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

Abstract

SUMMARY The passive electrosense is used by many aquatic animals to detect weak electric fields from other animals or from geoelectric sources. In contrast to the active electrosense, `passive' means that there are no electric organs,and only external fields are measured. Electroreceptors are distributed in the skin, but are different from other skin senses because they can detect and localize sources a considerable distance away. Distant sources, however,stimulate a large number of receptors at the same time and central circuits have to compute the exact location of the source from this distributed information. In order to gain insights into the algorithms involved, we compared the response properties of units in the dorsal octavolateral nucleus(DON) with primary afferent fibers in the paddlefish. The following parameters were tested: spontaneous activity, sensitivity, frequency tuning, receptive field size, movement sensitivity, and topography within the DON. Although there are some differences in spontaneous activity and receptive field size,there are no major differences between primary afferents and DON units that could reveal any substantial amount of spatial information processing. In particular the lack of any topographic order whithin the DON renders a lateral interaction between neighboring receptive fields unlikely.

Response properties of the electrosensory neurons in hindbrain of the white sturgeon, Acipenser transmontanus

“…spontaneous activity In this study, the mean rate of spon- taneous activity in DON units of the white sturgeon was 15 Hz, which is substantially higher than the 1.2 Hz in elasmobranchs [12] and the 6 Hz in catfish [16] ; but lower than that in paddlefish (31 Hz) [14] . Similar to paddlefish, the interspike intervals in the DON neurons of sturgeon had a mean CV lower than 1 [14] , suggesting relatively regular spontaneous firing.…”

“…Similar to paddlefish, the interspike intervals in the DON neurons of sturgeon had a mean CV lower than 1 [14] , suggesting relatively regular spontaneous firing.…”

“…This electric field is termed the global field [13] and was used to search for electrosensory neurons. The same setup was used in a previous study by Hofmann et al [14] . Due to potential polarization effects, noise and direct-current offset, only large-amplitude fields were detectable.…”

“…In a previous study, the maximum stimulus amplitude was chosen as 25 µV/cm to compare the results from sturgeon with those from paddlefish [14] . However, here we found that this stimulus amplitude was too low to evoke reliable responses in sturgeon.…”

“…One reason may be that the intensity of the stimulus was too small to evoke a response in DON neurons [14] . Another is that the phase of the signal, but does not change the waveform [8] .…”