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First published online November 4, 2005
Journal of Experimental Biology 208, 4213-4222 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01896

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Response properties of electrosensory afferent fibers and secondary brain stem neurons in the paddlefish

Michael H. Hofmann^1,*, Boris Chagnaud¹ and Lon A. Wilkens²

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

View larger version (26K): [in a new window]   Fig. 1. Responses of a DON neuron to a 2 Hz sinuosidal electric field moved at 0.5 cm s-1 along the rostro-caudal axis of the rostrum. (A) Firing rate as a function of time. (B) As in A, but filtered and multiplied by the 2 Hzstimulus, showing the phase relationship of the response to the stimulus.

View larger version (14K): [in a new window]   Fig. 2. Autocorrelation [C(n)] analysis of a primary afferent (PA) fiber (A) and a dorsal octavolateral nucleus (DON) unit (B). Solid lines, original data; dotted lines, shuffled data. Only the PA shows long-range autocorrelation. (C) Autocorrelation index of 30 PA fibers and 60 DON units plotted against the mean firing rate. Note the lack of higher autocorrelation values in DON units.

View larger version (43K): [in a new window]   Fig. 3. Peak firing rate of primary afferent (PA) fibers (A) and dorsal octavolateral nucleus (DON) units (B) during stimulation with sinusoidal electric fields of different frequency. The response magnitudes at each stimulus frequency are similar and the overall frequency tuning curves are not different between PA fibers and DON units.

View larger version (36K): [in a new window]   Fig. 4. Phase plots of the responses of 15 primary afferent (PA) fibers (A) and 15 dorsal octavolateral nucleus (DON) units (B) during stimulation with a small dipole field moved slowly along the rostro-caudal axis of the rostrum. Traces are sorted by the location of the receptive field. Stimulus frequency was 2 Hz and the speed 0.5 cm s-1. Stimulus electrodes were oriented perpendicular to movement direction.

View larger version (36K): [in a new window]   Fig. 5. Firing rates as a function of time for nine primary afferent (PA) fibers (A) and nine dorsal octavolateral nucleus (DON) units (B) during stimulation with a moving DC field (top nine traces); the lowest trace in each panel is the average. Traces are aligned by the receptive field position to allow averaging. The x-axis zero point marks the center of the receptive field. The speed of the DC stimulus was 5 cm s-1. Response amplitude and shape were similar for PA fibers and DON units.

View larger version (21K): [in a new window]   Fig. 6. x-y plots of receptive field position of dorsal octavolateral nucleus (DON) units vs cell location within the DON. The y-axis represents the normalized receptive field position. Zero is at the tip of the rostrum and 10 cm is the position of the nose opening just in front of the eye. Receptive field values for different sized fish were normalized and projected onto a standard fish with a tip-to-nose distance of 10 cm. (A) The x-axis represents the position of the cell along the rostro-caudal axis as % of total DON length. Zero represents the rostral end of the DON, 100 represents the caudal end of the DON. (B) The x-axis gives the cell position along the medio-lateral extent of the DON in percent. Zero means the medial border of the DON, 100 its lateral edge. Each symbol represents a DON unit whose receptive field position was measured. There is no correlation between the location of a cell in the DON and its receptive field along the rostro-caudal axis of the rostrum.