Prolonged changes in neurochemistry of dopamine neurones after chronic ethanol consumption

Imaging-based neurochemistry in schizophrenia: a systematic review and implications for dysfunctional long-term potentiation

Cognitive deficits are commonly observed in patients with schizophrenia. Converging lines of evidence suggest that these deficits are associated with impaired long-term potentiation (LTP). In our systematic review, this hypothesis is evaluated using neuroimaging literature focused on proton magnetic resonance spectroscopy, positron emission tomography, and single-photon emission computed tomography. The review provides evidence for abnormal dopaminergic, GABAergic, and glutamatergic neurotransmission in antipsychotic-naive/free patients with schizophrenia compared with healthy controls. The review concludes with a model illustrating how these abnormalities could lead to impaired LTP in patients with schizophrenia and consequently cognitive deficits.

Chronic binge-like moderate ethanol drinking in rats results in widespread decreases in brain serotonin, dopamine, and norepinephrine turnover rates reversed by ethanol intake

This research was initiated to assess the turnover rates (TORs) of dopamine (DA), norepinephrine (NA), serotonin (5-HT), aspartate, glutamate, and GABA in brain regions during rodent ethanol/sucrose (EtOH) and sucrose (SUC) drinking and in animals with a history of EtOH or SUC drinking to further characterize the neuronal systems that underlie compulsive consumption. Groups of five male rats were used, with two trained to drink EtOH solutions, two to drink SUC and one to serve as a non-drinking control. When stable drinking patterns were obtained, rats were pulse labeled intravenously and killed 60 or 90 min later and the TORs of DA, norepinephrine, 5-HT, aspartate, glutamate, and GABA determined in brain regions. Changes in the TOR of 5-HT, DA, and NA were detected specific to EtOH drinking, SUC drinking or a history of EtOH or SUC drinking. An acute EtOH deprivation effect was detected that was mostly reversed with EtOH drinking. These results suggest that binge-like drinking of moderate amounts of EtOH produces a deficit in neuronal function that could set the stage for the alleviation of anhedonic stimuli with further EtOH intake that strengthen EtOH seeking behaviors which may contribute to increased EtOH use in at risk individuals.

Changes in neuronal protein 22 expression and cytoskeletal association in the alcohol-dependent and withdrawn rat brain

The action of alcohol on neuronal pathways has been an issue of increasing research focus, with numerous findings contradicting the previously accepted idea that its effect is nonspecific. The human NP22 (hNP22) gene was revealed by its elevated expression in the frontal cortex of the human alcoholic. The sequences of hNP22 and the rat orthologue rNP22 contain a number of domains consistent with those of cytoskeletal-interacting proteins. Localization of rNP22 is restricted to the cytoplasm and processes of neurons and it colocalizes with elements of the microfilament and microtubule matrices including filamentous actin (F-actin), alpha-tubulin, tau, and microtubule-associated protein 2 (MAP2). Withdrawal of Wistar rats after alcohol dependence induced by alcohol vapor produced elevated levels of rNP22 mRNA and protein in the cortex, CA2, and dentate gyrus regions of the hippocampus. In contrast, there was decreased rNP22 expression in the striatum after chronic ethanol exposure. Chronic ethanol exposure did not markedly alter rNP22 colocalization with F-actin, alpha-tubulin, or MAP2, although colocalization at the periphery of the neuronal soma with F-actin was observed only after chronic ethanol exposure and withdrawal. Rat NP22 colocalization with MAP2 was reduced during withdrawal, whereas association with alpha-tubulin and actin was maintained. These findings suggest that the effect of chronic ethanol exposure and withdrawal on rNP22 expression is region selective. Rat NP22 may affect microtubule or microfilament function, thereby regulating the neuroplastic changes associated with the development of alcohol dependence and physical withdrawal.

Pharmacology of drugs of abuse

The pharmacology of most addictive substances is being studied extensively, not just for their acute effects but also the mechanisms that lead to drug seeking and addiction. The understanding of how these drugs alter their effects at the molecular level with continuing use gives promise toward investigation of novel substances that may be used for treatment. Genetic predisposition and gender differences are also some of the areas where more research is needed. Women who are addicted are likely to continue drug use during pregnancy, which can have an impact on the next generation. Prevention measures at the population level are as important. Programs need to address risks, social issues, and environmental factors that promote drug use and addiction.

