Electrical coupling is a widespread feature of developing neuronal circuits and it contributes to the generation of patterned activity. In the developing rat hippocampus, release of GABA by coactive hilar interneurones generates widespread synchronized activity. Here it is shown that hilar interneurones strongly rectify in the outward direction when depolarized. This depolarization-induced hyperpolarization, abolished by gap junction uncouplers, is modulated by nitric oxide. This phenomenon might represent a current-shunting mechanism of the excess current by providing functional inhibition at a developmental stage when GABA is excitatory. Spatial buffering of the current might represent an osmotic mechanism for growth and differentiation.