Interleukin (IL)-1β is a proinflammatory cytokine implicated in various pathophysiological conditions of the CNS involving NMDA receptor activation. Circumstantial evidence suggests that IL-1β and NMDA receptors can functionally interact. Using primary cultures of rat hippocampal neurons, we investigated whether IL-1β affects NMDA receptor function(s) by studying (1) NMDA receptor-induced [Ca²⁺]_iincrease and (2) NMDA-mediated neurotoxicity. IL1β (0.01-0.1 ng/ml) dose-dependently enhances NMDA-induced [Ca²⁺]_iincreases with a maximal effect of ∼45%. This effect occurred only when neurons were pretreated with IL-1β, whereas it was absent if IL-1β and NMDA were applied simultaneously, and it was abolished by IL-1 receptor antagonist (50 ng/ml). Facilitation of NMDA-induced [Ca²⁺]_iincrease by IL-1β was prevented by both lavendustin (LAV) A (500 nm) and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) (1 μm), suggesting an involvement of tyrosine kinases. Increased tyrosine phosphorylation of NMDA receptor subunits 2A and 2B and coimmunoprecipitation of activated Src tyrosine kinase with these subunits was observed after exposure of hippocampal neurons to 0.05 ng/ml IL-1β. Finally, 0.05 ng/ml IL-1β increased by ∼30% neuronal cell death induced by NMDA, and this effect was blocked by both lavendustin A and PP2.These data suggest that IL-1β increases NMDA receptor function through activation of tyrosine kinases and subsequent NR2A/B subunit phosphorylation. These effects may contribute to glutamate-mediated neurodegeneration.

Abnormal function of NMDA receptor has been suggested to be correlated with the pathogenesis of Parkinson’s disease (PD) as well as with the development ofl-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia. Here we show that NMDA receptor NR2 subunits display specific alterations of their subcellular distribution in striata from unilateral 6-hydroxydopamine-lesioned,l-DOPA-treated dyskinetic, andl-DOPA-treated nondyskinetic rats. Dyskinetic animals have significantly higher levels of NR2A subunit in the postsynaptic compartment than all other experimental groups, whereas NR2B subunit shows a significant reduction in both dopamine-denervated and dyskinetic rats. These events are paralleled by profound modifications of NMDA receptor NR2B subunit association with interacting elements, i.e., members of the membrane-associated guanylate kinase (MAGUK) protein family postsynaptic density-95, synapse-associated protein-97 and synapse-associated protein-102. Treatment of nondyskinetic animals with a synthetic peptide (TAT2B) able to affect NR2B binding to MAGUK proteins as well as synaptic localization of this subunit in nondyskinetic rats was sufficient to induce a shift of treated rats toward a dyskinetic motor behavior. These data indicate abnormal NR2B redistribution between synaptic and extrasynaptic membranes as an important molecular disturbance of the glutamatergic synapse involved inl-DOPA-induced dyskinesia.

Appearance of dyskinesia is a common problem of long-term l-DOPA treatment in Parkinson's disease patients and represents a major limitation for the pharmacological management of the motor symptoms in advanced disease stages. We have recently demonstrated that dopamine released from serotonin neurons is responsible for l-DOPA-induced dyskinesia in 6-hydroxydopamine (6-OHDA)-lesioned rats, raising the possibility that blockade of serotonin neuron activity by combination of 5-HT_1A and 5-HT_1B agonists could reduce l-DOPA-induced dyskinesia. In the present study, we have investigated the efficacy of 5-HT_1A and 5-HT_1B agonists to counteract l-DOPA-induced dyskinesia in 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine (MPTP)-treated macaques, the gold standard model of Parkinson's disease. In addition, we have studied the ability of this treatment to prevent development of l-DOPA-induced dyskinesia in 6-OHDA-lesioned rats. The results demonstrate the existence of a potent synergistic effect between 5-HT_1A and 5-HT_1B agonists in their ability to dampen l-DOPA-induced dyskinesia in the MPTP-treated macaques. Sub-threshold doses of the drugs, which individually produced no effect, were able to reduce the abnormal involuntary movements by up to 80% when administered in combination, without affecting the anti-parkinsonian properties of l-DOPA. Furthermore, chronic administration of low doses of the 5-HT₁ agonists in combination was able to prevent development of dyskinesia, and reduce the up-regulation of FosB after daily treatment with l-DOPA in the rat 6-OHDA model. Our results support the importance of a clinical investigation of the effect of 5-HT_1A and 5-HT_1B agonists, particularly in combination, in dyskinetic l-DOPA-treated Parkinson's disease patients.

Activation of dopamine D₁ receptors is critical for the generation of glutamate-induced long-term potentiation at corticostriatal synapses. In this study, we report that, in striatal neurons, D₁ receptors are co-localized with N-methyl-d-aspartate (NMDA) receptors in the postsynaptic density and that they co-immunoprecipitate with NMDA receptor subunits from postsynaptic density preparations. Using modified bioluminescence resonance energy transfer, we demonstrate that D₁ and NMDA receptor clustering reflects the existence of direct interactions. The tagged D₁ receptor and NR1 subunit cotransfected in COS-7 cells generated a significant bioluminescence resonance energy transfer signal that was insensitive to agonist stimulation and that did not change in the presence of the NR2B subunit, suggesting that the D₁ receptor constitutively and selectively interacts with the NR1 subunit of the NMDA channel. Oligomerization with the NR1 subunit substantially modified D₁ receptor trafficking. In individually transfected HEK293 cells, NR1 was localized in the endoplasmic reticulum, whereas the D₁ receptor was targeted to the plasma membrane. In cotransfected cells, both the D₁ receptor and NR1 subunit were retained in cytoplasmic compartments. In the presence of the NR2B subunit, the NR1-D₁ receptor complex was translocated to the plasma membrane. These data suggest that D₁ and NMDA receptors are assembled within intracellular compartments as constitutive heteromeric complexes that are delivered to functional sites. Coexpression with NR1 and NR2B subunits also abolished agonist-induced D₁ receptor cytoplasmic sequestration, indicating that oligomerization with the NMDA receptor could represent a novel regulatory mechanism modulating D₁ receptor desensitization and cellular trafficking.