Bay Trees - Bald in the Centre

I have two large standard bay trees and two large pyramid bay trees, all of which are in large pots.  The centre of all of these bay trees have no leaves so the leaves are only on the ends of the branches.  The plants need trimming to keep them in shape but it would mean that I would lose the leaves on the end of the branches and be left with bare branches - will any leaves or new shoots grow back on these branches and if so, should I stagger the pruning of all the branches so that the plant doesn't go into shock!!  I'd hate to cut all the leaves off and then the plant dies as I've had them for around 9/10 years.  Thanks