Depending on your specific topic of interest, you can find many many things... agressiveness/impulsivity? mood disorder/depression? cognition? in which species?
At least, here are some references on the serotoninergic system in general (in humans): they're freely accessible on Google Scholar:
- Carhart-Harris, R. L., & Nutt, D. J. (2017). Serotonin and brain function: a tale of two receptors. Journal of Psychopharmacology, 31(9), 1091-1120.
- Beliveau, V., Ganz, M., Feng, L., Ozenne, B., Højgaard, L., Fisher, P. M., ... & Knudsen, G. M. (2017). A high-resolution in vivo atlas of the human brain's serotonin system. Journal of Neuroscience, 37(1), 120-128.