Neuromodulation of the crustacean heart

In this thesis, the crustacean cardiac system was used to study how substances modulate rhythmic motor activity. Using mass spectrometry we identified a novel peptide, GAHKNYLRFamide from the pericardial organs of crabs. GAHKNYLRFamide, increased the cardiac ganglion (CG) burst frequency and the duty cycle, number of spikes per burst and spike frequency of the component neurons. GAHKNYLRFamide shows less sensitivity to peptidase degradation than other FMRFamide-like peptides (FLPs).; The physiological actions of the peptides Cancer borealis tachykinin-related peptide Ia (CabTRP Ia), red pigment concentrating hormone (RPCH) and allatostatin III type A (AST-3) have been characterized for the first time on the isolated CG of the crab, Cancer borealis. CabTRP Ia and RPCH had excitatory effects on the CG bursting pattern while AST-3 strongly inhibited its motor output. Other modulators such as dopamine, proctolin and pilocarpine increased the activity of the CG and the magnitude of their actions on different burst parameters was dependent on the naive state of the preparation.; The effects of CabTRP Ia and the FLPs were also studied in the CG of the lobster, Homarus americanus. The FLPs decreased the burst frequency and increased the CG burst duration, while CabTRP Ia had no significant effects on any of the burst parameters. The cholinergic agonists nicotine and carbachol have strong excitatory effects on the CG burst frequency.; The physiological action of peptides was also studied in the in vitro whole heart preparations of the crab, Cancer borealis and lobster, Homarus americanus. Modulators such as CabTRPIa, FLPs and RPCH increased the heartbeat frequency and the contraction amplitude, whereas AST-3 decreased the heartbeat in both species.; Finally, the role of nitric oxide (NO) in the cardiac system was studied in the lobster, Homarus americanus. The heart muscle synthesizes NO which reduces the heartbeat frequency and contraction amplitude by inhibiting the cardiac ganglion output. Thus, NO is an important inhibitory retrograde modulator in the crustacean cardiac system.; In conclusion, cardiac activity in crustaceans can be hormonally increased and decreased by peptides, amines and small molecules in a particular physiological context.