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 (1.0mg/kg) 15 min after administration of the N-methyl-d-aspartate receptor antagonist MK-801 (0.1mg/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 (3.0μg) into the intact striatum produced an increase in locomotor activity that was suppressed by MK-801 (1.0μg) co-infusion. In the dopamine-depleted rat, MK-801 (0.1mg/kg) administered prior to (±)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0mg/kg) increased, rather than suppressed, striatal preprotachykinin mRNA levels. Intrastriatal infusion of MK-801 (1.0μg) 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.