The mechanism of formation of neuronal spike trains on the basis of selective interaction between two processes called excitatory and inhibitory processes, is studied. The techniques of stationary point processes are used to study the delay and deletion models proposed by Ten Hoopen and Reuver. These models are further generalised by associating a random life time to the inhibitory events. The probability frequency function governing the interval between two consecutive response yielding excitatory events, is obtained for these models.