Philosophical transactions of the Royal Society of London. Series B, Biological sciences
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · Oct 2008
ReviewReview. Neurobiological mechanisms for opponent motivational processes in addiction.
The conceptualization of drug addiction as a compulsive disorder with excessive drug intake and loss of control over intake requires motivational mechanisms. Opponent process as a motivational theory for the negative reinforcement of drug dependence has long required a neurobiological explanation. Key neurochemical elements involved in reward and stress within basal forebrain structures involving the ventral striatum and extended amygdala are hypothesized to be dysregulated in addiction to convey the opponent motivational processes that drive dependence. ⋯ CRF receptor antagonists block excessive drug intake produced by dependence. A brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence and to contribute to stress-induced relapse. The combination of loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for the long hypothesized opponent motivational processes responsible for the negative reinforcement driving addiction.
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · Oct 2008
ReviewReview. The incentive sensitization theory of addiction: some current issues.
We present a brief overview of the incentive sensitization theory of addiction. This posits that addiction is caused primarily by drug-induced sensitization in the brain mesocorticolimbic systems that attribute incentive salience to reward-associated stimuli. If rendered hypersensitive, these systems cause pathological incentive motivation ('wanting') for drugs. We address some current questions including: what is the role of learning in incentive sensitization and addiction? Does incentive sensitization occur in human addicts? Is the development of addiction-like behaviour in animals associated with sensitization? What is the best way to model addiction symptoms using animal models? And, finally, what are the roles of affective pleasure or withdrawal in addiction?
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · Aug 2008
ReviewViolent behaviour among people with schizophrenia: a framework for investigations of causes, and effective treatment, and prevention.
Robust evidence has accumulated showing that individuals who develop schizophrenia are at elevated risk when compared to the general population to engage in violence towards others. This violence impacts negatively on victims as well as perpetrators and poses a significant financial burden to society. It is posited that among violent offenders with schizophrenia there are three distinct types defined by the age of onset of antisocial and violent behaviour. ⋯ The largest group of violent offenders with schizophrenia show no antisocial behaviour prior to the onset of the illness and then repeatedly engage in aggressive behaviour towards others. A small group of individuals who display a chronic course of schizophrenia show no aggressive behaviour for one or two decades after illness onset and then engage in serious violence, often killing, those who care for them. We hypothesize that both the developmental processes and the proximal factors, such as symptoms of psychosis and drug misuse, associated with violent behaviour differ for the three types of offenders with schizophrenia, as do their needs for treatment.
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · May 2008
Fire-mediated dieback and compositional cascade in an Amazonian forest.
The only fully coupled land-atmosphere global climate model predicts a widespread dieback of Amazonian forest cover through reduced precipitation. Although these predictions are controversial, the structural and compositional resilience of Amazonian forests may also have been overestimated, as current vegetation models fail to consider the potential role of fire in the degradation of forest ecosystems. We examine forest structure and composition in the Arapiuns River basin in the central Brazilian Amazon, evaluating post-fire forest recovery and the consequences of recurrent fires for the patterns of dominance of tree species. ⋯ Considering tree assemblage composition 9 years after the first fire contact, we observed (i) a clear pattern of community turnover among small trees and the most abundant shrubs and saplings, and (ii) that species that were common in any of the four burn treatments (unburned, once-, twice- and thrice-burned) were often rare or entirely absent in other burn treatments. We conclude that episodic wildfires can lead to drastic changes in forest structure and composition, with cascading shifts in forest composition following each additional fire event. Finally, we use these results to evaluate the validity of the savannization paradigm.
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Philos. Trans. R. Soc. Lond., B, Biol. Sci. · Feb 2008
ReviewOpportunities and challenges of sustainable agricultural development in China.
This paper introduces the concepts and aims of sustainable agriculture in China. Sustainable agricultural development comprises sustainability of agricultural production, sustainability of the rural economy, ecological and environmental sustainability within agricultural systems and sustainability of rural society. China's prime aim is to ensure current and future food security. ⋯ When productivities of cultivated land and other agricultural resources are all taken into consideration, China's food self-sufficiency ratio will increase from 94.4% in 2000 to 101.3% in 2030, suggesting that China will meet its future demand for food and need for food security. Despite this positive assessment, the country's sustainable agricultural development has encountered many obstacles. These include: agricultural water-use shortage; cultivated land loss; inappropriate usage of fertilizers and pesticides, and environmental degradation.