Rhythmic sensitization of nematocyst discharge in response to vibrational stimuli

Sea anemones capture prey by discharging nematocysts and other cnidae. Disc harge of microbasic p-mastigophore (mpm) nematocysts is regulated in part b y hair bundle mechanoreceptors on tentacles arising from multicellular comp lexes consisting of supporting cells and a sensory neuron. Anemone hair bun dles detect movements of prey and then sensitize cnidocytes (cnida-containi ng cells) to discharge mpm nematocysts in response to contact between the p rey and tentacle. Data from a simple bioassay based on counting nematocysts discharged into test probes, indicate that approximately twice as many nem atocysts discharge into test; probes touched to tentacles after sensitizati on than before sensitization. We here report that sub-second bursts of vibr ational stimuli at key frequencies (51, 55, 65, or 74 Hz; Watson GM, Mire P , Hudson RR. 1998. J Exp Zool 281:582-593) sensitize discharge for at least 90 sec. Very few complete cycles of vibration are sufficient to sensitize discharge. However, as the number of cycles of vibration is increased, disc harge is sensitized in rhythmic patterns. Computer analysis of the data by fast Fourier transforms indicates discharge to vibrations at 65 Hz is sensi tized every 6.75 cycles. At 51 Hz discharge is sensitized every 2.00 cycles . At 74 Hz, discharge is sensitized in a polyrhythm occurring every 4.26, 3 .76, 2.46, and 2.10 cycles, respectively. At 55 Hz, discharge is sensitized in a polyrhythm occurring every 6.09, 3.20, 2.91, and 2.0 cycles, respecti vely. Apparently, cells in the neuronal pathway interconnecting anemone hai r bundles with cnidocytes count cycles of vibration and then sensitize disc harge or not according to the tally. (C) 2000 Wiley-Liss, Inc.