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The Journal of Neuroscience, June 17, 2009, 29(24):7898-7908; doi:10.1523/JNEUROSCI.6129-08.2009

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Neurobiology of Disease
Regulation of Glutamate Transport in Developing Rat Oligodendrocytes

Tara M. DeSilva, Anatoli Y. Kabakov, Patricia E. Goldhoff, Joseph J. Volpe, and Paul A. Rosenberg

Department of Neurology and F. M. Kirby Neurobiology Center, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115

Correspondence should be addressed to Paul A. Rosenberg, Center for Life Sciences 13073, Department of Neurology, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115. Email: paul.rosenberg{at}childrens.harvard.edu

Glutamate released from synaptic vesicles mediates excitatory neurotransmission by stimulating glutamate receptors. Glutamate transporters maintain low synaptic glutamate levels critical for this process, a role primarily attributed to astrocytes. Recently, vesicular release of glutamate from unmyelinated axons in the rat corpus callosum has been shown to elicit AMPA receptor-mediated currents in glial progenitor cells. Glutamate transporters are the only mechanism of glutamate clearance, yet very little is known about the role of glutamate transporters in normal development of oligodendrocytes (OLs) or in excitotoxic injury to OLs. We found that OLs in culture are capable of sodium-dependent glutamate uptake with a K_m of 10 ± 2 µM and a V_max of 2.6, 5.0, and 3.8 nmol · min^–1 · mg^–1 for preoligodendrocytes, immature, and mature OLs, respectively. Surprisingly, EAAC1, thought to be exclusively a neuronal transporter, contributes more to [³H]L-glutamate uptake in OLs than GLT1 or GLAST. These data suggest that glutamate transporters on oligodendrocytes may serve a critical role in maintaining glutamate homeostasis at a time when unmyelinated callosal axons are engaging in glutamatergic signaling with glial progenitors. Furthermore, GLT1 was significantly increased in cultured mature OLs contrary to in vivo data in which we have shown that, although GLT1 is present on developing OLs when unmyelinated axons are prevalent in the developing rat corpus callosum, after myelination, GLT1 is not expressed on mature OLs. The absence of GLT1 in mature OLs in the rat corpus callosum and its presence in mature rat cultured OLs may indicate that a signaling process in vivo is not activated in vitro.

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Received Dec. 22, 2008; revised March 16, 2009; accepted April 8, 2009.

Correspondence should be addressed to Paul A. Rosenberg, Center for Life Sciences 13073, Department of Neurology, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115. Email: paul.rosenberg{at}childrens.harvard.edu

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