Brain neurotransmitter turnover rates during rat intravenous cocaine self-administration

The turnover rates of dopamine, norepinephrine, serotonin, aspartate, glutamate and GABA were measured in 27 brain regions of rats self-administering cocaine and in yoked cocaine- and yoked vehicle-infused controls using radioactive pulse-labeling procedures to identify brain neuronal systems underlying self-administration. Changes in the activity of heretofore unrecognized dopamine, norepinephrine, serotonin, glutamate and GABA innervations of the forebrain specific to cocaine self-administration were found. This included innervations of the nucleus accumbens, ventral pallidum, lateral hypothalamus and the anterior and posterior cingulate, entorhinal-subicular and visual cortices. Turnover rates also were calculated using metabolite/neurotransmitter ratios which were inconsistent with the pulse-label technologies indicating that ratio procedures are not accurate measures of neurotransmitter utilization. Results with the pulse-label technique provide evidence of the involvement of neuronal systems in cocaine self-administration not previously known, some of which may have a broader role in brain reinforcement processes for natural reinforcers (i.e. food, water, etc.) since drugs of abuse are thought to produce reinforcing effects by modulating activity in these endogenous systems.

Enduring effects of chronic ethanol in the CNS: basis for alcoholism

This symposium focused on functional alterations in the mesolimbic dopamine system during the abstinence phase after chronic alcohol intake. Mark Brodie first described his recordings from midbrain slices prepared after chronic alcohol treatment in vivo by daily injection in C57BL/6J mice. No changes were found in the baseline firing frequency of dopaminergic neurones in the VTA (ventral tegmental area), but the excitation produced in these neurones by an acute ethanol challenge was significantly increased in neurons from ethanol-treated mice compared with those from the saline-treated controls. There was also a significant decrease in the inhibitory response to GABA by the dopamine neurones following the chronic ethanol treatment. These data suggest that the timing pattern and mode of ethanol administration may determine the types of changes observed in dopaminergic reward area neurons. Annalisa Muntoni lectured on the relationship between electrophysiological and biochemical in vivo evidence supporting a reduction in tonic activity of dopamine neurons projecting to the nucleus accumbens at various times after suspension of chronic ethanol treatment and morphological changes affecting dopamine neurons in rat VTA. Hilary J. Little then described changes in dopaminergic neurone function in the VTA during the abstinence phase. Decreases in baseline firing were seen at 6 days after withdrawal of mice from chronic ethanol treatment but were not apparent after 2 months abstinence. Increases in the affinity of D1 receptors in the striatum, but not in the cerebral cortex, were seen however up to 2 months after withdrawal. Scott Steffensen then described his studies recording in vivo from GABA containing neurones in the VTA in freely moving rats. Chronic ethanol administration enhanced the baseline activity of these neurones and resulted in tolerance to the inhibition by ethanol of these neurones. His results demonstrated selective adaptive circuit responses within the VTA or in extrategmental structures that regulate VTA-GABA neurone activity.

Neurodevelopmental liabilities in alcohol dependence: central serotonin and dopamine dysfunction

Alcoholism is a complex disorder with symptoms ranging from abuse to dependence, often comorbid with depression, antisocial personality, or anxiety. Neurodevelopmental causes of the disorder are unknown but inferences are possible from current knowledge. Neurobiological studies implicate multiple brain changes, which may be characterized as premorbid or morbid. These studies have also examined specific aspects of the alcohol dependence syndrome, including alcohol reinforcement and craving. Here, we review the evidence for vulnerability factors in alcohol dependence, with an emphasis on central serotonin (5-HT) and dopamine (DA). Serotonin dysfunction likely contributes to the development of alcoholism since studies of alcohol-preferring rodents show decreased 5-HT function on many measures. We have shown that serotonin-enhancing drugs reduce consumption and craving in mild to moderate alcoholics, yet similar studies in severely dependent individuals remain inconclusive. Studies indicate that serotonin dysfunction may contribute to the development of dependence via impaired impulse control and/or mood regulation. The mesocorticolimbic dopamine pathway represents another important pathophysiological target in alcoholism. Differences in D(2) receptor density, dopamine sensitivity, and gene expression have been linked to consumption, reinforcement, craving, and relapse. However, while DA agonists reduce self-administration in animals, we found no effect in humans with long-acting bromocriptine, a D(2) agonist. Dopamine may contribute differentially to the development of dependence via its effects on alcohol wanting, reinforcement, and reward memory. Although animal experiments show consistent roles for serotonin and dopamine in alcohol dependence, human studies are not always concordant. Such discrepancies highlight the complexity of dependence-related behaviors in humans and of identifying vulnerabilities to alcoholism.

Behavioral neurobiology of alcohol addiction: recent advances and challenges

Addictive behavior associated with alcoholism is characterized by compulsive preoccupation with obtaining alcohol, loss of control over consumption, and development of tolerance and dependence, as well as impaired social and occupational functioning. Like other addictive disorders, alcoholism is characterized by chronic vulnerability to relapse after cessation of drinking. To understand the factors that compel some individuals to drink excessively, alcohol research has focused on the identification of brain mechanisms that support the reinforcing actions of alcohol and the progression of changes in neural function induced by chronic ethanol consumption that lead to the development of dependence. More recently, increasing attention has been directed toward the understanding of neurobiological and environmental factors in susceptibility to relapse.