Reciprocal inhibition is a primary mechanism through which oscillations are generated in nervous systems. We study the contribution of synaptic dynamics to rhythm generation in reciprocally inhibitory networks of the crustacean pyloric CPG. The inhibitory synapse from the LP to the PD neurons is the sole chemical synaptic feedback to the pyloric pacemaker group of neurons (AB/PD). This synapse consists of two components: a spike-mediated and a non-spike-mediated (graded) component. In the ongoing pyloric rhythm, the spike-mediated component of this synapse is dominant. In contrast, the inhibitory synapse from AB/PD to LP is mainly graded. We propose that the distinct dynamics of these two synapses play an important role in controlling the pyloric rhythm. To examine this hypothesis, we used a synaptic release model based on experimental data from the LP to PD synapse (LoMauro et al, SFN abst 657.17, 2004). This model can accurately predict the postsynaptic response of PD neurons to any temporally patterned ...