Synaptic Transmission, Plasticity, and Integration in the Subthalamic Nucleus

The debilitating motor symptoms of akinesia, bradykinesia and rigidity in Parkinson’s disease (PD) are intimately related to changes in the frequency and pattern of neuronal activity in the reciprocally connected GABAergic external globus pallidus (GPe) and glutamatergic subthalamic nucleus (STN) and associated cortico-basal ganglia-thalamocortical networks. In idiopathic and experimental PD the GPe and STN exhibit hypo- and hyper-activity, respectively, and abnormal synchronous, rhythmic, burst firing. Following acute loss of substantia nigra dopamine neurons in experimental models of PD abnormal STN activity emerges slowly and intensifies gradually until it reaches a stable maximum after 2-3 weeks. This process suggests that adaptive changes in cellular and network properties contribute to the development of parkinsonian STN activity. Because the GPe potently regulates the frequency and synchronization of STN activity and can generate rebound burst firing in the STN, GPe-STN transmission was compared in control and 6-hydroxydopamine-lesioned rodents using electrophysiological, molecular and anatomical approaches. These studies revealed that 2-3 weeks after loss of dopamine the GPe-STN projection had strengthened considerably through proliferation of synaptic connections. This alteration could therefore be a major contributor to the emergence of abnormal GPe-STN activity in PD. Here we propose to study the timecourse, nature, underlying mechanisms and functional consequences of alterations in GPe-STN transmission that follow the loss of dopamine. We propose to apply cellular physiology to measure GPe-STN synaptic function and dysfunction; anatomical approaches to define the structural and molecular bases of GPe-STN synaptic plasticity; 2-photon laser scanning microscopy and optogenetics to define the sources of Ca2+ that trigger synaptic plasticity; viral vector, molecular and biochemical approaches to define the underlying molecular mechanisms and enable us to manipulate GPe-STN transmission.