Preservation of the hyperdirect pathway of basal ganglia in a rodent brain slice.

Basal ganglia are a network of interconnected nuclei, involved in motor control, goal-directed behaviors and procedural learning. Basal ganglia process information from the cerebral cortex through three main pathways. The striatum is the input nucleus of the direct (cortico-striato-nigral) and indirect (cortico-striato-pallido-subthalamo-nigral) pathways while the subthalamic nucleus (STN) is the input structure of the hyperdirect (cortico-subthalamo-nigral) pathway. Despite the fact that the hyperdirect pathway constitutes a central part of most of basal ganglia models, experimental studies concerning its synaptic transmission and plasticity are still lacking. This is mainly because in vitro brain slices do not preserve the hyperdirect pathway. Here, we address this by developing a hyperdirect pathway brain slice where cortico-subthalamo-nigral connections were preserved. We characterized the transmission properties and its monosynaptic features between the frontal cortex and the STN, and between the STN and the substantia nigra pars reticulata (SNr), the output nucleus of the hyperdirect pathway. Cortical stimulation evoked monosynaptic glutamatergic events in STN neurons with a mean latency of 11.3 ms and a mean amplitude of 21 pA. STN stimulations evoked monosynaptic glutamatergic events in SNr neurons with a mean latency of 2.5 ms and a mean amplitude of 116 pA. This brain slice also preserved a part of the direct and indirect pathways such as the cortico-striatal connection. This novel slice configuration containing the hyperdirect pathway is a useful tool to better understand the transmission and plasticity in this pathway and hence the physiology and the pathophysiology of basal ganglia.