BEHAVIORAL AND ELECTROPHYSIOLOGICAL STUDIES OF HYDRA. I. ANALYSIS OF CONTRACTION PULSE PATTERNS

¹ Department of Biology and Department of Biometry, Case Western Reserve University, Cleveland, Ohio 44106

1. The temporal patterns of spontaneously produced Contraction Pulses (CP's) were investigated in two species of Hydra. It was found that H. pseudoligactis frequently give CP's as single, widely spaced events, whereas, H. pirardi produce many CP bursts. Inter-pulse interval histograms and joint order scatter diagrams, constructed on the basis of 10 to 12 hour recordings from 10 preparations of the two species, were employed to depict these contrasting temporal patterns of pulse production. The burst frequency and the burst length for CP's were found to be so different for the two species that these measurements alone allowed a unique designation of the animals into the two species classes.

2. CP bursts from unstimulated H. pirardi had the following characteristic features: (a) both positive and negative phases of the CP amplitudes increased progressively with successive pulses in a burst; (b) intervals were shorter in mid-burst than at the start or end of the burst; and (c) intervals progressively decrease in length with successive position in an inter-burst interval.

3. The CP pattern of H. pseudoligactis can be changed from one primarily of single CPs to one consisting predominantly of bursts of pulses by the following external stimulation: (a) increased electrode suction; (b) intermittant light stimulation; and (c) exposure to feeding stimuli. The three features of CP bursts found in unstimulated H. pirardi, are exhibited by the CP burst pattern induced by such stimuli in H. pseudoligactis.