Substantia nigra pars compacta (SNc) dopaminergic (DA) neurons display a peculiar electrical phenotype characterized in vitro by a spontaneous tonic regular activity (pacemaking activity), a broad action potential and a biphasic post-inhibitory response. Several studies in rodents have underlined the central role played by the transient A-type current (IA) in the control of pacemaking activity and post-inhibitory rebound properties, thereby influencing both DA release and the physiological response of SNc neurons to incoming inhibitory inputs. Kv4.3 potassium channels were considered to be fully responsible for IA in these neurons, their density being tightly related to pacemaking frequency. In spite of this crucial electrophysiological role, we show that Kv4.3-/- transgenic mice exhibit minor alterations in locomotion and motor learning, although no compensation by functionally overlapping ion channels is observed in Kv4.3-/- SNc DA neurons. Using antigen retrieval immunohistochemistry, we further demonstrate that Kv4.2 potassium channels are also expressed in SNc DA neurons, even though their contribution to IA appears significant only in a minority of neurons (~5-10%). Using correlative analysis on recorded electrophysiological parameters and multi-compartment modeling, we then demonstrate that, rather than its conductance level, IA gating kinetics (inactivation time constant) appear as the main biophysical property defining post-inhibitory rebound delay and pacemaking frequency. Moreover, we show that the hyperpolarization-activated current (IH) has an opposing and complementary influence on the same firing features, and that the biophysical properties of IA and IH are likely co-regulated in mouse SNc DA neurons.
bioRxiv Subject Collection: Neuroscience