Excitatory postsynaptic potentials trigger a plateau potential in rat subthalamic neurons at hyperpolarized states

The subthalamic nucleus (STN) directly innervates the output structures of the basal ganglia, playing a key role in basal ganglia function. It is ther efore important to understand the regulatory mechanisms for the activity of STN neurons. In the present study, we aimed to investigate how the intrins ic membrane properties of STN neurons interact with their synaptic inputs, focusing on their generation and the properties of the long-lasting, platea u potential. Whole cell recordings were obtained from STN neurons in slices prepared from postnatal day 14 (P14) to P20 rats. We found that activation of glutamate receptor-mediated excitatory synaptic potentials (EPSPs) evok ed a plateau potential in a subpopulation of STN neurons (n=13/22), in a vo ltage-dependent manner. Plateau potentials could be induced only when the c ell was hyperpolarized to more negative than about -75 mV. Plateau potentia ls, evoked with a depolarizing current pulse, again only from a hyperpolari zed state, were observed in about half of STN neurons tested (n=162/327). O nly in neurons in which a plateau potential could be evoked by current inje ction did EPSPs evoke plateau potentials. L-type Ca2+ channels, Ca2+-depend ent K+ channels, and TEA-sensitive K+ channels were found to be involved in the generation of the potential. The stability of the plateau potential, t ested by the injection of a negative pulse current during the plateau phase , was found to be robust at the early phase of the potential, but decreased toward the end. As a result the early part of the plateau potential was re sistant to membrane potential perturbations and would be able to support a train of action potentials. We conclude that excitatory postsynaptic potent ials, evoked in a subpopulation of STN neurons at a hyperpolarized state, a ctivate L-type Ca2+ and other channels, leading to the generation of a plat eau potential. Thus about half of STN neurons can transform short-lasting s ynaptic excitation into a long train of output spikes by voltage-dependent generation of a plateau potential.