The bee as a model system for addiction

Abstract

The consumption of chemical substances that generate fleeting feelings of pleasure and euphoria, and the progression of dependence to these substances in subsets of individuals, remains a pressing concern for society. Drug addiction carries not only substantial risk to the mental and physical wellbeing of the individual but also carries an enormous social and medical cost, with an annual cost of 15.4 billion pounds a year in the UK alone. There is, therefore, a strong motivation to identify the underlying causes of addiction to aid in identifying future therapeutic strategies. Historically, mammalian models have been utilised in an attempt to identify the neural substrates involved in the development of addiction. Although these models have proved invaluable in identifying the critical molecular targets of drugs of abuse, much remains unknown about the systems level neural plasticity involved in the development of an addictive state, largely due to the sheer complexity of the mammalian brain. The insect brain contains many orders of magnitude fewer neurons, but there is remarkable conservation of the molecular mechanisms involved in the encoding of reward. Given this, recently, attention has turned to the use of insects as potential models with which to study addiction. Using a caged behavioural design in the laboratory, I studied the viability of using honeybees and bumblebees as models of addiction for the alkaloids nicotine and caffeine. I found that both honeybees and bumblebees display preferential consumption of these alkaloids and that this preferential behaviour critically depended on both the compound concentration and the schedules of drug administration employed. The study conducted in this thesis is fundamental to being able to use insects to study the neural substrates of addiction. It also sheds further insight into how caffeine and nicotine produced by plants in floral nectar could manipulate bee behaviour and coevolve to improve plant fitness. Although my work on bee behaviour does not completely validate bees as models for addiction, it lays the groundwork for further studies that may examine maladaptive behaviour in line with the core diagnostic criteria for addiction.