Forsøksdyr: The brain reward system and the effects of junk food

Godkjenningsdato 08.07.2020

Godkjenningsperiode 08.07.2020-07.07.2024

The brain reward system is a collection of brain structures and neural pathways that are responsible for feelings of pleasure, reward and motivation. Food and sexual partners are examples of ‘natural rewards’ or ‘intrinsic rewards’, rewards that have an unconditioned, inherent pleasurable value. In a functional context, rewards will reinforce the receiver to repeat their behavior. In contrast, a dysfunctional reward system is implicated in mental disorders such as depression, addiction, obesity and sexual dysfunctions.
With food acting on the natural reward system, it is expected that excessive consumption of junk food could severely affect this brain circuitry. Surprisingly, science has not been able to determine the role of the combination of food palatability and binge eating in these brain changes, nor does it focus on the effects beyond the ‘primary reward’ food. Our project deals with these aspects by investigating the effects of excessive junk food consumption on the overall reward system measured by junk food consumption and sexual behavior. By investigating the neuronal reward mechanisms upon different intrinsic and extrinsic rewards, our project studies the consequences for the reward system as a whole.

The project uses a combination of the methods fiber photometry and chemogenetics. Both methods use genetics to allow neurons to express either calcium indicators or designer receptors respectively. Fiber photometry can measure the neural activity of a specific brain projection within a millisecond scale. Activation of neurons corresponds with increasing levels of intracellular calcium. This calcium then binds to the calcium indicators in the axons, resulting in the emission of a fluorescent signal that can be detected by an implanted fiber. With chemogenetics, on the other hand, specific neural projections can be activated or inhibited by the insertion of a designer drug acting on the designer receptor in the brain. The use of these techniques can reveal the functional roles the specific projections play in natural reward. In addition, a specially designed natural reward test will be used. This research proposal will be the first step in a sequence of experiments to unravel the complexity of the effects of junk food consumption on the natural reward system and generate a better understanding, which is translational to humans. This can help finding treatments for disorders linked to reward, like addiction and obesity.

This experiment will need a maximum of 902 Wistar rats (822 females and 80 males), which is carefully calculated with a power analysis. The severity category in this proposal is expected to be moderate.

This kind of experiments can not be replaced by other models. First of all, there are no methods to study brain mechanisms in humans at such a detailed level. Second, computer simulations or in vitro studies are too simplified compared to the reality. Finally, only in living animals it is possible to study these complex behavioral systems.