Investigating the Role of the Synaptic Transcriptome in Ethanol-Responsive Behaviors

Alcoholism is a complex neurological disorder characterized by loss of control in limiting intake, compulsion to seek and imbibe ethanol, and chronic craving and relapse. It is suggested that the characteristic behaviors associated with the escalation of drug use are caused by long-term molecular adaptations precipitated by the drug’s continual administration. These lasting activity-dependent changes that underlie addiction-associated behavior are thought, in part, to depend on new protein synthesis and remodeling at the synapses. It is well established that mRNA can be transported to neuronal distal processes, where it can undergo localized translation that is regulated in a spatially restricted manner in response to stimulation. Through two avenues of investigation, the research herein demonstrates that behavioral responses to ethanol result, at least in part, from alterations in the synaptic transcriptome which contribute to synaptic remodeling and plasticity. The synaptoneurosome preparation was utilized to enrich for RNAs trafficked to the synapse. Two complementary methods of genomic profiling, microarrays and RNA-Seq, were used to survey the synaptic transcriptome of DBA/2J mice subjected to ethanol-induced behavioral sensitization. A habituating expression profile, characteristic of glucocorticoid-responsive genes, was observed for a portion of synaptically targeted genes determined to be sensitive to repeated ethanol exposure. Other ethanol-responsive genes significantly enriched for at the synapse were related to biological functions such as protein folding and extra-cellular matrix components, suggesting a role for local regulation of synaptic functioning by ethanol. In a separate series of experiments, it was shown that altered trafficking of Bdnf, an ethanol-responsive gene, resulted in aberrant ethanol behavioral phenotypes. In particular, mice lacking dendritically targeted Bdnf mRNA exhibited enhanced sensitivity to low, activating doses and high, sedating doses of ethanol. Together these experiments suggest that ethanol has local regulatory effects at the synapse and lays the foundation for further investigations into the role of the synaptic transcriptome in ethanol-responsive behaviors. Supported by NIAA grants R01AA014717, U01 AA016667 and P20AA017828 to MFM, F31AA021035 to MAO, and NIDA T32DA007027 to WLD