Response of the ampullae of Lorenzini to static combined electric and thermal stimuli in Scyliorhinus canicula.

The effect of long-lasting electric currents on the Lorenzinian ampullae at constant temperatures between and 25 degrees C was investigated in the dogfish (Scyliorhinus canicula). Steady state neural impulse patterns in single afferent units were analyzed by plotting interval length histograms and computing mean values and standard deviations for currents between -100 and +100 nA. The mean values depended on temperature and on current strength; the relative standard deviations remained almost constant (ca. 20--30%). Negative currents, inserted at the orifice of the ampullary canal led to higher, and positive currents to lower, steady impulse rates in the whole temperature range investigated here. This static component of electrosensitivity again disappeared at higher currents (of 50 nA and more; electric overstimulation). The maximum static response was two orders of magnitude less than the maximum dynamic component of electroreception. The electrosensitivity depended on temperature: the ampullae were most sensitive to electric currents between 13 and 19 degrees C. The maximal neural activity at 19 degrees C was not shifted to higher or lower temperatures by electric stimulation. A constant equivalent of electric and thermal stimulation throughout the tested temperature and current range could not be found.