SCPB (small cardioactive peptide B) is an insect neuropeptides, the sequence of which was found in the accessory radula closer muscle, a muscle involved in biting movements. The ganglia and nerves that innervate the accessory radula closer muscle also contain SCPB. At nanomolar concentrations, SCPB enhances the contractions of this muscle. The effect of SCPB on the muscle resembles the effect of an identified serotonergic neuron that has been shown to mediate behavioral effects that reflect a food arousal state in Aplysia. Like serotonin, SCPB enhances contractions by a postsynaptic action, which appears to involve an increase in cAMP levels in the muscle.