Synergistic effects of the dopaminergic and glutamatergic system on hippocampal volume in alcohol-dependent patients

NAAG Peptidase Inhibitors Act via mGluR3: Animal Models of Memory, Alzheimer's, and Ethanol Intoxication

Glutamate carboxypeptidase II (GCPII) inactivates the peptide neurotransmitter N-acetylaspartylglutamate (NAAG) following synaptic release. Inhibitors of GCPII increase extracellular NAAG levels and are efficacious in animal models of clinical disorders via NAAG activation of a group II metabotropic glutamate receptor. mGluR2 and mGluR3 knock-out (ko) mice were used to test the hypothesis that mGluR3 mediates the activity of GCPII inhibitors ZJ43 and 2-PMPA in animal models of memory and memory loss. Short- (1.5 h) and long- (24 h) term novel object recognition tests were used to assess memory. Treatment with ZJ43 or 2-PMPA prior to acquisition trials increased long-term memory in mGluR2, but not mGluR3, ko mice. Nine month-old triple transgenic Alzheimer's disease model mice exhibited impaired short-term novel object recognition memory that was rescued by treatment with a NAAG peptidase inhibitor. NAAG peptidase inhibitors and the group II mGluR agonist, LY354740, reversed the short-term memory deficit induced by acute ethanol administration in wild type mice. 2-PMPA also moderated the effect of ethanol on short-term memory in mGluR2 ko mice but failed to do so in mGluR3 ko mice. LY354740 and ZJ43 blocked ethanol-induced motor activation. Both GCPII inhibitors and LY354740 also significantly moderated the loss of motor coordination induced by 2.1 g/kg ethanol treatment. These data support the conclusion that inhibitors of glutamate carboxypeptidase II are efficacious in object recognition models of normal memory and memory deficits via an mGluR3 mediated process, actions that could have widespread clinical applications.

Association of Dopamine D2 Receptor Gene Polymorphisms with Reproduction Traits in Domestic Pigeons (Columba livia)

Dopamine inhibited prolactin secretion via dopamine D2 receptor (DRD2) at the pituitary level, but its effects on reproduction in pigeons are unclear. In this study, Single Nucleotide Polymorphisms (SNPs) in the exons of DRD2 gene were identified and analyzed by using DNA sequencing methods in 60 female domestic pigeons (Columba livia), and the association between DRD2 polymorphisms and reproduction traits was also analyzed. Sequencing results showed that 7 nucleotide mutations were detected in the exon 1, 4, and 6 regions of DRD2 gene. The analysis revealed three genotypes (AA, AB, and BB) in exon 4 and two genotypes (AA, AB) in exon 6, in which the AA genotype was consistently dominant, and the A allele showed a dominant advantage. The C4532T genotypes located in exon 6 of DRD2 gene were significantly (P<0.05) associated with reproductive traits of pigeon. Moreover, the individuals with AB genotype had significantly higher fertility rate and total hatching number within 500 days of age than those with AA genotype (P<0.05). These findings suggested that the DRD2 gene should be included in future genetic studies of pigeon reproduction and the SNP of C4532T might be a potential candidate genetic marker for Marker-aid breeding in pigeon.

Transcranial Magnetic Stimulation and Deep Brain Stimulation in the treatment of alcohol dependence

Alcohol dependence is a major social, economic, and public health problem. Alcoholism can lead to damage of the gastrointestinal, nervous, cardiovascular, and respiratory systems and it can be lethal, costing hundreds of billions to the health care system. Despite the existence of cognitive-behavioral therapy, psychosocial interventions, and spiritually integrated treatment to treat it, alcohol dependence has a high relapse rate and poor prognosis, albeit with high interindividual variability. In this review, we discuss the use of two neuromodulation techniques, namely repetitive transcranial magnetic stimulation (rTMS) and deep brain stimulation (DBS), and their advantages and disadvantages compared to first-line pharmacological treatment for alcohol dependence. We also discuss rTMS and DBS targets for alcohol dependence treatment, considering experimental animal and human evidence, with careful consideration of methodological issues preventing the identification of feasible targets for neuromodulation treatments, as well as inter-individual variability factors influencing alcoholism prognosis. Lastly, we anticipate future research aiming to tailor the treatment to each individual patient by combining neurofunctional, neuroanatomical and neurodisruptive techniques optimizing the outcome.

Gene expression in the addicted brain

Addiction is due to changes in the structure and function of the brain, including neuronal networks and the cells that comprise them. Within cells, gene expression changes can track and help explain their altered function. Transcriptional changes induced by addictive agents are dynamic and divergent and range from signal pathway-specific perturbations to widespread molecular and cellular dysregulation that can be measured by "omic" methods and that can be used to identify new pathways. The molecular effects of addiction depend on timing of exposure or withdrawal, the stage of adaptation, the brain region, and the behavioral model, there being many models of addiction. However, the molecular neural adaptations across different drug exposures, conditions, and regions are to some extent shared and can reflect common actions on pathways relevant to addiction. Epigenetic studies of DNA methylation and histone modifications and studies of regulatory RNA networks have been informative for elucidating the mechanisms of transcriptional change in the addicted brain.

