Blockade ofNMDA receptors differentially affectsD-1 andD-2 mediated turning behavior in the 6-hydroxydopamine model of Parkinson

Antiparkinsonian effects of remacemide hydrochloride, a glutamate antagonist, in rodent and primate models of Parkinson's disease

Loss of dopaminergic innervation of the striatum results in overactivity of the glutamatergic pathways from the subthalamic nucleus to the internal segment of the globus pallidus and the substantia nigra pars reticulata, the output nuclei of the basal ganglia. Previous work has shown that local blockade of glutamate receptors in the internal segment of the globus pallidus or substantia nigra pars reticulata leads to marked suppression of parkinsonian signs. We have now examined whether systemic administration of a glutamate receptor antagonist has antiparkinsonian effects in rodent and primate models of Parkinson's disease. Remacemide hydrochloride is an anticonvulsant, neuroprotective compound with antagonist activity at the N-methyl-D-aspartate receptor ion channel. In normal rats and monoamine-depleted rats, remacemide hydrochloride did not cause locomotor hyperactivity, unlike MK-801. When monoamine-depleted rats were treated with a subthreshold dose of levodopa methylester, remacemide hydrochloride (5-40 mg/kg, orally) caused a dose-dependent increase in locomotor activity. Moreover, remacemide hydrochloride (10 mg/kg, orally) potentiated the effects of each suprathreshold dose of levodopa methylester tested (100-200 mg/kg, intraperitoneally). Parkinsonian rhesus monkeys were tested with oral doses of vehicle plus vehicle, vehicle plus levodopa-carbidopa, and remacemide hydrochloride (5 mg/kg) plus levodopa-carbidopa. Blinded clinical scoring of videotapes revealed that treatment with remacemide hydrochloride plus levodopa-carbidopa was substantially better than levodopa-carbidopa plus vehicle or vehicle plus vehicle. The effects of remacemide hydrochloride lasted at least 5 hours. We conclude that certain N-methyl-D-aspartate receptor antagonists have antiparkinsonian actions and low potential for side effects. Clinical trials of remacemide hydrochloride in patients with Parkinson's disease may be warranted.

Expression of mRNAs encoding dopamine receptors in striatal regions is differentially regulated by midbrain and hippocampal neurons

The glutamate analogue kainic acid was injected into the hippocampus of intact or 6-hydroxydopamine deafferented rats to investigate the influence of hippocampal neurons on the expression of dopamine D1 and D2 receptor mRNAs in subregions of the striatal complex and possible modulation by dopaminergic neurons. Quantitative in situ hybridization using 35S-labeled oligonucleotide probes specific for dopamine D1 and D2 receptor mRNAs, respectively, were used. It was found that an injection of kainic acid into the hippocampal formation had alone no significant effect on dopamine D1 or D2 receptor mRNA levels in any of the analyzed striatal subregions in animals analyzed 4 h after the injections. Kainic acid stimulation in the hippocampus ipsilateral to the dopamine lesion produced an increase in D1 receptor mRNA levels in the ipsilateral medial caudate-putamen, and a bilateral increase in core and shell of nucleus accumbens (ventral striatal limbic regions). A unilateral 6-hydroxydopamine lesion alone caused an increase in D2 receptor mRNA in the lateral caudate-putamen (dorsal striatal motor region) ipsilateral to the lesion and an increase in D1 receptor mRNA in the accumbens core ipsilateral to the lesion. However, in dopamine-lesioned animals, dopamine D1 receptor mRNA levels were increased bilaterally in nucleus accumbens core and shell and in the ipsilateral medial caudate-putamen following kainic acid stimulation in the hippocampus ipsilateral to the dopamine lesion. These results indicate a differential regulation of the expression of dopamine D1 and D2 receptor mRNAs by midbrain and hippocampal neurons.(ABSTRACT TRUNCATED AT 250 WORDS)