Bursting pacemaker activity in the solitary hydroid Tubularia solitaria

Spontaneous electrical activity recorded from solitary Tubularia solitaria Warren consisted of long bursts of potentials regularly alternating with series of short bursts. Hydranth pulse (HP) systems in isolated hydranths produce a pulse pattern similar to that in intact animals though at a much lower frequency. Stalk pulse (SP) systems in isolated stalks produced extremely regular bursts of pulses resembling bursting patterns in molluscan single neurones. The bursts were associated with strong bending movements. In contrast with hierarchies in other hydroids, T. solitaria's HP system dominates the SP system. Excised parts of the stalk produced bursting patterns. Interburst- and interpulse intervals were longer in these parts than in the whole stalk. Numbers of pulses per burst and overall pulse frequency were highest in the most distal part of the stalk, and lowest in the most proximal part.