Neural markers of genetic vulnerability to drug addiction

This chapter will summarize genetics findings derived from various strategies and highlight important neural markers (or correlates) in some specific and extensively studied genes. Most studies highlighted here focus on alcohol and nicotine dependence (AD and ND, respectively). AD and ND are among the most prevalent addictive disorders worldwide, are among the best studied, and are also associated globally with the largest socioeconomic impact.We describe different mechanisms through which genes can have an impact on the addictive behaviors, distinguishing between the genes that inscribe the proteins affecting the metabolism of the addictive substance (e.g., ADH/ALDH for alcohol or CYP2A6 for nicotine) and genes that code for the brain transmitter systems, such as genes involved in cerebral neurotransmission thought to be involved in addiction (e.g., brain reward system, mood regulation, opioid system). Strategies include linkage analyses, association studies, whole genome association studies as well as intermediate/endophenotype studies. Moreover, some important findings derived from animal studies and from neuroimaging studies are highlighted. In conclusion, we provide the reader with an overview of most important studies related to AD and ND and give an outlook how these findings may become useful and beneficial in the future.

Breaking barriers in the genomics and pharmacogenetics of drug addiction

Drug addiction remains a substantial health issue with limited treatment options currently available. Despite considerable advances in the understanding of human genetic architecture, the genetic underpinning of complex disorders remains elusive. On the basis of our current understanding of neurobiology, numerous candidate genes have been implicated in the etiology and response to treatment for different addictions. Genome-wide association (GWA) studies have also identified novel targets. However, replication of these studies is often lacking, and this complicates interpretation. The situation is expected to improve as issues such as phenotypic characterization, the apparent "missing heritability," the identification of functional variants, and possible gene-environment (G × E) interactions are addressed. In addition, there is growing evidence that genetic information can be useful in refining the choice of addiction treatment. As genetic testing becomes more common in the practice of medicine, a variety of ethical and practical challenges, some of which are unique to drug addiction, will also need to be considered.

A transposon in Comt generates mRNA variants and causes widespread expression and behavioral differences among mice

BACKGROUND

Catechol-O-methyltransferase (COMT) is a key enzyme responsible for the degradation of dopamine and norepinephrine. COMT activity influences cognitive and emotional states in humans and aggression and drug responses in mice. This study identifies the key sequence variant that leads to differences in Comt mRNA and protein levels among mice, and that modulates synaptic function and pharmacological and behavioral traits.

METHODOLOGY/PRINCIPAL FINDINGS

We examined Comt expression in multiple tissues in over 100 diverse strains and several genetic crosses. Differences in expression map back to Comt and are generated by a 230 nt insertion of a B2 short interspersed element (B2 SINE) in the proximal 3' UTR of Comt in C57BL/6J. This transposon introduces a premature polyadenylation signal and creates a short 3' UTR isoform. The B2 SINE is shared by a subset of strains, including C57BL/6J, A/J, BALB/cByJ, and AKR/J, but is absent in others, including DBA/2J, FVB/NJ, SJL/J, and wild subspecies. The short isoform is associated with increased protein expression in prefrontal cortex and hippocampus relative to the longer ancestral isoform. The Comt variant causes downstream differences in the expression of genes involved in synaptic function, and also modulates phenotypes such as dopamine D1 and D2 receptor binding and pharmacological responses to haloperidol.

CONCLUSIONS/SIGNIFICANCE

We have precisely defined the B2 SINE as the source of variation in Comt and demonstrated that a transposon in a 3' UTR can alter mRNA isoform use and modulate behavior. The recent fixation of the variant in a subset of strains may have contributed to the rapid divergence of inbred strains.

The genetics of schizophrenia

Research on the genetic factors conferring risk for schizophrenia has not provided definitive answers. In the present review, we will discuss potential clinical and genetic limitations intrinsic to the strategies using a diagnostic phenotype. Among clinical factors, uncertainty of the phenotype is certainly a major limitation. Genetic problems include locus heterogeneity and the complex genetic architecture of the phenotype. Given these limiting factors, we will also discuss another hypothesis-driven strategy to uncover genetic risk: the use of quantitative measures (intermediate phenotypes) within more specific neurobiological mechanisms. As a clear example of all these issues and because of the longstanding involvement in the pathophysiology of this disorder, we will review the association of the gene for dopamine D2 receptors (DRD2) with diagnosis of schizophrenia and with specific working memory behavioral and brain activity phenotypes. We conclude by suggesting that hypothesis-free and hypothesis-driven are not mutually exclusive strategies and may provide information at different levels that are both useful and equally valid about genetic risk for a complex diagnostic entity like schizophrenia and for a complex phenotype like psychosis.

Imaging the genetics of brain structure and function

Imaging genetics combines brain imaging and genetics to detect genetic variation in brain structure and function related to behavioral traits, including psychiatric endpoints, cognition, and affective regulation. This special issue features extensive reviews of the current state-of-the-art of the field and adds new findings from twin and candidate gene studies on functional MRI. Here we present a brief overview and discuss a number of desirable future developments which include more specific a priori hypotheses, more standardization of MRI measurements within and across laboratories, and larger sample sizes that allows testing of multiple genes and their interactions up to a scale that allows genetic whole genome association studies. Based on the overall tenet of the contributions to this special issue we predict that imaging genetics will increasingly impact on the classification systems for psychiatric disorders and the early detection and treatment of vulnerable individuals.