Fig. 6. (A) When axonal conduction in the stn was blocked with isotonic sucrose, and there was no ongoing pyloric rhythm, superfusion of the pentapeptide proctolin (10^–6 mol l^–1) induced rhythmic pyloric activity in 55% of preparations, including the one shown here. (B) Phase plot, showing two cycles of the pattern induced by proctolin in those preparations (N=6) that were activated. Phases of firing in the VD and IC neurons are not shown, because they were active in only three preparations (including the one shown in A). (C) Graph of average cycle period. In control saline there was no activity, whereas cycle period was nearly 15 s in the presence of proctolin; this is considerably longer than cycle period in control saline when the stn is not blocked (approximately 3.3 s in Fig. 3, for example.) (D,E) Graphs of spike frequency during bursts and of burst duration in each of the core pyloric neurons (the PD, LP and PY neurons) that were regularly activated during proctolin superfusion with the stn blocked. Because there was no rhythmic activity, and therefore no bursts in any of the neurons, values during saline superfusion are not shown. Nerves: mvn, medial ventricular nerve (recording action potentials of the VD and IC neurons); dlvn, dorso-lateral ventricular nerve (recording action potentials of the PD neurons); lvn, lateral ventricular nerve (recording action potentials of the PD, LP and PY neurons).