Immunoreactivity for the GABA transporter-1 and GABA transporter-3 is restricted to astrocytes in the rat thalamus. A light and electron-microscopic immunolocalization
There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
GABA plasma membrane transporters mediate GABA uptake into presynaptic terminals and
surrounding glial processes and thus play a key role in shaping the time course and
spatial extent of GABA's action. In the present study we have investigated the cellular
and subcellular localization of two GABA transporters (1 and 3) in the rat thalamus
using affinity-purified polyclonal antibodies. GABA transporter-1 and -3 immunoreactivity,
detected with immunoperoxidase and immunofluorescence methods, is present throughout
the thalamus in small punctate structures scattered in the neuropil among unlabelled
neuronal perikarya. Labelling for GABA transporter-3 is always more intense than that
for GABA transporter-1. Astrocytic processes, identified by their immunoreactivity
for glial fibrillary acidic protein, express both GABA transporters. Ultrastructural
investigations confirm that GABA transporter-1 and -3 labelling is restricted to astrocytes.
Labelled astrocytes are adjacent to terminals making either symmetric or asymmetric
synaptic contacts, and are close to neuronal profiles that do not form synaptic contacts
in the plane of the section. In double-labelled thin sections some GABA transporter-1-
or -3-positive astrocytic processes, detected with immunoperoxidase labelling, surround
GABA-positive terminals, detected with antibodies to GABA and immunogold labelling.
These findings demonstrate that in rat thalamus the GABA uptake system mediated by
GABA transporter-1 and -3 is localized exclusively to astrocytes near the synapses
and in the neuropil, and absent from GABAergic terminals. Astrocytes play therefore
an important role in mediating GABA transmission in the thalamus, compared to cortical
regions.