Basal ganglia, a set of interconnected nuclei, are implicated in the elaboration, control and memorization of cognitive-motor behaviors. One of the main output structure of this network, the substantia nigra pars reticulata (SNr), integrates and conveys neuronal information to cortical areas via a thalamic relay. However, this transmission requires an accurate regulation of the SNr neuronal activity since this structure inhibits its targets due to its spontaneous GABAergic activity. Among the different actors of this regulation, glutamate and GABA provide a tight balance between excitation and inhibition of the SNr neuronal activity. Several studies have explored the different mechanisms involved in this regulation but paradoxically, none concerned the astrocyte functions. In this work, our aim was to study astrocyte-neuron relations in order to define a potential astrocyte implication in the regulation of the neuronal activity in the SNr. We studied calcium and electrical activities of astrocytes and neurons using calcium imaging and patch-clamp techniques in parasagittal rat brain slices, conserving subthalamo- and pallido-nigral projections. We showed that astrocytes in the SNr displayed spontaneous calcium activities, both dependent and independent of glutamatergic and GABAergic tonic neuronal transmissions. Moreover, we showed that astrocytes calcium activities were regulated by the subthalamic nucleus high frequency stimulation. Our results revealed that, in turn, astrocytes calcium activities were involved in the regulation of the neuronal firing rate. Finally, we showed that astrocyte glutamatergic, and maybe GABAergic, reuptake was involved in the regulation of the neuronal firing rate. To conclude, this study revealed a bidirectional communication between astrocytes and neurons in the SNr. This communication seems to be important in the regulation of the activity in this structure.
Neuron-astrocyte interaction within the substantia nigra pars reticulata