Extensive evidence suggests that interactions between mesolimbic dopaminergic and glutamatergic systems are critically involved in the processes underlying ethanol dependence. Activation of dopamine D-1 receptors as well as NMDA receptors is required for various models of ethanol self-administration, dependence and sensitization. Evidence from our lab and others indicates that NMDA receptor-function and LTP are both markedly enhanced in NAc slices from rats chronically exposed to ethanol. We have recently identified a novel mechanism regulating the ethanol sensitivity of NMDA receptors mediated via D1 activation of an important intracellular component of dopaminergic signaling, DARPP-32. Knockout animals lacking DARPP-32 or D-1 receptors display strikingly similar defects in ethanol self-administration suggesting that this component of dopaminergic signaling may indeed be critical for the development of ethanol dependence. Here, we propose that D1/DARPP-32 dependent regulation of the ethanol sensitivity of NMDA receptors on medium spiny neurons (MSNs) of the NAc promotes NMDA receptor-function to support svnaptic plasticity and contribute to activation of mesolimbic structures in the development of ethanol dependence. This proposal focuses upon the interactions between D1, DARPP-32 and NMDA-dependent processes in ethanol neuroadaptation and uses two chronic ethanol model systems to identify these interactions: (1) an organotypic or brain slice explant culture system containing the major components of the mesocorticolimbic system, and (2) acute slices containing NAc prepared from rats treated with ethanol via inhalation.
Four aims are proposed to assess D1 modulation of ethanol sensitivity in NAc neurons following chronic ethanol treatment to model ethanol neuroadaptation.
Aim 1 is designed to directly measure ethanol sensitivity of NMDA receptors electrophysiologically though detection of NMDA mEPSCs evoked in the presence of Sr++.
Aim 2 measures changes in plasticity by assessing NMDA receptor-dependent LTP.
Aims 3 and 4 use immunoblot and confocal microscopy to determine the changes in phosphorylation of DARPP- 32 and NR1 (aim 4) and their subcellular co-localization (aim 5). Taken together, these aims should provide important new information into the synaptic and molecular alterations that underlie plasticity in mesolimbic structures that may contribute to alcohol addiction.
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