NR4A gene expression is dynamically regulated in the ventral tegmental area dopamine neurons and is related to expression of dopamine neurotransmission genes

Abstract

The NR4A transcription factors NR4A1, NR4A2, and NR4A3 (also known as Nur77, Nurr1, and Nor1, respectively) share similar DNA-binding properties and have been implicated in regulation of dopamine neurotransmission genes. Our current hypothesis is that NR4A gene expression is regulated by dopamine neuron activity and that induction of NR4A genes will increase expression of dopamine neurotransmission genes. Eticlopride and γ-butyrolactone (GBL) were used in wild-type (+/+) and Nurr1-null heterozygous (+/-) mice to determine the mechanism(s) regulating Nur77 and Nurr1 expression. Laser capture microdissection and real-time PCR was used to measure Nurr1 and Nur77 mRNA levels in the ventral tegmental area (VTA). Nur77 expression was significantly elevated 1 h after both GBL (twofold) and eticlopride (fourfold). In contrast, GBL significantly decreased Nurr1 expression in both genotypes, while eticlopride significantly increased Nurr1 expression only in the +/+ mice. In a separate group of mice, haloperidol injection significantly elevated Nur77 and Nor1, but not Nurr1 mRNA in the VTA within 1 h and significantly increased tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA expression by 4 h. These data demonstrate that the NR4A genes are dynamically regulated in dopamine neurons with maintenance of Nurr1 expression requiring dopamine neuron activity while both attenuation of dopamine autoreceptors activation and dopamine neuronal activity combining to induce Nur77 expression. Additionally, these data suggest that induction of NR4A genes could regulate TH and DAT expression and ultimately regulate dopamine neurotransmission.

Fig. 1

Dopamine neurons in the ventral tegmental area are shown after tyrosine hydroxylase immunohistochemistry (a). This area was used to determine the distribution of dopamine neurons and used to dissect tissue from an adjacent section processed for laser capture microdissection (b)

Fig. 2

Nur77 expression in the ventral tegmental area after either γ-butyrolactone or eticlopride in Nurr1 wild-type (+/+) and heterozygous (+/−) mice. Both γ-butyrolactone and eticlopride significantly increased Nur77 expression, with the exception of γ-butyrolactone in the +/− mice. *p < 0.05, significant difference from the vehicle treatment after ANOVA with post hoc comparison

Fig. 3

Nurr1 expression in the ventral tegmental area after either γ-butyrolactone or eticlopride in Nurr1 wild-type (+/+) and heterozygous (+/−) mice. While γ-butyrolactone significantly decreased Nurr1 expression in both +/+ and +/− genotypes, eticlopride significantly increased Nurr1 expression only in the +/+ mice with no effect in the +/− mice. *p < 0.05, significant difference from the vehicle treatment after ANOVA with post hoc comparison

Fig. 4

Dopamine neuron gene expression in the ventral tegmental area 1 h after a 1-mg/kg systemic injection of haloperidol. Nur77 and Nor1 were significantly elevated after treatment, while no changes in Nurr1 expression were found. *p < 0.05, significant difference from the vehicle treated after Student's t test

Fig. 5

Dopamine neuron gene expression in the ventral tegmental area 4 h after a 1-mg/kg systemic injection of haloperidol. Tyrosine hydroxylase and dopamine transporter were significantly elevated after haloperidol treatment. Dopamine decarboxylase, dopamine D2 receptor, and vesicular monoamine transporter 2 were not significantly affected. *p < 0.05, significant difference from the vehicle treated after Student's t test