Electroreceptors in the platypus

It has been known since the last century that the bill of the platypus contains densely packed arrays of specialized receptor organs and their afferent nerves. Until recently these were thought to be largely mechanoreceptive in function. However Scheich et al. provide both behavioural and electrophysiological evidence that there are electroreceptors in the bill of the platypus. These authors were able to record evoked potentials from the somatosensory cortex of the brain in response to weak voltage pulses applied across the bill. Behavioural observations showed that a platypus could detect weak electric dipoles and it was suggested the animal was able to locate moving prey by the electrical activity associated with muscle contractions. From these observations, and in view of the fact that it was known that the bill contained gland receptors which in several respects resembled the ampullary electroreceptors in fresh-water fish, Scheich et al. concluded that the receptor array of the platypus bill included electroreceptors. In this report we present direct electrophysiological evidence for the existence of such receptors.