Nam, Hyung W

AbstractThe corticostriatal circuitry and its glutamate‐γ‐aminobuturic acid (GABA) interactions play an essential role in regulating neuronal excitability during reward‐seeking behavior. However, the contribution of GABAergic interneurons in the corticostriatal circuitry remains unclear. To investigate the role of GABAergic interneurons, we focused on parvalbumin‐expressing fast‐spiking interneurons (Pv‐FSI) in the corticostriatal circuitry using the designer receptors exclusively activated by designer drugs approach in a Pv‐Cre mouse model. We hypothesize that Pv‐FSI activation elicits changes in cortical glutamate levels and reward‐seeking behaviors. To determine molecular and behavioral effects of Pv‐FSI, we performed microdialysis and operant conditioning tasks for sucrose and alcohol rewards. In addition, we also examined how alcohol reward itself affects Pv‐FSI functioning. Interestingly, our microdialysis results demonstrate that alcohol exposure inhibits Pv‐FSI functioning in the medial prefrontal cortex (mPFC) and this consequently can regulate glutamate levels downstream in the nucleus accumbens. For sucrose reward‐seeking behaviors, Pv‐FSI activation in the mPFC increases sucrose self‐administration whereas it does not promote alcohol seeking. For alcohol rewards, however, Pv‐FSI activation in the mPFC results in increased compulsive head entry in operant chambers during devaluation procedures. Overall, our results suggest that not only do Pv‐FSI contribute to changes in the cortical microcircuit and reward‐seeking behaviors but also that alcohol affects Pv‐FSI neurotransmission. Therefore, Pv‐FSI has prompted interest in their role in maintaining a balance in neuronal excitation/inhibition and in regulating reward‐seeking processes such as compulsivity, all of which are important factors for excessive alcohol seeking. image

AbstractDysfunction of glutamate neurotransmission in the nucleus accumbens (NAc) has been implicated in the pathophysiology of alcohol use disorders (AUD). Neurogranin (Ng) is exclusively expressed in the brain and mediates N‐methyl‐d‐aspartate receptor (NMDAR) hypo‐function by regulating the intracellular calcium‐calmodulin (Ca2+‐CaM) pathway. Ng null mice (Ng–/– mice) demonstrate increased alcohol drinking compared to wild‐type mice, while also showing less tolerance to the effect of alcohol. To identify the molecular mechanism related to alcohol seeking, both in vivo microdialysis and label‐free quantification proteomics comparing Ng genotype and effects of alcohol treatment on the NAc are utilized. There is significant difference in glutamate and gamma‐aminobutyric acid (GABA) neurotransmission between genotypes; however, alcohol administration normalizes both glutamate and GABA levels in the NAc. Using label‐free proteomics, 427 protein expression changes are identified against alcohol treatment in the NAc among 4347 total proteins detected. Bioinformatics analyses reveal significant molecular differences in Ng null mice in response to acute alcohol treatment. Ingenuity pathway analysis found that the AKT network is altered significantly between genotypes, which may increase the sensitivity of alcohol in Ng null mice. The pharmacoproteomics results presented here illustrate a possible molecular basis of the alcohol sensitivity through Ng signaling in the NAc.

AbstractAcamprosate is an FDA‐approved medication for the treatment of alcoholism that is unfortunately only effective in certain patients. Although acamprosate is known to stabilize the hyper‐glutamatergic state in alcoholism, pharmacological mechanisms of action in brain tissue remains unknown. To investigate the mechanism of acamprosate efficacy, the authors employ a pharmacoproteomics approach using an animal model of alcoholism, type 1 equilibrative nucleoside transporter (ENT1) null mice. The results demonstrate that acamprosate treatment significantly decreased both ethanol drinking and preference in ENT1 null mice compared to that of wild‐type mice. Then, to elucidate acamprosate efficacy mechanism in ENT1 null mice, the authors utilize label‐free quantification proteomics comparing both genotype and acamprosate treatment effects in the nucleus accumbens (NAc). A total of 1040 protein expression changes are identified in the NAc among 3634 total proteins detected. The proteomics and Western blot result demonstrate that acamprosate treatment decreased EAAT expression implicating stabilization of the hyper‐glutamatergic condition in ENT1 null mice. Pathway analysis suggests that acamprosate treatment in ENT1 null mice seems to rescue glutamate toxicity through restoring of RTN4 and NF‐κB medicated neuroimmune signaling compared to wild‐type mice. Overall, pharmacoproteomics approaches suggest that neuroimmune restoration is a potential efficacy mechanism in the acamprosate treatment of certain sub‐populations of alcohol dependent subjects.

Recent studies have demonstrated that the function of glia is not restricted to the support of neuronal function. Especially, astrocytes are essential for neuronal activity in the brain. Astrocytes actively participate in synapse formation and brain information processing by releasing or uptaking gliotransmitters such as glutamate, d ‐serine, adenosine 5′‐triphosphate ( ATP ), and adenosine. In the central nervous system, adenosine plays an important role in regulating neuronal activity as well as in controlling other neurotransmitter systems such as GABA , glutamate, and dopamine. Ethanol ( E t OH ) increases extracellular adenosine levels, which regulates the ataxic and hypnotic/sedative (somnogenic) effects of E t OH . Adenosine signaling is also involved in the homeostasis of major inhibitory/excitatory neurotransmission (i.e., GABA or glutamate) through neuron–glial interactions, which regulates the effect of E t OH and sleep. Adenosine transporters or astrocytic SNARE ‐mediated transmitter release regulates extracellular or synaptic adenosine levels. Adenosine then exerts its function through several adenosine receptors and regulates glutamate levels in the brain. This review presents novel findings on how neuron–glial interactions, particularly adenosinergic signaling and glutamate uptake activity involving glutamate transporter 1 ( GLT 1), are implicated in alcoholism and sleep disorders.