Gene-environment interplay in alcoholism and other substance abuse disorders: expressions of heritability and factors influencing vulnerability

Pairing mild stress with increased serotonin-1B receptor expression in the nucleus accumbens increases susceptibility to amphetamine

Both serotonin-1B (5-HT(1B)) receptors and stress modulate the behavioral and neurobiological effects of psychostimulant drugs. In order to examine how these factors interact to influence the development of behaviors associated with addiction, we used viral-mediated gene transfer to transiently increase expression of 5-HT(1B) receptors in the nucleus accumbens (NAc) shell along with exposure to repeated mild stress (novelty + saline injection) in rats. Once the viral-mediated increases in gene expression had dissipated, the resulting effects of this 5-HT(1B)/stress pairing on the acute locomotor response to amphetamine and on the development of psychomotor sensitization were examined. We report that the increasing expression of 5-HT(1B) receptors on the terminals of NAc shell neurons that project to the ventral tegmental area and repeatedly exposing rats to mild stress subsequently enhance the acute locomotor-activating effects of amphetamine. In addition, the development of psychomotor sensitization (both locomotor activity and stereotypy components) is facilitated. These results suggest that serotonin signaling through NAc 5-HT(1B) heteroreceptors can interact with stress to increase susceptibility to the enduring forms of drug-induced plasticity that are associated with addiction.

Affective status in relation to impulsive, motor and motivational symptoms: personality, development and physical exercise

The contributions of impulsive and risk-taking behaviour in depressive and bipolar disorders, motivational and motor behaviours in anhedonic and substance addictive states, and the factors, particularly distress and trauma, underlying the development of neuropathology in affective status are described from clinical, epidemiological and laboratory perspectives. In order to distinguish one case factor for biopsychological substrates of health, an array of self-reported characteristics, e.g., positive or negative affect, stress or energy, optimism, etc., that may be predictive or counterpredictive for the propensity for physical exercise and activity were analysed using a linear regression in twelve different studies. Several individual characteristics were found to be markedly and significantly predictive of the exercise propensity, i.e., positive affect, energy, health-seeking behaviour and character, while optimism was of lesser, though significant, importance. Several individual characteristics were found to be significantly counterpredictive: expression of BDI- and HAD-depression, major sleep problems and lack/negligence of health-seeking behaviour. The consequences of physical activity and exercise for both affective well-being, cognitive mobility and neurogenesis is noted, particularly with regard to developmental assets for younger individuals. Affective disorder states may be studied through analyses of personal characteristics that unfold predispositions for symptoms-profiles and biomarkers derived from properties of dysfunction, such as impulsiveness, temperament dimensions, anhedonia and 'over-sensitivity', whether interpersonal or to reward.

Infusing neuroscience into the study and prevention of drug misuse and co-occurring aggressive behavior

The etiology of behavioral precursors to substance misuse and aggression is viewed from the perspective of a developmental, multifactorial model of complex disorders. Beginning at conception, genetic and environmental interactions have potential to produce a sequence of behavioral phenotypes during development that bias the trajectory toward high-risk outcomes. One pathway is theorized to emanate from a deviation in neurological development that predisposes children to affective and cognitive delays or impairments that, in turn, generate dysregulatory behaviors. The plasticity of these neurobiological systems is highly relevant to the prevention sciences; their functions are reliant upon environmental inputs and can be altered, for better or for worse, contingent upon the nature of the inputs. Thus, social contextual factors confer significant influence on the development of this neural network and behavioral outcomes by increasing risk for, or protecting (1) against, dysregulatory outcomes. A well-designed intervention can exploit the brain's plasticity by targeting biological and social factors at sensitive time points to positively influence emergent neurobiological functions and related behaviors. Accordingly, prevention research is beginning to focus on perturbations in developmental neural plasticity during childhood that increase the likelihood of risky behaviors and may also moderate intervention effects on behavior. Given that the more complex features of neurobiological functions underlying drug misuse and aggression (e.g., executive cognitive function, coping skills, affect regulation) do not coalesce until early adulthood when prefrontal-limbic brain networks consolidate, it is critical that mechanisms underlying developmental risk factors are identified. An empirically driven prevention approach, thus, may benefit from consideration of (i) the type, effect, and developmental timing of the environmental impact on the brain, and (ii) the type and effect on brain function, and developmental timing of the intervention. This translational approach promises to eventually offer some direction for the design of effective interventions to prevent drug misuse and concomitant aggression.

