Fig. 8.

The effect of hyperpolarizing current injections to the PD neurons in an intact pyloric network with the LP → PD synapse pharmacologically blocked. In all the experiments shown, hyperpolarizing current pulses were intracellularly injected to a PD neuron while the neuron’s membrane potential was recorded with a second electrode. A, Simultaneous recording from PD and AB neurons. Two sweeps (from the same preparation) are overlaid. In both, a cycle with no current injection is followed by one with an inhibitory stimulus mimicking the LP inhibition of PD during DA (black) or Oct (gray) (for details, see Results). The time of current injection is shown by theblack and gray bars, and the phase of two cycles is shown based on the prestimulation cycle (the first spike in the AB neuron is defined as phase 0). B, The effect of inhibitory stimulation of PD on the pyloric cycle period. Single stimuli (three different stimulus protocols as shown in the graph’s legend) were given at different phases along the PD bursting cycle. The stimuli duration and intensity correspond to those generated by the LP neuron in a fully intact network in control (open squares), DA (black squares), or Oct (gray squares) conditions. The phase of the end of the inhibitory stimulus (calculated relative to the preceding cycle with no stimulus as shown in A) is plotted against the change in cycle period generated by the inhibition (period with inhibition/period in previous cycle with no inhibition × 100). The end phase could exceed 1.0, as for example in the sweep marked Oct in A. Data points from four different preparations are shown. The dashed line is a linear fit calculated for all the data points shown (pooled together). Theoval marked Control refers to the open data points, corresponding to LP inhibition of PD in a fully intact network in control conditions. Similarly, the areas markedDA and Oct refer to the filled black and filled gray data points, respectively, and represent LP inhibition of PD during DA or Oct bath application.C, The effect of repetitive inhibitory inputs to the PD neuron on the pyloric rhythm. The three PD traces (from the same neuron) show the effect of control- (cont.), DA-, and Oct-like repetitive inhibitory stimulation using stimulus parameters and phasing indicated by the ovals in B. The time of current injection is shown by thebars.