Mechanoreception in Zooplankton First Antennae: Electrophysiological Techniques

We describe methods for delivering calibrated mechanical displacements to antennal mechanoreceptors in zooplankton while simultaneously recording related neural traffic. Mechanosensory neural responses to small water displacements (0.0 1–1 μm) were studied over a wide frequency range (30 to >3000 Hz) Receptors could be localized and properties (thresholds, phase locking, habituation) examined. These methods have been tested on calanoid copepod first antennae (antennules), but may be suitable for other preparations. Extracellular recordings are made by holding the animal in stainless steel forceps and raising it into a layer of mineral oil, leaving one of the first antennae projecting into the underlying sea water. Nerve impulse traffic is recorded between the forceps and a chlorided silver wire in the seawater. Antennae are stimulated by water displacements produced by a vibrating sphere attached to either an electromagnetic or piezoekctric transducer. A fiberoptic sensor continuously monitors displacement. A computer-controlled waveform generator and amplifier drive the transducer with various frequencies, amplitudes and waveforms. The amplified sensor output and neural activity are digitized for later analysis.