Rhythmic sensitization of nematocyst discharge in response to vibrational stimuli

Sea anemones capture prey by discharging nematocysts and other cnidae. Discharge of microbasic p-mastigophore (mpm) nematocysts is regulated in part by hair bundle mechanoreceptors on tentacles arising from multicellular complexes consisting of supporting cells and a sensory neuron. Anemone hair bundles detect movements of prey and then sensitize cnidocytes (cnida-containing cells) to discharge mpm nematocysts in response to contact between the prey and tentacle. Data from a simple bioassay based on counting nematocysts discharged into test probes, indicate that approximately twice as many nematocysts discharge into test probes touched to tentacles after sensitization than before sensitization. We here report that sub-second bursts of vibrational 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, discharge is sensitized in rhythmic patterns. Computer analysis of the data by fast Fourier transforms indicates discharge to vibrations at 65 Hz is sensitized 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, respectively. Apparently, cells in the neuronal pathway interconnecting anemone hair bundles with cnidocytes count cycles of vibration and then sensitize discharge or not according to the tally. J. Exp. Zool. 286:262-269, 2000.