Glutamate transporter GLT-1 is highly expressed in activated microglia following facial nerve axotomy

Glutamate transporters play an important role in the re-uptake of glutamate after its release from glutamatergic synapses. So far five of such transporters subtypes have been cloned from rodent and human brains. The densities of glutamate transporters are recognised to be developmentally regulated, but the role of glutamate transporters in the mechanisms underlying the occurrence of neuronal traumatic injury has not been widely studied. In the present study quantitative Western blotting and immunohistochemical technique were employed to study the expression of GLT-1/EAAT2 in the facial nuclei of adult rats following unilateral facial nerve axotomy. The total content of GLT-1 protein decreased in the ipsilateral axotomised rat facial nucleus. However, activated microglia surrounding motoneurons showed high expression of GLT-1 after facial nerve axotomy. Parallel studies revealed that primary cultured microglial cells also showed GLT-1-immunoreactivity. To our knowledge, this is the first direct demonstration of the expression of GLT-1 protein in activated microglial cells, suggesting a neuroprotective role of microglia against glutamate excitotoxicity following nerve axotomy.