Dopamine and ethanol induced trafficking of viral mediated eGFP tagged dopamine D1 receptors in parasagittal explants

The mesolimbic pathway has been implicated in the rewarding effects of drugs of abuse, and an important component of this pathway is the D1 dopamine receptor (D1DR). D1DRs desensitize upon agonist stimulation by several mechanisms, including a process involving receptor clustering and internalization. This process removes postsynaptic D1DRs and may be a neuroadaptive mechanism associated with addiction to drugs of abuse, including ethanol. We measured localization of D1DRs in viable nucleus accumbens (NAcc) neurons from parasagittal explants. A sindbis RNA virus was used to mediate the expression of D1DRs containing an enhanced green fluorescent protein (eGFP) tag in these explants. The effects of dopamine and ethanol on D1DR localization were measured by changes in fluorescence intensity using two-photon laser scanning microscopy. Two-dimensional images from z-stacks of virally infected neurons displayed stable and homogenous fluorescence throughout the neuronal soma and processes. Dopamine (100 uM, 30 min) significantly enhanced the greatest increase of maximum fluorescence intensity in distinct regions of interest (ROIs) by approximately 40% compared to control neurons in the absence of dopamine. Ethanol pretreatment significantly enhanced dopamine-induced clustering. Neurons exposed to dopamine (50 uM, 30 min) displayed receptor clustering only when pretreated with ethanol. Ethanol (50 and 100 mM, 30 min.) pretreatment followed by dopamine (50 uM, 30 min.) enhanced the greatest increase of maximum fluorescence intensity by 44±3 and 108±9%, respectively, while dopamine (50 uM, 30 min) in the absence of ethanol pretreatment showed no clustering with peak increases in maximum fluorescence intensity of only 3±2%. Ethanol (50 and 100 mM, 60 min) alone enhance the greatest increase of maximum fluorescence intensity by about 60% for both concentrations. Receptor clustering induced by dopamine, ethanol pretreatment of dopamine, or ethanol alone was partially blocked by the D1DR antagonist SCH 23390 (20 uM). These findings show that both dopamine and ethanol alter D1DR localization in NAcc neurons and suggest that a physical restructuring of D1DRs in this region may be involved in neuroadaptive mechanisms of ethanol action