Age-related changes in dopamine signaling in Nurr1 deficient mice as a model of Parkinson's disease.

The nuclear receptor related 1 (Nurr1) transcription factor contributes to the development and maintenance of dopamine (DA) neurons in the brain. We found that heterozygous Nurr1 knockout (Nurr1 +/-) influenced the age-dependent decline in the number of DA neurons and influenced DA signaling. We examined the DA marker, tyrosine hydroxylase, using immunohistochemistry, and we measured DA signaling using fast-scan cyclic voltammetry in 3 age groups of wild-type (Nurr1 +/+) and mutant (Nurr1 +/-) mice: 3-6, 9-12, and 15-23 mo old. Prior to significant loss of DA neurons and to the onset of parkinsonian symptoms, young Nurr1 +/- mice (3-6 mo) exhibited a decrease in peak evoked DA release that was partially countered by a decrease in the rate of DA reuptake. As peak evoked DA release declined with age for both the wild-type and Nurr1 +/- mice, both genotypes manifested decreased DA reuptake. As the DA release fell further with age, decreased DA reuptake eventually could not adequately compensate the Nurr1 +/- mice. The results indicated that Nurr1 deficiency led to impaired DA release even before significant DA neuron loss.