Quantification of cardiac sac network effects on a movement-related parameter of pyloric network output in the lobster.

Cardiac sac network activity (cycle period tens of seconds to minutes) has long been known to alter pyloric network activity (cycle period approximately 1 s), but these effects have not been quantified. Some pyloric muscles extract cardiac sac timed variations in pyloric motor neuron firing, and consequently produce cardiac sac timed movements even though no cardiac sac neurons innervate them. Determining pyloric behavior therefore requires detailed description of cardiac sac effects on pyloric neural output. Pyloric muscle activity correlates well with motor neuron overall spike frequency (OSF, number of spikes per burst divided by cycle period). We therefore quantified the effects of cardiac sac activity on the OSF of all pyloric neurons in the lobster, Panulirus interruptus. The ventricular dilator (VD) neuron had a biphasic response, with its OSF first increasing and then decreasing during cardiac sac bursts. Lateral pyloric (LP) neuron OSF decreased during cardiac sac activity. The pyloric (PY) neurons had two responses, with OSF either decreasing or increasing just after the beginning of cardiac sac activity. The pyloric dilator (PD) neurons had a triphasic response, with OSF increasing slightly at the beginning of cardiac sac activity, decreasing during the cardiac sac burst, and strongly increasing after cardiac sac activity ended. The inferior cardiac (IC) neuron had a biphasic response, with OSF decreasing at the beginning of cardiac sac activity and strongly increasing when cardiac sac activity ceased. These data provide the quantitative description of cardiac sac effects on pyloric activity necessary to predict pyloric movement from pyloric neural output.