[Mbwagava]

> which is mostly in glutamergic cells in the shell of the nucleus accumbens(s)

i'm not really convinced this is any better fit for "reward" than other explanations. What evidence is there that such a reward system exists in the first place?

[superkuh]

What evidence? Asbsolutely libraries full. You can start with the review articles from Berridge Lab, https://sites.lsa.umich.edu/berridge-lab/publications/ . http://sites.lsa.umich.edu/berridge-lab/wp-content/uploads/s... is a good overview article.