Perinatal kynurenine 3-hydroxylase inhibition in rodents: pathophysiological implications

The kynurenine pathway (KP) of tryptophan degradation contains three neuroactive metabolites: the neuroinhibitory agent kynurenic acid (KYNA) and, in a competing branch, the free radical generator 3-hydroxykynurenine (3-HK) and the excitotoxin quinolinic acid (QUIN). These three "kynurenines" derive from a common precursor, L-kynurenine, and are recognized for their role in brain physiology and pathophysiology. Inhibition of kynurenine 3-hydroxylase, the enzyme responsible for 3-HK formation, shifts KP metabolism in the mature brain toward enhanced KYNA formation. We now tested the cerebral effects of kynurenine 3-hydroxylase inhibition in immature rodents. Rat pups treated with the kynurenine 3-hydroxylase inhibitor UPF 648 (30 mg/kg, i.p.) 10 min after birth showed substantial increases in cerebral and liver kynurenine and KYNA levels up to 24 hr later, whereas 3-HK and QUIN levels were simultaneously decreased. Administered to pregnant rats or mice on the last day of gestation, UPF 648 (50 mg/kg, i.p.) produced qualitatively similar changes (i.e., large increases in kynurenine and KYNA and reductions in 3-HK and QUIN) in the brain and liver of the offspring. Rat pups delivered by UPF 648-treated mothers and immediately exposed to neonatal asphyxia showed further enhanced brain KYNA levels. These studies demonstrate that acute kynurenine 3-hydroxylase inhibition effectively shifts cerebral KP metabolism in neonatal rodents toward increased KYNA formation. Selective inhibitors of this enzyme may therefore provide neuroprotection in newborns and will also be useful for the experimental evaluation of the long-term effects of perinatal KP impairment.

Genetic variation and shared biological susceptibility underlying comorbidity in neuropsychiatry

Genetic factors underlying alcoholism, substance abuse, antisocial and violent behaviour, psychosis, schizophrenia and psychopathy are emerging to implicate dopaminergic and cannabinoid, but also monoaminergic and glutamatergic systems through the maze of promoter genes and polymorphisms. Candidate gene association studies suggest the involvement of a range of genes in different disorders of CNS structure and function. Indices of comorbidity both complicate the array of gene-involvement and provide a substrate of hazardous interactivity. The putative role of the serotonin transporter gene in affective-dissociative spectrum disorders presents both plausible genetic variation and complication of comorbidity The position of genetic variation is further complicated through ethnic, contextual and social factors that provide geometric progressions in the comordity already underlying diagnostic obstacles. The concept of shared biological susceptibility to two or more disorder conditions of comorbidity seems a recurring observation, e.g., bipolar disorder with alcoholism or schizophrenia with alcohol/substance abuse or diabetes with schizopsychotic disorder. Several lines of evidence seem to suggest that the factors influencing variation in one set of symptoms and those affecting one or more disorders are observed to a marked extent which ought to facilitate the search for susceptibility genes in comorbid brain disorders. Identification of regional genetic factors is awaited for a more compelling outline that ought eventually to lead to greater efficacy of symptom-disorder arrangements and an augmentation of current pharmacological treatment therapies.

Neurotoxins and neurotoxicity mechanisms. an overview

Neurotoxins represent unique chemical tools, providing a means to 1) gain insight into cellular mechanisms of apopotosis and necrosis, 2) achieve a morphological template for studies otherwise unattainable, 3) specifically produce a singular phenotype of denervation, and 4) provide the starting point to delve into processes and mechanisms of nerve regeneration and sprouting. There are many other notable uses of neurotoxins in neuroscience research, and ever more being discovered each year. The objective of this review paper is to highlight the broad areas of neuroscience in which neurotoxins and neurotoxicity mechanism come into play. This shifts the focus away from neurotoxins per se, and onto the major problems under study today. Neurotoxins broadly defined are used to explore neurodegenerative disorders, psychiatric disorders and substance use disorders. Neurotoxic mechanisms relating to protein aggregates are indigenous to Alzheimer disease, Parkinson's disease. NeuroAIDS is a disorder in which microglia and macrophages have enormous import. The gap between the immune system and nervous system has been bridged, as neuroinflammation is now considered to be part of the neurodegenerative process. Related mechanisms now arise in the process of neurogenesis. Accordingly, the entire spectrum of neuroscience is within the purview of neurotoxins and neurotoxicity mechanisms. Highlights on discoveries in the areas noted, and on selective neurotoxins, are included, mainly from the past 2 to 3 years.

