Developmental expression of GABA transporters GAT1 and GAT4 suggests involvement in brain maturation

cDNA clones representing four pharmacologically distinct GABA transporters (GAT1-GAT4) were previously identified in mouse brain. Two of these, GAT1 and GAT4, were found to be brain specific. We studied GAT1 and GAT4 in the developing rat brain using polygonal antibodies against recombinant fusion proteins. Patterns of immunoreactivity were very similar in the embryonic and early postnatal stages for both transporters. However, whereas GAT1 immunoreactivity was detected in distinct patterns in gray matter and growing axons, GAT4 immunoreactivity was found in a subset of radial glial cell fascicles. These patterns usually oriented perpendicularly to the axons expressing GAT1. Our results suggest a transient relationship between GAT4-expressing radial glial elements and GAT1-expressing axons. The presence of GAT1 in the cortical marginal zone and the numerous GAT4-positive fascicles observed in the fetal anterior commissure indicate that both transporters may play a role in processes of brain maturation. Because the beginning of expression for both GAT1 and GAT4 correlates with the expression of the alpha1 subunit of the GABA receptor, the transporters may be connected with the maturation of adult-type GABAergic inhibitory system in the brain.