Costimulation of N -methyl- d -aspartate and muscarinic neuronal receptors modulates gap junctional communication in striatal astrocytes

Abstract

Cocultures of neurons and astrocytes from the rat striatum were used to determine whether the stimulation of neuronal receptors could affect the level of intercellular communication mediated by gap junctions in astrocytes. The costimulation of N-methyl-Dasparte (NMDA) and muscarinic receptors led to a prominent reduction of astrocyte gap junctional communication (GJC) in coculture. This treatment was not effective in astrocyte cultures, these cells being devoid of NMDA receptors. Both types of receptors contribute synergistically to this inhibitory response, as the reduction in astrocyte GJC was not observed after the blockade of either NMDA or muscarinic receptors. The involvement of a neuronal release of arachidonic acid (AA) in this inhibition was investigated because the costimulation of neuronal NMDA and muscarinic receptors markedly enhanced the release of AA in neuronal cultures and in cocultures. In addition, both the reduction of astrocyte GJC and the release of AA evoked by NMDA and muscarinic receptor costimulation were prevented by mepacrine, a phospholipase A 2 inhibitor, and this astrocyte GJC inhibition was mimicked by the exogenous application of AA. Metabolites of AA formed through the cyclooxygenase pathway seem to be responsible for the effects induced by either the costimulation of NMDA and muscarinic neuronal receptors or the application of exogenous AA because, in both cases, astrocyte GJC inhibition was prevented by indomethacin. Altogether, these data provide evidence for a neuronal control of astrocytic communication and open perspectives for the understanding of the modalities through which cholinergic interneurons and glutamatergic inputs affect local circuits in the striatum. T hrough their multiple processes, astrocytes are in close association with neurons and play multiple roles in brain functions. Besides their supporting role, these glial cells actively interact with neurons because they sense and respond to neuronal activity and can affect synaptic transmission by releasing chemical transmitters (1, 2). A typical feature of astrocytes is their widespread connection by gap junctions, which allows direct intercellular communication and defines astrocytic networks in culture and brain slice preparations (3). Gap junctions are constituted by clusters of intercellular channels composed of 12-subunit proteins, called connexins, 6 of them corresponding to a hemichannel that belongs to each coupled cell. Astrocytes express several connexins with a predominance for connexin 43 (Cx43), present from embryonic to adult stages, and connexin 30, which appears late in situ and in primary cultures (see refs. 4 and 5). The efficiency of gap junctions in astrocytes can be controlled by several classes of endogenous compounds, including neurotransmitters, neuropeptides, bioactive lipids, and growth factors (see refs. 6 and 7). These regulations, which up to now have only been revealed by exogenous applications of these compounds, suggest that astrocytic networks are subject to remodeling and to so...

Gap‐junction blocker carbenoxolone differentially enhances NMDA‐induced cell death in hippocampal neurons and astrocytes in co‐culture

“…Long‐term and short‐term regulation of gap junctional coupling of neural cells is important for many brain activities (Ransom and Ye 2005). Short‐term regulation through second messengers and protein kinase activity (Peracchia 2004; Rouach et al. 2002a) changes the opening probability of gap junctions within minutes.…”

The Role of Gap Junction Channels During Physiologic and Pathologic Conditions of the Human Central Nervous System

“…Cocultures of astrocyte-neurons increased Cx43 expression and GJC in astrocytes (Rouach et al 2004a, b). Treatment of astrocyte-neuronal cultures with NMDA or acetylcholine resulted in a prominent reduction of astrocytic GJ channels (Rouach et al 2002a), suggesting that neuronal activity can have different effects on GJ channels. Inflammatory and stress factors, such as IL-1β (John et al 1999; Duffy et al 2000), NO (Bolanos and Medina 1996), ATP (Meme et al 2004), FGF-2 (Reuss et al 1998), TGF-β (Reuss et al 1998), arachidonic acid (Martinez and Saez 1999), endothelins (Giaume et al 1992), glutamate/kainate (Muller et al 1996), and acidification (H + and lactic acid) (Morley et al 1996, 1997; Dunina-Barkovskaya 1998; Trexler et al 1999; Duffy et al 2002; Yamaguchi and Ma 2003; Duffy et al 2004; Gonzalez-Nieto et al 2008) reduce Cx43 expression and opening of GJ channels.…”

Astroglial networking contributes to neurometabolic coupling

“…Such approach has enabled to show that the permeability and selectivity of GJ channels control the extent of astroglial network diffusion and are regulated by a variety of endogenous molecules such as ions, peptides, and neurotransmitters, released by various brain cell types and acting on membrane channels and receptors (Giaume et al, 2010). Thus, astroglial networks are functionally plastic and are regulated by neuronal activity, as shown in several brain regions (Fischer and Kettenmann, 1985; Marrero and Orkand, 1996; Rouach et al, 2000, 2002b, 2008; Roux et al, 2011). Although mostly assessed by GJ coupling for passive dyes, a few pathways have been proposed to control activity-dependent astroglial networking.…”