Treatment of substance use disorders in schizophrenia: a unifying neurobiological mechanism?

Substance use disorders (SUDs) are highly prevalent and are associated with poor outcomes among individuals with schizophrenia. Integrating treatments for both disorders improves outcomes. Numerous individual pharmacologic and psychosocial treatments have shown effectiveness at reducing substance use in individuals with a primary diagnosis of schizophrenia and co-occurring substance use disorders. Of these treatments, medications such as certain atypical antipsychotics and naltrexone, and psychosocial treatments such as contingency management, seem to be particularly promising. The development and evaluation of psychopharmacologic and psychosocial treatments for SUDs in schizophrenia would benefit from a better understanding of the neurobiological mechanisms underlying the effectiveness of such treatments. Several theories have been put forth to explain the heightened risk for SUDs in schizophrenia. Of these, brain reward circuitry dysfunction, hypothesized to be etiologically important in SUDs, may be an especially salient target for treatments aimed at the reduction of substance use in patients with schizophrenia. We review current pharmacologic and psychosocial treatments for SUDs in schizophrenia, and theoretical mechanisms underlying the increased risk for SUDs in this population. We propose that effective treatments may in part work through the modulation of brain reward circuitry dysfunction.

Substance misuse and psychiatric comorbidity in adolescents

PURPOSE OF REVIEW

Many young people are misusing and becoming dependent on multiple substances (especially nicotine, alcohol, and cannabis), with a complex variety of psychological effects.

RECENT FINDINGS

Analysis of interactions between smoking, drinking, and cannabis use indicates that the relationship between substance use and psychiatric comorbidity is primarily explained by regular smoking. In some studies the use of cannabis on a regular basis was associated with an increased risk of psychiatric illness. This is by no means the case for all studies, so this area of work remains controversial. Children with attention deficit hyperactivity disorder who are substance misusers have a poorer prognosis than those without it so there is concern about treatment with stimulant drugs: this fear appears not to be substantiated by one study. Young people with anxiety disorders are at increased risk of substance use disorders. Clinical trials for adolescent substance abuse treatment have provided support for the benefits of cognitive behavioural interventions. There is an accumulating evidence base for pharmacological treatment for adult substance misusers that can inform treatment for younger patients. It is estimated that, of those adolescents who were likely to be in need of help, only about 9% received treatment.

SUMMARY

Since psychiatric disorders beginning in childhood may continue into adult life, there is an opportunity to intervene to prevent or reduce conditions complicated by substance misuse, if services are accessible. The need for longitudinal work is vital to explore the patterns of comorbidity, and implement and evaluate appropriate treatment interventions.

Gene-environment interplay in neurogenesis and neurodegeneration

Factors associated with predisposition and vulnerability to neurodegenerative disorders may be described usefully within the context of gene-environment interplay. There are many identified genetic determinants for so-called genetic disorders, and it is possible to duplicate many elements of recognized human neurodegenerative disorders in either knock-in or knock-out mice. However, there are similarly, many identifiable environmental influences on outcomes of the genetic defects; and the course of a progressive neurodegenerative disorder can be greatly modified by environmental elements. Constituent cellular defense mechanisms responsive to the challenge of increased reactive oxygen species represent only one crossroad whereby environment can influence genetic predisposition. In this paper we highlight some of the major neurodegenerative disorders and discuss possible links of gene-environment interplay. The process of adult neurogenesis in brain is also presented as an additional element that influences gene-environment interplay. And the so-called priming processes (i.e., production of receptor supersensitization by repeated drug dosing), is introduced as yet another process that influences how genes and environment ultimately and co-dependently govern behavioral ontogeny and outcome. In studies attributing the influence of genetic alteration on behavioral phenotypy, it is essential to carefully control environmental influences.