A selective group of dopaminergic neurons express Nurr1 in the adult mouse brain

Nurr1, an orphan receptor of the nuclear receptor superfamily, is widely expressed in the central nervous system (CNS) including brain regions where dopaminergic neurons are abundant. Recent analyses of Nurr1 null mutant mice have shown that Nurr1 is essential for the development and survival of midbrain dopaminergic neurons. However, other dopaminergic neuronal populations do not seem to be affected by ablation of the Nurr1 gene. The purpose of the present study was to investigate the degree of co-existence of Nurr1 mRNA and tyrosine hydroxylase (TH) immunoreactivity in the brain of adult mice to better characterize the selective effects of Nurr1 on catecholaminergic neurons. Our results indicate that the majority of TH-immunoreactive neurons in the substantia nigra (SN; 96%), ventral tegmental area (VTA; 95%), retrorubral field (91%), olfactory bulb (85%), linear nucleus raphe (91%) and central grey (61%) express Nurr1. In contrast, dopaminergic cells of the paraventricular and periventricular hypothalamic nucleus showed only a few Nurr1/TH double labeled neurons, while TH-immunoreactive neurons in the arcuate nucleus and zona incerta did not express Nurr1 mRNA. Nurr1 expression was also excluded from (nor)adrenergic neurons of the brainstem. In conclusion, Nurr1 transcripts were not found in all CNS catecholaminergic neurons. Nurr1 expression was confined to periglomerular and midbrain dopaminergic neurons. These results suggest that within the adult mouse brain, Nurr1 may participate in dopaminergic functions of the olfactory bulb and midbrain.