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First published online February 15, 2008
Journal of Experimental Biology 211, 773-779 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.009795
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Response properties of electrosensory units in the midbrain tectum of the paddlefish (Polyodon spathula Walbaum)

M. H. Hofmann1,2,*, S. N. Jung2, U. Siebenaller2, M. Preißner2, B. P. Chagnaud1 and L. A. Wilkens1

1 Center for Neurodynamics, Department of Biology, University of Missouri – St Louis, St Louis, MO 63121, USA
2 Institute of Zoology, University of Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany

* Author for correspondence (e-mail: hofmannm{at}umsl.edu)

Accepted 9 January 2008

Paddlefish use their peculiar rostrum to detect minute electric fields from their main prey, small water fleas. Electroreceptors over the rostrum and head sense these fields and send the information into a single hindbrain area, the dorsal octavolateral nucleus (DON). From there, information is sent to various midbrain structures, including the tectum. The response properties of primary afferent fibers and DON units has been well investigated, but nothing is known about electrosensory units in the midbrain. Here we recorded the responses of single units in the midbrain tectum and DON to uniform electric fields. Tectal units exhibited little spontaneous activity and responded to sine waves with a few, well phase-locked spikes. Phase locking was still significant at amplitudes one order of magnitude lower than in the DON. If stimulated with sinusoidal electric fields of different frequencies, phase locking in DON units decreased proportionally with frequency whereas the response of tectal units depended little on frequency. This is in agreement with behavioral studies showing that relevant frequencies range from DC to ca 20 Hz.

Key words: electroreception, paddlefish, mesencephalic tectum, single unit






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