A modulatory proctolin-containing neuron (MPN). I. Identification and characterization.

The pentapeptide proctolin has been localized previously to the crustacean stomatogastric nervous system and shown to modulate the rhythmic activity of the pyloric network in the stomatogastric ganglion (STG) (Marder et al., 1986; Hooper and Marder, 1987). We have now identified a pair of modulatory proctolin-containing neurons (MPNs) that cause proctolin-like modulation of the pyloric rhythm. Individual MPNs were identified by combining intracellular Lucifer yellow dye injection with rhodamine-visualized proctolin immunolabeling. Both MPNs are located in the esophageal nerve and send processes to the STG. Current injection into one MPN influences the second MPN, suggesting that they are electrically coupled. The 2 MPNs have similar effects on the pyloric rhythm of the STG. Intracellular stimulation of a single MPN was sufficient to enhance already active pyloric rhythms and initiated the pyloric rhythm in quiescent preparations.