Fig. 7. Mechanistic relationship between paired-pulse facilitation and tetanus-induced augmentation for (A,B) a A5-3 neuron, a type of neuron MB-extrinsic neuron that was characterized with respect to its branching pattern and the location of its soma by Rybak and Menzel (1993), and (C) a PE1 neuron. (A,B) The A5-3 neuron was first stimulated by repeated paired pulses with pulse intervals of 30 ms, then a tetanus (thick vertical line) was applied and the paired pulses were continued (A). Afterwards the neuron was stimulated with paired pulses with pulse intervals of 60 ms, then a tetanus was applied, followed by a continuation of paired-pulse stimuli (B). Before the tetanus the paired pulses caused a slight facilatory effect with little difference between the repeated paired pulses of 30 ms and 60 ms. Responses to the second pulse facilitated after the tetanus in the t=30 ms protocol, but not in the t=60 ms protocol. (C) The PE1 neuron was first stimulated with paired pulses at intervals of 30 ms, then tetanus was applied. The facilatory effect of the tetanus is expressed in the responses to both the first and the second pulse, and no change is found between paired pulse facilitation before and after the tetanus. Filled circles, number of spikes for the first stimulus in the paired pulses; open circles, those for the second stimulus. The ordinate in the diagrams gives the number of spikes elicited by a single stimulus, and the abscissa time in s.