Decision-making, environmental enrichment and the mesolimbic dopamine system in adult and aged rats

Abstract

The dopaminergic system plays a crucial role in learning, reward-processing, motivation, motor control and attention. The population of midbrain dopamine neurons projects extensively to many areas of the brain. This system is maintained in a homeostatic way, and it can self-regulate to maintain behavioural function in extreme cases such as Parkinson’s disease. However, Huttunen (2016) discovered a significant correlation between midbrain dopamine neuron number in male rats and their behavioural performances in a gambling task. It was unexpected that such non-clinical variation in dopamine neuron number can lead to differences in observable behaviours. Our project aims to investigate the link between dopamine structure and function in risk decision-making, and to explore possible factors that can manipulate the brain and behaviour. Chapter 1 reviewed the dopaminergic system and its adaptive role in conditions such as environmental enrichment and stress. Chapter 2 described the experiment using a modified risk task which failed to replicate the original results from Huttunen (2016). Chapter 3 examined the possible sex difference in the brain of behaviour of rats. Chapter 4 and 5 explored factors that can influence this dopamine-loss-stay relationship, including environmental enrichment and neurogenesis. We demonstrated that dopamine-expressing neurons in the rat midbrain may underlie loss-stay behaviours, which may reflect the animals’ risk-attitude. Moreover, the correlation was significant only when the age of the animal was considered. Therefore, this correlation may be a result of aging, or the compensatory mechanisms that often accompany ageing. Future research may shed light on possible treatment and interventions for neural decline in ageing and other clinical conditions.