Effects of age and sex on dendritic D2 autoreceptor inhibition in substantia nigra dopamine neurons

Substantia nigra pars compacta (SNc) dopamine neurons are required for voluntary movement and reward learning, and advanced age is associated with motor and cognitive decline. In the midbrain, D2-type autoreceptors located on dendrodendritic synapses between dopamine neurons control cell firing through G protein-activated potassium (GIRK) channels. We previously showed that aging disrupts dopamine neuron pacemaker firing in mice, but only in males. Here we show that D2-receptor inhibitory postsynaptic currents (D2-IPSCs) in aged male mice are moderately smaller compared to young males as well as females, regardless of age. Local application of dopamine revealed a reduction in the amplitude of the D2-receptor currents in old males compared to young, pointing to a postsynaptic mechanism that could not be explained by impairment of the GIRK channels or degeneration of the dendritic arbor. Kinetic analysis showed no differences in D2-IPSCs in old versus young mice or between sexes. Potentiation of D2-IPSCs by corticotropin releasing factor (CRF) is also conserved in aging, indicating preservation of plasticity mechanisms. These findings have implications for understanding dopamine transmission in aging in both sexes and could explain in part the increased susceptibility of males to SNc degeneration of dopamine neurons in neurodegenerative disorders such as Parkinsons disease (PD).