Developmental expression of gamma-aminobutyric acid transporters (GAT-1 and GAT-3) in the rat cerebellum: Evidence for a transient presence of GAT-1 in Purkinje cells

The cerebellar cortex contains several classes of GABAergic neurons. Previo us studies have shown that most GABAergic neurons in this region possess th e capacity for gamma-aminobutyric acid (GABA) uptake. The present study det ermined the postnatal expression of two GABA transporters, GAT-1 and GAT-3, in the cerebellar cortex and deep nuclei of the rat by using immunocytoche mistry. Immunoreactivity for GAT-1 and GAT-3 appears at postnatal day 7 (P7 ), emerges centroperipherally across the cerebellum during the following 2 weeks and reaches an adult-like pattern by P30. The mature patterns are ful ly established by P45, which for GAT-1 is characterized by immunolabeled pr ofiles localized exclusively to neuropil, mostly in the molecular layer and the pinceaux deep to the Purkinje cell bodies, and for GAT-3 as immunoreac tivity distributed in the neuropil of mainly the granular layer. Before the adult patterns are completed, GAT-1 immunoreactivity is present in the som ata of Purkinje, Golgi, basket and stellate cells between P7 and P21, while GAT-3 immunoreactivity is distinct in astrocytic somata which are organize d in regularly spaced clusters. During this period, there is also a banding pattern in the sagittal plane of GAT-1 immunoreactivity in developing Purk inje cells. The postnatal development of GAT-1 and GAT-3 in the rat cerebel lar cortex shares a similar spatiotemporal pattern with other GABAergic par ameters, including the GABA synthesizing enzyme, GABA content and uptake. S pecifically, the transient expression of GAT-1 in the somata and dendrites of cerebellar GABAergic neurons appears to correlate with the supra-adult l evels of whole-tissue GABA uptake capability during development. Further, G AT-1 expression in immature Purkinje cells may play a unique role in regula ting GABA's function during development, since mature Purkinje cells do not express GAT-1 or take up GABA. (C) 1998 Elsevier Science B.V. All rights r eserved.