Primary afferent electrosensory neurons represent paddlefish natural prey

The paddlefish detects electric fields of its planktonic prey. Each plankton particle, such as a moving Daphnia, is an electric dipole. Primary afferent neu-rons of the paddlefish electrosensory system were found to respond transiently to moving dipoles (i.e., Daphnia) within their receptive field. Positive plankton potential increases and negative potential decreases the primary afferent spike rate while biphasic plankton potentials elicit biphasic neuronal responses. That is to say, neuronal activity coincides with the plankton's electric dipole potentials. Consequently, responses of primary afferent neurons could have ambiguous effects on second-order pyramidal-like neurons: an increase of firing rate should depolarize and a decrease of firing rate should hyperpolarize the postsynaptic membrane potential of second-order neurons. Depending on its orientation, a plankton particle passing the receptive field would elicit opposite central effects. Nevertheless, because paddlefish feed successfully on plankton particles, the central nervous system must process primary afferent signals so as to unambiguously represent the position of a plankton particle. Introduction The ram-jet ventilating freshwater paddlefish (Polyodon spathula) feed on zooplankton and as juveniles they capture them individually [9]. The paddle-fish rostrum is covered with Ampullae of Lorenzini used to detect and locate electrical signals from planktonic prey. Typical plankton are Daphnia, a major component of the paddlefish's diet [3]. The objectives of this work were to characterize the weak electric fields from planktonic Daphnia. Furthermore, we described the responses of elec-troreceptor primary afferent neurons of the paddlefish to live moving plankton particle, which provided the generic stimulus condition. Primary afferent neu-rons target the second order pyramidal-like neurons in the hindbrain [7] which we describe here.