Insulin in the brain influences dopamins levels

In the human brain, the hormone insulin also acts on the most important neurotransmitter for the reward system, dopamine. Insulin lowers the dopamine level in a specific region of the brain (striatum) that regulates reward processes and cognitive functions, among other things. This interaction can be an important driver of the brain's regulation of glucose metabolism and eating behavior.

source https://www.sciencedaily.com/releases/2021/11/211118203800.htm