INCREASED EXPRESSION OF GABA TRANSPORTERS, GAT-1 AND GAT-3, IN THE DEAFFERENTED SUPERIOR COLLICULUS OF THE RAT

GABA transporters (GATs) play a critical role in the translemmal trans port of GABA in neurons and glial cells. Two major brain GATs, GAT-1 a nd GAT-3, are found in astrocytes in the adult brain. Astroglia demons trate morphological and molecular changes in response to brain injury and deafferentation. The present study was designed to determine wheth er the expression of GATs changes after nerve deafferentation using th e rat superior colliculus (SC) as a model. The immunoreactivity for GA T-1 and GAT-3, as well as GABA and glutamic acid decarboxylase (GAD)-6 5 and GAD-67, was studied in the SC of control rats and rats with unil ateral optic nerve transections. Immunolabeling for both GAT-1 and GAT -3 was increased in the neuropil of the denervated SC as compared to t hat for the SC of control rats or for the unaffected SC of experimenta l rats. In contrast, immunoreactivity for GABA, GAD-65 and GAD-67 was not altered. The change in the immunolabeling of GAT-1 and GAT-3 was d etectable at 1 day postlesion and became more evident between 3-30 day s postlesion. At the electron microscopic level, immunoreactivity for both GAT-1 and GAT-S in the unaffected SC was localized to astrocytic processes, whereas GAT-1 immunolabeling was also present in synaptic t erminals. In the deafferented SC, immunolabeling for both GATs was ele vated in the somata and processes of hypertrophied astrocytes as compa red to that in the unaffected SC, whereas GAT-1 labeling in neuronal p rofiles was largely unchanged. A substantial increase of GAT-1 and GAT -3 in astrocytes following optic nerve transection suggests that these cells play a role in modulating GABA's action in the deafferented SC. (C) 1998 Elsevier Science B.V.