Spike frequency adaptation is developmentally regulated in substantia nigra pars compacta dopaminergic neurons

Dopaminergic neurons of the substantia nigra pars compacta play a key role in the modulation of basal ganglia and provide a reward-related teaching signal essential for adaptative motor control. They are generally considered as a homogenous population despite several chemical and electrophysiological heterogeneities, which could underlie different preferential patterns of activity and/or different roles. Using whole-cell patch-clamp recordings in juvenile rat brain slices, we observed that the evoked activity of dopaminergic neurons displays variable spike frequency adaptation patterns. The intensity of spike frequency adaptation decreased during post-natal development. The adaptation was associated with an increase in the initial firing frequency due to faster kinetics of the afterhyperpolarization component of the spike. Adaptation was enhanced when small conductance calcium-activated potassium (SK) channels were blocked with bath application of apamine. Lastly, spike frequency adaptation of the evoked discharge was associated with more irregularity in the spontaneous firing pattern. Altogether these results show a developmental heterogeneity and electrophysiological maturation of substantia nigra dopaminergic neurons.