap junctions. With mRNA for connexins Cx36, Cx43 and Cx45 detected within ORN somata and Cx36 and Cx43 proteins reported in ORN somata and axons, abundant gap junctions were proposed to couple ORNs. We used freeze-fracture replica immunogold labeling (FRIL) and confocal immunofluorescence microscopy to examine Cx36, Cx43 and Cx45 protein in gap junctions in olfactory mucosa, olfactory nerve and OB in adult rats and mice and early postnatal rats. In olfactory mucosa, Cx43 was detected in gap junctions between virtually all intrinsic cell types except ORNs and basal cells; whereas Cx45 was restricted to gap junctions in sustentacular cells. ORN axons contained neither gap junctions nor any of the three connexins. In OB, Cx43 was detected in homologous gap junctions between almost all cell types except neurons and oligodendrocytes. Cx36 and, less abundantly, Cx45 were present in neuronal gap junctions, primarily at "mixed" glutamatergic/electrical synapses between presumptive mitral/tufted cell dendrites. Genomic analysis revealed multiple miRNA (micro interfering RNA) binding sequences in 3'-untranslated regions of Cx36, Cx43 and Cx45 genes, consistent with cell-type-specific post-transcriptional regulation of connexin synthesis. Our data confirm absence of gap junctions between ORNs, and support Cx36- and Cx45-containing gap junctions at glutamatergic mixed synapses between mitral/tufted cells as contributing to higher-order information coding within OB glomeruli.
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Affiliation(s)
- John E Rash
- Department of Biomedical Sciences, Colorado State University, Fort Collins, 80523, USA.
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15
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Christie JM, Bark C, Hormuzdi SG, Helbig I, Monyer H, Westbrook GL. Connexin36 mediates spike synchrony in olfactory bulb glomeruli. Neuron 2005; 46:761-72. [PMID: 15924862 DOI: 10.1016/j.neuron.2005.04.030] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Revised: 03/14/2005] [Accepted: 04/25/2005] [Indexed: 11/16/2022]
Abstract
Neuronal synchrony is important to network behavior in many brain regions. In the olfactory bulb, principal neurons (mitral cells) project apical dendrites to a common glomerulus where they receive a common input. Synchronized activity within a glomerulus depends on chemical transmission but mitral cells are also electrically coupled. We examined the role of connexin-mediated gap junctions in mitral cell coordinated activity. Electrical coupling as well as correlated spiking between mitral cells projecting to the same glomerulus was entirely absent in connexin36 (Cx36) knockout mice. Ultrastructural analysis of glomeruli confirmed that mitral-mitral cell gap junctions on distal apical dendrites contain Cx36. Coupled AMPA responses between mitral cell pairs were absent in the knockout, demonstrating that electrical coupling, not transmitter spillover, is responsible for synchronization. Our results indicate that Cx36-mediated gap junctions between mitral cells orchestrate rapid coordinated signaling via a novel form of electrochemical transmission.
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16
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Valiunas V, Mui R, McLachlan E, Valdimarsson G, Brink PR, White TW. Biophysical characterization of zebrafish connexin35 hemichannels. Am J Physiol Cell Physiol 2004; 287:C1596-604. [PMID: 15282192 DOI: 10.1152/ajpcell.00225.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A subset of connexins can form unopposed hemichannels in expression systems, providing an opportunity for comparison of hemichannel gating properties with those of intact gap junction channels. Zebrafish connexin35 (Cx35) is a member of the Cx35/Cx36 subgroup of connexins highly expressed in the retina and brain. In the present study, we have shown that Cx35 expression in Xenopus oocytes and N2A cells produced large outward whole cell currents on cell depolarization. Using whole cell, cell-attached, and excised patch configurations, we obtained multichannel and single-channel current recordings attributable to the Cx35 hemichannels (I(hc)) that were activated and increased by stepwise depolarization of membrane potential (V(m)) and deactivated by hyperpolarization. The currents were not detected in untransfected N2A cells or in control oocytes injected with antisense Cx38. However, water-injected oocytes that were not treated with antisense showed activities attributable to Cx38 hemichannels that were easily distinguishable from Cx35 hemichannels by a significantly larger unitary conductance (gamma(hc): 250-320 pS). The gamma(hc) of Cx35 hemichannels exhibited a pronounced V(m) dependence; i.e., gamma(hc) increased/decreased with relative hyperpolarization/depolarization (gamma(hc) was 72 pS at V(m) = -100 mV and 35 pS at V(m) = 100 mV). Extrapolation to V(m) = 0 mV predicted a gamma(hc) of 48 pS, suggesting a unitary conductance of intact Cx35 gap junction channels of approximately 24 pS. Channel gating was also V(m) dependent: open time declined with negative V(m) and increased with positive V(m). The ability to break down the complex gating of intact intercellular channels into component hemichannels in vitro will help to evaluate putative physiological roles for hemichannels in vivo.
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Affiliation(s)
- Virginijus Valiunas
- Department of Physiology and Biophysics, State University of New York, T5-147, Basic Science Tower, Stony Brook, NY 11794-8661, USA
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