No abstract

The goal of this study was to understand how dopamine receptors, which are activated during psychostimulant administration, might influence glutamate-dependent forms of synaptic plasticity that are increasingly recognized as important to drug addiction. Regulation of the surface expression of the a-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit GluR1 plays a critical role in longterm potentiation, a well-characterized form of synaptic plasticity. Primary cultures of rat nucleus accumbens neurons were used to examine whether dopamine receptor stimulation influences cell surface expression of GluR1, detected using antibody to the extracellular portion of GluR1 and fluorescence microscopy. Surface GluR1 labeling on processes of medium spiny neurons and interneurons was increased by brief (5-15 min) incubation with a D1 agonist (1 lM SKF 81297). This effect was attenuated by the D1 receptor antagonist SCH 23390 (10 lM) and reproduced by the adenylyl cyclase activator forskolin (10 lM). Labeling was decreased by glutamate (10-50 lM, 15 min). These results are the first to demonstrate modulation of AMPA receptor surface expression by a non-glutamatergic G protein-coupled receptor. Normally, this may enable ongoing regulation of AMPA receptor transmission in response to changes in the activity of dopamine projections to the nucleus accumbens. When dopamine receptors are over-stimulated during chronic drug administration, this regulation may be disrupted, leading to inappropriate plasticity in neuronal circuits governing motivation and reward.

Postsynaptic interactions between dopamine and glutamate receptors in the nucleus accumbens are critical for acute responses to drugs of abuse and for neuroadaptations resulting from their chronic administration. We tested the hypothesis that D 1 dopamine receptor stimulation increases phosphorylation of the AMPA receptor subunit GluR1 at the protein kinase A phosphorylation site (Ser845). Nucleus accumbens cell cultures were prepared from postnatal day 1 rats. After 14 days in culture, GluR1 phosphorylation was measured by western blotting using phosphorylation site-specific antibodies. The D 1 receptor agonist SKF 81297 increased Ser845 phosphorylation in a concentrationdependent manner, with marked increases occurring within 5 min. This was prevented by the D 1 receptor antagonist SCH 23390 and the protein kinase A inhibitor H89, and reproduced by forskolin. The D 2 receptor agonist quinpirole attenuated the response to D 1 receptor stimulation. Neither D 1 nor D 2 receptor agonists altered GluR1 phosphorylation at Ser831, the site phosphorylated by protein kinase C and calcium/calmodulin-dependent protein kinase II. In other systems, phosphorylation of GluR1 at Ser845 is associated with enhancement of AMPA receptor currents. Thus, the present results suggest that AMPA receptor transmission in the nucleus accumbens may be augmented by concurrent D 1 receptor stimulation.

Despite the significant cultural and linguistic barriers, Chinese Americans can be successfully recruited into longitudinal studies of aging and cognitive impairment. Clinical services are a critical component of such an effort, and low education and other factors that may be associated with it are clear barriers to research participation.