Figure 1.

Proctolin enhances the pyloric rhythm. A, Top, Schematic diagram of the stomatogastric nervous system. The paired commissural ganglia (CoGs) and oesophageal ganglion (OG) contain modulatory projection neurons that send axons to the STG through the stomatogastric nerve (stn). Bottom, Simplified diagram of the pyloric network shows the pacemaker group consisting of the AB, PD, and LPG neurons coupled strongly with electrical synapses (gap junctions) and synaptically inhibiting the follower neuron LP. The LP neuron in turn inhibits the two PD neurons, producing a reciprocally inhibitory subnetwork. B, Intracellular traces recorded in the normal ongoing pyloric rhythm with intact descending neuromodulatory inputs show the rhythmic alternation of the PD and LP neurons (Control). Blocking or cutting the stn removes all descending neuromodulatory input to the STG and disrupts the pyloric rhythm (Decentralized). Bath application of 10⁻⁶ m proctolin recovers the pyloric rhythm, increases the amplitude of the slow-wave oscillations in the PD and LP neurons and increases the spike frequency and number of spikes per burst (Proctolin). Line segments indicate the baselines for the membrane oscillations of PD (−56 mV) and LP (−59 mV) recorded in Control. stn, Stomatogastric nerve, lvn, lateral ventricular nerve, lpn, lateral pyloric nerve; pdn, pyloric dilator nerve.