Here’s an article I wrote that discussed some of the research https://medium.com/derek-develops/an-expert-explains-anxiety-depression-isnt-just-biology-ab5bd4800071?sk=46ccfc068741ef81d2fc538e3ac8ef1c

Here’s a good overview of the biology in mammals
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3334530/

Here’s a 2008 review cited by 1,600 studies about the HPA axis in depression https://www.psychiatry.wisc.edu/courses/Nitschke/seminar/Pariante%20CM,%20Trends%20Neurosci%2031,%202008.pdf

You can also search Pubmed for rats depression to find articles about how they induce it. The part about social defeat is from a hard to find book called Proxemics, which is the study of social distances from intimate to far.