I have...
1 cat - Hannah
8 rats - Koby, Tre', Kai, Tolliver, Oscar, Ron, Luka, Nanoonana(don't ask

)
2 greyhounds - Macy & Raiyne
btw:
Peaceout, this isn't meant nasty or anything, but have you tried to introduce your rat to a new one?
rats really do need company and will become depressed living alone, even with extra love from you.
Make sure you introduce rats on neutral territory, and take things slowly.
(sorry if you allready knew this, i don't mean to be patronising, i'm just a rat lover ! Lol

)
this site is great for ratty info:
www.fancy-rats.co.uk