Neuronal and glial localization of the GABA transporter GAT-1 in the cerebellar cortex

THE distribution and neuronal or glial localization of GAT-1, a high affinity GABA transporter, in the cerebellar cortex was analysed by means of double-label immunofluorescence experiments with GAT-1 combined with calbindin D, synaptophysin, or GFAP antibodies. In the Purkinje cell (Pc) layer, prominent synaptic GAT-1-immunoreactivity (IR) was found in the axon terminals of basket cells surrounding the Pc axon hillock. GAT-1-IR was also found in neuronal and glial processes ensheathing Pc somata and dendrites. Numerous immunoreactive fibres and puncta originating from basket and stellate cells, or from Golgi cells, were also detected in the molecular or granular layer, respectively. These observations suggest that GAT-1 is involved in the termination of the action of GABA at the inhibitory synapses of all cerebellar interneurones, primarily of basket cell terminals at the Pc axon hillock. GAT-1 in the astroglial processes presumably plays the additional role of regulating the extracellular concentrations of GABA.