Bergmann glia, the specialized cerebellar astrocytes, encapsulate synaptic terminals onto Purkinje cells and possess transporters that are precisely located to remove GABA and glutamate from synaptic clefts. Although astrocytes have been shown to sense neuronal activity, very little is known on their ability to influence synaptic transmission. The goal of this application is to determine whether astrocytic GABA/taurine and glutamate transporters contribute to fast GABAergic neurotransmission.
Three aims will be addressed with immunocytochemistry and whole-cell patch-clamp recordings in rat cerebellar slices.
The first aim will be to verify the hypothesis that Bergmann glia possess functional GABA and taurine transporters that can work in reverse and are activated by synaptically-released GABA.
The second aim will be to evaluate the hypothesis that astrocytic GABA transporters can influence neuronal activity by uptake of GABA or by non-vesicular release of GABA or taurine.
This aim will require simultaneous recordings of a Purkinje cell and an adjacent Bergmann glial cell encapsulating GABAergic inputs on the recorded Purkinje cell. While monitoring GABAergic synaptic currents, GABA transporters in Bergmann glia will be blocked by internal perfusion of a transport blocker during the recording. Similarly, the effect of non-vesicular release of GABA or taurine will be tested on neuronal baseline currents. Finally, glutamate has been shown to stimulate GABA release by activating presynaptic NMDA receptors on GABAergic terminals.
The third aim will be to verify the hypothesis that astrocytic glutamate transporters regulate presynaptic GABA release by limiting glutamate spillover from glutamatergic synapses and thus regulating glutamate levels at GABAergic synapses. These studies will define important functions of astrocytic transporters on synaptic efficacy and neuronal excitability. Because astrocytes from other brain regions also express similar transporters and encapsulate synapses, findings in the cerebellum can serve as a model of the function of astrocytic transporters at GABAergic synapses. These data will also be important for understanding pathological mechanisms affecting astrocytic transporters and GABA signaling
