Spinal cord transection on the day of birth in the rat increases the excitability of lumbar networks (Norreel et al., J. Neurosci. 2003) and prevents the typical switch from depolarizing to hyperpolarizing inhibitory post-synaptic potentials (IPSPs) that occurs during the first postnatal week (Jean-Xavier et al., SfN 2004). In the present study we investigated the excitatory role of depolarizing IPSPs, which were recorded either in normal saline solution or after blocking the transporters that regulate the intracellular chloride concentration (bumetanide), thereby inducing a positive shift of the reversal potential of IPSPs (Eipsp). The excitability of the recorded motoneurons was tested by injecting short sub-threshold depolarizing current pulses. Cells were inhibited in the early phase of the depolarizing IPSPs when the conductance increase dominates. However, a facilitation of action potential generation was observed in the late phase of the response when the conductance has returned to control values b...