Inhibitory synaptic transmission from the substantia nigra pars reticulata to the ventral medial thalamus in mice

The cortico-basal ganglia-thalamic loop circuit is involved in variety of motor, association and limbic functions. The basal ganglia receive neural information from various areas of the cerebral cortex and transfer them back to the frontal and motor cortex via the ventral medial (VM), and the anterior-ventral lateral thalamic complex. The projection from the basal ganglia to the thalamus is GABAergic, and, therefore, the output from the basal ganglia cannot directly evoke excitation in the thalamic nuclei. The mechanism underlying the information transfer via the inhibitory projection remains unclear. To address this issue, we recorded electrophysiological properties of nigro-thalamic synapses from the VM neuron. We developed a nigro-thalamic slice preparation, in which the projection from the substantia nigra pars reticulata (SNr) to VM nucleus is stored, to enable the selective activation of the projection from the SNr. We characterized synaptic properties and membrane properties of the VM neuron, and developed a VM neuron model to simulate the impacts of SNr inputs on VM neuron activity. Neural simulation suggested that the inhibitory projection from SNr can control neural activity in two ways: a disinhibition from the spontaneous nigral inhibition and a β-band synchronization evoked by combination of excitation and inhibition of SNr activity.