[NEST Users] Spike->Synapse->Update

I wrote a simple python code(without nest) for a E-I random balanced network with poisson noise stimulus. Then I try to build it on nest. However, the response firing rates are changed.(not a computing error) Is there anything wrong? neurons -> spike synapse -> wait delay post_neurons -> add weight from connected synapses to corresponding input channel neurons -> update ODE each step I figured out that without connections but with poisson noise input, the firing rates of my python code is the same as the code on nest. (Seems that the ODE calculations are the same in my python code and nest) However, the firing rates show differ greatly when I add the connections on both.