The stomatogastric nervous system in crustaceans is a well-studies simple model nervous system with reliably identifiable neurons, and extensively described connections and conductance properties. The conductance properties in this system are acted upon by neuromodulators as well as synaptic connections to modify the pyloric and gastric mill rhythms. Proctolin is a neuropeptide that increases the activity of the gastric mill rhythm and modifies the pyloric rhythm. In this research, we show how the stomatogastric nervous system of Panulirus interruptus reacts to exogenous proctolin that is injected daily into the lobster haemolymph over a three-day period. Extracellular and intracellular electrophysiological recordings were then obtained from the isolated stomatogastric nervous system. Our results show that the prolonger proctolin treatment modifies the neuron activities in stomatogastric nervous system.