I finally got around to updating the references regarding the effects of spay and neuter and you can find these here.
For those who don’t have access to some of these publications, you may be able to find at least abstracts of the articles by doing a search for the author’s name plus key words from the article’s title in Google Scholar or one of the other more academic search engines. Your local librarian or a college librarian also should be able to get copies for you.