Selective agenesis of mesencephalic dopaminergic neurons in Nurr1- deficient mice

Nurr1, a member of the nuclear receptor superfamily of transcription factors, has been found to be essential for the development of ventral midbrain dopamine (DA)ergic neurons. To study the regional selectivity and phenotypic specificity of regulation by Nurr1 of the genesis of DAergic neurons, we examined DAergic, serotonin (5-HT)ergic, norepinephrine (NE)ergic, cholinergic, glutamate (GLU)ergic, and γ-aminobutyric acid (GABA)ergic neurons in the brains of Nurr1-deficient mice by immunohistochemistry and biochemistry. We demonstrated that in homozygous Nurr1-deficient mice (Nurr1-/-), DAergic neurons were totally absent in substantia nigra and ventral tegmental area, but preserved in other regions including diencephalon and hypothalamus, olfactory bulb (OB). Levels of DA in Nurr1-/- mice were decreased by 98% in striatum (Str) and 65% in OB. NEergic neurons in locus ceruleus, 5-HTergic neurons in raphe nuclei, and cholinergic neurons in basal forebrain and other regions were not changed. A 30% reduction of NE was found in the Str of Nurr1-/- mice. The levels of GLU and GABA and the activity of choline acetyl transferase in the brains of Nurr1-/- mice were not significantly altered. Our results demonstrate a selective and specific deficit of DA and absence of DAergic neurons in the mesencephalic structures of Nurr1-deficient mice, which resembles the pattern similar to that seen in patients with Parkinson's disease (PD). This model may contribute to our understanding of the mechanisms influencing DAergic cell survival in PD.