Overlapping intracellular and differential synaptic distributions of dopamine D1 and glutamate N‐methyl‐D‐aspartate receptors in rat nucleus accumbens

Abstract

The dopamine D1 receptor (D1R) in the nucleus accumbens (Acb) shell is highly implicated in psychostimulant-evoked locomotor activity and reward, whereas the D1R in the Acb core is more crucial for appetitive instrumental learning. These behavioral effects depend in part on interactions involving glutamatergic NMDA receptors, whose essential NR1 subunit has physical associations with the D1R. To determine the relevant sites for D1R activation and interactions involving NMDA receptors, we examined the electron microscopic immunolabeling of D1R and NR1 Cterminal peptides in rat Acb shell and core. In each Acb subdivision, the D1Rs were located principally on extrasynaptic plasma membranes of dendritic shafts and spines and more rarely associated with cytoplasmic endomembranes. Many D1R-labeled somata and dendrites also contained NR1 immunoreactivity. In comparison with D1R, NR1 immunoreactivity was more often seen in the cytoplasm and near asymmetric synapses on somatodendritic profiles. In these profiles, notable overlapping distributions of D1R and NR1 occurred near endomembranes. The exclusively D1R or D1R and NR1 containing dendrites were most prevalent in the Acb shell, but also present in the Acb core. In each region, NR1 was also detected in axon terminals without D1R, which formed excitatory-type synapses with D1R-labeled dendrites. These results provide ultrastructural evidence that D1Rs in the Acb have subcellular distributions supporting, 1) intracellular co-trafficking with NR1, and 2) modulation of the postsynaptic excitability in spiny neurons affected by presynaptic NMDA receptor activation. The region-specific differences in receptor distributions suggest a major, but not exclusive, involvement of Acb D1R in rewardrelated processing.

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

“…Electron microscopy showed that D1R distribution seen in the VEH group was similar to that of naïve rats of the same strain from a previous study, even though these particles were not quantitatively compared (Hara and Pickel, 2005). It also showed treatment-specific differences in D1R dendritic distributions in rats receiving apomorphine and/or AS.…”

“…The D1R antibody has been well characterized and shown to specifically recognize the antigenic peptide by Western blot, immunoprecipitation and blocking control experiments used for immunocytochemistry (Levey et al, 1993). This D1R antibody has also been localized by electron microscopic immunocytochemistry in the Acb shell and core (Hara and Pickel, 2005;Hara et al, 2006). To determine the level of non-specific attachment of the primary antibody or secondary gold-conjugated IgGs, we examined the number of immunogold particles overlying myelin, where D1R is not known to be expressed.…”

“…In rare cases, when more than 50% of the gold particle was outside the membrane, this particle was not counted as dendritic labeling. The number of D1R-labeled dendrites determined using these criteria parallels that seen with immunoperoxidase labeling in the Acb (Hara and Pickel, 2005). Two or more gold particles next to each other, but without defined boundaries, were counted as one particle.…”

“…Furthermore, D1R activation in the striatum facilitates sensorimotor cortical functions (Steiner and Kitai, 2000). Unlike D2Rs, D1Rs are predominantly located in distal dendrites and dendritic spines, which are major sites for synaptic plasticity (Delle Donne et al, 2004;Hara and Pickel, 2005). The surface expression of D1R is not stationary, but dynamically changed by synaptic activity and the availability of D1R agonists (Dumartin et al, 1998;Lamey et al, 2002).…”

“…Auditory stimulation (AS), such as that used in acoustic startle testing, transiently decreases extracellular dopamine in the Acb (Humby et al, 1996). Moreover, glutamate activation of NMDA receptors that are coexpressed with D1R in many Acb dendrites, can increase D1R plasma membrane insertion, as well as recruitment of D1Rs to dendritic spines (Scott et al, 2002;Pei et al, 2004;Hara and Pickel, 2005). Thus, either apomorphine binding to D1/D2 receptors or AS resulting in decreased dopamine and/or altered activation of glutamatergic inputs to Acb may affect the expression of D1Rs in selective neuronal compartments within the Acb shell and core neurons.…”