Somatodendritic ion channel expression in substantia nigra pars compacta dopaminergic neurons across postnatal development

Dopaminergic neurons of the substantia nigra pars compacta (SNc) are involved in the control of movement, sleep, reward, learning, and nervous system disorders and disease. To date, a thorough characterization of the ion channel phenotype of this important neuronal population is lacking. Using immunohistochemistry, we analyzed the somatodendritic expression of voltage-gated ion channel subunits that are involved in pacemaking activity in SNc dopaminergic neurons in 6-, 21-, and 40-day-old rats. Our results demonstrate that the same complement of somatodendritic ion channels is present in SNc dopaminergic neurons from P6 to P40. The major developmental changes were an increase in the dendritic range of the immunolabeling for the HCN, T-type calcium, Kv4.3, delayed rectifier, and SK channels. Our study sheds light on the ion channel subunits that contribute to the somatodendritic delayed rectifier (Kv1.3, Kv2.1, Kv3.2, Kv3.3), A-type (Kv4.3) and calcium-activated SK (SK1, SK2, SK3) potassium currents, I_H (mainly HCN2, HCN4), and the L- (Cav1.2, Cav1.3) and T-type (mainly Cav3.1, Cav3.3) calcium currents in SNc dopaminergic neurons. Finally, no robust differences in voltage-gated ion channel immunolabeling were observed across the population of SNc dopaminergic neurons for each age examined, suggesting that differing levels of individual ion channels are unlikely to distinguish between specific subpopulations of SNc dopaminergic neurons. This is significant in light of previous studies suggesting that age- or region-associated variations in the expression profile of voltage-gated ion channels in SNc dopaminergic neurons may underlie their vulnerability to dysfunction and disease.