Saw this animated movie on HBO circa 1992. It is not either of the NIMH movies.
Mice live in the drains/sewers
Green goo floods the sewers and turns the mice into green (glowing?) globs
Mice can also become glowing blobs by touching an infected mouse
Female/mother mouse saves child(ren?) by defeating evil big mouse/rat guy
Sorry I don’t remember too many specifics, I was fairly young when I saw the movie on tv