Appetitive behaviours in rats: routes to addiction?

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What starts and stops the occurrence of positively motivated, appetitive behaviours in people and animals is not well understood. It is also not clear how and why these behaviours become disturbed. Despite our lack of understanding, these disturbed appetitive behaviours (for example, drug addiction and eating disorders) and their consequences (such as obesity) are major health problems. Animal models help clarify biological and psychological aspects of these behaviours. Based on work with animal studies it appears access conditions play an important role in the development of excessive behaviour expression. I am exploring the pattern of and interactions of two appetitive behaviours in rats; sugar solution consumption and wheel running. Daily long 6 h access to wheels results in high levels of running but short 1 h access does not. Continuous access to sugar results in much lower consumption than does every third day access. Young rats can voluntarily come to run (in 6 h) over 2.5 km, and with intermittent access can drink over 300 g of a 4% sugar solution a day (normal water consumption is about 40 g). By studying these two behavioural addictions and comparing them to what we know about other addiction models, like drug self-administration in rats, it may prove possible to elucidate the critical variables responsible for the transition to excessive levels of consumption. By determining if the characteristics of drug addiction also apply to these two appetitive behaviours we will be able to argue that addiction-like patterns can occur with many appetitive behaviours. This would suggest that addiction is something that has roots in natural appetitive behaviours. A better understanding of factors responsible for the transition to excessive consumption in rats may provide clues to human addiction, suggest warning signs for vulnerability, and could lead to suggestions for treatment.