Modulation of heart activity in the terrestrial slug Limax maximus by the feeding motor program, small cardioactive peptides and stimulation of buccal neuron B1.

Activation of the feeding motor program (FMP) increases the force of ventricular contractions in heart/central nervous system (CNS) preparations of the terrestrial slug Limax maximus (Linnaeus). The FMP-induced increase in ventricular activity requires innervation of the heart by abdominal ganglion nerves N9 and N11. Application of the small cardioactive peptides SCPA and SCPB to isolated preparations of the heart causes dose-dependent increases in the force of ventricular contractions. In addition, the SCPs induce rhythmic contractions in quiescent heart preparations. The effects of the SCPs appear to be specific in that the neuropeptide FMRFamide has an inhibitory effect on ventricular activity. SCP-like and FMRFamide-like immunoreactive material is found in the heart, kidney and pericardium and in the nerves that innervate these organs. Unilateral intracellular stimulation of buccal neuron B1, which contains SCP-like and FMRFamide-like immunoreactive material, mimics the FMP- and SCP-induced increases in ventricular activity. The effect of B1 on ventricular activity is frequency dependent and requires innervation of the heart by N11. These results are consistent with the hypothesis that the SCPs are involved in feeding-related alterations in heart activity in Limax and that the control of this effect involves neuron B1.