Extracellular Electrophysiological Recording of Visually Evoked Swim Pacemaker Signals from the Isolated Rhopalium of Tripedalia cystophora.

The box jellyfish Tripedalia cystophora combines image-forming lens eyes and well-characterized visually guided behaviors with a tractable rhopalial nervous system of approximately 1000 neurons, making it an emerging model for systems-level investigation of visual information processing and sensorimotor integration. Swim pacemaker neurons generate motor commands directly controlling bell contractions, and these signals can be recorded extracellularly from the epidermal stalk nerve of an isolated rhopalium, providing a quantitative proxy for visually driven motor output. The strength of the pacemaker response, quantified as standardized neural activity derived from pacemaker signal count and instantaneous frequency, scales with stimulus contrast above the decision transition threshold (DTT), enabling graded evaluation of visually driven sensorimotor integration. In this protocol, we cover the fabrication of extracellular suction electrodes, rhopalial isolation, recording chamber configuration, visual stimulus delivery to the lower lens eye, hardware-level stimulus timing verification, electrode placement on the epidermal stalk nerve, and synchronized electrophysiological and stimulus data acquisition using standard laboratory hardware.