Breaks up bridges (5)
I believe the answer is:
snaps
'breaks' is the definition.
(I know this)
'up bridges' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'bridges' becomes 'spans' ('span' can be a synonym of 'bridge').
'spans' written backwards gives 'SNAPS'.
(Other definitions for snaps that I've seen before include "Informal photographs" , "Photos" , "Spells of cold weather" , "Breaks suddenly" , "Breaks in two" .)