Striatal preprotachykinin mRNA levels are regulated by stimulatory agents and dopamine D1 receptor manipulation in rodent organotypic slice cultures

D1 receptor regulation of preprotachykinin-A gene by extracellular signal-regulated kinase pathway in striatal cultures

In animal models of Parkinson's disease, a supersensitive response to dopamine (DA) is associated with a switch in the coupling of striatal DA D1 receptors from a cyclic AMP/protein kinase A signaling pathway to one involving extracellular signal-regulated kinase/mitogen-associated protein kinase. In this study, we found that generation of organotypic striatal cultures, with concomitant loss of DA innervation, led to a downregulation in preprotachykinin-A gene expression, which was reinstated by D1 receptor activation in an extracellular signal-regulated kinase/mitogen-associated protein kinase-dependent manner. These data demonstrate that acute organotypic slice cultures recapitulate important changes in D1 receptor-mediated signal transduction seen in DA-denervated animals, providing a valuable model system to study denervation effects on DA signaling and striatal gene expression.

C/EBPβ couples dopamine signalling to substance P precursor gene expression in striatal neurones

Dopamine-induced changes in striatal gene expression are thought to play an important role in drug addiction and compulsive behaviour. In this study we report that dopamine induces the expression of the transcription factor CCAAT/Enhancer Binding Protein beta (C/EBP)-beta in primary cultures of striatal neurones. We identified the preprotachykinin-A (PPT-A) gene coding for substance P and neurokinin-A as a potential target gene of C/EBPbeta. We demonstrated that C/EBPbeta physically interacts with an element of the PPT-A promoter, thereby facilitating substance P precursor gene transcription. The regulation of PPT-A gene by C/EBPbeta could subserve many important physiological processes involving substance P, such as nociception, neurogenic inflammation and addiction. Given that substance P is known to increase dopamine signalling in the striatum and, in turn, dopamine increases substance P expression in medium spiny neurones, our results implicate C/EBPbeta in a positive feedback loop, changes of which might contribute to the development of drug addiction.

Failure of MK-801 to suppress D1 receptor-mediated induction of locomotor activity and striatal preprotachykinin mRNA expression in the dopamine-depleted rat

N-methyl-D-aspartate receptor antagonism exerts suppressive influences over dopamine D1 receptor-mediated striatal gene expression and locomotor behavior in the intact rat. The present study examined the effects of the N-methyl-D-aspartate receptor antagonist MK-801 on locomotor activity and striatal preprotachykinin mRNA expression stimulated by the D1 agonist (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide in rats with bilateral dopamine lesions. Two months after neonatal dopamine lesions with 6-hydroxydopamine, rats were challenged with (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0 mg/kg) 15 min after administration of the N-methyl-D-aspartate receptor antagonist MK-801 (0.1 mg/kg). In the intact rat, MK-801 prevented the induction of striatal preprotachykinin mRNA by D1 agonism. Similarly, direct infusion of (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (3.0 microg) into the intact striatum produced an increase in locomotor activity that was suppressed by MK-801 (1.0 microg) co-infusion. In the dopamine-depleted rat, MK-801 (0.1 mg/kg) administered prior to (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0 mg/kg) increased, rather than suppressed, striatal preprotachykinin mRNA levels. Intrastriatal infusion of MK-801 (1.0 microg) failed to inhibit D1-mediated induction of motor activity in dopamine-depleted animals. Together, these data provide further support that N-methyl-D-aspartate receptor antagonists lose their ability to block D1-mediated behavioral activation following dopamine depletion. The activation, rather than suppression, of tachykinin neurons of the direct striatonigral pathway may play a facilitatory role in this mechanism.

MK-801 prevents dopamine D1 but not serotonin 2A stimulation of striatal preprotachykinin mRNA expression

We examined dopamine (DA) and serotonin (5-HT) receptor-mediated influences on striatal preprotachykinin (PPT, tachykinin precursor) mRNA regulation in organotypic slice cultures. A 3 h exposure to SKF-38393 (10 microM, DA D1 agonist) or DOI (10 microM, 5-HT2 agonist) increased PPT mRNA levels to 196.4% and 154.0%, respectively. Responses to SKF-38393 were prevented by SCH-23390 (10 microM, D1 antagonist) whereas DOI-stimulated increases were prevented by ketanserin (10 microM, 5-HT2A antagonist). Since striatal tachykinin neurons also possess NMDA receptors that regulate gene expression, stimulation of PPT message levels was examined in the presence of MK-801, a non-competitive NMDA antagonist. Alone, MK-801 (10 nM) did not significantly alter basal PPT message levels. However, MK-801 prevented SKF-38393-stimulated increases in PPT mRNA expression while DOI-induced expression was not affected. These results provide evidence that D1 regulation of striatal tachykinin expression is dependent on NMDA-type glutamate neurotransmission while 5-HT2A regulation appears independent.