Before revision:  We have obtained a general relation allowing calculating exactly the probability density function ( pdf ) p(t) of output interspike intervals (ISI) values for a neuronwith feedback based on known pdf p^0(t) for the same neuron without feedback, intensity of the input stream \lambda and the properties of the feedback line.
After revision:  We have obtained a general relation allowing calculating exactly the probability density function ( pdf ) p(t) for distribution of the first passage time of crossing the threshold, which is the distribution of output interspike intervals (ISI) values for a neuronwith feedback based on known pdf p^0(t) for the same neuron without feedback, intensity of the input stream \lambda and the properties of the feedback line.