Ability of retinal M�ller glial cells to protect neurons against excitotoxicity in vitro depends upon maturation and neuron-glial interactions

Abstract

Glutamate is the most abundant excitatory amino acid in the central nervous system. It has also been described as a potent toxin when present in high concentrations because excessive stimulation of its receptors leads to neuronal death. Glial influence on neuronal survival has already been shown in the central nervous system, but the mechanisms underlying glial neuroprotection are only partly known. When cells isolated from newborn rat retina were maintained in culture as enriched neuronal populations, 80% of the cells were destroyed by application of excitotoxic concentrations of glutamate. Massive neuronal death was also observed in newborn retinal cultures containing large numbers of glia, or when neurons were seeded onto feeder layers of purified cells prepared from immature (postnatal 8 day) rat retina. When newborn retinal neurons were seeded onto feeder layers of purified glial cells prepared from adult retinas, application of excitotoxic amino acids no longer led to neuronal death. Furthermore, neuronal death was not observed in mixed neuron/glial cultures prepared from adult retina. However, in all cases (newborn and adult) application of kainate led to amacrine cell‐specific death. Activity of glutamine synthetase, a key glial enzyme involved in glutamate detoxification, was assayed in these cultures in the presence or absence of exogenous glutamate. Whereas pure glial cultures alone (from young or adult retina) showed low activity that was not stimulated by glutamate addition, mixed or co‐cultured neurons and adult glia exhibited up to threefold higher levels of activity following glutamate treatment. These data indicate that two conditions must be satisfied to observe glial neuroprotection: maturation of glutamine synthetase expression, and neuron‐glial signalling through glutamate‐elicited responses. GLIA 25:229–239, 1999. © 1999 Wiley‐Liss, Inc.

Effect of electrical stimulation on IGF-1 transcription by L-type calcium channels in cultured retinal Müller cells

“…20 Another possibility may be the lack of neuron-glial interactions in the present study. Heidinger et al 22 showed a paradoxical response of cultured Müller cells to excitotoxic amino acids: glutamine synthetase activity in pure Müller cell cultures was not increased by glutamine application, whereas the activity was upregulated by glutamine in a mixture of neuron/glial cultures. This would indicate that intimate interconnections of Müller cells with retinal neurons appear to be necessary to yield high expression levels of glutamine synthetase in vitro.…”

Slit modulates cerebrovascular inflammation and mediates neuroprotection against global cerebral ischemia

“…Slit's ability to protect against neuronal injury in this model, the first demonstration of its kind that we are aware of, must result from Slit-mediated signaling of cytoprotective pathways in glia and/or neurons independent of any reduction in leukocyte chemotaxis. Although further studies are required to elucidate the mechanistic basis for the observed protective effect, a direct effect of Slit that improves the glial response to ischemia is possible, since the ability of glial cells to promote neuronal viability in the setting of ischemia is well established (Lee et al, 2004;Rosenberg et al, 1989;Heidinger et al, 1999;Trendelenburg et al, 2005;Swanson et al, 2004). In Drosophila, glial Slit receptors play an important role in neuron-glia interactions by influencing the survival and migration of both cell types; moreover, interfering with these interactions alters their responsiveness to Slit-Robo signaling (Kinrade et al, 2001).…”

Neuroprotective effects of agmatine against cell damage caused by glucocorticoids in cultured rat hippocampal neurons

“…Cultured neurons are more vulnerable to the potential neurotoxicity of corticosterone when few glial cells are present in this culture (Dugan et al, 1995;Lewis et al, 1998). For example, when neuronal cells isolated form newborn rat were maintained in culture as enriched neuronal populations, 80% of the cells were killed by application of excitotoxic concentrations of glutamate and this neuronal death was not observed in mixed neuron/glial cultures (Heidinger et al, 1999). …”