There is compelling evidence that midbrain dopamine (DA) neurons and their projections to the ventral striatum provide a mechanism for motivating reward-seeking behavior, and for utilizing information about unexpected rewards (prediction errors, RPEs) to guide behavior based on current, rather than historical, outcomes. When this mechanism is compromised in addictions, it may produce patterns of maladaptive behavior that remain obdurate in the face of contrary information and even adverse consequences. Nonetheless, DAergic contributions to performance on behavioral tasks that rely on an ability to flexibly update stimulus-reward relationships remains incomplete understood. In the current study, we used a discrimination and reversal paradigm to monitor subsecond DA release in mouse NAc core (NAc) using in vivo fast-scan cyclic voltammetry (FSCV). We observed post-choice elevations in phasic NAc DA release; however, increased DA transients were only evident during early reversal when mice made responses at the newly-rewarded stimulus. Based on this finding, we used in vivo optogenetic (halorhodopsin (eNpHR3.0)) photosilencing and (Channelrhodopsin2 (ChR2)) photostimulation to assess the effects of manipulating VTA-DAergic fibers in the NAc on reversal performance. Photosilencing the VTA→NAc DAergic pathway during early reversal increased errors, while photostimulation did not demonstrably affect behavior. Taken together, these data provide additional evidence of the importance of NAc DA release as a neural substrate supporting adjustments in learned behavior after a switch in expected stimulus-reward contingencies. These findings have possible implications for furthering understanding the role of DA in persistent, maladaptive decision-making characterizing addictions. This article is protected by copyright. All rights reserved.

This review summarizes the proceedings of a symposium presented at the "Alcoholism and Stress: A Framework for Future Treatment Strategies" conference held in Volterra, Italy on May 9-12, 2017. Psychiatric diseases, including alcohol-use disorders (AUDs), are influenced through complex interactions of genes, neurobiological pathways, and environmental influences. A better understanding of the common neurobiological mechanisms underlying an AUD necessitates an integrative approach, involving a systematic assessment of diverse species and phenotype measures. As part of the World Congress on Stress and Alcoholism, this symposium provided a detailed account of current strategies to identify mechanisms underlying the development and progression of AUDs. Dr. Sean Farris discussed the integration and organization of transcriptome and postmortem human brain data to identify brain regional- and cell type-specific differences related to excessive alcohol consumption that are conserved across species. Dr. Brien Riley presented the results of a genome-wide association study of DSM-IV alcohol dependence; although replication of genetic associations with alcohol phenotypes in humans remains challenging, model organism studies show that COL6A3, KLF12, and RYR3 affect behavioral responses to ethanol, and provide substantial evidence for their role in human alcohol-related traits. Dr. Rob Williams expanded upon the systematic characterization of extensive genetic-genomic resources for quantifying and clarifying phenotypes across species that are relevant to precision medicine in human disease. The symposium concluded with Dr. Robert Hitzemann's description of transcriptome studies in a mouse model selectively bred for high alcohol ("binge-like") consumption and a non-human primate model of long-term alcohol consumption. Together, the different components of this session provided an overview of systems-based approaches that are pioneering the experimental prioritization and validation of novel genes and gene networks linked with a range of behavioral phenotypes associated with stress and AUDs.

Repetitive excessive alcohol intoxication leads to neuronal damage and brain shrinkage. We examined cytoskeletal protein expression in human post-mortem tissue from Brodmann's area 9 of the prefrontal cortex (PFC). Brain samples from 44 individuals were divided into equal groups of 11 control, 11 alcoholic, 11 non-alcoholic suicides, and 11 suicide alcoholics matched for age, sex, and post-mortem delay. Tissue from alcoholic cohorts displayed significantly reduced expression of α- and β-tubulins, and increased levels of acetylated α-tubulin. Protein levels of histone deacetylase-6 (HDAC6), and the microtubule-associated proteins MAP-2 and MAP-tau were reduced in alcoholic cohorts, although for MAPs this was not significant. Tubulin gene expressions increased in alcoholic cohorts but not significantly. Brains from rats administered alcohol for 4 weeks also displayed significantly reduced tubulin protein levels and increased α-tubulin acetylation. PFC tissue from control subjects had reduced tubulin protein expression that was most notable from the sixth to the eighth decade of life. Collectively, loss of neuronal tubulin proteins are a hallmark of both chronic alcohol consumption and natural brain ageing. The reduction of cytosolic tubulin proteins could contribute to the brain volumetric losses reported for alcoholic patients and the elderly.

Endocannabinoid (eCB)-mediated long-term depression (LTD) requires dopamine (DA) D2 receptors (D2Rs) for eCB mobilization. The cellular locus of the D2Rs involved in LTD induction remains highly debated. We directly examined the role in LTD induction of D2Rs expressed by striatal cholinergic interneurons (Chls) and indirect pathway medium spiny neurons (iMSNs) using neuron-specific targeted deletion of D2Rs. Deletion of Chl-D2Rs (Chl-Drd2KO) impaired LTD induction in both subtypes of MSNs. LTD induction was restored in the Chl-Drd2KO mice by an M1-selective muscarinic acetylcholine receptor antagonist. In contrast, after the deletion of iMSN-D2Rs (iMSN-Drd2KO), LTD induction was intact in MSNs. Separate interrogation of direct pathway and iMSNs revealed a deficit in LTD induction only at synapses onto iMSNs that lack D2Rs. LTD induction in iMSNs was restored by D2R agonist application. Our findings suggest that Chl D2Rs strongly modulate LTD induction in MSNs, with iMSN-D2Rs having a weaker, iMSN-specific, modulatory effect.