Allosteric changes of the NMDA receptor trap diffusible dopamine 1 receptors in spines

Abstract

The dopaminergic and glutamatergic systems interact to initiate and organize normal behavior, a communication that may be perturbed in many neuropsychiatric diseases, including schizophrenia. We show here that NMDA, by allosterically modifying NMDA receptors, can act as a scaffold to recruit laterally diffusing dopamine D1 receptors (D1R) to neuronal spines. Using organotypic culture from rat striatum transfected with D1R fused to a fluorescent protein, we show that the majority of dendritic D1R are in lateral diffusion and that their mobility is confined by interaction with NMDA receptors. Exposure to NMDA reduces the diffusion coefficient for D1R and causes an increase in the number of D1R-positive spines. Unexpectedly, the action of NMDA in potentiating D1R recruitment was independent of calcium flow via the NMDA receptor channel. Thus, a highly energy-efficient, diffusiontrap mechanism can account for intraneuronal interaction between the glutamatergic and dopaminergic systems and for regulation of the number of D1R-positive spines. This diffusion trap system represents a molecular mechanism for brain plasticity and offers a promising target for development of antipsychotic therapy.organotypic cultures ͉ fluorescence recovery after photo-bleaching ͉ lateral diffusion ͉ receptor movement A variety of pharmacological, biochemical, and molecular genetic evidence indicates that the schizophrenic state is associated with hypoglutamatergia and a high ratio of D2 dopaminergic to D1 dopaminergic signaling (1, 2). We recently reported a cellular interaction between NMDA receptors and D1 receptors (D1Rs) that can explain how such abnormalities in glutamate and dopamine signaling might be causally related. Specifically, activation of NMDA receptors was shown to increase recruitment of D1Rs but not of D2Rs in the plasma membrane of primary cultures of striatal neurons (3). In view of the potential clinical relevance of NMDA-induced selective recruitment of dopamine D1Rs, we have, in the present study, explored the underlying mechanism. Here, we provide evidence that dopamine D1Rs, laterally diffusing in the dendritic plasma membrane, can be trapped in spines by ligand-occupied NMDA receptors. ResultsTo monitor its mobility in live neurons, the D1R was tagged with the fluorescent protein Venus (D1R-Venus) (4) and expressed in organotypic cultures from rat striatum (Fig. 1a). The fluorescent signal was evenly distributed in the cell body and plasma membrane. A strong signal was also recorded from the dendritic tree (Fig. 1b). Approximately five D1R-positive spines were detected per 10 m of dendrite. D1R-positive spines were mushroom shaped, thin, or stubby. Filopodia-like D1R-positive structures were rare. The subcellular distribution of D1R-Venus was similar to that described in electron microscope studies of endogenous D1R (5, 6). No distinct D1R signal was observed in glial cells. This lack of signal from glial cells minimized the background signal and made this study feasible (Fig. 1c). The selective distribution of t...

Dopaminergic signaling in dendritic spines

“…glutamate, GABA, and glycine), may also apply to DA receptors. In cultured rat striatal slices, D1 receptors laterally diffuse in the dendritic plasma membrane and their mobility appears to be confined by ligand-occupied NMDARs, perhaps mediated by a direct D1-NMDAR interaction [48]. Interestingly, the action of NMDA in the synaptic recruitment of D1 receptors appears to be independent of Ca2+ flow through the NMDAR channel, but instead depends on an allostericl modification of NMDARs.…”

“…Interestingly, the action of NMDA in the synaptic recruitment of D1 receptors appears to be independent of Ca2+ flow through the NMDAR channel, but instead depends on an allostericl modification of NMDARs. Thus, NMDARs can act as scaffolds to recruit laterally diffusing D1 receptors to spines, providing a probable mechanism by which DA receptors can be enriched in the PSD [48].…”

Dendritic distributions of dopamine D1 receptors in the rat nucleus accumbens are synergistically affected by startle-evoking auditory stimulation and apomorphine

“…an hour after vehicle or apomorphine injection. We chose this time point as one that would enable not only internalization, but also recycling, and lateral movement of D1R (Vargas and von Zastrow, 2004;Scott et al, 2006). A longer time point would be more likely to evoke changes in gene expression.…”

Functional disturbances in the striatum by region-specific ablation of NMDA receptors

“…Recently, molecular interactions between NMDA receptors and dopamine receptors have been reported. For example, NMDA receptors trap diffusible D1 receptors by direct physical interaction (9)(10)(11). The interaction between NR2B, a subunit of the NMDA receptor, and the D2 receptor can also disrupt the association of Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) with NR2B and inhibit NMDA receptor-mediated currents in MSNs (12).…”