Female mice are resilient to age-related decline of substantia nigra dopamine neuron firing parameters
The degeneration of substantia nigra (SN) dopamine neurons is a central feature in the pathology associated with Parkinsons disease, which is characterized by progressive loss of motor and cognitive functions. The largest risk factors for Parkinsons disease are age and sex; most cases occur after age 60 and males have nearly twice the incidence as females. While much research in Parkinsons has focused on the mechanisms underlying dopamine neuron degeneration, very little work has considered the influence of these two risk factors to disease risk and presentation. In this work, we performed whole cell patch clamp recordings in brain slices to study the alterations in intrinsic firing properties of single dopamine neurons in C57BL/6 mice across ages and between sexes. We observed a progressive decline in dopamine neuron firing activity in males by 18 months of age, while dopamine neurons from females remained largely unaffected. A semiquantitative analysis of midbrain dopamine neuron populations revealed a slight decrease only in substantia nigra dopamine neurons in males, while females did not change. This was also accompanied by increases in the expression of genes that have been linked to Parkinsons including PTEN-induced kinase 1 (PINK1) in both males and females, and the ubiquitin ligase parkin, primarily in the substantia nigra of males. These impairments in dopamine neuron function in males may represent a vulnerability to further insults that could predispose these cells to neurodegenerative diseases such as in Parkinsons.