Non-technical summary Even when the bladder is full, emptying can be deferred voluntarily until individuals find themselves in a socially appropriate environment. This indicates that the brain is important in the control of bladder function. This study used drugs that either mimic or block the effects of the neurotransmitter chemicals involved in communication between nerve cells to investigate the brain nerve circuits that govern the control of the bladder. A small region in the midbrain was shown to be critical for normal bladder emptying to occur. Normally the excitability of the nerve circuits in this region was controlled by the action of an inhibitory neurotransmitter chemical called GABA. However, if GABA's effect was removed, bladder emptying became abnormally frequent. These results advance our understanding of the normal control of bladder function, and have implications for the development of new treatments for some forms of incontinence.