Drosophila brain: The systems that mediate the pleasure component of reward in mammals, including those involving the endogenous opioid & endocannabinoid systems, are unlikely to be present in insects

Drosophila reward system - A summary of current knowledge. Jiri Dvoracek, Dalibor KodrIk. Neuroscience & Biobehavioral Reviews, January 6 2021. https://doi.org/10.1016/j.neubiorev.2020.12.032

Rolf Degen's take: https://twitter.com/DegenRolf/status/1347063544802635778

Highlights

• Drosophila has a very well-developed brain enabling the associative learning.

• Reward functions of Drosophila represent a complex network system.

• Drosophila has activity-enhancing systems associated with wanting component of reward.

• Hedonic component of reward system is unlikely to be present in Drosophila.

Abstract: The fruit fly Drosophila melanogaster brain is the most extensively investigated model of a reward system in insects. Drosophila can discriminate between rewarding and punishing environmental stimuli and consequently undergo associative learning. Functional models, especially those modelling mushroom bodies, are constantly being developed using newly discovered information, adding to the complexity of creating a simple model of the reward system. This review aims to clarify whether its reward system also includes a hedonic component. Neurochemical systems that mediate the ´wanting´ component of reward in the Drosophila brain are well documented, however, the systems that mediate the pleasure component of reward in mammals, including those involving the endogenous opioid and endocannabinoid systems, are unlikely to be present in insects. The mushroom body components exhibit differential developmental age and different functional processes. We propose a hypothetical hierarchy of the levels of reinforcement processing in response to particular stimuli, and the parallel processes that take place concurrently. The possible presence of activity-silencing and meta-satiety inducing levels in Drosophila should be further investigated.

Keywords: Reward systemDopamineEndogenous opioidsMushroom bodyDrosophila